Fig. 2.

Two different circuit-based models for gamma oscillation production. In the Interneuron Network Gamma (ING) model (left panel), the oscillation depends on reciprocal inhibitory interactions between parvalbumin (PV)-positive basket cells. Some form of continuous (tonic) excitatory current is the main source of interneuron activation in ING. Important for the ING model are the electrical gap-junction connections (zig-zag wires) between PV-positive basket cells. In ING, pyramidal cells are synchronized rhythmically by the interneuron network but are not directly involved in rhythm production. In the Pyramidal Interneuron Network Gamma (PING) model (right panel), oscillations depend on the interplay between pyramidal cells and gamma-amino butyric acid neurons via recurrent synaptic connections. In PING models, interneurons are driven by the phasic (synaptic) excitatory glutamate–mediated currents arriving from the pyramidal cells, which are synchronized rhythmically by feedback inhibition. Monosynaptic excitation from pyramidal cells is the main source of interneuron activation in PING. Therefore, in PING, pyramidal cells are directly involved in the gamma rhythm mechanisms. As reviewed in the main text, some current data favor the PING over the ING model.