Columns and Collaterals
There is important local processing in cortex as well as the more dramatic massive projections back and forth between cortical regions. Using short, slow, local connections eliminates many long, expensive, fast interregional connections. Cortical pyramidal cells connect to neighbors over several millimeters in the form of patchy connections. Connections are often reciprocal between patches. Groups of cells called cortical columns are ubiquitous in cortex and seem to be fundamental architectural units. A functional column is perhaps .3 mm in diameter containing perhaps 10,000 cells. Intrinsic imaging studies of columns in inferotemporal cortex show they respond selectively to complex aspects of images. A small number of columns respond to a complex object. In inferotemporal cortex, these responses might be “words” in a language of vision. There is evidence for scaling of computation from single units to cortical regions. Understanding the function of such ensembles is the future.
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