| Theta oscillations clock hippocampal activity during awake behavior and REM sleep. These oscillations are prominent in the local field potential, and they also reflect the subthreshold membrane potential and strongly modulate the spiking of hippocampal neurons. The prevailing view has been that theta oscillations are synchronized throughout the hippocampus, despite the lack of conclusive experimental evidence. In this talk I will describe experiments in which we examined how theta oscillations are organized across anatomical space by topographically sampling activity over a large section of the hippocampus using multi-tetrode arrays in freely behaving rats. Our results show that theta oscillation are traveling waves that pattern hippocampal activity not only in time, but also across anatomical space. They further indicate that the instantaneous output of the hippocampus is topographically organized and represents a segment, rather than a point, of physical space. |
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