Friday, October 31, 2008
Just a quick appreciation: I love your blog. I don’t know how you do it but just about every day there’s something that I really want to read. You appear to write a blog that is bang on some of my interests, in particular, building the full - crazy, intelligent, imaginative, smart, musical, superstitious, religious, even - human from biology. We appear to be living in a very exciting time where a lot of stuff that was in what I’d call the realm of superstition – is being dusted off and actually inspected. Maybe it’ll go on like this forever, but I can’t imagine that we won’t run out of things pretty soon at the current rate.
Thursday, October 30, 2008
In the past ten years, the evolutionary and cognitive study of religion has begun to mature. It does not try to identify the gene or genes for religious thinking. Nor does it simply dream up evolutionary scenarios that might have led to religion as we know it. It does much better than that. It puts forward new hypotheses and testable predictions. It asks what in the human make-up renders religion possible and successful. Religious thought and behaviour can be considered part of the natural human capacities, such as music, political systems, family relations or ethnic coalitions. Findings from cognitive psychology, neuroscience, cultural anthropology and archaeology promise to change our view of religion.
Unlike other social animals, humans are very good at establishing and maintaining relations with agents beyond their physical presence; social hierarchies and coalitions, for instance, include temporarily absent members. This goes even further. From childhood, humans form enduring, stable and important social relationships with fictional characters, imaginary friends, deceased relatives, unseen heroes and fantasized mates. Indeed, the extraordinary social skills of humans, compared with other primates, may be honed by constant practice with imagined or absent partners.
It is a small step from having this capacity to bond with non-physical agents to conceptualizing spirits, dead ancestors and gods, who are neither visible nor tangible, yet are socially involved. This may explain why, in most cultures, at least some of the superhuman agents that people believe in have moral concerns.
In addition, the neurophysiology of compulsive behaviour in humans and other animals is beginning to shed light on religious rituals. These behaviours include stereotyped, highly repetitive actions that participants feel they must do, even though most have no clear, observable results, such as striking the chest three times while repeating a set formula. Ritualized behaviour is also seen in patients with obsessive-compulsive disorders and in the routines of young children. In these contexts, rituals are generally associated with thoughts about pollution and purification, danger and protection, the required use of particular colours or numbers or the need to construct a safe and ordered environment.
So is religion an adaptation or a by-product of our evolution? Perhaps one day we will find compelling evidence that a capacity for religious thoughts, rather than 'religion' in the modern form of socio-political institutions, contributed to fitness in ancestral times. For the time being, the data support a more modest conclusion: religious thoughts seem to be an emergent property of our standard cognitive capacities.
Religious concepts and activities hijack our cognitive resources, as do music, visual art, cuisine, politics, economic institutions and fashion. This hijacking occurs simply because religion provides some form of what psychologists would call super stimuli. Just as visual art is more symmetrical and its colours more saturated than what is generally found in nature, religious agents are highly simplified versions of absent human agents, and religious rituals are highly stylized versions of precautionary procedures. Hijacking also occurs because religions facilitate the expression of certain behaviours. This is the case for commitment to a group, which is made all the more credible when it is phrased as the acceptance of bizarre or non-obvious beliefs.
Some form of religious thinking seems to be the path of least resistance for our cognitive systems. By contrast, disbelief is generally the result of deliberate, effortful work against our natural cognitive dispositions — hardly the easiest ideology to propagate.
Wednesday, October 29, 2008
As an organism interacts with the world, how good or bad things are at the moment, the value of the current state of the organism, is an important parameter that is likely to be encoded in the brain. As the environment changes and new stimuli appear, estimates of state value must be updated to support appropriate responses and learning. Indeed, many models of reinforcement learning posit representations of state value. We examined how the brain mediates this process by recording amygdala neural activity while monkeys performed a trace-conditioning task requiring fixation. The presentation of different stimuli induced state transitions; these stimuli included unconditioned stimuli (USs) (liquid rewards and aversive air puffs), newly learned reinforcement-predictive visual stimuli [conditioned stimuli (CSs)], and familiar stimuli long associated with reinforcement [fixation point (FP)]. The FP had a positive value to monkeys, because they chose to foveate it to initiate trials. Different populations of amygdala neurons tracked the positive or negative value of the current state, regardless of whether state transitions were caused by the FP, CSs, or USs. Positive value-coding neurons increased their firing during the fixation interval and fired more strongly after rewarded CSs and rewards than after punished CSs and air puffs. Negative value-coding neurons did the opposite, decreasing their firing during the fixation interval and firing more strongly after punished CSs and air puffs than after rewarded CSs and rewards. This representation of state value could underlie how the amygdala helps coordinate cognitive, emotional, and behavioral responses depending on the value of one's state.
The results are in: Australia is the most prosperous country in the world; Yemen drags at the bottom of the list. But it's not just wealth that makes a country prosperous, according to the 2008 prosperity index, also known as the "happiness index," published last week by the Legatum Institute (LI) in Dubai (see www.prosperity.com). The institute based its rankings on surveys of economic competitiveness and comparative livability from 140 countries, including factors such as capital investment and the degree of social equality.You might enjoy playing with the 'prosperiscope' on the site.
This year, for the first time, countries' environmental efforts counted toward their scores, says LI Senior Vice President William Inboden. The institute selected an objective measurement--the ratio of developed land to land remaining in its natural state in each country--and added questions about how respondents felt about their country's environmental policies. Depending on a country's wealth, the environmental measures could count for as much as 4% of a country's prosperity score. Although Australia was the most prosperous country overall, New Zealand topped the environmental measures. The most environmentally unhappy people were Ukrainians, who particularly dislike their air quality.
"The Legatum Prosperiscope™ is a powerful interactive online tool that allows users to customise analyses across 104 countries using 22 different factors. Users can also compare countries against each other to identify their relative strengths and weaknesses. Follow the simple steps on the right to start using the Prosperiscope."
Tuesday, October 28, 2008
Brain imaging studies have traced the approximate number sense to a specific neural structure called the intraparietal sulcus, which also helps assess features like an object’s magnitude and distance. Symbolic math, by contrast, operates along a more widely distributed circuitry, activating many of the prefrontal regions of the brain that we associate with being human. Somewhere, local and global must be hooked up to a party line.
...open questions include how malleable our inborn number sense may be, whether it can be improved with training, and whether those improvements would pay off in a greater appetite and aptitude for math. If children start training with the flashing dot game at age 4, will they be supernumerate by middle school?
