Intrathalamic Interaction in the Medial Geniculate Body

All sensory signals other than olfactory ones go through the thalamus before reaching to the cortex. The thalamus receives massive feedback from the cortex. Both thalamocortical and corticothalamic projects pass through a thin sheet structure in the ventral thalamus called thalamic reticular nucleus (TRN) and give collateral inputs to its neurons. It has been suggested that the thalamus together with the TRN is not a simple relay station but a complicated processor. Previous studies have shown that the corticofugal projections have a strong modulation on the thalamic relay neurons. In this study, we investigated the intrathalamic interaction between different nuclei in the auditory system of rats and guinea pigs.;Specifically, we investigated the gain adjustment in medial geniculate body (MGB) by TRN and the cross modality modulation via the TRN, and confirmed the pathway through which the MGB was modulated, by in-vivo extracellular and intracellular recording.;In this project, we examined the modulating effect of electrical activation of one site in the MGB on neuronal responses to acoustic stimuli in another site of the same nucleus. We found that the inhibitory modulation was diminished after TRN inactivation and IC was not involved in this modulating pathway. Auditory responses of MGB neurons were modulated by preceding electrically stimulation of the lateral geniculate nuclei (LGN). In the randomly sampled coronal plane, the modulation range was 2.8-4.0mm laterally to the bregma and depth was from 5.0-6.5mm vertically to the brain surface. 52%-56% points of all points tested in the plane caused modulation effects. No tonotopic correlation in the modulation map was found.;The present results indicate that a strong intrathalamic modulation occurs in the auditory thalamus. The modulation is via the TRN in the guinea pig. The results suggest that intrathalamic interaction between the TRN and MGB is likely an additional gain processor in the auditory signal pathway. The modulation via the TRN has cross-modal influences. The cross-modal influences and the results that each MGB receives modulations from a large thalamic area within the MGB suggest that the intrathalamic interaction may perform a global modulation function on the top of gain adjustment.