Oxyopia Abstract
March 4, 2005
Friday, 4 PM
489 Minor Hall
R. Clay Reid, MD, PhD
Professor of Neurobiology, Harvard Medical School, Harvard University
Host: Ralph Freeman
Russell De Valois Memorial Lecture
Title
Micro-architecture of visual cortex: functional maps with single-cell precision
Abstract
In the visual cortex, neurons within a column have similar functional properties, such as selectivity for stimulus orientation. Columns with distinct properties, such as different preferred orientations, tile the cortical surface in orderly patterns. This functional architecture was discovered with the relatively sparse sampling of microelectrode recordings. Optical imaging of membrane voltage or metabolic activity elucidated the overall geometry of functional maps, but averaged over many cells (resolution >100 mm). Consequently, the purity of functional domains and the precision of borders between them could not be resolved. In recent experiments, we have labeled thousands of visual cortical neurons with a calcium-sensitive indicator, in vivo. We then imaged the activity of neuronal populations at single-cell resolution with two-photon microscopy up to a depth of 400 mm. In rat primary visual cortex, neurons had robust orientation selectivity but there was no discernible local structure; neighboring neurons often responded to different orientations. In area 18 of cat visual cortex, functional maps were organized at a fine scale. Neurons with opposite preferences for stimulus direction were segregated with extraordinary spatial precision in three dimensions, with columnar borders one to two cells wide. These results indicate that cortical maps can be built with single-cell precision.
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