966 



HANDBOOK OF PinsKJLCJGY 



NEUROPHYSIOLOGY II 



motilitv, cardiac depression and vasodilatation. While 

 attempts have been made to delineate separate para- 

 sympathetic and sympathetic areas in the hypo- 

 thalamus (20, 21), there appears to be considerable 

 mingling of the elements responsible for these re- 

 sponses throughout the hypothalamus. Responses 

 are in general most easily obtained from the lateral 

 hypothalamic area, which is relatively rich in fibers 

 and poor in neurons. 



Granted that these striking results may be obtained 

 by stimulation of the hypothalamus we would not be 

 justified in assigning to this region the predominant 

 role in producing such effects in normal life. Similar 

 results can be obtained from stimulating many other 

 regions, including the limbic and orbitofrontal re- 

 gions of the cerebral cortex, as well as the motor areas 

 of the frontal lobe. Nevertheless, these responses are 

 most easily provoked from the hypothalamus. When 

 they are obtained by stimulation of this region in 

 unanesthetized animals, the sympathetic components 

 are usually associated with patterns of behavior which 

 have all the appearance of rage and fear (73, 75, 92). 

 This type of observation in man has been rare and 

 restricted, Ijut cardiac acceleration has been ob- 

 served upon electrical stimulation of the anterior 

 part of the human tuber cinereum (173). While 

 cardiac depression followed stimulation of the pre- 

 optic area, there were no signs of emotional stress 

 but rather a tendency to drowsiness and unconscious- 

 ness. In other cases, however, in which the walls of the 

 third ventricle were manipulated at operation or were 

 irritated by small tumors, violent autonomic dis- 

 charges have been seen, sometimes accompanying 

 manic behavior (40, 130). Recently Segundo and 

 his co-workers have stimulated the fornix and the 

 wall of the third ventricle in human patients and ob- 

 served expiratory apnea and occasional clouding of 

 consciousness from the fornix while stimulation of the 

 wall of the third ventricle produced polypnea. 



Assuming that the hypothalamus participates in 

 the initiation of such specific autonomic effects, it is 

 easy to see how certain of these alone or in combi- 

 nation may take part in more general functions. 

 These include regulation of body temperature, regu- 

 lation of some activities of the posterior and anterior 

 lobes of the pituitary, regulation of appetite and 

 perhaps thirst, reinforcement of the waking state, 

 facilitation of somatic motor activity, and integration 

 of the behavior patterns of certain emotional states. 

 Brief discussions of these follow. 



BODY TEMPERATURE CONTROL. Complete destruction 

 of the hypothalamus in lower mammals and in man 



practically abolishes all temperature control and 

 allows the body temperature to fluctuate with en- 

 vironmental variations. Destruction of the anterior 

 part of the hypothalamus (the preoptic and supra- 

 optic regions) abolishes the heat loss mechanisms 

 which include peripheral vasodilatation, sweating 

 and panting (139). Subjects are unable to defend 

 themsehes against high environmental tempera- 

 ture; the posttraumatic and postoperative hyper- 

 thermias which follow injury to the base of the brain 

 are in this class. It has been shown experimentally 

 that heating the blood which bathes this area elicits 

 the usual heat disposal responses, and the descending 

 nervous pathways in\olved have been described 

 (106). Heat production and conservation are con- 

 trolled by more caudal regions of the hypothalamus, 

 but precise location of the structures in\ol\ed is not 

 yet possible. Since bilateral lesions in the posterior 

 regions of the hvpothalamus also involve the de- 

 scending paths tor heat disposal, such lesions are as 

 effecti\e in producing poikilothermia as is complete 

 hypothalamic destruction. A careful attempt to segre- 

 gate the various mechanisms for temperature regu- 

 lation was made by McCrum (113). While it was 

 confirmed that the heat disposal mechanisms are 

 largely concentrated in the anterior part of the hypo- 

 thalamus, it was also found that there is considerable 

 intermingling of the 'thermostatic' neurons and it is 

 impossible to draw a sharp line of distinction between 

 separate areas. Birzis & Hemingway {28) have found 

 that the lateral hypothalamic area participates in the 

 e\okation of shixering. The descending pathway 

 mediating shi\ering descends through the midbrain 

 just lateral to the red nucleus, into the lateral part of 

 the reticular formation of the midijrain, pons and 

 medulla oblongata, and into the lateral funiculus of 

 the spinal cord. Inhiljition or suppression of shiver- 

 ing may be produced by stimulation in the hypo- 

 thalamus and midi)rain, the most sensitive area being 

 the preoptic region. Hemingway and his co-workers 

 (72) propose that this effect is a means for suppression 

 of shivering when the musculature is needed for 

 skeletal moxement. Perhaps this mechanism par- 

 ticipates in the inhibition of shivering which occurs 

 upon stimulation of peripheral nerves as shown by 

 Boyarsky & Stewart (31). Further discussion of the 

 nervous mechanism of temperature regulation may 

 be found in C'hapter XL\"I of this work ijy Strom. 

 .Since the basal metaliolic rate is involved in heat 

 production, it may be mentioned that basal me- 

 tabolism falls after destruction of the hypothalamus. 

 It has also been shown that activation of the thyroid 

 during exposure to cold is a function of the hypo- 



