July 20th, 2010
Henry Markram talks about the Blue Brain project
Greg, I figured you’d be able to clarify this a little since you’ve written a paper on anesthetics. When Markram says that anesthesia simply creates “noise in the brain”, preventing us from making decisions, what is he really trying to say? Under anesthesia are we really just trying (in vain) to “make up our minds”? It sounded a little fishy to me.
Oh, and one more thing: Did he really just say that the neocortex is the “final product” of evolution? Final product?!? I was under the impression that evolution does not work towards ultimate goals, but perhaps I was mistaken?
Anesthetics work either by enhancing the function of inhibitory ion channels or inhibiting excitatory channels. The majority of these molecular targets are the GABA-A receptors, which are ubiquitous, making the effect widespread (although it seems that thalamic nuclei and cortical interneurons are the key to loss of consciousness).
Clinically, a key feature of most general anesthetics is the high-amplitude low-frequency EEG waves (delta waves), which are also observed during deep non-REM sleep. Ketamine (a general anesthetic that acts via NMDA receptors) is different: the EEG during ketamine anesthesia shows gamma waves (40Hz), same as when subjects are awake, suggesting some activity in cortical neurons (noise). This is the sole example of anesthesia “introducing noise” into the system.
Anesthetics such as propofol (which acts via GABAARs) affect oscillations in cortex (via GABA-ergic interneurons) and thalamus (inhibition of thalamocortical neurons produces slow oscillations in the 4Hz delta wave range). This prevents the transmission of information among cortical cells and to cortex from thalamus, respectively. This is silencing rather than introducing noise.
As for evolution – there obviously is no goal or endpoint. The neocortex is certainly not the pinnacle of evolution….
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