Monday, October 27, 2008
"Warmth" is the most powerful personality trait in social judgment, and attachment theorists have stressed the importance of warm physical contact with caregivers during infancy for healthy relationships in adulthood. Intriguingly, recent research in humans points to the involvement of the insula in the processing of both physical temperature and interpersonal warmth (trust) information. Accordingly, we hypothesized that experiences of physical warmth (or coldness) would increase feelings of interpersonal warmth (or coldness), without the person's awareness of this influence. In study 1, participants who briefly held a cup of hot (versus iced) coffee judged a target person as having a "warmer" personality (generous, caring); in study 2, participants holding a hot (versus cold) therapeutic pad were more likely to choose a gift for a friend instead of for themselves.
Metaphors such as icy stare depict social exclusion using cold-related concepts; they are not to be taken literally and certainly do not imply reduced temperature. Two experiments, however, revealed that social exclusion literally feels cold. Experiment 1 found that participants who recalled a social exclusion experience gave lower estimates of room temperature than did participants who recalled an inclusion experience. In Experiment 2, social exclusion was directly induced through an on-line virtual interaction, and participants who were excluded reported greater desire for warm food and drink than did participants who were included. These findings are consistent with the embodied view of cognition and support the notion that social perception involves physical and perceptual content. The psychological experience of coldness not only aids understanding of social interaction, but also is an integral part of the experience of social exclusion.More detail on the two experiments:
In one, they split 65 students into two groups, instructing those in one to recall a time when they felt socially rejected, and those in the other to summon a memory of social acceptance.
Many of the students were recent immigrants and had fresh memories of being isolated in the dorms, left behind while roommates went out, Dr. Zhong said.
The researchers then had each of the participants estimate the temperature in the lab room. The students who had recalled being excluded estimated the temperature to be, on average, 5 degrees Fahrenheit lower than the others.
In the second experiment, the researchers had 52 students come into the lab and play a computer game, one at a time. The students “threw” a ball back and forth with three other figures on the computer screen that — so the participants thought — represented other students playing from remote locations.
In fact a computer program was running the game, and it excluded half the study participants, throwing them the virtual ball a couple of times in the beginning, then ignoring them altogether. The other group of students in the study were included in the virtual game of catch.
After playing the game, the participants in this study then rated their preferences for a variety of foods and drinks, including hot soup, coffee, an apple and crackers. Those who had been isolated in the computer game showed a strong preference for the soup and coffee over the other items; the included students had no such preference.
Sunday, October 26, 2008
Friday, October 24, 2008
In economic theory the winner’s curse refers to the idea that someone who places the winning bid in an auction may have paid too much. Consider, for example, bids to develop an oil field. Most of the offers are likely to cluster around the true value of the resource, so the highest bidder probably paid too much.
The same thing may be happening in scientific publishing, according to a new analysis. With so many scientific papers chasing so few pages in the most prestigious journals, the winners could be the ones most likely to oversell themselves—to trumpet dramatic or important results that later turn out to be false. This would produce a distorted picture of scientific knowledge, with less dramatic (but more accurate) results either relegated to obscure journals or left unpublished.
It starts with the nuts and bolts of scientific publishing. Hundreds of thousands of scientific researchers are hired, promoted and funded according not only to how much work they produce, but also to where it gets published. For many, the ultimate accolade is to appear in a journal like Nature or Science. Such publications boast that they are very selective, turning down the vast majority of papers that are submitted to them.
The assumption is that, as a result, such journals publish only the best scientific work. But Dr Ioannidis and his colleagues argue that the reputations of the journals are pumped up by an artificial scarcity of the kind that keeps diamonds expensive. And such a scarcity, they suggest, can make it more likely that the leading journals will publish dramatic, but what may ultimately turn out to be incorrect, research.
Four different accounts of the relationship between third-person mindreading and first-person metacognition are compared and evaluated. While three of them endorse the existence of introspection for propositional attitudes, the fourth (defended here) claims that our knowledge of our own attitudes results from turning our mindreading capacities upon ourselves. Section 1 introduces the four accounts. Section 2 develops the “mindreading is prior” model in more detail, showing how it predicts introspection for perceptual and quasi-perceptual (e.g. imagistic) mental events while claiming that metacognitive access to our own attitudes always results from swift unconscious self-interpretation. It also considers the model’s relationship to the expression of attitudes in speech. Section 3 argues that the commonsense belief in the existence of introspection should be given no weight. Section 4 argues briefly that data from childhood development are of no help in resolving this debate. Section 5 considers the evolutionary claims to which the different accounts are committed, and argues that the three introspective views make predictions that aren’t borne out by the data. Section 6 examines the extensive evidence that people often confabulate when self-attributing attitudes. Section 7 considers “two systems” accounts of human thinking and reasoning, arguing that although there are inrospectable events within System 2, there are no introspectable attitudes. Section 8 examines alleged evidence of “unsymbolized thinking”. Section 9 considers the claim that schizophrenia exhibits a dissociation between mindreading and metacognition. Finally, Section 10 evaluates the claim that autism presents a dissociation in the opposite direction, of metacognition without mindreading.
Thursday, October 23, 2008
We hypothesized that individual differences in intelligence (Spearman's g) are supported by multiple brain regions, and in particular that fluid (gF) and crystallized (gC) components of intelligence are related to brain function and structure with a distinct profile of association across brain regions. In 225 healthy young adults scanned with structural and functional magnetic resonance imaging sequences, regions of interest (ROIs) were defined on the basis of a correlation between g and either brain structure or brain function. In these ROIs, gC was more strongly related to structure (cortical thickness) than function, whereas gF was more strongly related to function (blood oxygenation level-dependent signal during reasoning) than structure. We further validated this finding by generating a neurometric prediction model of intelligence quotient (IQ) that explained 50% of variance in IQ in an independent sample. The data compel a nuanced view of the neurobiology of intelligence, providing the most persuasive evidence to date for theories emphasizing multiple distributed brain regions differing in function.As background:
gC, sometimes described as verbal ability, is more dependent on accumulated knowledge in long-term storage, including semantic memory. gF refers to reasoning ability, and is known to depend on working memory. Although gC and gF are typically correlated and can be considered subfactors of g (Jensen), they are conceptually and empirically separable. For instance, gC continues to increase over the lifespan, but gF peaks in early adulthood and then declines . Furthermore, at the neural level, lesion studies demonstrated that patients with anterior temporal damages perform poorly on tests of semantic knowledge, whereas prefrontal patients typically show profound deficits in solving diverse reasoning tasks.
