Figure 2.

PI evoked in vivo by ipsilateral stimulation. A, Peristimulus-time histograms (bin size, 1 ms) showing the responses of a DNLL neuron to an excitatory pure tone on the right ear (200 ms at BF of 18 kHz; 20 dB above threshold; black bar) plus a 20-ms-long inhibitory tone burst on the left ear (at BF; gray bar) delayed by 90 ms. Sound intensity on the left ear was varied in 10 dB steps to create IIDs between +20 dB (louder on the right ear) and −20 dB (louder on the left ear). At an IID of +20 dB (top), the neuron exhibited a sustained response during the entire duration of the excitatory stimulus. By increasing the intensity at the inhibitory ear by 10 dB (IID, +10 dB; second panel), the response was suppressed for the duration of the inhibitory stimulus. At an IID of 0 dB, the duration of inhibition increased to 28 ms, persisting 8 ms longer than the inhibitory stimulus (20 ms) (third panel). The duration of PI was further increased to 16 and 21 ms for IIDs of −10 and −20 dB, respectively (fourth and fifth panels). B, Suppression of responses to trailing sounds. B1, Dependency of PI on IPI. Raster displays of the responses to a sequence of three sounds are shown. First, a binaural sound favoring the left, inhibitory ear (IID, −30 dB; gray bar; I) was presented, followed by two monaural sounds presented only to the right, excitatory ear (black bars; E). Time periods during which responses to the first monaural excitatory sound were expected are illustrated by gray shaded areas. At an IPI of 2 ms (top), the neuron responded neither to the initial inhibitory sound nor to the first monaural sound at the right ear. The neuron responded weakly and with a long delay to the second monaural sound. At an IPI of 10 ms (middle), the response to the first monaural sound was still suppressed, and the response to the second monaural sound was strong and occurred with a short latency. For IPIs of 20 ms (bottom), the cell had overcome PI and responded to both monaural sounds at the right ear. B2, Dependency of PI on IID. Raster displays of the responses of the same neuron as in B1 to different initial IIDs at a fixed IPI (10 ms). When the initial sound was presented at an IID of +10 dB, the neuron responded to all three stimuli. At an IID of −10 dB, the initial sound did not elicit a response, but the cell responded to both trailing monaural sounds (middle). At even more negative IIDs of the leading sound (bottom), PI was created by the leading sound, and hence the response to the first trailing sound was suppressed.