"If all you have is a hammer, everything looks like a nail." This so-called "law of the instrument" has shaped neuroscience to core. It can be rephrased as, if all you have a fancy voltmeter, everything looks like a transient electrical event. No one in the field understands this more Douglass Fields, an NIH researcher who has re-written every neuroscience dogma he has turned his scrupulous eye to. In a paper published yesterday in Nature, Fields questions the conventional wisdom that informs recent efforts to map the brain’s connectivity, and ultimately, its electrical activity. In particular, he questions the value of making detailed maps of neurons, while at the same time neglecting the more abundant, and equally complex “maps” that exist for glia.
When first discovered, the “action potential” generated by a neuron was a rich and multiphysical event. It has since degenerated into a sterile, directionally-rectified electrical blip, whose only interesting parameter is a millisecond-scrutinized timestamp. In the last two years alone, Fields has re-generalized the spike. Having highlighted many of the fine scale physical events that accompany a neuron’s firing, like temperature and volume changes, optical effects, displacement, and myriad nonsynaptic effects, Fields demonstrated the intimate knitting of reverse propagating spikes into the behavior and function of neuronal networks. He also showed how spikes directly control non-neuronal events, in particular, myelination.
The Eyewire project at MIT is a fantastic effort to create detailed neuronal maps—it expands neuroscience to the larger community, and generates much worthwhile scientific spin-off. It is also completely absurd. To have so much talk about brain maps without drawing clear distinction between the glaring contrast in the value of white matter maps and grey matter maps is telling. Maps of the white matter will be indespensible to understanding our own brains. They are highly personal, yet at the same time will be one of the most valuable things we might soon come to share. For the moment here, we can liken them to the subway or transportation map of a complex city.
To try and map the grey matter, at least in our foreseeable era, is to attempt to record the comings and goings of all the people entering and exiting the doors of the trains of our subway system. Not only is the task infinitely harder, pound for pound, it is equally less valuable, and impermanent. Looked at another way, if we imagine some hyper-detailed ecologist mapping the different trees in a forest, one valuable piece of information to have would be the tree species or type. Their age, size, density and distribution would similarly be worthwhile parameters. Also maybe some detail about their finer structure would be predictive of what kind of animals species might live and move about their arbors. Eyewire, on the other hand, is mapping every twig down to the finest termination as a leaf. The problem is that leaves are shed and regenerated anew each year, and while Eyewire might map a few neurons in the same time, synapses morph to a faster drum.