Locomotion-related oscillatory body movements at 6-12 Hz modulate the hippocampal theta rhythm

The hippocampal theta rhythm is required for accurate navigation and spatial memory but its relation to the dynamics of/nlocomotion is poorly understood. We used miniature accelerometers to quantify with high temporal and spatial resolution/nthe oscillatory movements associated with running in rats. Simultaneously, we recorded local field potentials in the CA1/narea of the hippocampus. We report that when rats run their heads display prominent vertical oscillations with frequencies/nin the same range as the hippocampal theta rhythm (i.e., 6–12 Hz). In our behavioral set-up, rats run mainly with speeds/nbetween 50 and 100 cm/s. In this range of speeds, both the amplitude and frequency of the ‘‘theta’’ head oscillations were/nincreasing functions of running speed, demonstrating that the head oscillations are part of the locomotion dynamics. We/nfound evidence that these rhythmical locomotor dynamics interact with the neuronal activity in the hippocampus. The/namplitude of the hippocampal theta rhythm depended on the relative phase shift with the head oscillations, being maximal/nwhen the two signals were in phase. Despite similarity in frequency, the head movements and LFP oscillations only/ndisplayed weak phase and frequency locking. Our results are consistent with that neurons in the CA1 region receive inputs/nthat are phase locked to the head acceleration signal and that these inputs are integrated with the ongoing theta rhythm.This work was funded by a national grant from the Ministerio de Ciencia e Innovación (BFU2008-03946, to D.R.) and a Marie Curie International Reintegration Grant (IRG230976 to D.R.). A.L. and D.R. were supported by Ramon-Y-Cajal fellowships from the Ministerio de Ciencia e Innovación. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript