Harnessing a noncanonical vestibular input in the head-direction network to rectify age-related navigational deficits.

Navigational decline is a metric distinct from aging-related cognitive degradation, yet the affected circuits and synaptic changes remain elusive. This study identified a long-range excitatory projection from parvalbumin (PV) neurons in the brainstem medial vestibular nucleus (MVN) of mice that monosynaptically innervates the midbrain dorsal tegmental nucleus (DTN). This PV^MVN→DTN projection exhibits high neuronal excitability and synaptic plasticity as electrophysiological traits. In vivo chemogenetic inhibition of the PV^MVN→DTN projection impaired the navigational performance of adult mice. Navigational deficits in aged mice linked to both diminished innervation and synaptic drive of the PV^MVN→DTN pathway were pinpointed as hallmarks of the aging process. Strikingly, targeted activation of this pathway mitigated navigational impairments in older mice. In sum, our results revealed an excitatory PV^MVN→DTN pathway that impacts navigation. Rescue from aging-related navigational decline by activation of a spared projection pathway further highlights the potential for targeted therapies.