Figure 4. The relationship of oscillatory field activity with the sequential timing of intracellularly recorded sub- and suprathreshold events.

A, rheobasic action potentials were elicited in a regular spiking neuron of an oscillating slice. Spike-triggered averages of the concomitantly recorded extracellular field activity revealed action potentials to be located near the peak negativity of an oscillatory cycle. B, when using field triggered data acquisition and constructing spike latency histograms, it was apparent that action potentials could occur during any part of an oscillatory cycle, but with the peak of their probability distribution overlapping with the trough of the averaged extracellular field. C, when adjusting the membrane potential during intracellular recordings to the apparent point of IPSP reversal (−70 mV), it was feasible to discriminate depolarizing events, presumably EPSPs, which were clearly correlated with the extracellular population activity. D, field triggered averages of such recordings were nearly matching, albeit with a slight precession of the intracellular waveform. E, field triggered acquisition of intracellular recordings displaying numerous IPSPs at depolarized holding potentials showed the peak positivity of the intracellular trace to coincide with the trough of the averaged field. All recordings in A-E were obtained within layer 5/6.