A picture’s worth a 1000 words but for the visual system, an image represents over 100 million puzzles to solve. This is the number of light-sensitive cells – called rods and cones (comb shapes in this drawing of the retinal cell layers) – that each sends a signal from the retina when we open our eyes. To avoid being overwhelmed, the visual system needs to extract the most important aspects of the scene from this deluge. Horizontal cells (in yellow), whose tentacles connect to multiple rods and cones, play this important role. They compare activity from groups of cells and then block all but the strongest signals from reaching the brain for processing. And they can even deal simultaneously with the different demands of spatial and temporal information. This ability that’s long-puzzled scientists now appears to involve an enzyme (shown by small green patches) that adapts nerve pathways to judge temporal cues.
Written by Jan Piotrowski