A split-brain patient is unable to say what he sees with his nonverbal right brain, but he can draw it.
Half a century ago, patients with intractable epilepsy were presented with a radical surgery: severe the corpus callosum. Cutting this bundle of fibers that allows the left and right brain hemispheres to communicate created split-brain patients. Their epilepsy got better, but a whole host of other strange things happened, such as left and right hands that would fight over what to get at the supermarket.
Nowadays, these patients have access to better drugs and less invasive surgeries, and severing the corpus callosum is no longer done. A dozen or so of these patients have been the subject of countless scientific studies, but they’re all getting older. A recent Nature News feature talks about just how invaluable these patients have been to neuroscience.
Split-brain patients allow neuroscientists to probe the separate workings of the verbal left brain and nonverbal right brain as well as how they would work together. Michael Gazzaniga, who has been working with split-brain patients for decades, came up with the interpreter theory to explain why patients tend to have a unified sense of self despite having “two brains.” The left hemisphere is pretty darn good at making up explanations:
In one of Gazzaniga’s favourite examples, he flashed the word ‘smile’ to a patient’s right hemisphere and the word ‘face’ to the left hemisphere, and asked the patient to draw what he’d seen. “His right hand drew a smiling face,” Gazzaniga recalled. “’Why did you do that?’ I asked. He said, ‘What do you want, a sad face? Who wants a sad face around?’.” The left-brain interpreter, Gazzaniga says, is what everyone uses to seek explanations for events, triage the barrage of incoming information and construct narratives that help to make sense of the world.
What’s most striking, though, is the human aspects of this research. Patients and researchers have been together for decades, and “Gazzaniga can tick through the names of his ‘endlessly patient patients’ with the ease of a proud grandparent doing a roll call of grandchildren.” Read more about one particular split-brain patient, Vicki, and how patients like her have advanced neuroscience at Nature.