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.