Fig. 2.

Voltage traces and interspike-interval histograms for 2 exemplar units, one regular (A and B) and the other irregular (C and D). For the regular unit, the interspike trajectory is characterized by a prominent, prolonged afterhyperpolarization (AHP). The AHP for the irregular unit is shallow and rapid so that the voltage trajectory is flat for much of the interspike interval. Relatively large, easily discerned miniature excitatory postsynaptic potentials (mEPSPs) are seen in the irregular record (C, arrows), but are less evident in the regular record (A). Voltage traces, 1-s duration; interval histograms based on 5-s samples of resting activity; number of intervals; n = 82 (C) and 143 (D).