Abstracts

There is substantial interest in the use of small, thermoelectric cooling devices to treat focal seizures. Thus far, we have shown that these devices are capable of effectively reducing the temperature of an immediately contiguous region of rat or neonatal pig neocortex. However, we have not yet established that these devices can cool primate neocortex and interrupt function. All experiments were carried out on a single Rhesus monkey that had already been trained for electrophysiological studies of hand movement. A recording chamber and base had been placed above the hand area in the right precentral gyrus. The animal was placed in a primate chair that allowed her to freely reach with her left hand. The cortex was cooled with an 8 x 8 mm thermoelectric device glued to the end of a custom machined copper bar designed to fit into the micromanipulator. The bar also served as an efficient heat sink. The thermoelectric device was lowered until it touched the pial surface of the precentral gyrus. A thermocouple on the thermoelectric surface controlled a feedback loop that maintained the device temperature. The monkey was videotaped while reaching for a piece of apple held in a plexiglass well. In order to extract the food, the monkey had to insert and flex her index finger. We recorded each extraction attempt and counted the number of index finger flexions per attempt (larger number of flexions suggests impaired dexterity) . An attempt was scored as unsuccessful if the monkey either failed to extract or dropped the apple. We activated the device for 1 minute periods, reducing pial temperature to 10 - 13^o C. There were 141 control attempts to extract the apple and 70 cooled attempts. There were 11 unsuccessful control attempts (counting 3 when the food was stuck) and 17 unsuccessful cooled attempts (p[lt]0.001 by McNemar[apos]s test). During 7 control attempts (including 3 when the food was stuck), we observed 5 or more flexions. There were 8 cooling attempts with 5 or more flexions (p[lt]0.001). The failures and increased flexions began several seconds after cooling onset. The thermoelectric device maintained the reduced temperature for entire 1 minute cooling periods. There was no behavioral evidence that cooling disturbed the monkey in any other way and she remained awake and alert for the entire recording session. There was a correlation between cooling and an increased number of flexions and failures. The cooling effect could have been delayed, because the hand representation is buried in the anterior bank of the central sulcus and relatively inaccessible to surface cooling. Moreover, normal motor function may be redundant in cortex. We saw no evidence that focal cooling caused widespread cortical dysfunction. These experiments demonstrate that a small thermoelectric device can remove sufficient heat to lower local neocortical temperature in a primate. (Supported by R01 NS42936 (SR) and R01 NS27686 (MS) from the NIH.)