Monday, November 19, 2007

Place Cells and Grid Cells: Part I

I spoke of Sandra Blakeslee's new book, The Body Has a Mind of it's Own, here and here.

On page 128, at a nice little section called "A Sense of Where You Are". The authors describe the eerie way certain basketball players and other athletes have of knowing exactly where they are in space, how balls go through hoops precisely even with backs turned. They duly note the advantages top athletes are born with: fast-twitch muscles, long limbs, high anabolic thresholds, extraordinary hand-eye coordination, lightning fast reflexes, excellent vision (including peripheral). They describe how certain athletes look at everything, focusing on nothing until the last moment of commitment; due respect is paid to the thousands of hours of accumulated practice manipulating ball and body in space. Then they go on:

"But there is one trait among great athletes especially those whose game is played on open courts or fields (like soccer, basketball, American football, rugby, lacrosse and hockey), that has not been described on ESPN or elsewhere. It explains why some people have an extraordinary sense of where their bodies are located in space, as well as the fast-moving bodies of all their teammates and opponents. Namely, the very best athletes have really great "place cells." And maybe even more important, they have spectacular "grid cells.

Place cells and grid cells are space-mapping neurons linked to a memory-forming region called the hippocampus. The hippocampus is evolutionarily much older than the cortex. So despite the amazing power and flexibility of our cortical space and body maps, this ancient system of place and grid cells is still very much with us - you could say it was "grandfathered in." Instead of mapping personal space from an egocentric point of view, as your parietal and premotor circuits do, place cells and grid cells are what scientists call geocentric."

The rest of the section is what they are, how they differ. Place cells were discovered in 1971 by researchers John O'Keefe and John Dostrovsky, who studied the hippocampus and memory. They appeared to encode parts of a maze the researchers' rats explored. Thousands of place cells combined in millions of ways to give the rats endless place-learning capacity.

The authors remark:
"You have place cells too. When you walk into your kitchen, certain place cells fire when you are standing in front of your refrigerator. As you move toward the sink, a different set of place cells will mark your new position in the room. If you walk into your dining room or living room, another combination of place cells will mark your spot in space."
Place cells help you navigate around your home if the lights go off, help you find a candle. They internally map where you keep your objects in relation to one another, and in relation to your body as you move through space. Some keep track of where your head is turned and update you about your balance and your body schema. If you spin in place you'll be lost until you find an object you recognize - then you'll 'know' where the door is.
"place fields are calibrated according to fixed reference points - sofa, chair, table, window, door - that do not usually change. If you move your furniture around, your place fields reconfigure your map."

More to come on this. Much more.

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