Neural correlates of the jamming avoidance response ofEigenmannia

Summary

• 1. Single unit responses of electroreceptors, of Posterior Lateral Line Lobe cells and of Torus Semicircularis cells were studied. Three types of stimuli were used; one was sufficient for evoking the jamming avoidance response and the other two lacked key features necessary for the behavior's occurrence. Responses to each of these stimuli were compared to determine which stimulus parameters were measured by each cell type.

• 2. The receptor population was divided into two groups. The P-receptors, probability coders, responded primarily to changes in the amplitude of the stimulus. No differences were seen in the phases of their peak activity during stimulation with either +ΔF or −ΔF beats or with amplitude modulations of a pure tone (Figs. 4,5). The T-receptors, tonic receptors, usually fired one spike during each stimulus cycle with a very constant phase. These receptors can provide information that will allow detection of the presence and the sign of theΔF of beats since the phase of the individual cycles within the beat change in a systematic fashion relative to either pure tone component of the beat (Fig. 3).

• 3. Posterior Lateral Line Lobe T-cells behaved similarly to T-receptors (Fig. 7). P-cells from this region responded to increases in stimulus amplitude with either an increase (E Type) or a decrease (I Type) in firing frequency. As in the case of P-receptors, no differences in the firing patterns of these P-cells were found when + or −ΔF beats or AM were used as stimuli (Figs. 8,9).

• 4. Many Torus Semicircularis T-cells responded to beats capable of evoking the jamming avoidance behavior with little or no phase modulation compared to the T-cells seen in antecedent areas. These cells could therefore supply a necessary temporal reference for the evaluation of the changing phase of a beat stimulus relative to one of its pure tone components (Fig. 10). A subset of the Torus P-cells behaved the same as did the Posterior Lateral Line lobe P-cells. The remainder (sign-sensitive cells) showed strikingly different responses to + and −ΔF beats and AM stimuli (Figs. 11, 12, 13). These cells are shown to be sensitive to phase differences between electrical stimuli received at near by regions of the body (Fig. 15). ThisΔF sign sensitivity is only found when stimuli capable of evoking a JAR are used.

• 5. Mechanisms are proposed to explain the behavior of the sign-sensitive cells which rely on comparison of a reference signal and a beat driven signal supplied by different populations of T-units (Fig. 16). Based on these results, a simple neural circuit is proposed (Fig. 17) which is sufficient to account qualitatively for the known properties of the jamming avoidance behavior.