Figure 3. Spiking receptors encode pulse duration, whereas oscillating receptors do not.
(A, B) Extracellular recordings from a spiking receptor in B. niger during stimulation with positive-polarity (black) and negative-polarity (red) monopolar square pulses of 0.10-ms duration (A) and 0.2-ms duration (B). In both cases, the difference in spike times (Δt) matches the pulse duration. Traces from five stimulus repetitions are superimposed. (C) Spike probability vs square pulse duration for responses to positive-polarity stimuli for spiking receptors of three species. Horizontal bars indicate the behaviorally relevant ranges of total durations measured in 10 conspecific electric organ discharge (EOD) waveforms. (D) Spike-timing differences between responses to positive- and negative-polarity stimuli vs square pulse duration for the same receptors in C. (E, F) Extracellular recordings from an oscillating receptor in P. tenuicauda during stimulation with positive- (black) and negative- (red) polarity monopolar square pulses of 0.10-ms duration (E) and 0.20-ms duration (F). In both cases, the timing difference (Δt) between oscillatory peaks elicited by opposite-polarity stimuli does not match the pulse duration. Traces from five stimulus repetitions are superimposed. (G) Evoked oscillation amplitudes normalized to prestimulus oscillation amplitudes vs square pulse duration for oscillating receptors. Curves for each receptor are shown in gray, and the averages across receptors are shown in black. The horizontal bar indicates the range of total durations of 10 conspecific EODs. (H) Oscillation-timing differences between responses to positive- and negative-polarity stimuli vs square pulse duration for the same receptors shown in G. (I, J) Extracellular recordings from an oscillating receptor in P. tenuicauda in response to a head-positive (‘normal polarity’) conspecific EOD waveform (black) and the reverse-polarity waveform (red) at an intensity of 316 nA (I) and 32 nA (J). Traces from five stimulus repetitions are superimposed. (K) Vector strength vs phase difference of oscillatory responses to opposite-polarity conspecific EODs in P. tenuicauda. Each point represents the mean of responses from six receptors. Vector strength was averaged across stimulus polarity within each receptor before averaging across receptors. Error bars represent S.E.M. Closed circles indicate phase resets that were significantly different for normal- vs reversed-polarity EODs (Hotelling test for paired circular data, F > Fcrit = 6.9, p < 0.05). The stimulus intensities that evoked significantly different phase resets for opposite polarity EODs were 56, 178, and 316 nA. Intensities of 100 nA and <56 nA did not result in significantly different phase resets. (L) Phase differences between responses to positive- and negative-polarity stimuli vs square pulse duration for oscillatory responses to monopolar square electric pulses.