A, The principal connections of the MSO include not one but two sets of inputs. First, AVCNspherical bushy cells from both sides project directly to MSO neurons providing binaural excitation. Second, glycinergic inhibitory neurons in the MNTB (evoked by contralateral stimulation) and LNTB (evoked by ipsilateral stimulation) project to the MSO.B, PST histograms (PSTHs) for the three sources of MSO inputs: AVCN (ipsilateral and contralateral; fromVater, 1982); MNTB (contralateral), andLNTB (ipsilateral). All of the four inputs show phase-locking in response to SAM stimuli (temporal resolution of the PSTH: 0.1 msec).