A Dual Inhibitory Network in the Thalamic Reticular Nucleus Delineated by Pallidal and Intra-Reticular Inhibition

Long described as an inhibitory "guardian of the gateway," the thalamic reticular nucleus (TRN) shapes which thalamic signals reach the cortex during attention, arousal, and sensory processing. However, how the inhibitory wiring within TRN supports this flexible gating—from modality-specific tuning to global control—remains poorly defined. Using cell type-specific optogenetic input mapping and whole-cell patch-clamp recordings in mice, we dissect inhibitory connectivity in TRN from two major GABAergic sources: the TRN itself and the external globus pallidus (GPe). All recorded TRN neurons received inhibition from the GPe, whereas a subset also received intra-TRN inhibition. Intra-TRN inhibition arose predominantly from somatostatin-expressing onto parvalbumin-expressing TRN neurons (SOM→PV), revealing subtype-specific connectivity recruited by thalamic excitation to form a feedforward motif. These findings delineate a dual inhibitory architecture: local intra-TRN circuits provide spatially selective inhibition, whereas pallidal inputs deliver diffuse inhibition. These complementary mechanisms may support both modality-specific gating and global state-dependent control of thalamic output.