The Interaction of Stimulus-specific Adaptation between the Thalamic Reticular Nucleus and Medial Geniculate Body

The long-term goal of our research is to understand the interaction between the thalamus and the cerebral cortex. The thalamus is reciprocally connected with cerebral cortex. Both thalamocortical and corticothalamic projections send collaterals to the thalamic reticular nucleus (TRN) of the ventral thalamus. The TRN consists of only GABAergic inhibitory neurons which only project back to the dorsal thalamus. Recently we found that neurons in both TRN and MGB showed great adaptation and the adaptation was stimulus specific, preferring deviant stimulus can called stimulus specific adaptation (SSA)[1, 2]. We have understood with extracelluar recordings that the deviant stimulus detection of TRN neurons either enhanced or suppressed MGB neuronal responses to the following auditory stimulus[1]. The SSA feature of the TRN has been proposed to induce attention shift to fresh stimulus at the dorsal thalamus, echoing the old ‘searchlight’ hypothesis [4]. Comparing with the SSA in the TRN neurons, that of the MGB neurons was much smaller [3]. The questions arise here. 1) Do TRN neurons have a modulation of the SSA of the MGB neurons? 2) The TRN inhibitory innervations to different subnuclei are different: strong inhibition to the non-lemniscal nuclei, weak or void inhibition to the central core of lemniscal nucleus [8, 9]. Whether TRN modulations are even on the SSA of MGB neurons in different subnuclei. 3) In the ventral MGB, ON and OFF neurons are segregated from each other [10, 11, 12], so how would the TRN innervations modulate differently on those two types of neurons? 4) There was a disagreement in the range of TRN innervations to the MGB [14-24]. The question is whether the SSAs in the TRN and MGB has any correlation; the questions will be addressed with both the extracellular and intracellular recordings from TRN and MGB neurons with oddball paradigm, while the TRN is manipulated with drug application. With intracellular recording, we would be able to measure the membrane potential of MGB neurons at the subthreshold level while they are modulated with TRN innervations. The results of the proposed study would advance our understanding on the deviance-detection in the TRN and its interaction with the dorsal thalamus, and thus the selective gating function of the thalamus. The results would also add an important piece of knowledge on potential functional implications of the highly integrative brain processes of attention.