Working memory (WM) performance, which is an important factor for determining problem-solving and reasoning ability, has been firmly believed to be constant. However, recent findings have demonstrated that WM performance has the potential to be improved by repetitive training. Although various skills are reported to be improved by sleep, the beneficial effect of sleep on WM performance has not been clarified. Here, we show that improvement in WM performance is facilitated by posttraining naturalistic sleep. A spatial variant of the n-back WM task was performed by 29 healthy young adults who were assigned randomly to three different experimental groups that had different time schedules of repetitive n-back WM task sessions, with or without intervening sleep. Intergroup and intersession comparisons of WM performance (accuracy and response time) profiles showed that n-back accuracy after posttraining sleep was significantly improved compared with that after the same period of wakefulness, independent of sleep timing, subject's vigilance level, or circadian influences. On the other hand, response time was not influenced by sleep or repetitive training schedules. The present study indicates that improvement in n-back accuracy, which could reflect WM capacity, essentially benefits from posttraining sleep.
Wednesday, October 22, 2008
Studies have shown that cognitive therapy is as efficacious as antidepressant medication at treating depression, and it seems to reduce the risk of relapse even after its discontinuation. Cognitive therapy and antidepressant medication probably engage some similar neural mechanisms, as well as mechanisms that are distinctive to each.
Cognitive therapy and antidepressant medication have comparable effects. This graph shows the response of outpatients who had moderate-to-severe depression to cognitive therapy (CT), antidepressant medication (ADM) or placebo. Patients who were assigned to ADM or to CT showed a significantly higher response rate after 8 weeks of treatment than those who were assigned to placebo. After 16 weeks of treatment the response rates of ADM and CT were almost identical.
Less relapse after cognitive therapy compared with antidepressant medication. The second phase of the parent antidepressant medication (ADM) versus cognitive therapy (CT) study followed patients who had responded to ADM or to CT3. Patients who had responded to ADM were randomly assigned to either continue ADM treatment for one year (beige and red lines) or to change to placebo treatment for 1 year (green line). Patients who responded to CT were allowed three sessions of CT during the 1-year continuation period. In the follow-up period, none of the patients received any treatment. The figure shows that prior treatment with CT protected against relapse of depression at least as well as the continued provision of ADM, and better than ADM treatment that was subsequently discontinued. Note that the patient group that was given ADM in the continuation year contained a number of patients who did not adhere to the medication regimen. The red line indicates the response of the ADM-continuation group including these non-compliant patients, whereas the beige line shows the response of the patients in this group after the non-compliant patients had been removed from the analysis.
After a graphic showing changes in blood-oxygen-level-dependent (BOLD) signal in response to cognitive and emotional tasks associated with cognitive therapy, the authors offer a summary hypothetical time course of the changes to amygdala and prefrontal function that are associated with antidepressant medication and cognitive therapy.
a | During acute depression, amygdala activity is increased (red) and prefrontal activity is decreased (blue) relative to activity in these regions in healthy individuals. b | Cognitive therapy (CT) effectively exercises the prefrontal cortex (PFC), yielding increased inhibitory function of this region. c | Antidepressant medication (ADM) targets amygdala function more directly, decreasing its activity. d | After ADM or CT, amygdala function is decreased and prefrontal function is increased. The double-headed arrow between the amygdala and the PFC represents the bidirectional homeostatic influences that are believed to operate in healthy individuals.
Humans are especially interested in faces, as a means of sending signals--witness the sizeable arc of somatosensory cortex devoted to representation of one's own face--and as a substrate for social cognition. Pitcher et al. describe results supporting theories of embodied cognition and emotion, which posit cognition and emotion as being shaped by our bodily movements and perceptions. They used repetitive transcranial magnetic stimulation (rTMS) to interfere with neural activity in the face areas of the somatosensory cortex while people discriminated the emotional expressions of faces (happy, sad, surprised, fearful, angry, and disgusted) and found that accuracy dropped significantly, as it also did when the occipital face area was similarly stimulated. The temporal sequence of neural processing was then delineated using double-pulse TMS, showing that the occipital area acted in the time window from 60 to 100 ms after the face stimulus was shown, whereas the somatosensory area was active a bit later, between 100 and 170 ms.
Tuesday, October 21, 2008
Agreement is emerging that selective pressures over the course of human evolution can explain the wide cross-cultural re-occurrence, historical persistence, and predictable cognitive structure of religious beliefs and behaviors. The tendency to detect agency in nature likely supplied the cognitive template that supports the pervasive belief in supernatural agents. These agents are widely believed to transcend physical, biological, and psychological limitations. However, other important details are subject to cultural variation. Although in many societies supernatural agents are not directly concerned with human morality, in many others, morally concerned agents use their supernatural powers to observe and, in some cases, to punish and reward human social interactions. Examples include the God of Abrahamic religions and Viracocha, the Incan supreme God, but also many morally concerned deities found in traditional societies, such as the adalo, ancestral spirits of the Kwaio Solomon islanders. These beliefs are likely to spread culturally to the extent that they facilitate ingroup cooperation. This could occur by conforming to individual psychology that favors reputation-sensitive prosocial tendencies, as the by-product account holds; by competition among social groups, as the cultural group selection account would suggest; or possibly by some combination of the two. Religious behaviors and rituals, if more costly to cooperating group members than to freeloaders, may have reliably signaled the presence of devotion and, therefore, cooperative intention toward ingroup members, in turn, buffering religious groups against defection from freeloaders and reinforcing cooperative norms. Religious prosociality, thus, may have softened the limitations that kinship-based and (direct or indirect) reciprocity-based altruism place on group size. In this way, the cultural spread of religious prosociality may have facilitated the rise of stable, large, cooperative communities of genetically unrelated individuals.
Figure - Implicit activation of God concepts, relative to a neutral prime, increased offers in the one-shot, anonymous Dictator Game. Priming secular concepts indicating moral authority had a similar effect. The results showed not only a quantitative increase in generosity, but also a qualitative shift in social norms. In the control group, the modal response was selfishness, a plurality of players pocketed all $10. In the God group, the mode shifted to fairness, a plurality of players split the money evenly (N = 75). It remains to be seen, however, whether these effects
would occur if the recipient was clearly marked as an outgroup member.
Figure - Life expectancy of religious versus secular communes. An analysis of 200 religious and secular communes in 19th-century America (29), for every year of their life course, religious communes were about four times as likely to survive than their secular counterparts. This difference remained after statistically controlling for type of commune movement, year founded, and year at risk of dissolution (the last control assesses major historical trends that may independently impact commune dissolution).
In their recent book “The Loss of Sadness” (Oxford, 2007), Allan V. Horwitz and Jerome C. Wakefield assert that for thousands of years, symptoms of sadness that were “with cause” were separated from those that were “without cause.” Only the latter were viewed as mental disorders.
