STUART, D. G. 
cessation of stimulation or when visible shivering began at some 
latent period after the beginning of stimulation but ceased when the 
stimulus was teminated. A response was coded as "dubious" and 
coded with a small filled- in circle when neither visual inspection 
nor the pattern of EMG recording indicated whether or not the 
muscle activity evoked by the stimulus was truly shivering or 
merely an increase in muscle tone. Stimuli of 50 and 100 pulses/sec 
required less intensity to evoke shivering than stimuli of 10, 25 
and 100 pulses/sec. The best shivering response evoked by a 10 
pulse/sec stimulus was mild shivering lacking continuity. Con- 
versely, the best response evoked by stimulation at 200 pulses/sec 
was a tremor in which background muscle tone appeared excessive. 
In Cat No. ST 17, shivering could not be evoked by stimuli of 1600 
/i A/ pulse intensity even though well defined shivering was evoked at 
25 pulses/sec of 400 //A/pulse intensity. In this experiment 200 
pulses/sec stimuli were not applied, but less intense stimuli were 
necessary at 25 pulses/sec than at 100 pulses/sec. In both experi- 
ments 50 pvilses/sec stimuli evoked well defined shivering at min- 
imal stimulus intensities. 
In early experiments (Cats No. ST 5 to ST 17) a stimulus pulse 
duration of 3 msec was utilized. In Cat No. ST 17, using a variety 
of frequencies, less intense stimuli were necessary to evoke shiv- 
ering with a pulse duration of 1 msec than with 3 msec. Following 
this experiment, a pulse duration of 1 msec was used, but no sys- 
tematic study was attempted of the intensity of stimulation needed 
to evoke shivering at a variety of pulse duration- frequency combin- 
ations. 
Comments. The dorsomedial region of the posterior hypothal- 
amus, which, when stimulated electrically, induces shivering, is 
dorsal and medial to the shivering pathway described by Birzis 
and Hemingway (1956, 1957). These investigators abolished shiv- 
erir^ by ventrolateral posterior hypothalamic destruction in anes- 
thetized cats. In our laboratory it is now the contention that there 
is a conflict in interpretation but not experimental results. For 
example, Figure 7 illustrates an experiment in which bipolar elec- 
trodes were inserted into bilateral ventrolateral posterior hypo- 
thalamic loci (the center of the lesions noted with insert A and B) 
and into the dorsomedial posterior hypothalamus (tip of electrode 
noted C). With the brain intact, 30- second stimulation of locus A 
324 
