Fig. 8.

Excitation spreads preferentially along rows compared with arcs. The left column shows a series of voltage-sensitive dye images demonstrating the time-dependent spread of excitation, along with a schematic drawing of the orientation of the barrel field (top). The earliest response (10 msec) has no preferred orientation, with a small signal amplitude that is confined horizontally to a single barrel-column. Subsequently (images at 20 and 50 msec), excitation extends into neighboring barrel-columns with a preferential spread along the rows of barrel cortex. Theright column provides quantification of the spread of excitation. Gaussian functions are fitted to line sections of the voltage-sensitive dye response oriented along the row (red curves) or arc (blue curves) through the epicenter. The broader Gaussian curves calculated along the row indicated the preferred orientation of the delayed spread of excitation. The propagation velocity of the Gaussian wave front is twice as fast along the row compared with along the arc (top).