The human brain’s visual working memory holds and keeps track of mental images even when a person shifts their gaze and looks away from objects, according to a new MIT study, providing direct evidence for the first time that this occurs because the brain is able to transfer those images from one hemisphere to the other.
In a new study published Feb. 8 in the journal Neuron, a team of researchers explored the inner workings of visual working memory, which is the ability to maintain images in mind in their absence. They found that when you look around, your mind is able to keep track of objects because the brain is transferring mental images between its hemispheres by synchronizing brainwaves between the right and left brain.
Earl Miller, a professor of neuroscience at the Picower Institute for Learning and Memory at the Massachusetts Institute of Technology and senior author of the paper, explained to The Academic Times that when a person is looking ahead, the two halves of the brain analyze different halves of the visual scene. Everything to the right of center gaze is analyzed by the left half of the brain, and everything to the left of center is analyzed by the right half.
Though it’s long been assumed and understood that the brain is able to put the visuals together into a unified whole, there hasn’t been much research into exactly how this happens. Miller’s laboratory at MIT studies cognitive functions such as working memory, decision-making and attention in healthy brains to better learn how they work and to potentially develop cures for brain diseases.
For the current paper, Miller and his team measured neuron activity in the prefrontal cortex of animals as they did a working memory task, which prompted them to hold an image in their mind. In the experiment administered on a computer, photos of everyday objects flashed on the screen in different locations.
The subjects, two rhesus macaque primates, had their gaze shifted to other points and then had to recall certain photos and where they had been located on the screen. The researchers were testing for whether the subjects were able to hold the object as a mental image in their mind and remember it.
“While they’re holding this image in working memory, they shift their gaze. If the picture was still there, the gaze shift would have caused the other side of the brain to ‘see’ the picture. The brain responds to this by shifting the working memory from one side of the brain to the other,” Miller said.
The researchers ultimately concluded that visual working memory traces, the mental images held “in mind” by the brain, can be transferred from one hemisphere to the other while looking around. It is the first study to show this, the authors said.
This particular research used animals, but the findings are applicable to humans because they have similar working memory functions, according to the researchers. The brain is able to transfer a memory of an image from one side to the other by synchronizing brainwaves. A group of neurons in the prefrontal cortex of the opposite brain hemisphere stores the memory and encodes its new position, but these memories look and are represented differently in the brain when they switch between sides.
Miller gives an example of this function in air traffic controllers who need to keep track of flights. They monitor a flight and then have to rapidly move their eyes to check another, while still keeping in mind the first flight location, and continue checking their status back and forth.
“The mental images move from one side of the brain to the other to keep the mental images in register with what you are currently looking at,” Miller said. “It allows the brain to keep track of the things you are not looking at. This transferring of mental images helps heal the split between the left and right brain.”
According to the authors, fast and reliable interhemispheric communication is critical for many real-world behaviors, including air traffic control, sports and driving. And in individuals with some disorders such as dyslexia, it is thought that normal interhemispheric communication is disrupted.
“We hope that an understanding of the neural mechanisms of interhemispheric communication may lead to new ways to repair and optimize it,” the authors said in the paper.
Research like this that offers a deeper understanding of how vision works has the added benefit of making everyday life easier, Miller said. Signs and displays can be made more informative, and cars can be manufactured safer. Beyond healing brains with diseases, he said, this work can improve quality of life for both humans and animals.
The study, “Interhemispheric transfer of working memories” was published in the journal Neuron on Feb. 8. Scott Brincat, a postdoctoral researcher at the Picower Institute, was the lead author. Earl Miller, Jacob Donoghue, Meredith Mahnke, Simon Kornblith and Mikael Lundqvist, all of the Picower Institute at MIT, served as co-authors.