Temporal interaction between single spikes and complex spike bursts in hippocampal pyramidal cells

Cortical pyramidal cells fire single spikes and complex spike bursts, Howev er, neither the conditions necessary for triggering complex spikes, nor the ir computational function are well understood, CA1 pyramidal cell burst act ivity was examined in behaving rats. The fraction of bursts was not reliabl y higher in place field centers, but rather in places where discharge frequ ency was 6-7 Hz. Burst probability was lower and bursts were shorter after recent spiking activity than after prolonged periods of silence (100 ms-1 s ). Burst initiation probability and burst length were correlated with extra cellular spike amplitude and with intracellular action potential rising slo pe. We suggest that bursts may function as "conditional synchrony detectors ," signaling strong afferent synchrony after neuronal silence, and that sin gle spikes triggered by a weak input may suppress bursts evoked by a subseq uent strong input.