UC Santa Barbara has reported an important discovery in the interdisciplinary study of split-brain research. The findings uncover dynamic changes in brain coordination patterns between left and right hemispheres.
Split-brain research has been conducted for decades, and scientists have long ago shown that language processing is largely located in the left side of the brain. When words appear only in the left visual field -- an area processed by the right side of the brain -- the right brain must transfer that information to the left brain, in order to interpret it. The new study at UCSB shows that healthy test subjects respond less accurately when information is shown only to the right brain.
While hemispheric specialization is considered accurate, the new study sheds light on the highly complex interplay -- with neurons firing back and forth between distinct areas in each half of the brain. The findings rely on extremely sensitive neuroscience equipment and analysis techniques from network science, a fast-growing field that draws on insights from sociology, mathematics, and physics to understand complex systems composed of many interacting parts. These tools can be applied to systems as diverse as earthquakes and brains.
Fifty years ago, UC Santa Barbara neuroscientist Michael S. Gazzaniga moved the field forward when he was a graduate student at the California Institute of Technology and first author of a groundbreaking report on split-brain patients. The study, which became world-renowned, was published in the Proceedings of the National Academy of Sciences (PNAS) in August 1962. This week, in the very same journal, Gazzaniga and his team announced major new findings in split-brain research. The report is an example of the interdisciplinary science for which UCSB is well known.
"The occasion of this paper is on the 50th anniversary of the first report on human split-brain research reported in PNAS," said Gazzaniga. "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.
"In the present study, new techniques -- not present 50 years ago -- begin to allow for an understanding of how the normal, undivided brain integrates the special functions of each half brain. It is a new beginning and very exciting," said Gazzaniga, professor of psychology in UCSB's Department of Psychological and Brain Sciences, and director of UCSB's SAGE Center for the Study of Mind.
Karl W. Doron, first author and a postdoctoral scholar with Gazzaniga, said: "This study shows that the strength of communication across the brain changes dynamically, when information is exchanged between the right and left hemispheres via the corpus callosum, which connects both sides of the brain. The findings shed light on the neural underpinnings of inter-hemispheric communication first reported 50 years ago in the classic split-brain studies performed by Gazzaniga and colleagues."
Doron explained that years of research -- in both clinical patient populations and healthy individuals -- have shown that the brain is made up of specialized modules that preferentially process certain types of information.
When linguistic information, such as a word or pronounceable non-word, is shown directly to the left brain, people are better at deciding whether or not it is a real word, said Doron.
"In contrast, when the information is shown directly to the right brain, people perform worse," he said. "It has long been assumed that language information shown to the right brain must be transferred through the corpus collosum. In other words, right brain information must be directly transferred to the language-specialized left brain, in order to be processed correctly."
In the new study, researchers used magnetoencephalography, or MEG, a non-invasive tool that measures the continuous brain activity of nine healthy young adults. The participants were briefly flashed a stimulus that was either a real word or a "word-like" non-word. The stimulus was randomly shown either to the left or right brain, using a split-visual field experimental technique.