Alteration of EEG activity of the hypothalamus by thermal stimulation of the spinal cord

Summary EEG activity of various parts of the hypothalamus was recorded in unanaesthetized guinea pigs during thermal stimulation of the spinal cord. In the anterior hypothalamus fast waves became more prominent when the spinal cord temperature (T_sc) was raised from 40° to 42° C, resulting in an increase of the mean frequency by about 50%. The electrical activity remained unaffected whenT_sc was raised from 38° to 40° C. In the posterior hypothalamus, spinal cord heating from 39.5° to 42° C led to a decrease of the mean frequency by about 30%, while temperature changes from 38° to 39.5° C were less effective.Corresponding studies in cold-adapted animals showed that the EEG response to spinal cord heating is modified by thermal adaptation. In this group of animals electrical activity of the posterior hypothalamus could be influenced clearly by heating the spinal cord from 38° to 39.5° C, while a temperature change in this range was nearly ineffective in animals reared at 20° C.