Influence of the septum and inferior colliculus on medial geniculate body units

Abstract

The septum has been found to have direct projections to the medial geniculate body (MGB) and the inferior colliculus; this study was undertaken to determine whether or not the septum might influence the function of the MGB. Excitatory and inhibitory effects on MGB unit firing were observed after stimulation of the septum and inferior colliculus. In addition, interacting effects between the septum and inferior colliculus on MGB units were observed using a focus in each in turn as a test or conditioning stimulus origin. Ablation of the inferior colliculus or removal of the posterior reticular formation did not eliminate MGB unit activation. 1. 1. A tungsten micro-electrode was used to record from units of the MGB, and small concentric bipolar electrodes were used to stimulate the septum and inferior colliculus. 2. 2. Single shocks of 40 V, 0.1 msec pulse duration were delivered at a frequency of 0.5 /sec. 3. 3. Units in the MGB were excited from 15 foci and inhibited from 2 other foci after stimulation of the septum. 4. 4. Units in the MGB were excited from 45 foci and inhibited from 11 other foci after stimulation of the inferior colliculus. 5. 5. Both the septum and inferior colliculus, when used respectively as a conditioning and a test stimulus, were found either to excite or to inhibit unit firing produced by the test stimulus. From this and similar evidence it is likely that the septum modulates auditory inputs or their subsequent impact on cerebral function via the MGB and temporal lobe cortex.