Survey of hippocampal responses to sound in naive mice reveals widespread activation by broadband noise onsets

Recent studies suggest some hippocampal (HC) neurons respond to passively presented sounds in naive subjects, but the specificity and prevalence of these responses remain unclear. We used Neuropixels probes to record unit activity in HC and auditory cortex (ACtx) of awake, untrained mice during presentation of diverse sound stimuli. A subset of HC neurons exhibited reliable, short-latency responses to passive sounds, including tones and broadband noise. HC units showed evidence of tuning for tone frequency but not spectrotemporal features in continuous dynamic moving ripples. Across sound types, HC responses overwhelmingly occurred at stimulus onset; they quickly adapted to continuous sounds and did not respond at sound offset. Among all sounds tested, broadband noise was by far most effective at driving HC activity, with response prevalence scaling with increasing spectral bandwidth and density. Responses to noise were also far more common than visual flash stimuli. Sound-evoked face movements, quantified by total facial motion energy (FME), correlated with population-level HC activity, but many individual units responded regardless of movement, indicating both auditory and motor-related inputs. These results show that abrupt, acoustic events are sufficient to activate HC neurons in the absence of learning or behavioral engagement. This suggests a possible role for HC in detecting salient environmental changes and supports the idea that auditory inputs contribute directly to HC function. Given emerging links between hearing loss and dementia, these findings highlight a potential pathway by which auditory deafferentation could impact cognitive health.