Figure 5.

CA1b pyramidal cells were recorded in voltage clamp. A, example of a simultaneous recording of the field potential (grey trace) and membrane current (I_m) in a pyramidal cell clamped at −10 mV (black trace). IPSCs coincide with positive-going field potentials. B, waveform averages of I_m, time-zeroed at the trough of medium-sized γ cycles (dashed line) were made for six different γ cycle amplitude ranges (see Methods). Traces are transposed for clarity. C, the relation between I_m amplitude and γ cycle amplitude (both normalised to their maximum) was fitted with a linear function. Data are means ± SEM of ten cells in nine slices. D, the relation between normalised I_m amplitude and instantaneous frequency (inverse of interval to next γ cycle) shows only a weak relationship. Data as in C. E, waveform averages of I_m at different holding potentials (10 mV increments) show reversal near −70 mV without a change in waveform kinetics (demonstrated by continuous grey line through amplitude maxima). Traces are transposed for clarity. F, waveform averages of I_m for the cell in B held at ­10 mV (grey line, representing mostly IPSCs) or at −70 mV (black line, representing mostly EPSCs), show that the EPSC trough precedes the IPSC peak.