Fig. 1. The low-responsiveness window of the fast electrosensory pathway is elicited by natural (A) and artificial (B–D) stimuli. (A) Field potentials evoked by the self-(black triphasic artifact around time zero in each trace) and conspecific (green)-generated EODs at the magnocellularis nucleus in a freely moving fish. The triphasic waveform at the beginning of each trace (labeled 1–5) is the sEOD artifact, followed by a spike corresponding to the fast electrosensory pathway evoked response. The cEOD artifact is the small triphasic waveform highlighted in green (labeled a–g). The fast electrosensory pathway response evoked by the conspecific-generated EOD (green spikes) is absent at short delays (a and f) and increases in amplitude with the interval between the self-generated EOD and the conspecific-generated EOD (green evoked spikes labeled e, d, c and b). Note that a similar, but smaller, decrease in the response to the self-generated EOD is provoked by the activation of the fast electrosensory pathway when the conspecific-generated EOD (second trace, blue spike) occurs just before the self-generated EOD (red spike). (B) Field potential responses evoked in the magnocellularis nucleus of a curarized fish by a two-threshold artificial stimulus delivered at different periods (28–100 ms) after a conditioning stimulus (evoking a response similar to that evoked by the self-generated EOD). With short delays after the activation of the fast electrosensory pathway responsiveness is reduced, as indicated by a decrease in amplitude (C) and an increase in latency (D) of the response elicited by the artificial test stimulus.