Hippocampal theta rhythm and running speed: A reconsideration using within-single trial analysis

Abstract

Previous studies of the connection between frequency of hippocampal rhythmical slow activity (theta rhythm) and speed of locomotion using both linear tracks and wheels have provided inconsistent if not contradictory results. To help clarify the situation single trials of hippocampal EEG were analysed using wavelet time-frequency analysis and we found that theta frequency within single trials shows positive or negative correlation with wheel running speed, even when mean theta frequency is not correlated with mean wheel running speed. As the mean running speed increases and the standard deviation of running speed decreases in a single trial, the correlation between theta frequency and wheel running speed within the single trial tends to be positive. Trials with abrupt decelerations have lower means and higher standard deviations of speed and tend to have negative correlations within single trials. In addition, we observed a shift of dominant theta frequency from 7.5– 8 Hz to 8.5– 9 Hz during spontaneous deceleration behaviour without involving any cognitive task, which has been connected to learning, attention and cognition.