On average, the contralateral excitatory synaptic response (measured around the best frequency and at 70 dB SPL) was stronger than the binaural excitatory response (p < 0.01, paired t test), whereas the

contralateral inhibitory synaptic response was not different from its binaural counterpart (p > 0.2, paired t test) ( Figure 4D). In contrast, ipsilateral excitatory and inhibitory inputs were both weaker than their binaural counterparts (p < 0.01, paired t test), but the difference was far smaller for inhibition than excitation ( Figure 4D). Figure 4E plots the scaling factor for the contralateral-to-binaural synaptic response transformation. In all the recorded cells, the scaling factor for excitation was below 1, indicating click here a suppressive effect despite the fact that ipsilateral stimulation alone evoked excitation. The scaling factor for inhibition was close to 1, indicating a much weaker modulation of inhibition by ipsilateral stimulation. As for receptive field shape, binaural synaptic TRFs closely resembled their contralateral counterparts, as demonstrated by their similar bandwidths ( Figure 4F) and CFs (

Figures S3C and S3D). On the other hand, ipsilateral synaptic TRFs were significantly narrower than Caspase inhibitor their binaural counterparts ( Figure 4F). Together, these summaries strengthen the notion that ipsilateral ear input serves a modulatory function in generating binaural spike responses primarily by scaling mafosfamide down contralaterally evoked excitatory input. To test whether the observed

scaling of excitatory input contributes to the apparent linear transformation of the contralateral into binaural spike response, we employed a conductance-based neuron model (Liu et al., 2011, Zhou et al., 2012a, Zhou et al., 2012b and Sun et al., 2013). Figures 5A and 5B show the tone-evoked excitatory and inhibitory synaptic inputs at 70 dB SPL for a typical ICC neuron. We fit the frequency distribution of synaptic response amplitudes with a Gaussian function (Figures 5C and 5D). The normalized Gaussian functions for binaural and contralateral synaptic responses superimposed well (Figures 5C and 5D, inset), indicating little difference in tuning shape and again supporting the notion of scaling. We utilized these Gaussian fits to simulate frequency tuning of excitatory and inhibitory synaptic inputs in our model. For simplicity, the best frequencies of excitation and inhibition were chosen to be the same (see Figures S3C and S3D), and their tuning shapes were both symmetric (Figure 5E). Tone-evoked excitatory and inhibitory conductances (Figure 5E, inset) were simulated by fitting experimental data with an alpha function (see Experimental Procedures).