With the advent of modern diagnostic criteria, these authors argue, doctors were directed to ignore the context of the patient’s complaints and focus only on symptoms — poor appetite, insomnia, low energy, hopelessness and so on. The current criteria for major depression, they say, largely fail to distinguish between “abnormal” reactions caused by “internal dysfunction” and “normal sadness” brought on by external circumstances. And they blame vested interests — doctors, researchers, pharmaceutical companies — for fostering this bloated concept of depression.
But while this increasingly popular thesis contains a kernel of truth, it conceals a bushel basket of conceptual and scientific problems.
For one thing, if modern diagnostic criteria were converting mere sadness into clinical depression, we would expect the number of new cases of depression to be skyrocketing compared with rates in a period like the 1950s to the 1970s. But several new studies in the United States and Canada find that the incidence of serious depression has held relatively steady in recent decades.
Second, it may seem easy to determine that someone with depressive complaints is reacting to a loss that touched off the depression. Experienced clinicians know this is rarely the case.
Third, and perhaps most troubling, is the implication that a recent major loss makes it more likely that the person’s depressive symptoms will follow a benign and limited course, and therefore do not need medical treatment. This has never been demonstrated, to my knowledge, in any well-designed studies. And what has been demonstrated, in a study by Dr. Sidney Zisook, is that antidepressants may help patients with major depressive symptoms occurring just after the death of a loved one.
Monday, October 20, 2008
Our high-tech revolution has plunged us into a state of “continuous partial attention,” which software executive Linda Stone, who coined the term in 1998, describes as continually staying busy—keeping tabs on everything while never truly focusing on anything. Continuous partial attention differs from multitasking, wherein we have a purpose for each task and we are trying to improve efficiency and productivity. Instead, when our minds partially attend, and do so continuously, we scan for an opportunity for any type of contact at every given moment. We virtually chat as our text messages flow, and we keep tabs on active buddy lists (friends and other screen names in an instant message program); everything, everywhere, is connected through our peripheral attention. Although having all our pals online from moment to moment seems intimate, we risk losing personal touch with our real-life relationships and may experience an artificial sense of intimacy as compared with when we shut down our devices and devote our attention to one
individual at a time.
When paying continuous partial attention, people may place their brain in a heightened state of stress. They no longer have time to reflect, contemplate or make thoughtful decisions. Instead they exist in a sense of constant crisis—on alert for a new contact or bit of exciting news or information at any moment. Once people get used to this state, they tend to thrive on the perpetual connectivity. It feeds their ego and sense of self-worth, and it becomes irresistible. Neuroimaging studies suggest that this sense of selfworth may protect the size of the hippocampus—the horseshoeshaped brain region in the medial (inward-facing) temporal lobe, which allows us to learn and remember new information. Psychiatry professor Sonia J. Lupien and her associates at McGill University studied hippocampal size in healthy younger and older adult volunteers. Measures of self esteem correlated significantly with hippocampal size, regardless of age. They also found that the more people felt in control of their lives, the larger the hippocampus. But at some point, the sense of control and self-worth we feel when we maintain continuous partial attention tends to break down—our brains were not built to sustain such monitoring for extended periods. Eventually the hours of unrelenting digital connectivity can create a unique type of brain strain. Many people who have been working on the Internet for several hours without a break report making frequent errors in their work. On signing off, they notice feeling spaced out, fatigued, irritable and distracted, as if they are in a “digital fog.” This new form of mental stress, what Small terms “techno-brain burnout,” is threatening to become an epidemic. Under this kind of stress, our brains instinctively signal the adrenal gland to secrete cortisol and adrenaline. In the short run, these stress hormones boost energy levels and augment memory, but over time they actually impair cognition, lead to depression, and alter the neural circuitry in the hippocampus, amygdala and prefrontal cortex—the brain regions that control mood and thought. Chronic and prolonged techno-brain burnout can even reshape the underlying brain structure.
While the brains of today’s digital natives are wiring up for rapid-fire cyber searches, however, the neural circuits that control the more traditional learning methods are neglected and gradually diminished. The pathways for human interaction and communication weaken as customary one-on-one people skills atrophy. Our U.C.L.A. research team and other scientists have shown that we can intentionally alter brain wiring and reinvigorate some of these dwindling neural pathways, even while the newly evolved technology circuits bring our brains to extraordinary levels of potential.
In the winner-take-all world of politics, candidates know that even a modest lead in the polls can spell almost certain victory. Sheldon Jacobson, an operations research specialist at the University of Illinois, Urbana-Champaign, and colleagues, including a group of students, have attempted to quantify that insight for the current United States presidential election, putting their predictions for the Electoral College on a Web site, election08.cs.uiuc.edu. Using a statistical method known as Bayesian estimation, they combined an analysis of results from the 2004 Bush-versus-Kerry contest with current state-by-state polls for Obama versus McCain to produce probabilities for each candidate of carrying each state. They then converted the estimates into a probability distribution for the total number of Electoral College votes a candidate might receive. In Indiana, for example, polls as of 4 October gave McCain a slight 2.5% lead. But given that Bush carried Indiana in 2004 by 20.7%, a Bayesian calculation indicates McCain's chance of winning the state's 11 Electoral College votes at about 87%. Most states are now in the bag for one candidate or the other; only a handful are truly in Bayesian play. Current calculations give McCain no chance of victory. "However," Jacobson cautions, "if the polls move, then so will our forecasts."
Friday, October 17, 2008
We are living, we have long been told, in the Information Age. Yet now we are faced with the sickening suspicion that technology has run ahead of us. Man is a fire-stealing animal, and we can’t help building machines and machine intelligences, even if, from time to time, we use them not only to outsmart ourselves but to bring us right up to the doorstep of Doom.
We are still fearful, superstitious and all-too-human creatures. At times, we forget the magnitude of the havoc we can wreak by off-loading our minds onto super-intelligent machines, that is, until they run away from us, like mad sorcerers’ apprentices, and drag us up to the precipice for a look down into the abyss.
As the financial experts all over the world use machines to unwind Gordian knots of financial arrangements so complex that only machines can make — “derive” — and trade them, we have to wonder: Are we living in a bad sci-fi movie? Is the Matrix made of credit default swaps?
When Treasury Secretary Paulson (looking very much like a frightened primate) came to Congress seeking an emergency loan, Senator Jon Tester of Montana, a Democrat still living on his family homestead, asked him: “I’m a dirt farmer. Why do we have one week to determine that $700 billion has to be appropriated or this country’s financial system goes down the pipes?”
“Well, sir,” Mr. Paulson could well have responded, “the computers have demanded it.”
