Pathway-specific habituation of induced gamma oscillations in the hippocampal slice

Brief tetanic stimulation (eight pulses at 100 Hz) of afferent fibers innervating area CAI of the hippocampus produce gamma oscillations. When delivered every minute the oscillation habituated markedly after the first stimulus. This habituation could be transiently reversed by stimulating a different pathway to the recorded area. Gamma oscillation-induced beta frequency oscillations were only seen in response to the first (novel) stimulus and the gamma oscillation itself was markedly attenuated by on-going, non-oscillogenic, synaptic activity. The NMDA receptor antagonist ketamine abolished the response to novel stimuli but left the habituated response relatively unaffected. The pattern of habituation parallelled that seen for sensory induced gamma and beta oscillations in the clinical EEG. (C) 2000 Lippincott Williams & Wilkins.