How the Brain Unifies Vision Across Hemispheres

The brain divides vision between its two hemispheres-what’s on your left is processed by your right hemisphere and vice versa-but your experience with every bike or bird you see zipping by is seamless.A new study by neuroscientists at The Picower Institute for Learning and Memory at MIT reveals how the brain handles this transition.

It’s surprising to some people to hear that there’s some independence between the hemispheres,because that doesn’t really correspond to how we perceive reality.In our consciousness, everything seems to be unified.

Earl K. Miller, Picower Professor in The Picower Institute and MIT’s Department of Brain and Cognitive Sciences

There are advantages to separately processing vision on either side of the brain, including the ability to keep track of more things at once, Miller and other researchers have found. However, neuroscientists have been eager to fully understand how perception ultimately appears so unified.

Led by postdoctoral Picower Fellow Matthew Broschard and Research Scientist Jefferson Roy, the research team measured neural activity in the brains of animals as thay tracked objects crossing their field of view. The results reveal that different frequencies of brain waves encoded and then transferred information from one hemisphere to the other in advance of the crossing. Then, both hemispheres held onto the object representation until after the crossing was complete.This process is similar to how relay racers hand off a baton, how a child swings from one monkey bar to the next, and how cell phone towers hand off a call from one to the next as a train passenger travels through their area. In all cases,both towers or hands actively hold what’s being transferred until the handoff is confirmed.

Witnessing the Handoff

To conduct the study, published in the Journal of Neuroscience, the researchers measured both the electrical spiking of individual neurons and the various frequencies of brain waves that emerge from the coordinated activity of many neurons. They studied the dorsal and ventrolateral prefrontal cortex in both hemispheres, brain areas associated with executive brain functions.

The power fluctuations of the wave frequencies in each hemisphere told the researchers a clear story about how the subject’s brains transferred information from the “sending” to the “receiving” hemisphere.