Subcortical correlates of the auditory brainstem potentials in the monkey: referential responses.

Referential responses correlated with the vertex auditory brain-stem potentials (ABSP) were recorded from different brainstem and diencephalic structures of large monkeys under barbiturate anesthesia. Polarity, latency, and amplitude of various response components were determined from structures located 2 mm apart along five different vertical trajectories aiming at the trapezoid body (TB), superior olivary complex (SOC), mesencephalic reticular formation (MRF), medial geniculate nucleus thalami (MG), and inferior colliculus (IC). Latency correlations, amplitude differences, voltage profiles, current-source-density-distribution, and current flows of the various response components were subsequently calculated. Subcortical referential responses were formed by seven initial fast positive components (I, II, A, B, C, D and E) and one late slow negative component (F) correlated to waves I to VII and SP3 of the vertex ABSP respectively. Positive components C and D' also correlated to SP1 and SN1 of ABSP respectively. Amplitude of component B at contralateral SOC and C, D' and F at contralateral MRF was significantly larger than those of other subcortical responses and vertex ABSP. A single component of the subcortical referential responses accompanied changes in voltage, CSD, and current flows of various brainstem structures. However, considering only major changes in these parameters, component B accompanied a voltage positive and a CSD positive-negative peak and an ascending current flow at the SOC; component C accompanied similar changes at MRF, and components D' and F accompanied voltage negative and CSD negative-positive-negative peaks and ascending and descending current flows at MRF. In contrast, no systematic changes in voltage, CSD and current flows accompanied components I, II, A, D and E.