Primates' brains make visual maps using triangular grids

October 28, 2012

Primates' brains see the world through triangular grids, according to a new study published online Sunday in the journal Nature.

Scientists at Yerkes National Primate Research Center, Emory University, have identified grid cells, neurons that fire in repeating triangular patterns as the eyes explore visual scenes, in the brains of .

The finding has implications for understanding how humans form and remember mental maps of the world, as well as how such as Alzheimer's erode those abilities. This is the first time grid cells have been detected directly in primates. Grid cells were identified in rats in 2005, and their existence in humans has been indirectly inferred through .

Grid cells' electrical activities were recorded by introducing electrodes into monkeys' entorhinal cortex, a region of the brain in the medial temporal lobe. At the same time, the monkeys viewed a variety of images on a computer screen and explored those images with their eyes. Infrared eye-tracking allowed the scientists to follow which part of the image the monkey's eyes were focusing on. A single grid cell fires when the eyes focus on multiple discrete locations forming a grid pattern.

"The entorhinal cortex is one of the first 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," says senior author Elizabeth Buffalo, PhD, associate professor of neurology at Emory University School of Medicine and Yerkes National Primate Research Center. "We think these neurons help provide a context or structure for to be stored in memory."

"Our discovery of grid cells in primates is a big step toward understanding how our brains form memories of visual information," says first author Nathan Killian, a graduate student in the Wallace H. Coulter Department of Biomedical Engineering at Georgia Tech and Emory University. "This is an exciting way of thinking about memory that may lead to novel treatments for neurodegenerative diseases."

In the experiments in which rats' grid cells were identified, the cells fired whenever the rats crossed lines on an invisible triangular grid.

"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."

Another aspect of grid cells not previously seen with rodents is that the cells' responses change when monkeys are seeing an image for the second time. Specifically, the grid cells reduce their firing rate when a repeat image is seen. Moving from the posterior (rear) toward the anterior (front) of the , more neurons show memory responses.

"These results demonstrate that grid cells are involved in memory, not just mapping the visual field," Killian says.

Consistent with previous reports on grid cells in rats, Killian and Buffalo observed "theta-band" oscillations, where grid cells fire in a rhythmic way, from 3 to 12 times per second. Some scientists have proposed that theta oscillations are important for grid cell networks to be generated in development, and also for the brain to put together information from the grid cells. In the monkeys, populations of neurons exhibited theta oscillations that occurred in intermittent bouts, but these bouts did not appear to be critical for formation of the spatial representation.

Vision is thought to be a more prominent sense for primates (monkeys and humans) compared with rodents, for whom touch and smell are more important. While grid cells in rodents and primates were detected in different types of experiments, Buffalo says that it doesn't mean grid cells necessarily have a different nature in primates.

"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 says.

Buffalo says future experiments could examine how monkeys navigate in real space, including changes in head or body orientation, to determine how respond.

Explore further: Researchers probe link between theta rhythm, ability of animals to track location

Related Stories

Researchers probe link between theta rhythm, ability of animals to track location

April 28, 2011
In a paper to be published today in the journal Science, a team of Boston University researchers under the direction of Michael Hasselmo, professor of psychology and director of Boston University's Computational Neurophysiology ...

Electrical oscillations critical for storing spatial memories in brain: study

April 28, 2011
Biologists at UC San Diego have discovered that electrical oscillations in the brain, long thought to play a role in organizing cognitive functions such as memory, are critically important for the brain to store the information ...

Understanding how our brain perceives space

May 28, 2012
European scientists looked into the cellular properties of neurons responsible for space coordination. Insight into the neuronal network of the entorhinal cortex will help understand what determines space and movement perception, ...

Recommended for you

Nature or nurture? Innate social behaviors in the mouse brain

October 18, 2017
Adult male mice have a simple repertoire of innate, or instinctive, social behaviors: When encountering a female, a male mouse will try to mate with it, and when encountering another male, the mouse will attack. The animals ...

Brain activity predicts crowdfunding outcomes better than self-reports

October 18, 2017
Surveys and self-reports are a time-honored way of trying to predict consumer behavior, but they have limitations. People often give socially desirable answers or they simply don't know or remember things clearly.

Navigational view of the brain thanks to powerful X-rays

October 18, 2017
If brain imaging could be compared to Google Earth, neuroscientists would already have a pretty good "satellite view" of the brain, and a great "street view" of neuron details. But navigating how the brain computes is arguably ...

'Wasabi receptor' for pain discovered in flatworms

October 18, 2017
A Northwestern University research team has discovered how scalding heat and tissue injury activate an ancient "pain" receptor in simple animals. The findings could lead to new strategies for analgesic drug design for the ...

Changing stroke definitions is causing chaos, warns professor

October 18, 2017
Proposals to change the definitions of stroke and related conditions are causing confusion and chaos in clinical practice and research, a Monash University associate professor has warned.

Brain-machine interfaces to treat neurological disease

October 18, 2017
Since the 19th century at least, humans have wondered what could be accomplished by linking our brains – smart and flexible but prone to disease and disarray – directly to technology in all its cold, hard precision. Writers ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

MrVibrating
not rated yet Oct 28, 2012
So is there some benefit to organising and analysing visual information this way, or is it purely a consequence of grid cell physiology? In other words, do the cells serve the grid, or does the grid serve the cells?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.