Uninterrupted wireless long-term recording of sleep patterns and autonomic function in freely moving rats

When studying long-period oscillations and subtle physiological variations, including sleep/wake transitions, autonomic functions, and physical activities, a technique that provides uninterrupted recordings of the various physiological signals for more than one day with the lowest possible artificial disturbances and with a minimum number of physiological effects is necessary. This study integrates a wireless recharging circuit into a miniature physiological wireless sensor to develop an uninterrupted wireless recording system for parietal electroencephalograms, occipital electroencephalograms, nuchal electromyograms, electrocardiograms, and 3-axis acceleration signals. The wireless recharging circuit captures power from an alternating magnetic field. Control and sham rats underwent traditional head-mount surgery but only the sham rats were implanted with a non-functional advanced wireless sensor in their abdomen. Functional advanced wireless sensor units were intra-abdominally implanted into the experimental rats. All physiological signals were recorded without interruption for over ten days. There was no difference in the sleep/wake patterns, physical activity, body weight, and autonomic functioning, which was assessed by heart rate variability (HRV), among the control, sham, and experimental rats. Furthermore, the continuous recording revealed the circadian rhythms in the HRV variables, namely a 24-hour cycle in R-R intervals (RR) and the total power, high-frequency power, and low-frequency power of the RR spectrum. It is confirmed that the proposed system creates minimal disturbances to the rat's physiology and is capable of ultra-long-term recording of daily, weekly, monthly, or even lifelong rhythms on the animals' sleep/wake structure and autonomic functioning.