October 29, 2012
Rhesus Monkeys Process Visual Information In A Triangular Grid
Brett Smith for redOrbit.com - Your Universe Online
Researchers at Emory University have shown that some primates visually deconstruct the world through triangular grids.According to their report in the journal Nature, the scientists have identified grid cells in the brains of rhesus monkeys that fire in triangular patterns as their eyes scan a scene.
Uncovering this brain activity in primates could have larger ramifications as the grid cells are connected to how we view and recall visual information. These cells are often the first to degrade in certain neurodegenerative diseases, like Alzheimer´s.
"Our discovery of grid cells in primates is a big step toward understanding how our brains form memories of visual information," said study co-author Nathan Killian, a graduate student at Emory University. "This is an exciting way of thinking about memory that may lead to novel treatments for neurodegenerative diseases."
During the study, the researchers recorded the grid cells' electrical activity by placing electrodes into monkeys' entorhinal cortex.
"The entorhinal cortex is one of the first brain regions to degenerate in Alzheimer's disease, so our results may help to explain why disorientation is one of the first behavioral signs of Alzheimer's," said co-author Elizabeth Buffalo, an associate professor of neurology at Emory University School of Medicine. "We think these neurons help provide a context or structure for visual experiences to be stored in memory."
The monkeys were then shown a series of images on a computer screen that they scanned with their eyes. Infrared imaging tracked the eye movements of the monkeys to see which part of the image they were focused on, allowing the researchers to correlate the grid cells activity to physical eye motion.
"The surprising thing was that we could identify cells that behaved in the same way when the monkeys were simply moving their eyes," Buffalo says. "It suggests that primates don't have to actually visit a place to construct the same kind of mental map."
In 2005, previous experiments had identified grid cells in rats, but their activity in primates was found to be much different. The primates´ grid cells behaved differently when an image was shown for the second time. The scientists recorded a reduction in firing rate when a repeated image was seen, however more neurons fired to indicate memory responses.
"These results demonstrate that grid cells are involved in memory, not just mapping the visual field," Killian said.
The main reason for the difference in behavior could be that primates rely more on their vision to explore the world than rodents, which rely more on touch and smell. Despite these differences, Buffalo said, grid cells in both types of animals are similar in nature.
The researchers said their future studies will focus on how primates utilize grid cells as they find the way around an environment, in both the real world and a virtual environment.
"We are now training a monkey to move through a virtual 3-D space. My guess is that we'll find grid cells that fire in similar patterns as the monkey navigates through that space," she said.
Read redOrbit's exclusive interview with Professor Elizabeth Buffalo.