S. Department of State (A.M.B.). R.O. and J.-M.S. gratefully acknowledge the support of the BrainGain Smart Mix Programme of the Netherlands Ministry of Economic Affairs and the Netherlands Ministry of Education, Culture, and Science. “
“Distinct behaviors are associated with distinct patterns of activity, presumably underlying specific cognitive functions. In the hippocampus, immobility, slow-wave sleep, and automatic behaviors (sniffing, chewing,

champing, grooming, etc.) are accompanied by intermittent sharp-wave ripples (SPW) at high frequency (150–200 Hz), while locomotion, attention and REM sleep are accompanied by continuous theta oscillation (5–10 Hz) (Vanderwolf, 1969; Whishaw, 1972). These oscillations have been hypothesized to provide a common temporal reference for distributed neurons and support temporal coding, as illustrated in place cells’ theta phase precession where selleck screening library the phase of a cell’s spikes, relative to theta oscillations, systematically varies with the animal’s position VX-809 within its place field, so that additional spatial information is specifically

carried by the phase of spike discharge within the theta cycle (Huxter et al., 2003, 2008; O’Keefe and Recce, 1993; Skaggs et al., 1996). Therefore, depending on brain state, neuronal populations oscillate at various frequencies which regulate the timing of neuronal interactions to support neuronal encoding and information processing. A related phenomenon, although less well understood, lies in the cyclic modulation of LFP oscillations or cross-frequency

coupling (Bragin et al., 1995; Chrobak and Buzsáki, 1998). Recent studies in humans and monkeys emphasized the expression of rhythmic modulations of only neuronal oscillations (Canolty et al., 2006; Drew et al., 2008; Lakatos et al., 2005; Lakatos et al., 2008; Leopold et al., 2003; Nir et al., 2008), but the potential involvement of these “second-order” rhythms in information coding remains an open question. Here, we report slow modulation of theta power and neuronal firing at a time scale of about 1 s, expressed in the rat hippocampus during both REM sleep and motor/cognitive behaviors. We show that second-order spectral analysis is relevant for decoding neuronal information on a slower time scale than usually assumed for brain rhythms. Recording spontaneous LFP and unit activity from the hippocampal CA1 pyramidal layer of freely behaving rats during various behavioral situations including REM sleep, open-field exploration and a protocol in which the animals were trained to alternatively run in a maze and in a wheel to get a reward (data recorded in and provided by the Buzsáki lab [Pastalkova et al., 2008]), we observed that theta oscillations were not stable in amplitude but rather increased and decreased on a reproducible time basis of about 1 s.