Computational model of carbachol‐induced delta, theta, and gamma oscillations in the hippocampus

Abstract

Field potential recordings from the rat hippocampus in vivo contain distinct frequency bands of activity, including δ (0.5–2 Hz), θ (4–12 Hz), and γ (30–80 Hz), that are correlated with the behavioral state of the animal. The cholinergic agonist carbachol (CCH) induces oscillations in the δ (CCH‐δ), θ (CCH‐θ), and γ (CCH‐γ) frequency ranges in the hippocampal slice preparation, eliciting asynchronous CCH‐θ, synchronous CCH‐δ, and synchronous CCH‐θ with increasing CCH concentration (Fellous and Sejnowski, Hippocampus 2000;10:187–197). In a network model of area CA3, the time scale for CCH‐δ corresponded to the decay constant of the gating variable of the calcium‐dependent potassium (K‐AHP) current, that of CCH‐θ to an intrinsic subthreshold membrane potential oscillation of the pyramidal cells, and that of CCH‐γ to the decay constant of GABAergic inhibitory synaptic potentials onto the pyramidal cells. In model simulations, the known physiological effects of carbachol on the muscarinic and K‐AHP currents, and on the strengths of excitatory postsynaptic potentials, reproduced transitions from asynchronous CCH‐θ to CCH‐δ and from CCH‐δ to synchronous CCH‐θ. The simulations also exhibited the interspersed CCH‐γ/CCH‐δ and CCH‐γ/CCH‐θ that were observed in experiments. The model, in addition, predicted an oscillatory state with all three frequency bands present, which has not yet been observed experimentally. Hippocampus 2001;11:251–274.