STUART, D. G. 
alteration in brain volume and the alteration in brain size caused 
by formalin perfusion in brain fixation. 
Locus 14 in Figure 4 does, however, include responses evoked 
by stimulation of a locus 1 mm dorsal to it. Such loci stimulation 
responses were included under locus 14 rather than 13 becuase 
stimulation of a site 1 mm dorsal to the latter locus never evoked 
responses similar to those seen during stimulation of locus 13 and 
the intermediate locus. 
In Figure 4 the somatic responses presented are a generalized 
increase in muscle tone, or more precisely an increase in fore and 
hind limb rigidity, arrhythmic muscle twitching, alternating tremor 
and shivering. Alternating tremor is a4to7 cycle/sec limb tremor 
in which agonists relax when antagonists contract. In shivering the 
rate of tremor is faster (9 to 11 cycles/sec) and the muscles con- 
tract synergistically. Additionally, shivering characteristically 
waxes and wanes in intensity. Differences between these two tremors 
were observed both visually and electromyographically. Alpha 
cholralose anesthesia customarily evokes muscle twitching as the 
animal enters and emerges from the anesthetic state, but no stimuli 
were applied at such stages. All stimulation responses of the pre- 
sented loci were repeatable in the same preparation. 
The table in Figure 4 demonstrates that shivering was best and 
consistently producedby stimulation of a diencephalic regionbounded 
dorsally by a plane 9 mm dorsal to the interauricular line, ventrally 
by a plane 7 mm dorsal to the interauricular line, laterally by a 
plane 1.5 to 2.0 ram lateral to the midline and medially by the 
midline. Anatomically the region is bordered by ventral thalamic, 
dorsal hypothalamic, and medial subthalamic structures. Systematic 
exploration of a plane 1 mm rostral to Plane A was performed in 5 
cats (No.'s ST 9, 10, 11, 13,andl7). Shivering was never evoked by 
stimulation of any such loci, but alternating tremor was evoked by 
stimulating loci 1 mm rostral to loci 1 and 2 . Shivering was evoked 
by stimulation of loci 1 mm caudal to loci 14 and 17 but not in any 
other loci of this plane in Cats No. ST 9 and 11. Loci 3.5 mm lateral 
to the midline in frontal planes corresponding to A and B were 
stimulated in Cats No. ST 14 and ST 33 , but shivering was not 
evoked by any such stimulation. 
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