The brain's GPS has a buddy system

January 11, 2018, RIKEN
Four types of spatial models for the hippocampus that are proposed in this paper. Credit: RIKEN

To be successful as a social animal, you need to know where you stand relative to others. Brain cells that perform precisely this function—locating the 'self' and others in space—have now been identified. In rats, the same brain area that stores the animal's own location also maps the movements of other rats. Sometimes these representations are processed jointly by the same cells, depending on a rat's goals and actions. This discovery, from Japan's RIKEN Brain Science Institute, deepens our understanding of the hippocampus and its role as the brain's positioning system.

It has been known for some time that the maintains a mental map of space—in fact, the 2014 Nobel Prize in Physiology or Medicine was awarded precisely for this research. 'Place ' and 'grid cells' in the hippocampus register the of the brain's owner in its environment, but until now, little was known about how the movements of others are tracked in the . Researchers put this to the test by observing the activity of in one rat (the 'self') watching another rat (the 'other') go through a simple T-maze. The self's neurons registered what the other was doing and changed their responses based on the self's location and subsequent actions. This study was published on January 11 in Science, which also contains a report of similar location awareness in the brains of bats.

Hippocampal place cells light up only for certain locations in the environment, and some of these cells clearly preferred the location of the other rat. Besides activation to places, the timing of neural activity in the hippocampus is also important. A 'refresh rate' of around 8 Hz dictates how often neurons update their activity, a phenomenon called theta-cycle phase precession. Three-quarters of cells updated based on the other's location, not only the self's. "It is very interesting that the trajectories of the other, that is, the past, current, and future positions of the observed rat, are compressively represented in 100-millisecond cycles in the hippocampus," says Shigeyoshi Fujisawa, research group leader at the RIKEN Brain Science Institute.

In two versions of the maze, the self-rat had to learn to visit the same T-arm as the other or the opposite arm. The majority of neurons were 'goal-focused', signaling the location of the goal, but a small number of neurons preferred the other's location regardless of whether it was on the same side as the goal. There were also cells that fired when either the other or the self were in specific spatial locations. "These cells are not confused," says Fujisawa. "We can reconstruct the paths of the pair of and reliably decode the location of the self or the other from the activity of these joint ."

Fujisawa and colleagues propose that the hippocampus has four different kinds of spatial models, one for the locations of the self, one for that of others, another for joint locations that are tuned relative to where the self and other are, and one for 'common' locations that activate when either the self or other are there (see image). This extends the existing cognitive map theory of how the hippocampus processes spatial locations and memories. "We think the cognitive map in the hippocampus is not just for knowing where the self is located," says Fujisawa, "but also for plotting the locations of other people, animals, or objects, and to comprehend the spatial environment surrounding the self."

Explore further: Brain's hippocampus can organize memories for events as well as places

More information: T. Danjo el al., "Spatial representations of self and other in the hippocampus," Science (2018). science.sciencemag.org/cgi/doi … 1126/science.aao3898

Related Stories

Brain's hippocampus can organize memories for events as well as places

June 8, 2017
People organize memories in photo albums, journals or calendars, but how does the brain first put events in order? Though a great deal of work has been done on how the brain encodes memory for locations, leading to the discovery ...

Navigation and spatial memory—new brain region identified to be involved

August 16, 2017
Navigation in mammals including humans and rodents depends on specialized neural networks that encode the animal's location and trajectory in the environment, serving essentially as a GPS, findings that led to the 2014 Nobel ...

'Brain GPS' network allows brain to track location when at rest

March 3, 2016
UC San Francisco scientists have discovered a network of brain cells that allows animals to keep track of where they are when they are not moving through space, such as when they are eating, engaged in social interactions, ...

Brain's 'GPS' does a lot more than just navigate

March 30, 2017
The part of the brain that creates mental maps of one's environment plays a much broader role in memory and learning than was previously thought, according to new research published this week in the journal Nature by researchers ...

Neurons in the brain tune into different frequencies for different spatial memory tasks

April 17, 2014
Your brain transmits information about your current location and memories of past locations over the same neural pathways using different frequencies of a rhythmic electrical activity called gamma waves, report neuroscientists ...

Explainer: What happens in the hippocampus?

October 7, 2014
This year's Nobel Prize in medicine recognises work on "cells that constitute a positioning system in the brain." Those cells are found in the hippocampus. It is just one tiny part of the brain, but this structure gets at ...

Recommended for you

Common painkiller not effective for chronic pain after traumatic nerve injury

September 24, 2018
A new study out today in the Journal of Neurology finds that pregabalin is not effective in controlling the chronic pain that sometimes develops following traumatic nerve injury. The results of the international study, which ...

Implant helps paralysed man walk again

September 24, 2018
Five years after he was paralysed in a snowmobile accident, a man in the US has learned to walk again aided by an electrical implant, in a potential breakthrough for spinal injury sufferers.

Study of protein 'trafficker' provides insight into autism and other brain disorders

September 22, 2018
In the brain, as in business, connections are everything. To maintain cellular associates, the outer surface of a neuron, its membrane, must express particular proteins—proverbial hands that reach out and greet nearby cells. ...

Breast milk may be best for premature babies' brain development

September 21, 2018
Babies born before their due date show better brain development when fed breast milk rather than formula, a study has found.

White matter repair and traumatic brain injury

September 20, 2018
Traumatic brain injury (TBI) is a leading cause of death and disability in the U.S., contributing to about 30 percent of all injury deaths, according to the CDC. TBI causes damage to both white and gray matter in the brain, ...

'Gut sense' is hardwired, not hormonal

September 20, 2018
If you've ever felt nauseous before an important presentation, or foggy after a big meal, then you know the power of the gut-brain connection.

0 comments

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.