Researchers discover workings of brain's 'GPS system'

Friday, March 8, 2013

Just as a global posi?tion?ing sys?tem (GPS) helps find your loca?tion, the brain has an inter?nal sys?tem for help?ing deter?mine the body's loca?tion as it moves through its surroundings.

A new study from researchers at Prince?ton Uni?ver?sity pro?vides evi?dence for how the brain per?forms this feat. The study, pub?lished in the jour?nal Nature, indi?cates that cer?tain position-tracking neu?rons ? called grid cells ? ramp their activ?ity up and down by work?ing together in a col?lec?tive way to deter?mine loca?tion, rather than each cell act?ing on its own as was pro?posed by a com?pet?ing theory.

Grid cells are neu?rons that become elec?tri?cally active, or "fire," as ani?mals travel in an envi?ron?ment. First dis?cov?ered in the mid-2000s, each cell fires when the body moves to spe?cific loca?tions, for exam?ple in a room. Amaz?ingly, these loca?tions are arranged in a hexag?o?nal pat?tern like spaces on a Chi?nese checker board.

"Together, the grid cells form a rep?re?sen?ta?tion of space," said David Tank, Princeton's Henry L. Hill?man Pro?fes?sor in Mol?e?c?u?lar Biol?ogy and leader of the study. "Our research focused on the mech?a?nisms at work in the neural sys?tem that forms these hexag?o?nal pat?terns," he said. The first author on the paper was grad?u?ate stu?dent Cristina Dom?nisoru, who con?ducted the exper?i?ments together with post?doc?toral researcher Amina Kinkhabwala.

Dom?nisoru mea?sured the elec?tri?cal sig?nals inside indi?vid?ual grid cells in mouse brains while the ani?mals tra?versed a computer-generated vir?tual envi?ron?ment, devel?oped pre?vi?ously in the Tank lab. The ani?mals moved on a mouse-sized tread?mill while watch?ing a video screen in a set-up that is sim?i?lar to video-game vir?tual real?ity sys?tems used by humans.

She found that the cell's elec?tri?cal activ?ity, mea?sured as the dif?fer?ence in volt?age between the inside and out?side of the cell, started low and then ramped up, grow?ing larger as the mouse reached each point on the hexag?o?nal grid and then falling off as the mouse moved away from that point.

This ramp?ing pat?tern cor?re?sponded with a pro?posed mech?a?nism of neural com?pu?ta?tion called an attrac?tor net?work. The brain is made up of vast num?bers of neu?rons con?nected together into net?works, and the attrac?tor net?work is a the?o?ret?i?cal model of how pat?terns of con?nected neu?rons can give rise to brain activ?ity by col?lec?tively work?ing together. The attrac?tor net?work the?ory was first pro?posed 30 years ago by John Hop?field, Princeton's Howard A. Prior Pro?fes?sor in the Life Sci?ences, Emeritus.

The team found that their mea?sure?ments of grid cell activ?ity cor?re?sponded with the attrac?tor net?work model but not a com?pet?ing the?ory, the oscil?la?tory inter?fer?ence model. This com?pet?ing the?ory pro?posed that grid cells use rhyth?mic activ?ity pat?terns, or oscil?la?tions, which can be thought of as many fast clocks tick?ing in syn?chrony, to cal?cu?late where ani?mals are located. Although the Prince?ton researchers detected rhyth?mic activ?ity inside most neu?rons, the activ?ity pat?terns did not appear to par?tic?i?pate in posi?tion calculations.

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Domnisoru, Cristina, Amina A. Kinkhab?wala & David W. Tank. 2013. Mem?brane poten?tial dynam?ics of grid cells. Nature. doi:10.1038/nature11973. Pub?lished online Feb. 10, 2013.

Princeton University: http://www.princeton.edu

Thanks to Princeton University for this article.

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Source: http://www.labspaces.net/127189/Researchers_discover_workings_of_brain_s__GPS_system_

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