Hypothermia and cortical evoked potentials.

Abstract

The behavior of the recruiting response during hypothermia was investigated, and the following results were obtained. 1. Recruiting response was recorded from the frontal area by stimulation of the nucleus ventralis anterior or the anterior pole of the reticular nucleus in rat. The brain temperature was lowered gradually till 18°C. and then raised slowly to normal temperature. All the changes to be stated below were reversible. 2. Spontaneous background EEG was decreased in amplitude, and slowed in rate as the brain temperature was lowered, and flattened at 18°C. Dominant spindle bursts of high amplitude and low frequency appeared between 29°C.-25°C. 3. The optimal frequency of stimulation was determined for each temperature. There was linear relationship between the logarithm of the optimal frequency and the brain temperature in a range from 36°C. to 18°C. 4. A value of temperature characteristic (μ) 7500 cal. was obtained from the law of Arrhenius applied to the data. 5. Large and small responses appeared alternately when the frequency of stimulation was somewhat higher than the optimal one, and only small ones appeared when the frequency was much higher. The mechanism of alternation was discussed. I wish to thank Prof. K. Motokawa for his invaluable discussion and suggestion throughout the course of the experiment and the preparation of the manuscript.