CENTRAL AUTONOMIC MECHANISMS 



971 



of motor initiative, loss of appetite and serious defects 

 of visceral function and body temperature control 

 (85, 87). The animals can be aroused from the som- 

 nolent state for brief intervals and rough handling 

 may evoke defensive behavior at times. Survival time 

 is relatively short, in terms of days or weeks, even with 

 careful nursing. Lesions restricted to the posterior 

 part of the hypothalamus which interrupt the de- 

 scending and ascending fiber connections yield a simi- 

 lar picture, with the somnolence and loss of affective 

 response being especially marked. If there is also 

 involvement of the upper end of the adjacent mid- 

 brain in cats, motor activity may be greatly depressed 

 and spastic states ensue. These animals may retain 

 their somnolence for some weeks but may finally 

 have periods of wakefulness, especially when unfed, or 

 when bowel and bladder are full. 



Experimental lesions invohing the rhinencephalic 

 (limbic) systems have also produced marked disturb- 

 ances in behavior (14, 98, 149). Thus lesions of the 

 piriform areas in a wide variety of species have been 

 found to produce bland, tame, often hypersexual 

 animals (149). Other regions nearby have been de- 

 stroyed by Bard & Mountcastle (14) and the subse- 

 quent dex'elopment of savage behavior described. It 

 will be recalled that important functional connections 

 exist between the limbic system and the hypothal- 

 amus. Many of these connections are multisynaptic, 

 although some direct connections from the amygdala 

 have been described, chiefly by way of the stria termi- 

 nalis. A very well-known and conspicuous connection 

 is provided by the fornix which arises from the hippo- 

 campus, ends in various places in the hypothalamus, 

 but especially in the mammillary body, which is then 

 connected with the anterior thalamic nuclei by the 

 mammillothalamic tract. This thalamic region is con- 

 nected with the anterior part of the gyrus cinguli. In 

 our experience, bilateral lesions of the fornix and of 

 the mammillary bodies in cats hav-e not led to any 

 very striking behavior change except perhaps an in- 

 creased euphoric response to petting. However, in 

 man, lesions of the mammillothalamic system have 

 been described in cases of Korsakoff's syndrome (140). 

 The physiology and autonomic relationships of the 

 limbic and associated systems are discussed in Chap- 

 ters L\T, LVII and L\ III of this work and, there- 

 fore, need no further consideration here. 



stimuli are used. It is well-known that the pathological 

 sleep of encephalitis lethargica may be associated 

 with lesions of the walls of the third ventricle and 

 upper end of the central gray of the aqueduct. The 

 subject of sleep has an extensive literature and the 

 present consideration must be very brief. Philosophi- 

 cally speaking, it seems that attention should be 

 directed at the state of wakefulness, for sleep is, in 

 part at least, just a condition which occurs in the 

 absence of wakefulness. The factors which contribute 

 to maintenance of wakefulness are extrinsic and in- 

 trinsic. Extrinsic factors involve streams of afferent 

 impulses derived from exteroceptive and interocep- 

 tive stimuli. When the number or intensity of such 

 impulses is sufficient, activation of the cerebral cortex 

 necessary for the waking state is produced. This 

 change in cortical activity is well shown by the 

 arousal or activation type of change seen in the 

 electrocorticogram. These streams of direct afferent 

 impulses may be maintained by a variety of types of 

 stimuli: light, sound, pressure, heat and cold, disten- 

 tion and the like. It is obvious that the intensity of 

 such stimulation will vary, even as the sun rises and 

 sets or as the urinary bladder fills and empties. These 

 cyclic variations and extrinsic stimulation may ac- 

 count in part at least for a diurnal periodicity of sleep. 

 However, one should not forget that experimental 

 animals deprived of the corte.x seem to show alternat- 

 ing periods of sleep and wakefulness of a sort, although 

 just what kind of awareness is possible in these animals 

 is difficult to imagine (97). 



'Intrinsic' influences acting upon the cortex are 

 derived from subcortical structures. These, of course, 

 are in turn affected by afferent impulses, metabolic 

 changes and other changes of the internal environ- 

 ment. The intrinsic factors are necessary to maintain 

 the wakefulness which is possible at low levels of ex- 

 trinsic stimulation and must pla\' very important 

 roles indeed; for when the areas of the brain contain- 

 ing these crucial regions are disabled, sleep ensues in 

 spite of normal levels of extrinsic stimulation. Magoun 

 (105) and his co-workers have developed the idea of 

 an activating system in the reticular formation of the 

 brain stem responsible for cortical wakefulness. The 

 role of the reticular system in this matter is discussed 

 in Chapter LI I of this work by French. Sleep is con- 

 sidered in Chapter LXI\' written by Lindsley. 



SLEEP-WAKING MECHANISMS. As has been noted, experi- 

 mental lesions of the posterior part of the hypothal- 

 amus produce somnolence and deep sleep. This sleep 

 has many characteristics of normal sleep in that it is 

 to a certain extent reversible if sutticiently strong 



OTHER DIENCEPHALIC RELATIONSHIPS. Diencephalic 

 and preoptic lesions have been noted to be associated 

 with gastric erosions which approach severe ulcera- 

 tion and also with pulmonary edema. The gastric 

 erosions are a manifestation of a fairly general dis- 



