Cat Psychology book PDF
Specifically, he opened up the skulls of a few cats and severed their corpus callosums, dividing their brains in two. (Aside from the pain of cutting open the scalp, the surgery didn’t hurt the cats, since the brain itself cannot feel pain.) After the cats recovered, Sperry then taught them to navigate a maze while wearing an eye patch. As expected, after several attempts, these “split-brain” cats could negotiate the twists and turns without trouble.
But when Sperry switched the patch to the other eye and put the cat back into the maze, something funny happened: it started getting lost again. Why? First, in addition to cutting their corpus callosums, Sperry had doctored the cats’ optics nerves, so that one eye provided information to only one half of the brain. (In keeping with the brain’s general cross-wiring, he wired the left eye to the right hemisphere and vice-versa.) So the eye patch, by blocking sight in one eye, also restricted information to one half of each cat’s brain.
Second, when the information did arrive in that half of the brain, it remained stuck there, in a silo, because of the severed corpus callosum. As a result, even though each split-brain cat could learn the maze with half its brain, when Sperry switched the patch—forcing the other half of the brain to navigate—the cat had no idea where to go suddenly. Crucially, this didn’t happen to full-brain control cats. They could navigate just as well with either eye, no matter which eye they’d used to learn the maze, because their intact corpus callosums could share any information between both hemispheres.
Overall, this was a big enough deal on its own—real proof that the purpose of the corpus callosum was to share information between the left and right hemispheres. But it led to even greater insight into the human brain.
To see why, we have to take a quick detour into epilepsy. No one knows quite the reason, but surgically severing the corpus callosum can reduce the rate and intensity of seizures. So in the early 1960s, a few patients with severe epilepsy had their corpus callosums cut, turning them into split-brain people.
Follow-up tests showed that the patients did remarkably well afterward: the surgery provided the first real relief many had known in decades, and it did so with no discernible side effects. Still, a few recent disasters with aggressive neurosurgeries—the amnesiac H.M. being the best example—had left the surgeons involved wary. They wanted to make double-sure there weren’t any lurking side effects. So they called in Sperry, a world expert on the corpus callosum, to test the patients. Neuroscience (especially pop neuroscience) was never the same.
I won’t belabor the experimental details, but Sperry placed the patients in front of a screen and then flashed pictures to the far left side or the far right side of it. In this way, much like with the cats’ eye patches, he could channel information into either the left or the right hemisphere alone. And again, because of a lack of a corpus callosum, the information couldn’t escape that hemisphere. In other words, Sperry had effectively isolated each hemisphere, something that wasn’t possible before, since the vast majority of us have an intact corpus callosum.