Figure 5. Direct feedback input enhances while indirect input optimizes neural responses.
Results are shown before and after indirect feedback inactivation was achieved via bilateral injection of lidocaine into the PET. Data obtained from ELL pyramidal neurons were pooled as there are no significant differences between the envelope response of ON- and OFF-type pyramidal cells (Huang and Chacron, 2016). (A) Top: Sinusoidal envelope waveform (red). Middle: Time dependent firing rate from a typical ELL pyramidal cell before (black) and after (orange) lidocaine application. Bottom: spiking activity from this same neuron in response to stimulation before (black) and after (orange) lidocaine application. (B) Population-averaged tuning curve quantified by neural gain to sinusoidal envelopes as a function of envelope frequency before (black) and after (green) lidocaine application. The dashed lines show the best power law fits to the data. Inset: population-averaged best-fit power law exponent before (black) and after (orange) lidocaine injection (p=0.0039, Wilcoxon Signed-Rank Test). (C) Population-averaged neural response power as a function of envelope frequency before (black) and after (orange) lidocaine application. The dashed lines show the best power law fits to the data. (D) Top: sinusoidal envelope waveform (red). Bottom: Time dependent EOD frequency from a typical fish before (black) and after bilateral (orange) lidocaine injection. (E) Population-averaged behavioral gain as a function of envelope frequency before (black) and after (orange) lidocaine injection. Inset: population-averaged best-fit power law exponent before (black) and after (orange) lidocaine injection (p=0.0234, Wilcoxon Signed-Rank Test). The dashed lines show the best power law fits to the data. (F) Left: population-averaged white index before (black) and after (orange) lidocaine application (p=0.0273, Wilcoxon Signed-Rank Test). Right: population-averaged relative changes in neural and behavioral sensitivity following lidocaine application (neuron: p=7.03*10−6, Wilcoxon Signed-Rank Test, behavior: p=6.74*10−4, Wilcoxon Signed-Rank Test). ‘*' indicates statistical significance at the p=0.05 level.
Figure 5—figure supplement 1. Indirect feedback inactivation achieved by injecting lidocaine bilaterally into PET increases ELL pyramidal cell responses to AMs, consistent with previous results (Bastian, 1986b).
Figure 5—figure supplement 2. Indirect feedback inactivation achieved by injecting CNQX within the ELL molecular layer gives rise to effects on ELL pyramidal cell responses to envelopes that are qualitatively similar to those observed when injecting lidocaine into PET.
Figure 5—figure supplement 3. Indirect feedback inactivation achieved by injecting CNQX within the ELL molecular layer increases ELL pyramidal cell responses to AMs, consistent with previous results (Bastian et al., 2004; Clarke and Maler, 2017).
