Visual cortical LFP in relation to the hippocampal theta rhythm in track running rats

Jack P Kennedy; Yuchen Zhou; Yu Qin; Sarah D Lovett; Tara Cooper; Alex Sheremet; Sara N Burke; Andrew P Maurer

doi:10.3389/fncel.2023.1144260

Visual cortical LFP in relation to the hippocampal theta rhythm in track running rats

Front Cell Neurosci. 2023 Jun 20:17:1144260. doi: 10.3389/fncel.2023.1144260. eCollection 2023.

Authors

Jack P Kennedy¹, Yuchen Zhou², Yu Qin^{1

3}, Sarah D Lovett¹, Tara Cooper¹, Alex Sheremet^{1

3}, Sara N Burke¹, Andrew P Maurer^{1

3

4}

Affiliations

¹ Department of Neuroscience, College of Medicine, McKnight Brain Institute, University of Florida, Gainesville, FL, United States.
² Department of Psychiatry, School of Medicine, Yale University, New Haven, CT, United States.
³ Engineering School of Sustainable Infrastructure and Environment, Herbert Wertheim College of Engineering, University of Florida, Gainesville, FL, United States.
⁴ Department of Biomedical Engineering, University of Florida, Gainesville, FL, United States.

Abstract

Theta oscillations in the primary visual cortex (VC) have been observed during running tasks, but the mechanism behind their generation is not well understood. Some studies have suggested that theta in the VC is locally generated, while others have proposed that it is volume conducted from the hippocampus. The present study aimed to investigate the relationship between hippocampal and VC LFP dynamics. Analysis of power spectral density revealed that LFP in the VC was similar to that in the hippocampus, but with lower overall magnitude. As running velocity increased, both the power and frequency of theta and its harmonics increased in the VC, similarly to what is observed in the hippocampus. Current source density analysis triggered to theta did not identify distinct current sources and sinks in the VC, supporting the idea that theta in the VC is conducted from the adjacent hippocampus. Phase coupling between theta, its harmonics, and gamma is a notable feature in the hippocampus, particularly in the lacunosum moleculare. While some evidence of coupling between theta and its harmonics in the VC was found, bicoherence estimates did not reveal significant phase coupling between theta and gamma. Similar results were seen in the cross-region bicoherence analysis, where theta showed strong coupling with its harmonics with increasing velocity. Thus, theta oscillations observed in the VC during running tasks are likely due to volume conduction from the hippocampus.

Keywords: ephaptic coupling; hippocampus; local field potential; visual cortex; volume conduction.

Grants and funding

This work was supported by the McKnight Brain Research Foundation and NIH grants—Grant Sponsor: National Institute on Aging; Grant Number: AG055544 and Grant Sponsor: National Institute of Mental Health; Grant Numbers: MH109548 and MH126236; and a Diversity Supplement to NIH grant R01MH109548 (JK).