+Is Theta a Traveling Wave in the Medial Entorhinal Cortex?

TEAM MEMBERS:

• Jesús Hernández-Pérez (Project Lead)

• Keiland Cooper

• Ilinca Ungunereau

• Nishell Savory

• Hannah Wang

PROJECT DESCRIPTION:

Background

The hippocampus and medial entorhinal cortex support spatial learning, yet the relationship between their dynamics and information processing during learning remains unknown. Both exhibit clear theta rhythms, 6-10 Hz fluctuations in the local field potentials, that are thought to track information processing by these areas. Remarkably, in the hippocampus, theta is not synchronous throughout, but rather, precesses steadily across the long axis to span a total of 180 degrees phase offset (Lubenov and Siapas, 2009; Patel, 2002). It remains unknown whether theta phase also shifts along the long axis of the medial entorhinal cortex.

Methods

To resolve this, we built custom electrode arrays designed to simultaneously record across the entire long axis of the region (spanning >4.5 mm) at regular intervals (~580 um).

PRELIMINARY RESULTS:

Using these arrays to record theta in awake behaving rats, we find consistent evidence of a systematic theta phase shift along the length of medial entorhinal cortex. To address whether this reflects a traveling wave or phase-shifted standing wave, we asked if there are comparable lags in theta power changes across the long axis. We found zero-lag in theta power indicating that, in the entorhinal cortex, theta is a phase-shifted standing wave. We also find that the properties of theta along the long axis of the entorhinal cortex are consistent with those previously reported for the hippocampus in that there is a 180 degree total shift and that theta coherence decreases between distal sites. We discuss the functional implications of these results for the hippocampal information processing.

Example Data of the Finding:

The image on the left is the averaged theta signal over each channel in the MEC.

The image on the right is the raw signal with each theta peak ID'd and a slope fitted

Five core papers to understand the project:

• 1. Lubenov, E. V., & Siapas, A. G. (2009). Hippocampal theta oscillations are travelling waves. Nature, 459(7246), 534.

  2. Patel, J., Fujisawa, S., Berényi, A., Royer, S., & Buzsáki, G. (2012). Traveling theta waves along the entire septotemporal axis of the hippocampus. Neuron, 75(3), 410-417.

1. Long, L. L., Bunce, J. G., & Chrobak, J. J. (2015). Theta variation and spatiotemporal scaling along the septotemporal axis of the hippocampus. Frontiers in systems neuroscience, 9, 37.

2. Fanselow, M. S., & Dong, H. W. (2010). Are the dorsal and ventral hippocampus functionally distinct structures?. Neuron, 65(1), 7-19.

3. Colgin, L. L. (2013). Mechanisms and functions of theta rhythms. Annual review of neuroscience, 36, 295-312.

Be sure to check out the poster! (attached)

Also here is a video depiction