Exercise-induced slow waves in the EEG of cats

The aim of the present study was to investigate the early signs of fatigue. Cats were chronically implanted with electrodes in the frontal and occipital cortical areas, and a thermocouple was inserted into the nasal orifice to record respiratory rate. After a recovery of 10 days, the animals were trained for running on treadmill. On the day before recording, a catheter was tied into one of the common carotid arteries to record arterial blood pressure. The electroencephalogram (EEG), arterial blood pressure, and respiration were recorded continuously. At the time of deceleration of running high amplitude, slow waves appeared both in the sensorimotor and occipital cortical regions. The power spectra showed a significant increase in frequencies of 1-6 Hz in the sensorimotor cortex, and of 1-10 Hz in the occipital cortex, with a great increase in the total power. During rest the pre-running, brain activity reappeared gradually. The arterial blood pressure, the heart rate, and the respiratory rate were elevated during running, but no special changes occurred at the onset of the slow waves in the EEG. The blood glucose level was somewhat higher after the first 2-min running than the pre-running level. It is concluded that the appearance of slow waves in the EEG is an early manifestation of fatigue. The cardiorespiratory changes and the blood sugar concentrations play no role in the slowing of the electrocorticogram. The present results show the involvement of brain mechanisms in the onset of tiredness.