THALAMIC POPULATION BURSTS LINK SUBCORTICAL NAVIGATION CIRCUITS WITH CORTICAL MEMORY SYSTEMS

The head-direction (HD) system is a critical component of the brain’s spatial navigation network and is thought to provide internally generated directional signals during sleep that support memory consolidation in parahippocampal regions. Central to this network is the mammillary-thalamic-subicular loop, where the anterodorsal thalamic nucleus (ADn) integrates inputs from the lateral mammillary nucleus (LMN) and projects to parahippocampal cortices.
We identify a previously uncharacterized population event in this circuit: brief (<20 ms) highly synchronous bursts that we termed the Ultra Fast Oscillation (UFO). These events, which are observable in both the LMN and ADn, occur predominantly during sleep and reliably recruit spiking across the HD circuit and dentate gyrus neurons. Furthermore, these events are positively coupled with dentate spikes and negatively coupled with hippocampal sharp-wave ripples. During sleep, short auditory tones reliably evoke UFOs, indicating that even when ADn is decoupled from the main inputs to the HD system, the circuit remains responsive and selectively excitable to certain stimuli.
Together, these findings uncover a novel thalamocortical population pattern linking the HD system to hippocampal processing. Our results highlight how thalamic activity may serve to coordinate cortical and subcortical network states, providing a mechanism through which internally generated HD dynamics may influence memory consolidation.