Computing direction

Inhibitory signals and overlapping dendrites are enough to allow the sensing of direction, say Seunghoon Lee and Z. Jimmy Zhou (University of Arkansas for Medical Sciences, Little Rock, AR). These signals allow starburst amacrine cells (SACs) to send signals when light is moving in one direction but not when it is moving in another direction.

Direction-selective ganglion cells (DSGCs) have been studied since the 1960s, but the source of their selectivity was only more recently defined as coming from SACs. Now, the Arkansas group has followed the activity of SACs in retinal preparations. Light going out along a SAC dendrite centrifugally (away from the cell body) resulted in SAC activation; the activated SAC then inhibits the downstream DSGC. But light coming in along a SAC dendrite centripetally activated the SAC far...