Figure 7.

Influence of single cells on population activity A, firing induced in single cells (top trace) elicited local field potentials (lower traces). B, field potentials could be associated with increased multi unit activity. In these records synaptic inhibition was blocked (20 μm bicuculline). Either excitability was reduced (4 mm Ca, 4 mm Mg) to abolish epileptiform events or the effects of single cell firing were tested between population bursts. C, the latency of the field potential in the interaction from B was about 6 ms. Average of 100 traces. D, in another interaction, pyramidal cell firing elicited unit discharges of similar form at short latency. Note that the second action potential failed occasionally. E, CA3a cells initiate increased multi unit firing (right panel) either in CA3a or in CA3b regions in a significantly more efficient manner than CA3b cells (P < 0.05, Fisher's exact test). About half of the cells in both regions are able to induce local field potential (right panel).