Figure 4. In vivo firing patterns of four types of interneurone during two oscillatory network states.

Action potentials (filtered 0.8–5 kHz) of a parvalbumin immunopositive basket, an axo-axonic, a bistratified and an O-LM cell are shown during theta oscillations (3–6 Hz) and ripple episodes (filtered 90–140 Hz) recorded extracellularly in the pyramidal cell layer. During theta oscillations the PV basket cell fired at the descending phase, the axo-axonic cell around the peak and the bistratified and the O-LM cell discharged mainly at the trough of theta wave. Note the different inter-spike intervals during single theta cycles between bistratified and O-LM cells. During ripple episodes the PV basket cell fired preferentially at the highest amplitude of the ripple, the axo-axomic cell sometimes fired before the ripple but was depressed afterwards, the bistratified cell fired throughout, before and after the ripple episode and the O-LM cell was silent. Scales: ripples, 0.1 mV, 50 ms; spikes, 0.5 mV; theta, 0.2 mV, 0.3 s. (Data modified from Klausberger et al. 2003, 2004.)