Figure 1.

Gamma and beta oscillations in vitro. Intracellular recordings of gamma and beta oscillations in a CA1 hippocampal pyramidal neuron. Oscillations were induced by brief tetanic stimulation [see Whittington et al. (9) for methods]. The initial posttetanic response is a gamma oscillation with action potentials (frequency 38 Hz) separated by a period of hyperpolarization made up of both AHP and inhibitory synaptic activity. After the transition to beta activity, the underlying gamma membrane potential oscillation is still apparent (frequency 42 Hz), but spiking occurs on every second or third period (frequency 18 Hz). Action potentials are separated by the initial AHP/IPSP hyperpolarization and additional IPSPs. (Bar = 1 mV, 100 ms.)