A thalamic reticular circuit for head direction cell tuning and spatial navigation

To navigate in space, an animal must reference external sensory landmarks to the spatial orientation of its body and head. Circuit and synaptic mechanisms that integrate external cues with internal head-direction (HD) signals to drive navigational behavior remain, however, poorly described. We identify an excitatory synaptic projection from the presubiculum and retrosplenial cortex to the anterodorsalmost sector of the thalamic reticular nucleus (TRN), so far classically implied in gating sensory information flow. Projections to TRN showed driver characteristics and involved AMPA/NMDA-type glutamate receptors that initiated TRN cell burst discharge and feedforward inhibition of anterior thalamic nuclei, where HD-tuned cells relevant for egocentric navigation reside. Chemogenetic anterodorsal TRN inhibition broadened the tuning of thalamic HD cells and compromised egocentric search strategies in the Morris water maze. Besides sensory gating, TRN-dependent thalamic inhibition is an integral part of limbic navigational circuits to recruit HD-cell-dependent search strategies during spatial navigation.