Chronic recording of the vagus nerve to analyze modulations by the light–dark cycle

Objective. The vagus nerve is considered to play a key role in the circadian rhythm. Chronic continuous analysis of the vagus nerve activity could contribute to a better understanding of the role of the vagus nerve in light–dark modulations. This paper presents a continuous analysis of spontaneous vagus nerve activity performed in four rats. Approach. We analyzed the vagus electroneurogram (VENG) and electroencephalogram (EEG) over a recording period of 28 d. Spike activity and heart rate estimation were derived from the VENG, and slow-wave activity was derived from the EEG. The presence of repetitive patterns was investigated with periodograms, cosinor fitting, autocorrelation, and statistical tests. The light–dark variations derived from the VENG spikes were compared with EEG slow waves, an established metric in circadian studies. Results. Our results demonstrate that light–dark variations can be detected in long-term vagus nerve activity monitoring. A recording period of about 7 d is required to characterize accurately the VENG light–dark variations. Significance. As a major outcome of this study, vagus nerve recordings hold the promise to help understand circadian regulation.