Experience-driven rate modulation is reinstated during hippocampal replay

Replay, the sequential reactivation within a neuronal ensemble, is a central hippocampal mechanism postulated to drive memory processing. While both rate and place representations are used by hippocampal place cells to encode behavioral episodes, replay has been largely defined by only the latter – based on the fidelity of sequential activity across neighboring place fields. Here, we show that dorsal CA1 place cells in rats can modulate their firing rate between replay events of two different contexts. This experience-dependent phenomenon mirrors the same pattern of rate modulation observed during behavior and can be used independently from place information within replay sequences to discriminate between contexts. Our results reveal the existence of two complementary neural representations available for memory processes., Animals
Five male Lister-Hooded rats (350-450g) were implanted with a microdrive with 24 independently moveable tetrodes. Prior to surgery, rats were kept at 90% of their free-feeding weight and housed in pairs on a 12-hour light/dark cycle, with 1 hour of simulated dusk/dawn. All experimental procedures and postoperative care were approved and carried out in accordance with the UK Home Office, subject to the restrictions and provisions contained within the Animal (Scientific Procedures) Act of 1986
Surgery
Animals were deeply anaesthetized under isoflurane anesthesia (1.5-3% at 2L/min) and implanted with a custom-made microdrive array carrying 24 independently moveable tetrodes (modified from microdrive first published by (Davidson et al., 2009)). Each tetrode consisted of a twisted bundle of four tungsten microwires (12µm diameter, Tungsten 99.95% CS, California Fine Wire), gold-plated to reduce impedance to < 200kΩ. Three rats were implanted with a dual-hippocampal microdrive tar..., Files can be viewed in Matlab. Details available in companion README.txt