TEMPERATURE REGULATION "CENTERS" 
have chosen these three examples becausethe classical approach to 
centers involves these three techniques. 
This problem involved an extension of Dr. Hemingway's work 
with Dr. Birzis on electrical recording of unit activity from the 
brain stem of the cat in association with shivering (Birzis and Hem- 
ingway, 1957). You recall seeing yesterday Dr. Kawamura's work 
on the correspondence between the electromyographic potentials of 
shivering and inspiration or the onsetof pain. The same correspon- 
dence was found between the electromyogram (Fig. 7, a, lower line) 
during a brief painful stimulus and, concomitantly, the interruption 
of a unit discharge associated with shivering, recorded in the brain 
stem with a rebound phenomenon occurring before the end of the 
painful stimulus. In Figure 7, b-d, you see phasic variations in 
shivering during its onset, when the relationship with respiration 
was most apparent, the temporal association of the unit spikes to 
the electromyographic change being quite clear. 
These unit discharges were related to shivering in their fre- 
quency. When shivering was present, they were present; when it 
was suppressed by whole body warming, these units stopped firing 
(Fig. 8). When shivering was re -introduced by cooling the animal 
again, shivering and the unit potentials returned, with the unit po- 
tential coming 5 to 15 seconds after the beginning of shivering. In 
general, this was a pulse modulated system, meaningthat the strong- 
er the shivering, the higher the frequency of the discharge. 
The location of these recording sites is shown in Figure 9 and 
reflects the distribution of a pathway in the nervous system which 
subserves shivering. Of particular interest was the origin of these 
unit potentials in the nucleus of the field of Forel. The efferent 
pathway of this nucleus goes down through the central tegmental 
fasciculus, turns laterally and, passing dorsal and lateral to the 
superior olive, goes to or throu^ the inferior medulla. These po- 
tentials in general had the same distribution. As I>r. Clark suspects, 
they were rather widely spread through the brain stem, but they 
showed a concentration in this pathway. These sites also correspond 
to the anterior and posterior placement of the lesions that Birzis 
and Hemingway (1956) found would prevent shivering in anesthetized 
animals. The suspicion arose that if lesions could be placed bilater- 
ally within the nucleus of Forel or the central tegmental fasciculus, 
273 