Gene expression profiles were assessed in the hippocampus, entorhinal cortex, superior-frontal gyrus, and postcentral gyrus across the lifespan of 55 cognitively intact individuals aged 20–99 years. Perspectives on global gene changes that are associated with brain aging emerged, revealing two overarching concepts. First, different regions of the forebrain exhibited substantially different gene profile changes with age. For example, comparing equally powered groups, 5,029 probe sets were significantly altered with age in the superior-frontal gyrus, compared with 1,110 in the entorhinal cortex. Prominent change occurred in the sixth to seventh decades across cortical regions, suggesting that this period is a critical transition point in brain aging, particularly in males. Second, clear gender differences in brain aging were evident, suggesting that the brain undergoes sexually dimorphic changes in gene expression not only in development but also in later life. Globally across all brain regions, males showed more gene change than females. Further, Gene Ontology analysis revealed that different categories of genes were predominantly affected in males vs. females. Notably, the male brain was characterized by global decreased catabolic and anabolic capacity with aging, with down-regulated genes heavily enriched in energy production and protein synthesis/transport categories. Increased immune activation was a prominent feature of aging in both sexes, with proportionally greater activation in the female brain. These data open opportunities to explore age-dependent changes in gene expression that set the balance between neurodegeneration and compensatory mechanisms in the brain and suggest that this balance is set differently in males and females, an intriguing idea.
Thursday, October 16, 2008
...his overall task is to address the befuddled dualism that still dominates most of our intellectual disciplines...Slingerland's central theme is that everything human has evolved in the interests of the materiality of the body. He identifies objectivist realism and postmodern relativity, both insufficiently attentive to the body, as the major epistemologies to be swept away, followed by the dualism of body and soul. For Slingerland, the presiding genii behind such a cleansing are George Lakoff and Mark Johnson, with heavier debts to Johnson [whose terse summary of embodiment in (1) appeared too late for Slingerland to reference]. They view all thought and human behavior as generated by the body and expressed as conceptual metaphors that translate physical categories (such as forward, backward, up, and down) into abstract categories (such as progress, benightedness, divinity, immorality). These body-driven metaphors, Slingerland writes, are a "set of limitations on human cognition, constraining human conceptions of entities, categories, causation, physics, psychology, biology, and other humanly relevant domains."
The supposedly objective world is not "some preexisting object out there in the world, with a set of invariant and observer-independent properties, simply waiting to be found the way one finds a lost sock under the bed." All we can ever see or understand is what our own bodily faculties permit via the current structure of the brain.
In opposition to objective realism, postmodern relativity regards language and culture as constituting the only "real" world possible for us. It posits an endless hall of mirrors with no access to outside--epitomized by Derrida's notorious remark that there is nothing (at least for humans) outside of texts (i.e., culture). This view, which dominated the humanities for several decades, is mercifully beginning to fade as the cognitive sciences have matured and are increasingly promulgated.
Even though the knowing human subject is itself just a thing and not an immaterial locus of reason, the universe it experiences is as real and functional for us as any "thing" could possibly be. We do get some things "right," even if we can never know the noumenal genesis behind our knowledge. And the very concept of noumena (things in themselves independent of any observer) now seems somewhat obsolete, given that the intuition of discrete, self-bounded "things" is as built-in to the human psyche as the Kantian intuitions of space and time, grounding all experience.
Our million billion synapses produce a "person" with the illusion of a self. Slingerland holds that "we are robots designed to be constitutionally incapable of experiencing ourselves and other conspecifics as robots." Our innate and overactive theory of mind (that other people, like ourselves, have "intentions") projects agency onto everything--in the past, even onto stones and trees. The "hard problem" for philosophy of consciousness (to use David Chalmers's phrase) remains: what are thoughts, cogitations, thinkers, qualia? Chalmers's solution, alas, swept away Cartesian dualism only to sneak his own magic spook, conscious experience (for him, on par with mass, charge, and space-time), in through the back door (2, 3).
Slingerland starts with Darwin and eventually follows Daniel Dennett so far as to agree that consciousness can be done full justice through third-person descriptions that require no mysterious, unaccounted-for, nonmaterial, first-person entity as substrate. Thus the famous "Mary," who intellectually knows everything there is to know about color despite having been sequestered for life in a color-free lab, will recognize red the first time she steps outside (4). And Thomas Nagel's famous bats don't know anything about bathood that we can't figure out for ourselves from observation (5). No first-person construct, no locus of consciousness, need be invoked.
The next step, if you want to go so far (the jury is out), is to eliminate consciousness altogether, because there's nothing for it to do that can't be done without it. And with it, you need a spook to keep the show on the road. Choose your insoluble problem: eliminate consciousness altogether as superfluous or explain it (if there's really a you who makes such choices). Slingerland prefers the first option.
His conclusion, which I can hardly do justice to here, is relatively satisfying. He notes that although we don't have great difficulty knowing that Earth revolves around the Sun while feeling that the Sun is rising and setting (Dennett's favorite example of folk psychology), "no cognitively undamaged human being can help acting like and at some level really feeling that he or she is free"--however nonsensical the notion of agencyless free will (i.e., "choices" without a self to make them). Still, once the corrosive acid of Darwinism [to use Dennett's figure from (6)] has resolved the body-mind dualism into body alone, some but not most of us are able "to view human beings simultaneously under two descriptions: as physical systems and as persons."
1. M. Johnson, The Meaning of the Body: Aesthetics of Human Understanding (Univ. of Chicago Press, Chicago, 2007).
2. D. J. Chalmers, J. Consciousness Stud. 2, 200 (1995).
3. D. J. Chalmers, The Conscious Mind: In Search of a Fundamental Theory (Oxford Univ. Press, Oxford, 1996).
4. F. Jackson, Philos. Q. 32, 127 (1982).
5. T. Nagel, Philos. Rev. 83, 435 (1974).
6. D. C. Dennett, Darwin's Dangerous Idea: Evolution and the Meaning of Life (Simon and Schuster, New York, 1995).
Neural circuits that allow for reciprocal communication between the brain and viscera are critical for coordinating behavior with visceral activity. At the same time, these circuits are positioned to convey signals from pathologic events occurring in viscera to the brain, thereby providing a structural basis for comorbid central and peripheral symptoms. In the pons, Barrington's nucleus and the norepinephrine (NE) nucleus, locus coeruleus (LC), are integral to a circuit that links the pelvic viscera with the forebrain and coordinates pelvic visceral activity with arousal and behavior. Here, we demonstrate that a prevalent bladder dysfunction, produced by partial obstruction in rat, has an enduring disruptive impact on cortical activity through this circuit. Within 2 weeks of partial bladder obstruction, the activity of LC neurons was tonically elevated. LC hyperactivity was associated with cortical electroencephalographic activation that was characterized by decreased low-frequency (1–3 Hz) activity and prominent theta oscillations (6–8 Hz) that persisted for 4 weeks. Selective lesion of the LC–NE system significantly attenuated the cortical effects. The findings underscore the potential for significant neurobehavioral consequences of bladder disorders, including hyperarousal, sleep disturbances, and disruption of sensorimotor integration, as a result of central noradrenergic hyperactivity. The results further imply that pharmacological manipulation of central NE function may alleviate central sequelae of these visceral disorders.
