Margaret Funnell, the Assistant Dean of Faculty for Undergraduate Research, spoke about split-brain patients at a College Student Interest Group in Neuroscience (Co-SIGN) event last Tuesday.

Split-brain patients have undergone a surgical procedure called a corpus callosotomy to sever the corpus callosum, a part of the brain integral to communication between the left and right hemispheres.  Historically thought to keep the brain from collapsing, the corpus callosum is Greek for ‘hard body.’  Scientists now have more insight into its functions.

Candidates for a corpus callosotomy suffer from epileptic seizures that affect both sides of the brain, severely impair day-to-day activity, and have not responded to anti-seizure medication.  The procedure stops generalization of the seizure across both hemispheres to allow patients to maintain more control and function.

Funnell’s talk centered on how attitudes toward split-brain patients have changed over time in terms of both the procedure and its effects.

Early attempts at this surgical procedure were improperly performed and thus had little effect. But contemporary techniques make the corpus callosotomy a two-stage process and have yielded significant improvement in split-brain patients’ quality of life. 

Since each hemisphere controls the opposite side of the body, many people initially thought that the effects of the split-brain procedure would be easily observed; however, some sensory and motor controls exist in both sides.  Thus, to test split-brain procedure’s effects, neuroscientists rely on the visual system and use fixation tasks to perform lateralized testing.

Patients were asked to fixate on a cross as images were flashed on either side. Images flashed to the right visual field were processed in the left hemisphere, the side of the brain associated with language and speech.  Thus, the patients could easily vocalize only what they saw in their right visual field. 

In contrast, images flashed to the left visual field are processed in the right hemisphere, which lacks speech areas, so patients verbally deny seeing an image or knowing what the image was.  Interestingly enough, they can still draw objects flashed in the left visual field with their left hands.

Split-brain patients can also transfer emotion.  When a disturbing picture is flashed in the left visual field, and is then processed by the right hemisphere, patients again cannot describe what they saw.  But interestingly, they do express negative feelings, which indicates that emotion has reached both hemispheres of the brain. When asked why they feel this way, the left hemisphere tries to rationalize this feeling; patients often end up attributing their feelings to a “rude” experimenter.

Split-brain patients have given neuroscientists insight into many structure-function relationships of the brain.  Future work hopes to improve upon the procedure and help the scientific community understand the complex relationship between the mind and the brain.