Summary: A new study reveals how the brain integrates vision across both hemispheres when objects cross the visual field. Researchers tracked neuronal spikes and brainwave frequencies and showed that distinct wave patterns predict, implement, and confirm the transfer of information from one hemisphere to the other.
Gamma and beta waves facilitated sensory coding, while alpha waves increased before the transition and theta waves peaked later, indicating completion. These results demonstrate that perception is not simply reordered from one hemisphere to the other, but is actively integrated, providing new insights into disorders such as autism, schizophrenia, and dyslexia.
Key facts
- Golf Coordination: Gamma and beta waves encode sensory information. Alpha and theta waves coordinate transmission.
- Perfect perception: The two hemispheres temporarily share object data before the transfer is complete.
- Medical perspective: The results may explain deficits in interhemispheric coordination in neurological disorders.
Source: Picower Institute at MIT
The brain divides vision between the two hemispheres (what’s on your left is processed by your right and vice versa), but your perception of every bicycle or bird passing by is perfectly accurate.
A new study by neuroscientists at MIT’s Picower Institute for Learning and Memory reveals how the brain handles this transition.
“Some people are surprised to hear that there is a certain independence between the cerebral hemispheres, because it doesn’t correspond to our perception of reality,” says Earl K. Miller, Picower Professor at the Picower Institute and the Department of Brain and Cognitive Sciences at MIT. “In our consciousness, everything is one.”
Miller and other researchers have discovered that there are advantages to having the brain’s two hemispheres process images separately, such as the ability to track more things at once. However, neuroscientists are eager to fully understand how perception ultimately becomes so unambiguous.
The research team, led by postdoctoral researcher Matthew Broshard of Pecor and scientist Jefferson Roy, measured neural activity in the animals’ brains as they tracked objects that crossed their line of sight. The results showed that different brainwave frequencies encode information and then transfer it from one hemisphere to the other before it is transferred. The representation of the object is then maintained in both hemispheres until the transfer is complete.
The process is similar to how relay runners pass a baton, how a child waves from one pole to another, and how cell phone towers send calls back and forth when a train passenger passes through their zone. In all cases, both towers or hands actively hold the object until the handover is confirmed.
Witnessing the handoff
To carry out the study, which was published in the Journal of Neuroscience, the researchers measured the frequency of different brain waves generated by the electrical spikes of individual neurons and the coordinated activity of many neurons.
They studied the dorsal and ventrolateral prefrontal cortex in both hemispheres, areas of the brain associated with executive brain functions. Fluctuations in the strength of the waves’ frequencies in each hemisphere told the researchers a clear story about how the subjects’ brains transferred information from the “sending” to the “receiving” hemisphere when a target object passed through the center of their visual field.
In the experiments, there was a distractor on the other side of the screen with the target. This confirmed that the subjects were consciously paying attention to the movement of the target object and not just staring at objects that randomly appeared on the screen.
High-frequency gamma waves, which encode sensory information, peaked in both hemispheres when subjects first looked at the screen and again when the two objects appeared. When a color change indicated which object was the target, the increase in gamma was only visible in the transmitting hemisphere (on the opposite side of the target), as expected.
Meanwhile, the strength of the slightly lower-frequency “beta” waves, which regulate gamma wave activity, varied inversely with gamma waves. This sensory coding dynamic was stronger at ventrolateral locations than at dorsolateral locations.
Meanwhile, two distinct bands of low-frequency waves showed increasing intensity in dorsolateral locations at critical moments of transmission. About a quarter of a second before an object passed through the center of the visual field, alpha waves increased in both hemispheres, peaking immediately after the object crossed the boundary. In contrast, theta waves peaked only in the receiving hemisphere (opposite the object’s new position) as the boundary was crossed.
Along with the wave spike pattern, the neuronal spiking data revealed how the brain’s representation of the target location was transmitted. Using decoding software, which interprets information from the spikes, the researchers were able to observe how the target representation emerged in the ventrolateral location of the transmitting hemisphere when the color change initially signaled it.
They could then see that, as the target approached the center of the visual field, the receiving hemisphere joined the sending hemisphere in representing the object, so that both encoded the information during the transfer.
In summary, the results suggest that after the sending hemisphere initially encodes the target with a ventrolateral interaction of beta and gamma waves, the receiving hemisphere infers transmission by mirroring the sending hemisphere’s encoding of the target information due to a dorsolateral increase in alpha waves.
Alpha peaked immediately after the target passed through the center of the visual field. Once the transfer was complete, theta peaked in the receiving hemisphere, as if to say, “I got it.”
And in tests where the target object never passed through the center of the visual field, these transfer dynamics were not visible in the measurements. Research shows that the brain doesn’t just track objects in one hemisphere and then pick them up again when they enter the other hemisphere’s field of view.
“These results suggest that there are active mechanisms that transfer information between the brain’s hemispheres,” the authors wrote. “The brain anticipates the transfer and recognizes its completion.”
But they also point out, based on other studies, that certain neurological disorders, such as schizophrenia, autism, depression, dyslexia, and multiple sclerosis, sometimes show a breakdown in the interhemispheric coordination system. The new study may shed light on the specific dynamics required for its success.
In addition to Brossard, Roy, and Miller, Scott Brinkett and Meredith Mahnke are responsible for this article.
Funding: Funding for the research came from the Office of Naval Research, the National Eye Institute of the National Institutes of Health, the Freedom Together Foundation, and the Pecor Institute for Learning and Memory.
About this visual neuroscience research news
Author: David Orenstein
Source: Picower Institute at MIT
Contact: David Orenstein – Picower Institute at MIT
Image: The image is credited to StackZone Neuro
Original Research: Closed access.
“Evidence for an active handoff between hemispheres during target tracking” by Earl K. Miller et al. Journal of Neuroscience
Abstract
Evidence for active interhemispheric transfer during target tracking.
The brain has relatively separate cognitive resources for the left and right sides of our visual field. Despite this background, we have a fluid and consistent perception of our environment.
This raises the question of how the cerebral hemispheres work together to transmit information between them.
We recorded neural activity in the lateral prefrontal cortex bilaterally while two male primates covertly tracked a target that moved from one visual hemifield (i.e., one cerebral hemifield) to the other.
Beta energy (15–30 Hz), gamma energy (30–80 Hz), and peak information reflect sensory processing of the target. In contrast, alpha energy (10–15 Hz), theta energy (4–10 Hz), and spike information appeared to reflect active transfer of attention as target information was transferred between hemispheres.
Specifically, alpha and peak energy increased in anticipation of the hemifield crossing. Theta energy peaked after the crossing, signaling its completion.
Our results support functional information transfer between cerebral hemispheres. This “handshake” operation can be crucial for minimizing data loss, much like how cell towers communicate with each other when connecting calls.