Wednesday, October 15, 2008
fear now seems to rule, with investors often exhibiting a Wall Street version of the fight-or-flight mechanism — selling first, and asking questions later...some analysts are starting to suggest the markets are showing signs of “capitulation” — what happens when even the bullish holdouts, the unflagging optimists, throw up their hands and join the stampede out of the market...To some, signs of capitulation can be read as an indicator that the bottom may be near.The opposite swing of the cycle is buying at the top of a bubble. I remember during my winter stays in Ft. Lauderdale in 2005 and 2006, every fourth person I chatted with seemed to be a realtor and dinner conversations were dominated by stories about fast profits on flipped condominiums.
Predicting how they will govern. Most language dimensions that we study are probably better markers of how people will lead than who will vote for them. Some dimensions that are relevant include:
Cognitive complexity. A particularly reliable marker of cognitive complexity is the exclusive word dimension. Exclusive words such as but, except, without, exclude, signal that the speaker is making an effort to distinguish what is in a category and not in a category. Those who use more exclusive words make better grades in college, are more honest in lab studies, and have more nuanced understanding of events and people. Through the primaries until now, Obama has consistently been the highest in exclusive word use and McCain the lowest.
Categorical versus fluid thinking. Some people naturally approach problems by assigning them to categories. Categorical thinking involves the use of articles (a, an, the) and concrete nouns. Men, for example, use articles at much higher rates than women. Fluid thinking involves describing actions and changes, often in more abstract ways. A crude measure of fluid thinking is the use of verbs. Women use verbs more than men.
McCain and Obama could not be more different in their use of articles and verbs. McCain uses verbs at an extremely low rate and articles at a fairly high rate. Obama, on the other hand, is remarkably high in his use of verbs and low in his use of articles. These patterns suggest that McCain’s natural way of understanding the world is to first label the problem and find a way to put it into a pre-existing category. Obama is more likely to define the world as ongoing actions or processes.
Personal and socially connected. Individuals who think about and try to connect with others tend to use more personal pronouns (I, we, you, she, they) than those who are more socially detached. Bush was higher than Kerry or Gore. McCain has consistently been much higher than any other candidate in this election cycle. His use of 1st person singular (I, me, my) is particularly high which often signals an openness and honesty. Obama uses personal pronouns at moderate levels - similar to Hillary Clinton and most other primary candidates of both parties.
Restrained versus impulsive. People vary in the degree to which they act quickly or shoot from the hip versus stand back and consider their options. Over the last few years, some have argued that the use of negations (e.g., no, not, never) indicate a sign of inhibition or constraint. Low use of negations may be linked to impulsiveness. Bush was low in negations whereas Kerry was quite high. Across the election cycle, Obama has consistently been the highest user of negations - suggesting a restrained approach - where as McCain has been the lowest - a more impulsive way of dealing with the world.
Tuesday, October 14, 2008
The statement "An agent harms a victim" depicts a situation that triggers moral emotions. Depending on whether the agent and the victim are the self or someone else, it can lead to four different moral emotions: self-anger ("I harm myself"), guilt ("I harm someone"), other-anger ("someone harms me"), and compassion ("someone harms someone"). In order to investigate the neural correlates of these emotions, we examined brain activation patterns elicited by variations in the agent (self vs. other) and the victim (self vs. other) of a harmful action. Twenty-nine healthy participants underwent functional magnetic resonance imaging while imagining being in situations in which they or someone else harmed themselves or someone else. Results indicated that the three emotional conditions associated with the involvement of other, either as agent or victim (guilt, other-anger, and compassion conditions), all activated structures that have been previously associated with the Theory of Mind (ToM, the attribution of mental states to others), namely, the dorsal medial prefrontal cortex, the precuneus, and the bilateral temporo-parietal junction. Moreover, the two conditions in which both the self and other were concerned by the harmful action (guilt and other-anger conditions) recruited emotional structures (i.e., the bilateral amygdala, anterior cingulate, and basal ganglia). These results suggest that specific moral emotions induce different neural activity depending on the extent to which they involve the self and other.
Slime moulds exhibit the kind of "contemplative behaviour" that Hamlet is famous for, muses Toshiyuki Nakagaki of Hokkaido University in Japan. ...The slime mold's puzzle-solving ability — Shakespearean or otherwise — is a discovery that is unlikely to change the world, but it won Nakagaki and his colleagues an Ig Nobel Prize for cognitive science last week at the annual event held at Harvard University in Cambridge, Massachusetts. Their research... showed that slime molds looking for food have "the ability to find the minimum-length solution between two points in a labyrinth".
Subsequently, the team has found that molds can find the shortest path between 30–50 points, which is something even supercomputers cannot yet work out. "We can't even check the mold's solution," notes Nakagaki, "but it looks good."
Monday, October 13, 2008
How does selective attention to affect influence sensory processing? In a functional magnetic resonance imaging investigation, when subjects were instructed to remember and rate the pleasantness of a jasmin odor, activations were greater in the medial orbitofrontal and pregenual cingulate cortex than when subjects were instructed to remember and rate the intensity of the odor. When the subjects were instructed to remember and rate the intensity, activations were greater in the inferior frontal gyrus. These top–down effects occurred not only during odor delivery but started in a preparation period after the instruction before odor delivery, and continued after termination of the odor in a short-term memory period. Thus, depending on the context in which odors are presented and whether affect is relevant, the brain prepares itself, responds to, and remembers an odor differently. These findings show that when attention is paid to affective value, the brain systems engaged to prepare for, represent, and remember a sensory stimulus are different from those engaged when attention is directed to the physical properties of a stimulus such as its intensity. This differential biasing of brain regions engaged in processing a sensory stimulus depending on whether the cognitive demand is for affect-related versus more sensory-related processing may be an important aspect of cognition and attention. This has many implications for understanding the effects not only of olfactory but also of other sensory stimuli.
