“Evolution doesn’t give a damn what you think a brain region is called”
“The danger is that naming a bit of brain makes us think it is a discrete thing, a bit that just lifts right out, which we can study and marvel at in isolation. But how evolution (and development) conspire to disperse and wire together neurons pays no attention to these names.
Consider primary motor and somatosensory cortex. They sit next to each other. But they appear in different chapters in textbooks. Entirely separate fields of research have grown up around them. Work on primary somatosensory cortex looks at how the activity of its neurons represent touch. Work on motor cortex looks how the activity of its neurons represent movement. These are starkly different: work on somatosensory cortex focuses on its inputs; work on motor cortex focuses on its outputs. They are treated so separately that papers merely showing the flow of activity from one to the other end up in high-profile journals.
But these bits of cortex are next to each other. Either we believe that there are border guards who turn away the motor cortex neuron axons at the crossing with somatosensory cortex, and the same from the other direction. Or we have to assume that these two names loosely delineate a continuous network of neurons by the fact that a small set of neurons in somatosensory cortex get direct sensory input, and small set of neurons in motor cortex connect to the spinal cord. Most of the neurons in these bits of cortex neither get sensory input from the thalamus nor project to the spinal cord. They are wired to other neurons all over cortex, and very much to each other…
Our best evidence that it is not — that we can cling to our names of all the bits — come from studies where we cut a bit out or turn a bit off. When we cut out area X and we see a “deficit” in behaviour Y of an animal (like tying its shoelaces), then we think “aha! Area X is for tying shoelaces”. No. For starters, we never see a complete and permanent end to behaviour Y. We normally see that the animal is simply worse at doing or learning Y — not that it cannot do Y at all. The brain can carry on doing Y just fine, thanks, just not as well — there is massive redundancy in the brain. Like what you’d find if it was a giant bag of cells, wired together.
Moreover, seeing that behaviour Y gets worse logically tells us little about what area X is actually doing. It just tells us that damaging area X causes problems. Which on reflection isn’t surprising as you just ripped a chunk out of the brain.”
Related: “When scientific paradigms lead to tunnel vision: lessons from the study of fear”
