Our brains are divided into 2 sections, or hemispheres: left and right. Common knowledge tells us that the left and right brains are responsible for different subjects. The left brain manages language, math and analytical thinking, while the right brain controls of expression, creativity and imagination. But how much of that is true? What if we could isolate each hemisphere to really find out what it’s in charge of?
That’s exactly what Roger Sperry, American neuropsychologist, set out to do.
Roger Sperry’s experiments
Before we dive deeper, it’s important to understand what contralateral control is. Essentially, it’s when the left brain controls muscle movement in the right side of the body, and vice versa. It also happens when the left brain only receives information from the right visual field, and vice versa.
In Sperry’s experiments, he isolated the left and right hemisphere by cutting the corpus callosum, a bundle of nerves that connects the two sides of the brain. That way, both sides are physically separated from each other.
Here’s what he found:
Sperry first experimented with cats and monkeys. After their corpus callosa was cut, the animals showed no obvious change in behavior but sometimes acted like they had two brains. In one experiment, Sperry closed one of the cat’s eyes and presented two different blocks to it, one of which had food underneath. Then, he closed the other eye and put the food under the other block. When the cat had both eyes open, it could not distinguish between the blocks, almost as if its hemispheres couldn’t combine the information they received! Sperry concluded that once the corpus callosum was cut, the hemispheres couldn’t communicate with each other.
Next, Sperry moved on to human volunteers who had their corpus callosum cut to treat severe epilepsy, called split-brain patients. With the help of Michael Gazzaniga (also an American neuropsychologist), he conducted a series of experiments that would demonstrate how the left and right hemispheres specialize in some areas, a phenomenon known today as brain lateralization. When they showed an image to the patients’ right visual field (or left brain), they could easily describe it. But when only the patients’ right brain saw the image, they said they didn’t see anything! They could, however, point with their left hand to an object that matched the image. This showed that while the right brain understood the image, it couldn’t communicate the information with the left brain. And because the left brain controls verbal speech, the patient could not say out loud what the image was.
Yep, it’s confusing. Here‘s a diagram for better understanding.
An end to split-brain experiments…
Nowadays, people with severe epilepsy take drugs to manage their condition. The surgery cutting the corpus callosum is too invasive, permanent and risky. The very few split-brain patients that remain are getting too old to participate in experiments. Although split-brain experiments look like they are coming to a close, I think that researchers like Sperry and Gazzaniga contributed very invaluable insight on brain function. Their experiments showed a compelling picture of how our brain works and changed neuroscience for the better.