UCSB researchers recently garnered international attention from a new study on split-brain research revealing that healthy test subjects respond less accurately to stimuli when information is shown only to the right hemisphere of the brain.
Technological advances and interdisci- plinary collaboration allowed the team to map signaling across left and right sides of the brain in response to visual stimuli, veri- fying hypotheses in split-brain research com- piled over the past few decades. Conducted by psychology professor Michael Gazzinga and postdoctoral scholars Karl Doron and Danielle Bassett, the study, “Dynamic Network Structure of Interhemispheric Coordination,” was published in the sci- entific journal Proceedings of the National Academy of Sciences.
According to Gazzinga, the research builds upon his own postdoctoral studies in the 1960s at the California Institute of Technology and subsequent findings by sci- entists testing how the brain processes visual information. “The occasion of this paper is on the 50th anniversary of the first report on human split-brain research reported in PNAS,” Gazzinga said in a press release. “That study showed how surgically dividing the two hemispheres of the human brain — in an attempt to control epilepsy — allowed for studying how each isolated half-brain was specialized for cognitive function.”
Normal brains consist of left and right hemispheres connected by the corpus callosum, a wide, flat bundle of neural fibers that allows for the transferring and processing of language and visual information from one side of the brain to the other. Split-brain patients are missing this communicative bridge connecting their brain hemispheres. While they can function normally, scientists have spent the past 50 years researching the functional specialties of each hemisphere and how split-brain patients accommodate without their corpus callosum.
In the study, test subjects were presented with either a word or a pronounceable “non-word,” a made-up term, to the left or right visual field. By pressing a button, the subject indicated whether the word he or she saw was actually a word.
Brain imaging and timing of the response revealed that participants took longer to identify a word shown to the left visual field. In other words, subjects took longer to process information on the right side of the brain since visual stimuli is processed on the opposite brain side. Images shown in the left visual field, or the right brain hemisphere, had to be transferred over to the left-brain before the subject could accurately give a response.
Gazzinga and his team used a mag- netoencephalography machine at Otto- von-Guericke University in Magdeburg, Germany to map activity in the subjects’ brains during the experiment. In contrast to fMRI and other traditional imaging machinery available at UCSB, which is used to take still pictures of brain activity, the MEG is capable of taking many successive images in a short time frame.
According to Doron, these images are compiled into movies so scientists can watch neural activity move from one hemisphere to another. He said MEG is important in gathering temporal data. “MEG gives us the ability to measure brain activity at roughly the speed transfer [that] is actually occurring,” Doron said. “Basically, when you don’t have that time element, all of the interesting stuff has already happened.”
As a whole, the study’s findings not only confirm hemispheric specialization but also carry implications for treating brain diseases and understanding the complexities of nor- mal brain function.
Even though MEG has been around since the 1960s, only recently have com- puters attained a high enough processing power to make use of the machine’s data. According to Doron, his team has still only put together a rough visual of brain signaling direction. In the future, he hopes to be able to pinpoint specific sources of neural communication.
“All we can show with this imaging data is that two areas are connected,” Doron said. “We want to confirm that one area causes another to perform some function and find where changes in signal direction are initiated.”