Hippocampal theta sequences
Article first published online: 30 JUL 2007
Copyright © 2007 Wiley-Liss, Inc.
Volume 17, Issue 11, pages 1093–1099, November 2007
How to Cite
Foster, D. J. and Wilson, M. A. (2007), Hippocampal theta sequences. Hippocampus, 17: 1093–1099. doi: 10.1002/hipo.20345
- Issue published online: 15 OCT 2007
- Article first published online: 30 JUL 2007
- Manuscript Accepted: 7 JUN 2007
- place cells;
- theta precession;
The activity of individual hippocampal principal neurons is spatially localized such that each neuron is active only when the animal occupies an area of the environment known as the cell's place field. Additionally, the activity of hippocampal neurons exhibits a particular temporal relationship to the hippocampal EEG, such that spikes fired by the neuron occur at progressively earlier phases of the co-occurring theta rhythm in the EEG as the animal traverses the place field. This relationship is known as theta precession. A long-standing prediction following the observation of theta precession has been that among a collection of hippocampal neurons recorded simultaneously, the neurons will fire in sequences reflecting the behavioral order of the place fields. Here we examine this prediction. We show that clear, ordered sequences occur during theta, which we name theta sequences, in which a portion of the animal's spatial experience is played out in forwards order. We further investigate the relationship of theta sequences to phase precession by shuffling spike phases in such a way as to preserve the relationship between spike phase and position. This jitter significantly reduces the prevalence of theta sequences while leaving theta phase precession intact, suggesting that the presence of theta phase precession is not trivially predictive of theta sequences. Finally, we discuss the relationship between theta sequences and individual place fields, and the possible functional role of theta sequences in navigational learning. © 2007 Wiley-Liss, Inc.