In vivo properties of neurons of the precruciate cortex of cats

The electrical properties of 409 cells of the precruciate cortex of cats were measured intracellularly, in vivo. Resting potentials (RP) averaged -54 +/- 11 mV (SD), and action potentials (AP) of up to 80 mV were found. The magnitude of RP was correlated with the size of AP recorded. Input resistance averaged 8.4 +/- 8.0 megohms (n = 180 cells) and was uncorrelated with AP or RP. There were no significant differences in the above electrical properties between HRP-identified layer V pyramidal cells (n = 56) and unidentified cells (n = 353). However, within layer V pyramidal cells, the size of the soma was relatable to input resistance. Comparisons of present in vivo data with in vitro data obtained by other investigators from cells of the same region, type and species indicate that resting potentials are more positive in vivo than in vitro, but that critical firing thresholds are the same. Injections of ramp depolarizing currents in 118 unidentified cells disclosed 82% simple (no or minimal accommodation) responses. 18% ceiling (small accommodation) responses, and no minimal gradient (large accommodation or injury) responses. This finding was similar to that found in layer V pyramidal cells in vitro.