Abstract
Traveling waves are hypothesized to support the long-range coordination of anatomically distributed circuits. Whether separate strongly interacting circuits exhibit traveling waves remains unknown. The hippocampus exhibits traveling 'theta' waves and interacts strongly with the medial entorhinal cortex (MEC). To determine whether the MEC also activates in a traveling wave, we performed extracellular recordings of local field potentials (LFP) and multi-unit activity along the MEC. These recordings revealed progressive phase shifts in activity, indicating that the MEC also activates in a traveling wave. Variation in theta waveform along the region, generated by gradients in local physiology, contributed to the observed phase shifts. Removing waveform-related phase shifts left significant residual phase shifts. The residual phase shifts covaried with theta frequency in a manner consistent with those generated by weakly coupled oscillators. These results show that the coordination of anatomically distributed circuits could be enabled by traveling waves but reveal heterogeneity in the mechanisms generating those waves.
Highlights
The recent recognition that numerous cortical circuits exhibit traveling waves when engaged motivates the hypothesis that traveling waves are a basic organizing principle of cortical activity (Muller et al, 2018)
Dorsal sites were phase advanced relative to ventral, as can be seen in the cycle-triggered averages of the raw local field potentials (LFP), with the phase shifting at an average rate of 26.36 ̊/mm ± 2.64 ̊/mm (Figure 2A and D)
The goal of the work described here was to establish whether traveling waves in the entorhinal-hippocampal circuit are restricted to the hippocampus proper or whether the medial entorhinal cortex (MEC) exhibits traveling theta waves
Summary
The recent recognition that numerous cortical circuits exhibit traveling waves when engaged motivates the hypothesis that traveling waves are a basic organizing principle of cortical activity (Muller et al, 2018). By this hypothesis, traveling waves generate macroscopic activation dynamics that coordinate interaction between anatomically distributed circuits. The hippocampus, for example, has been established to activate in a traveling wave (Lubenov and Siapas, 2009; Patel et al, 2012; Zhang and Jacobs, 2015) It is unknown, whether the entorhinal cortex, an anatomically separated area but one that is highly inter-connected with the hippocampus, activates in a traveling wave. A goal of this work was to test whether the entorhinal cortex, like the hippocampus, activates in a traveling wave
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