Friday, October 10, 2008
Former studies have suggested that imprinting-like processes influence the shaping of human mate preferences. In this study, we provide more direct evidence for assessing facial resemblance between subjects' partner and subjects' parents. Fourteen facial proportions were measured on 312 adults belonging to 52 families, and the correlations between family members were compared with those of pairs randomly selected from the population. Spouses proved to be assortatively mated in the majority of measured facial proportions. Significant correlations have been found between the young men and their partner's father (but not his mother), especially on facial proportions belonging to the central area of the face. Women also showed resemblance to their partner's mother (but not to their father) in the facial characteristics of their lower face. Replicating our previous studies, facial photographs of participants were also matched by independent judges who ascribed higher resemblance between partners, and subjects and their partners' opposite-sex parents, compared with controls. Our results support the sexual imprinting hypothesis which states that children shape a mental template of their opposite-sex parents and search for a partner who resembles that perceptual schema. The fact that only the facial metrics of opposite-sex parents showed resemblance to the partner's face tends to rule out the role of familiarity in shaping mating preferences. Our findings also reject several other rival hypotheses. The adaptive value of imprinting-related human mating is discussed, and a hypothesis is made of why different facial areas are involved in males' and females' search for resemblance.
a, Rhodopsin, shown here in its inactivated conformation, is a light-sensing receptor found in cell membranes. It consists of a protein (opsin, green) and a ligand (retinal, pink, also shown in its inactivated conformation). When activated by light, rhodopsin binds to part of an adjacent G protein (binding region in red), triggering a cascade of biological responses. The protein plug (blue) is part of the extracellular domain of opsin, and immobilizes the extracellular transmembrane segments of the receptor. b, Scheerer et al. have determined the activated structure of opsin in complex with the receptor-binding peptide fragment of the G protein (the Galpha peptide). The most notable difference when compared with the inactivated receptor is that transmembrane helix 6 (TM-VI) has moved substantially outward (indicated by the red arrow), thereby creating the binding pocket for the G-protein peptide.
Thursday, October 09, 2008
Wednesday, October 08, 2008
The fury is based in instincts that have had a protective and often stabilizing effect on communities throughout human history. Small, integrated groups in particular often contain members who will stand up and — often at significant risk to themselves — punish cheaters, liars and freeloaders...The catch in this highly sensitive system, most researchers agree, is that it most likely evolved to inoculate small groups against invasive rogues, and not to set right the excesses of a vast and wildly diverse community like the American economy. Some experts believe that Japan’s disastrous delay in bailing out its banks in the early 1990s was caused in part by a collective urge to punish corrupt bankers, and they fear a similar outcome today.Carey describes a variety of investment game experiments that probe, for example, how our retribution behaviors depend on whether we are being observed by others.
We present six experiments that tested whether lacking control increases illusory pattern perception, which we define as the identification of a coherent and meaningful interrelationship among a set of random or unrelated stimuli. Participants who lacked control were more likely to perceive a variety of illusory patterns, including seeing images in noise, forming illusory correlations in stock market information, perceiving conspiracies, and developing superstitions. Additionally, we demonstrated that increased pattern perception has a motivational basis by measuring the need for structure directly and showing that the causal link between lack of control and illusory pattern perception is reduced by affirming the self. Although these many disparate forms of pattern perception are typically discussed as separate phenomena, the current results suggest that there is a common motive underlying them.
Tuesday, October 07, 2008
I am doing a unique experiment with my course this semester, "Biology of Mind." The course has a history of collaborative peer review on writing assignments, and the students do a lot of writing -- students who earn an "A" in the course will be required to produce 10,000 words of written assignments during the semester. In the past, I have used the university's online course system to administer the assignments, and the students have really benefited from their peers' feedback as well as my own.
This semester, I've decided to take it all public. The students are collaborating as before, except this semester they are doing it on a blog. The blog's name is "Biology of Mind", and it has been up and running for a couple of weeks. Right now there are over 200 posts over there, and the number continues to grow.
The students write weekly reviews of papers in psychology, neuroscience, evolutionary biology, philosophy of mind, and naturally anthropology -- a broad scope. Many of the students have been following new research, others have chosen to delve more deeply into the history of one or more fields. In any event, if you're interested in the brain, you may like this site. I think the students (mostly seniors with some graduate students) are producing some nice work, and the site is open for feedback from the public as well.
One of the major lessons of memory research has been that human memory is fallible, imprecise, and subject to interference. Thus, although observers can remember thousands of images, it is widely assumed that these memories lack detail. Contrary to this assumption, here we show that long-term memory is capable of storing a massive number of objects with details from the image. Participants viewed pictures of 2,500 objects over the course of 5.5 h. Afterward, they were shown pairs of images and indicated which of the two they had seen. The previously viewed item could be paired with either an object from a novel category, an object of the same basic-level category, or the same object in a different state or pose. Performance in each of these conditions was remarkably high (92%, 88%, and 87%, respectively), suggesting that participants successfully maintained detailed representations of thousands of images. These results have implications for cognitive models, in which capacity limitations impose a primary computational constraint (e.g., models of object recognition), and pose a challenge to neural models of memory storage and retrieval, which must be able to account for such a large and detailed storage capacity.
Figure: Example test pairs presented during the two-alternative forced-choice task for all three conditions (novel, exemplar, and state). The number of observers reporting the correct item is shown for each of the depicted pairs.
The floating fractal (top, left) is formed 90 seconds after a drop of instant coffee falls into a cup of milk.
Coffee is heavier than milk and the battle between gravity and surface tension plays out at the boundary between the two liquids. The coffee falls vertically through the milk (bottom, left, with water replacing milk for ease of viewing), and the fractal pattern emerges.
The pattern constantly shifts as parts of it are sucked into the milk, producing a fractal structure with the same dimension as a Sierpi´nski carpet — formed when a square is cut into nine identical squares; the central square is removed; and the procedure is repeated with the remaining eight squares and so on infinitely.
Michiko Shimokawa and Shonosuke Ohta, fluid scientists at Kyushu University in Fukuoka City, Japan, say that it is the first time this kind of fractal has been shown experimentally (http://www.arxiv.org/abs/0809.2458), and they managed to recreate the process using a magnetic liquid instead of coffee (far right).
Monday, October 06, 2008
Although political views have been thought to arise largely from individuals' experiences, recent research suggests that they may have a biological basis. We present evidence that variations in political attitudes correlate with physiological traits. In a group of 46 adult participants with strong political beliefs, individuals with measurably lower physical sensitivities to sudden noises and threatening visual images were more likely to support foreign aid, liberal immigration policies, pacifism, and gun control, whereas individuals displaying measurably higher physiological reactions to those same stimuli were more likely to favor defense spending, capital punishment, patriotism, and the Iraq War. Thus, the degree to which individuals are physiologically responsive to threat appears to indicate the degree to which they advocate policies that protect the existing social structure from both external (outgroup) and internal (norm-violator) threats.
