O1: What is the network activity of RSC during memory processing?
Using two-photon calcium imaging and mouse behavior, we found that a proportion of neuronal responses in the RSC respond either to the presentation of sensory stimuli or to specific time points between the presented stimuli. While responses to sensory stimuli were relatively reliable over days, neuronal responses representing temporal information varied at a timescale of hours to days. The representation of temporal information between the presented sensory stimuli was context-dependent. Thus, neuronal responses differed depending on the identity of the preceding sensory stimulus.
O2: What is the relationship between the hippocampus and RSC during memory processing?
By recording hippocampal oscillations and simultaneously imaging neurons in the RSC we showed that the presentation of sensory stimuli not only evoke neuronal discharges in RSC, but also synchronize neuronal oscillations in the hippocampus. Thus, responses in RSC are phase-locked to hippocampal oscillations.
O3: Is RSC activity critical for memory processing?
Silencing neuronal activity in the RSC did not reveal a clear effect on memory performance. In other words, diminished RSC activity does not lead to worse memory performance. Mouse behavior underlying memory processing in our study therefore does not critically depend on RSC activity. However, we found that silencing neuronal activity in the medial septum, the brain’s theta rhythm generator (also see O2), diminishes the strength of hippocampal theta oscillations. In addition, diminished strength of hippocampal theta oscillations the decreases the overall number of RSC neurons that process sensory and temporal information, respectively. Thus, memory processing in the RSC is mediated by hippocampal oscillatory activity at 4-8
