Figure 5. Scaling of excitation can lead to a gain modulation effect.

(A and B) An enlargement of tone evoked excitatory (A) and inhibitory (B) responses at 70 dB SPL under contralateral and binaural stimulation. Each small trace (350 ms record) represents the response to a given tone frequency.

(C and D) Plot of the response amplitudes at different frequencies for the same cell. Curves are Gaussian fits of the data. Inset, the Gaussian functions are normalized and superimposed for comparison.

(E) Simulated frequency tuning curves for excitation and inhibition. The tuning curves are centered on the same characteristic frequency. The inhibitory tuning curve is broader than the excitatory tuning curve. Inset, temporal profiles of the simulated tone-evoked excitatory and inhibitory conductances. Scale, 0.5 nS, 40 ms.

(F) Tuning curves of peak membrane depolarization resulting from the integration of the modeled synaptic conductances. Excitatory responses were scaled by a factor of 0.8 – 1.2 while fixing the inhibitory responses. The resting membrane potential is set at −60 mV.

(G) Tuning curves of spike rate under different scaling factors for manipulating excitatory strength. Spike rate was calculated from the peak Vm response based on a power-law function. Inset, spike tuning curves are normalized and superimposed for comparison.

(H) Normalized CF-tone evoked firing rate (blue) and spike tuning width (black) at different scaling factors for scaling excitatory strength. Note that within the physiological range of firing rate changes (0.4–1.4), there is only a very small variation in spike tuning width (0.93–1.03).

(I) Normalized firing rate and spike tuning width at different scaling factors for scaling inhibition (0.5 – 2), with the excitation fixed.

(J) Normalized spike tuning width at different scaling factors for scaling excitation. The inhibitory tuning shape was varied. Cotuned, excitation and inhibition have the same tuning shape; constant, inhibitory tuning is flat.