Friday, October 03, 2008
Mathias Pessiglione et al. repeatedly showed 20 subjects abstract symbols as they played a gambling game. Each symbol presentation involved one of three choices and was followed by a 'masking image' in a series that flickered so fast that the subjects could not consciously perceive the symbol shapes. The subjects were told that the symbols were associated with winning or losing, and then allowed to gamble.
The subjects won more than they lost, indicating that their brains recognized the unperceived symbols and learned to associate them with reward or punishment. Functional neuroimaging showed that the mechanism involves the ventral striatum (see figure), a brain area associated with assessing reward value.
Exposure measurements from several countries indicate that humans are routinely exposed to low levels of bisphenol A (BPA), a synthetic xenoestrogen widely used in the production of polycarbonate plastics. There is considerable debate about whether this exposure represents an environmental risk, based on reports that BPA interferes with the development of many organs and that it may alter cognitive functions and mood. Consistent with these reports, we have previously demonstrated that BPA antagonizes spine synapse formation induced by estrogens and testosterone in limbic brain areas of gonadectomized female and male rats. An important limitation of these studies, however, is that they were based on rodent animal models, which may not be representative of the effects of human BPA exposure. To address this issue, we examined the influence of continuous BPA administration, at a daily dose equal to the current U.S. Environmental Protection Agency's reference safe daily limit, on estradiol-induced spine synapse formation in the hippocampus and prefrontal cortex of a nonhuman primate model. Our data indicate that even at this relatively low exposure level, BPA completely abolishes the synaptogenic response to estradiol. Because remodeling of spine synapses may play a critical role in cognition and mood, the ability of BPA to interfere with spine synapse formation has profound implications. This study is the first to demonstrate an adverse effect of BPA on the brain in a nonhuman primate model and further amplifies concerns about the widespread use of BPA in medical equipment, and in food preparation and storage.
Thursday, October 02, 2008
A suite of complex electroencephalographic patterns of sleep occurs in mammals. In sleeping zebra finches, we observed slow wave sleep (SWS), rapid eye movement (REM) sleep, an intermediate sleep (IS) stage commonly occurring in, but not limited to, transitions between other stages, and high amplitude transients reminiscent of K-complexes. SWS density decreased whereas REM density increased throughout the night, with late-night characterized by substantially more REM than SWS, and relatively long bouts of REM. Birds share many features of sleep in common with mammals, but this collective suite of characteristics had not been known in any one species outside of mammals. We hypothesize that shared, ancestral characteristics of sleep in amniotes evolved under selective pressures common to songbirds and mammals, resulting in convergent characteristics of sleep.
How children learn from positive and negative performance feedback lies at the foundation of successful learning and is therefore of great importance for educational practice. In this study, we used functional magnetic resonance imaging (fMRI) to examine the neural developmental changes related to feedback-based learning when performing a rule search and application task. Behavioral results from three age groups (8–9, 11–13, and 18–25 years of age) demonstrated that, compared with adults, 8- to 9-year-old children performed disproportionally more inaccurately after receiving negative feedback relative to positive feedback. Additionally, imaging data pointed toward a qualitative difference in how children and adults use performance feedback. That is, dorsolateral prefrontal cortex and superior parietal cortex were more active after negative feedback for adults, but after positive feedback for children (8–9 years of age). For 11- to 13-year-olds, these regions did not show differential feedback sensitivity, suggesting that the transition occurs around this age. Pre-supplementary motor area/anterior cingulate cortex, in contrast, was more active after negative feedback in both 11- to 13-year-olds and adults, but not 8- to 9-year-olds. Together, the current data show that cognitive control areas are differentially engaged during feedback-based learning across development. Adults engage these regions after signals of response adjustment (i.e., negative feedback). Young children engage these regions after signals of response continuation (i.e., positive feedback). The neural activation patterns found in 11- to 13-year-olds indicate a transition around this age toward an increased influence of negative feedback on performance adjustment. This is the first developmental fMRI study to compare qualitative changes in brain activation during feedback learning across distinct stages of development.
Wednesday, October 01, 2008
Dreher et al. have published an interesting bit of work that deals specifically with the muting of the intensity of the pleasures we feel during anticipation and reward, in their article on “Age-related changes in midbrain dopaminergic regulation of the human reward system.” Their data show what is going on as we experience less excitement at opening a present when we are 60 than when we are 10 years old. There are changes in the brain's production of dopamine, which plays a central role in our reward system, as well as in which parts of the brain respond to it, and by how much they respond. (a recent brief article on dopamine and the reward system of the brain is here.) Here is their abstract, followed by a figure from the paper.
The dopamine system, which plays a crucial role in reward processing, is particularly vulnerable to aging. Significant losses over a normal lifespan have been reported for dopamine receptors and transporters, but very little is known about the neurofunctional consequences of this age-related dopaminergic decline. In animals, a substantial body of data indicates that dopamine activity in the midbrain is tightly associated with reward processing. In humans, although indirect evidence from pharmacological and clinical studies also supports such an association, there has been no direct demonstration of a link between midbrain dopamine and reward-related neural response. Moreover, there are no in vivo data for alterations in this relationship in older humans. Here, by using 6-[18F]FluoroDOPA (FDOPA) positron emission tomography (PET) and event-related 3T functional magnetic resonance imaging (fMRI) in the same subjects, we directly demonstrate a link between midbrain dopamine synthesis and reward-related prefrontal activity in humans, show that healthy aging induces functional alterations in the reward system, and identify an age-related change in the direction of the relationship (from a positive to a negative correlation) between midbrain dopamine synthesis and prefrontal activity. These results indicate an age-dependent dopaminergic tuning mechanism for cortical reward processing and provide system-level information about alteration of a key neural circuit in healthy aging. Taken together, our findings provide an important characterization of the interactions between midbrain dopamine function and the reward system in healthy young humans and older subjects, and identify the changes in this regulatory circuit that accompany aging.
Legend (click on figure to enlarge). Statistical t maps of the within-groups effects in the different phases of the reward paradigm. (A) (Left) Main effect of anticipating reward in young subjects during the delay period, showing activation in the left intraparietal cortex, ventral striatum, caudate nucleus, and anterior cingulate cortex. (Right) Main effect of anticipating reward in older subjects during the delay period, showing activation in the left intraparietal cortex only. The glass brain and the coronal slice indicate that no ventral striatum activity was observed in older subjects. (B) (Left) Main effect of reward receipt in young subjects at the time of the rewarded outcome showing activation in a large bilateral prefronto-parietal network. (Right) Main effect of reward receipt in older subjects at the time of the rewarded outcome showing bilateral prefronto-parietal activation.