Way back in the 70’s I read an incredible paper in Science (whose citation I can’t give) stating that you could remove the cerebral cortex of a gerbil, and the animal still acted pretty normally (able to build a nest as I recall). This saved me a lot of reading time over the years as I was able to ignore roomfuls of papers on rats running mazes, etc. etc. without noticeable harm to my patients.
Why? First, some background. Chemists, molecular biologists and the general populace aren’t expected to know much neuroanatomy, neurophysiology or neurology. The pictures of the human brain you have seen, show it to be roughly spherical, with the surface all corrugated like a walnut (the part inside the shell). The brain surface (aka the cerebral cortex, a terrible name since ‘cortex’ evokes something in the center) is thrown into folds because humans have so much of it. In contrast the brain of various monkeys is smooth with only a few folds. Another name for the cerebral cortex is gray matter — because it looks gray because it is packed with cell bodies (about 100,000 under each square milliMeter). The white matter which underlies the cortex is white because it is mostly nerve fibers wrapped in fat (aka myelin).
There are areas of our cortex which can be lost without much obvious change in behavior, and a colleague’s wife had an orange sized (fortunately benign) tumor in her frontal lobe with almost no cognitive changes. But: remove another area the size of a postage stamp and you can’t speak, remove another and you can’t move your arm etc. etc. The point is, that most of what makes us human and sentient requires our cerebral cortex.
This brings us to [ Neuron vol. 66 pp. 69 – 84 ’10 ]. They knocked out a gene called Pals1 in mice. There’s a lot of interesting biochemistry in the paper, but it’s irrelevant for what follows. At birth, the animals had no cerebral cortex at all. Despite this they (1) survived (2) ate (3) bred. They did fail some tests of coordination (but not all — pretty amazing when you consider they had no motor cortex or its connection to the spinal cord (pyramidal tract)). The paper doesn’t talk much about tests of learning.
This sort of thing is what makes neurology and neuroscience so hard. Pig liver or pig kidney is a pretty reasonable model for the human liver or kidney, but our brains are what really set us apart, and which makes any inference from animal work exceedingly tenuous (but it’s all we have).
Newton and Einstein were probably lousy at running mazes.
Back to matters chemical shortly.