Frequency dependence of spike timing reliability in cortical pyramidal cells and interneurons

Pyramidal cells and interneurons in rat prefrontal cortical slices exhibit subthreshold oscillations when depolarized by constant current injection. F or both types of neurons, the frequencies of these oscillations for current injection just below spike threshold were 2-10 Hz. Above spike threshold, however, the subthreshold oscillations in pyramidal cells remained low, but the frequency of oscillations in interneurons increased up to 50 Hz. To ex plore the interaction between these intrinsic oscillations and external inp uts, the reliability of spiking in these cortical neurons was studied with sinusoidal current injection over a range of frequencies above and below th e intrinsic frequency. Cortical neurons produced 1:1 phase locking for a li mited range of driving frequencies for fixed amplitude. For low-input ampli tude, 1:1 phase locking was obtained in the 5- to 10-Hz range. For higher-i nput amplitudes, pyramidal cells phase-locked in the 5- to 20-Hz range, whe reas interneurons phase-locked in the 5- to 50-Hz range. For the amplitudes studied here, spike time reliability was always highest during 1:1 phase-l ocking, between 5 and 20 Hz for pyramidal cells and between 5 and 50 Hz for interneurons. The observed differences in the intrinsic frequency preferen ce between pyramidal cells and interneurons have implications for rhythmoge nesis and information transmission between populations of cortical neurons.