CHOLINERGIC INDUCTION OF NETWORK OSCILLATIONS AT 40 HZ IN THE HIPPOCAMPUS IN-VITRO

Acetylcholine is vital for cognitive functions of the brain. Although its actions in the individual cell are known in some detail(1), its ef fects at the network level are poorly understood(2). The hippocampus, which receives a major cholinergic input from the medial septum/diagon al band(3), is important in memory(4,5) and exhibits network activity at 40 Hz during relevant behaviours(6). Here we show that cholinergic activation is sufficient to induce 40-Hz network oscillations(7) in th e hippocampus in vitro. Oscillatory activity is generated spontaneousl y in the CA3 subfield and can persist for hours. During the oscillator y state, principal neurons fire action potentials that are phase-relat ed to the extracellular oscillation, but each neuron fires in only a s mall proportion of the cycles. Both excitatory and inhibitory synaptic events participate during the network oscillation in a precise tempor al pattern. These results indicate that subcortical cholinergic input can control hippocampal memory processing by inducing fast network osc illations.