Fig. 4.

Arousal modulates network suppression underlying lateral inhibition. (A) EPSCs in response to a preferred (Top) and nonpreferred (Bottom) tone during different arousal levels from 1 cell. Gray traces, subset of single trials. Bold traces, average. Dashed line, baseline. (B) Loss of network suppression is not due to less spontaneous excitation. (B₁) Current (−70 mV) and pupil diameter from 1 cell show a decrease in current variability during increased arousal. (B₂) Expansion of periods marked by small bars in B₁. (B₃) All points histogram of current (20 s) from B₁. (B₄) Increases in arousal decrease current variability (I_m SD) while mean current is unchanged (n = 14 cells). (C) Arousal modulates EPSCs and IPSCs similarly. (C₁) Averaged tone-evoked EPSCs and IPSCs from the same cell during different arousal states. (C₂) Absolute charge above (below) baseline for IPSCs (EPSCs) during different arousal levels (n = 35 tone responses at each arousal level, 12 cells, *P = 0.010 and 0.048, respectively, paired t test). (D) EPSC onset (ON) responses in C₁) peak during moderate arousal. (D₁) Normalized ON responses aligned to BF (n = 16 cells). (D₂) Summary of all significant ON responses recorded at each arousal level shows that ON component increased from low to moderate arousal and then decreased during high arousal (*P < 0.003, paired t test, and n = 32 frequencies,16 cells). (E) NS of EPSCs (in C₁) was biased to high frequencies and decreased monotonically with increasing arousal. (E₁) Normalized NS aligned to BF (n = 16 cells). (E₂) Summary of significant responses shows that NS steadily decreased with increases in arousal (*P < 0.001, paired t test, and n = 27 frequencies, 11 cells). Error bars, SEM.