Vertical motion detectors and their synaptic relations in the third optic lobe of the fly.

The synaptic relations of the giant vertical cells in the lobula plate of the fly were investigated using electron microscopical procedures and Lucifer yellow dye backfill and injection techniques. Histological features of the giant vertical cells are described. The giant vertical cells are exclusively postsynaptic in the lobula plate. They function to integrate input from dense arrays of chemical synapses and have a wide spatial input from the lobula plate. The giant vertical cells are postsynaptic to perpendicularly occurring cells. There are two classes of cells presynaptic to the vertical cells, one of which contains large dense-core vesicles. The giant vertical cells are not the only cells postsynaptic to these two classes of perpendicular cells. A second group of smaller tangential cells, the twin vertical cells, were also found postsynaptic to many of the same cells that synapsed with the giant vertical cells. The twin vertical cells and the giant vertical cells are therefore integrating some of the same information in the lobula plate.

Intensity and motion responses of giant vertical neurons of the fly eye.

There are nine "giant vertical" neurons in the lobula plate of the fly optic lobe. Intracellular recordings were obtained from the three most peripheral of these cells. These cells respond to a light flash with graded changes in the membrane potential. The response consists of an "on" transient, a sustained depolarization, an increase in membrane potential fluctuations, and an "off" transient. Signal averaging showed that only the "on" and "off" transients are correlated to the stimulus. A pattern of horizontally oriented stripes moving in the vertical direction evokes a response larger than the response to a stationary pattern. The response is most sensitive to vertical movement; motion in the downward direction evokes a net membrane potential depolarization, and upward motion results in a net hyperpolarization. We conclude that the giant vertical cells function primarily as vertical motion detectors and that the direction of the motion is encoded in the polarity of the shift in the membrane potential.