Event:

Sharp wave-ripples (SWRs) are transient (below 50ms) episodes displayed in the local field potential of the mammalian hippocampus during slow-wave sleep and immobile resting periods. These episodes are believed to be involved in memory consolidation. A SWR in the CA1 region of the rodent hippocampus is characterized by a slow sharp wave, which is generated by excitatory input from CA3, and a fast oscillation (up to approx. 200 Hz ripples), the mechanisms of which are not well understood. Using a computational model, I show that ripple oscillations can be generated by a recurrent network of parvalbumin-immunoreactive basket cells. Such a network can explain several key features of SWRs: (1) The oscillation frequency assumes its maximum in the first half of a SWR episode and then decreases (intra-ripple frequency accommodation). (2) In vitro, the ripple frequency is insensitive to drug-induced changes of the GABAA-receptor peak conductance and decay time constant. (3) In vivo, oscillation frequencies are bimodally distributed and occur both in the ripple band (above 140 Hz) and in the fast-gamma band (90-140 Hz). Together, these results favor recurrent interneuron networks as pacemakers for ripple oscillations.