Smooth Pebbles

Place fields tied to a single grid cell in a rat's entorhinal cortex. From Hafting, Fyhn, Molden, Moser, and Moser, "Microstructure of a spatial map in the entorhinal cortex," Nature, 11 August 2005. By permission of the authors.

I wanted to give a heads-up and a link to a set of blog posts on spatial cognition that ScienceBlog readers might find of interest. These posts compose the first installment in Mind Matters, a new, researcher-authored "seminar blog" that (full disclosure dept:) I conceived, and yesterday launched, at sciam.com, the Scientific American website.

In their posts, cogntive scientists James J. Knierim and A. David Redish describe and discuss the August 11, 2005, Nature paper that announced the discovery of grid cells, which was perhaps the biggest thing to happen in spatial cognition in 30 years.

The beauty of spatial cognition was long lost on me. But lately I've found nothing, other than my children's antics and my wife's voice, so absorbing. At its most basic, spatial cognition simply refers to the neural mechanisms by which we understand and navigate space: How we learn routes, extrapolate maps, orient ourselves when lost. These mechanisms are fascinating in their own right. But they are made trebly absorbing by the many suggestions that the mechanisms that we use for finding our way around underlie our broader, more abstract powers of memory, cognition, and even emotion -- that we navigate life, in short, much as a rat does a maze.

As Knierim and Redish describe, few discoveries have done more to advance this view than the grid cell discovery. A clever and personable team at the Center for the Biology of Memory in Trondheim, Norway made the discovery, which beggars the imagination. Searching the entorhinal cortex for what they thought would be some vague set of inputs feeding the hippocampus (where place cells and other assets help us find our way around), they discovered that certain cells in the rat's brain, which they dubbed cells, project a rolling, multilayered, virtual gridwork over the landscape that tracks the rat's location and movement. Tens of thousands of these virtual grids tesselate the rat's world. No two grids are the same, and each is tied to a single grid cell. In ensemble, with one grid or another firing virtually everywhere the rat goes, they generate massive data that the rat, exercising impressive computational powers, uses to track its own location.

Ludicrously, almost impossibly elaborate and orderly. Yet there it was, as James Knierim puts it in his Mind Matters post -- "a neural response property ... so geometrically regular, so crystalline, so perfect" that it prompted Knierim, reading the paper at his desk, to mutter to himself, "'This changes everything.'" 

I can't get enough of this stuff. If you've a taste for more, go here to read Knierim's and Redish's description and comments.