EPSP amplification and the precision of spike timing in hippocampal neurons

The temporal precision with which EPSPs initiate action potentials in posts ynaptic cells determines how activity spreads in neuronal networks. We foun d that small EPSPs evoked from just subthreshold potentials initiated firin g with short latencies in most CA1 hippocampal inhibitory cells, while acti on potential timing in pyramidal cells was more variable due to plateau pot entials that amplified and prolonged EPSPs. Action potential timing apparen tly depends on the balance of subthreshold intrinsic currents. In interneur ons, outward currents dominate responses to somatically injected EPSP wavef orms, while inward currents are larger than outward currents close to thres hold in pyramidal cells. Suppressing outward potassium currents increases t he variability in latency of synaptically induced firing in interneurons. T hese differences in precision of EPSP-spike coupling in inhibitory and pyra midal cells will enhance inhibitory control of the spread of excitation in the hippocampus.