Regulatory mechanisms, brain activity and behavior during deep hibernation in the squirrel, Citellus beecheyi

¹ Department of Zoology, University of California at Los Angeles, Los Angeles, California

During deep hibernation in the squirrel, Citellus beecheyi, focusing of attention, discrimination, attempts to localize sound stimuli in space, vocalization and complex motor coordinations are all possible at brain temperatures of 6.1°C and compatible with the 90% reduction of amplitude of general brain wave activity present at these temperatures. Brain temperatures during deep hibernation are maintained within ±0.05°C at 2°–3°C above environmental temperature, while skin temperature is fluctuating ten to twenty times as much. Other significant details of cardiovascular, temperature and muscle tone regulation during this state are analyzed. Cortical and subcortical neuronal activity is present in deep hibernation and can have the appearance of that of an alert squirrel brain at merely reduced amplitude. Quiet areas are shown not to be merely temperature depressed in excitability. It is tentatively suggested that the deeply hibernating animal may be extremely dependent on maintaining the spontaneous cerebral electrical activity normally present and any drug which completely eliminates it for too long a time, by preventing the dynamic patterns of activity normally present from being reorganized, allows the break of the final link between animal and environment. This is considered responsible for the ‘death’ of the animal rather than any failure of the supply systems.