Annu. Rev. Neurosci. 2004. 27:247–78 doi: 10.1146/annurev.neuro.27.070203.144303 Copyright c  2004 by Annual Reviews. All rights reserved First published online as a Review in Advance on February 23, 2004 CELLULAR MECHANISMS OF NEURONAL POPULATION OSCILLATIONS IN THE HIPPOCAMPUS IN VITRO Roger D. Traub, 1 Andrea Bibbig, 1 Fiona E.N. LeBeau, 2 Eberhard H. Buhl, 2* and Miles A. Whittington 2 1 Department of Physiology and Pharmacology, State University of New York Downstate Medical Center, Brooklyn, New York 11203; email: roger.traub@downstate.edu, andrea.bibbig@downstate.edu 2 School of Biomedical Sciences, The Worsley Building, University of Leeds, Leeds LS2 9NQ, United Kingdom; email: f.e.n.lebeau@leeds.ac.uk, m.a.whittington@leeds.ac.uk Key Words gamma oscillation, 40 Hz, theta oscillation, ripple, gap junctions ■ Abstract A variety of population oscillations, at frequencies ∼5 Hz up to 200 Hz and above, can be induced in hippocampal slices either by (a) manipulation of the ionic environment, or (b) by stimulation of metabotropic receptors; brief oscillations can even occur spontaneously. In this review, we consider in vitro theta (4–12 Hz), gamma/beta (15–70 Hz), and very fast oscillations (VFO) (>70 Hz). Many in vitro oscillations are gated by synaptic inhibition but are influenced by electrical coupling as well; one type depends solely on electrical coupling. For some oscillations dependent upon inhibition, the detailed firing patterns of interneurons can influence long-range syn- chronization. Two sorts of electrical coupling are important in modulating or generating various in vitro oscillations: (a) between interneurons, primarily between dendrites; and (b) between axons of pyramidal neurons. VFO can exist in isolation or can act as gen- erators of gamma frequency oscillations. Oscillations at gamma frequencies and below probably create conditions under which synaptic plasticity can occur, between selected neurons—even those separated by significant axonal conduction delays. IMPORTANCE OF STUDYING OSCILLATIONS IN VITRO Network oscillations in vivo have been proposed to be important in sensory pro- cessing, for example in the olfactory system (Laurent & Davidowitz 1994, Freeman 1972), in sensory and perceptual binding (Gray et al. 1989, Miltner et al. 1999, Rodriguez et al. 1999, Roelfsema et al. 1994, Singer & Gray 1995), in motor pro- gramming (Murthy & Fetz 1996), in associative learning (Buzs´ aki 2002, Larson & * Deceased. 0147-006X/04/0721-0247$14.00 247