Fig. 3. Responses of a DON unit (A) and two tectal units (B,C) to a 5 Hz sinusoidal electric field (D). Dashes indicate the occurrence of spikes. Five repetitions of the stimulations are shown for each unit. The DON unit had a spontaneous rate that was modulated by the stimulus. Tectal units exhibited little or no spontaneous activity and showed a few spikes phase locked to the stimulus. (C) A few units in the tectum developed spikes a few seconds after stimulus onset.