A computational model could explain the positively correlated tone frequency and ILD selectivity in inhibitory neurons by an increase in the number of presynaptic inhibitory inputs. a, Top panel, Normalized ILD (left) and tone frequency (bottom) tuning curves and ILD-tone frequency combined tunings (top right) of an example excitatory neuron. Bottom panel, An example inhibitory neuron. Notice that the tone frequency response area (# repeats by 9 Hz) was calculated based on the averaged responses among seven ILDs and the ILD response area (# repeats by 7 ILD) was calculated based on the averaged responses among nine tone frequencies. b, Pairwise ILD response area (y-axis) versus tone frequency response area (x-axis) of excitatory (left) and inhibitory (right) neurons. c, Pairwise ILD half-peak value (y-axis) versus tone frequency response area (x-axis). d, Top panel, Stronger inhibition could be due to stronger presynaptic inhibition strength (thick line) and a larger number of presynaptic inhibitory neurons. Bottom panel, Goodness-of-fit or R-squared between ILD selectivity and tone frequency selectivity could be modulated by the number of their presynaptic neurons. When ILD and tone frequency responses both have five presynaptic inhibitory neurons (jitter, 0%), the R-squared between ILD and tone frequency selectivity should be highest. Thus, zero jitter indicates that the postsynaptic neurons that exhibit ILD and tone frequency responses either have the same number of presynaptic inhibitory neurons or have the same strength of presynaptic inhibition. e, Example ILD tuning curves that have the best ILD at the center and far contralateral location. Individual dots represent neural responses on each ILD value. f, Stronger presynaptic inhibition strength (blue dots) and a larger number of presynaptic inhibitory neurons (red dots) both reduce neural responses. g, Top panel, ILD half-peak width decreases gradually with an increased number of presynaptic inhibitory neurons but not the strength of presynaptic inhibition. Bottom panel, ILD half-peak value increases gradually (shift toward larger ILD values) with an increased number of presynaptic inhibitory neurons. h, Top panel, p-values and correlation coefficients (r) from the linearly regressed ILD selectivity against tone frequency selectivity across six different jitter ranges (0%, 20%…100%). Bottom panel, ILD half-peak value against tone frequency selectivity.