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HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



extensor thrust and to rhythm in the scratch reflex. 

 In the thalamic animal it leads to clavvina;, jumping 

 and running mo\ements, and in righting enables 

 the under limb, by alternate flexion and extension 

 with increasing abduction, to push the body from the 

 lateral to the upright position. It is this tendency to 

 alternation that gives the thalamic preparation its 

 kinetic, dynamic behavioral aspect, compared with 

 the static fixity of response of the decerebrate animal. 

 Only with an intact subthalamic region does more 

 regular and progressive righting of the body appear 

 and then only after an interval of time after section. 

 Thus the "midbrain animal' is an inconstant anomaly 

 exhibiting transitional states. In man, however, 

 classical decerebrate rigidity is rarely compatible with 

 survival, and as a result of disorder at midbrain 

 level a static posture of rigidity in flexion of the upper 

 limbs with extension of the lower limbs ("decorticate 

 rigidity') is frequent. 



The elements of postural adaptation are all present 

 as spinal reflexes. Their development of energy ade- 

 quate to overcome gravity actively and of sequences 

 capable of effectise performance requires the pres- 

 ence of the pontine and midbrain reticulum and 

 cerebellum. 



Cerebellar Fumtton 



The early physiologists thought that the cerebellum 

 coordinated labyrinthine with other postural re- 

 flexes, for the symptoms of cerebellar disease .so 

 closely resemble those of vestibular disorder. The 

 demonstration that the labyrinthine and neck-right- 

 ing reflexes remained intact after decerebellation 

 appeared to deny this hypothesis. Yet the ingenious 

 analysis of Rademaker (78) demonstrated that it is 

 the overactivity of some righting reactions, particu- 

 larly of those involving lateral displacement of the 

 limijs in space, and of the positive supporting reaction 

 which give cerebellar ataxia its most characteristic 

 features. The modulation of these kinetic responses 

 that make them appropriate in relation to correction 

 of total bodily posture is lacking. The means by 

 which the cerebellum performs such adjustments 

 still eludes us. It is probably significant that the 

 body-on-body righting reflex is abolished by de- 

 cerebellation, while the effect of posture of one limb 

 on that of the others (a true spinal reflex effect) is 

 greatly increased. In some way the cerebellum must 

 interrelate these two (together with \isual and 

 labyrinthine effects). The intense asynimetr\ in the 

 postural effects of one limb on the others produced by 



unilateral lesions of the fastigial nuclei by Sprague & 

 Chambers (g6) and by Moruzzi & Pompeiano (73) 

 indicate an amplifying system for proprioceptive 

 righting reflexes, in both positive and negati\'e senses. 

 The response has its origin in the vermis and reaches 

 the pons via the inferior peduncle (74). The remain- 

 ing neocerebellum and its outflow via the superior 

 peduncle would appear to be the likely mechanism 

 for modulation of contactual types of positive sup- 

 porting reactions and body-on-body righting. If, 

 as we have seen, coordination by combination of 

 effects is in its essential elements a function of spinal 

 reflexes, the contribution of the cerebellum appears 

 to be in the general area of adjustments of posture 

 by environmental factors. Its effects are most obvious 

 on proximal limb muscles. 



Hvpo/halarniis 



In addition to its control of endocrine function 

 through the pituitary gland, its regulation of water 

 balance and temperature, the hypothalamus is iin- 

 portant in the integration of emotional effects, 

 both vegetative and motor. Graham Brown & 

 Sherrington (41 ) showed that stimulation of a sharply 

 localized point on the cut surface of the midbrain of 

 the decerebrate cat could regularly elicit the reflex 

 mimesis of anger, including side-to-side lashing of 

 the tail, protrusion of the claws, a pilomotor reaction 

 and a great rise of arterial pressure. The same re- 

 sponse can be elicited by certain acoustic stimuli in 

 the decerebrate cat (36). Graham Brown has elicited 

 a respiratory rhythm closely resembling laughing 

 from a nearby point in the midbrain of the chimpan- 

 zee (40). These points both are closely related to 

 that from which pupillary changes, vasomotor and 

 visceromotor phenomena can be obtained, and cor- 

 respond approximately with the descending hypo- 

 thalamic pathway of Magoun (70) which evidently 

 has relays in the brain-stem reticular formation (12). 

 The coordination of these different effects into a 

 characteristic ijehavioral displa\' must therefore be 

 related to patterns of connections in the reticular 

 formation of the brain stem and spinal cord. The 

 total reactions of anger and pleasure are uncommon 

 in the decerebrate cat, even when kept in the chronic 

 state (7). Bard (i, 3, 6) showed that the integrity of 

 the hypothalamus was the essential factor which 

 accounted for the facility of pseudaffective reactions 

 of decorticate animals. The reactions ('sham rage") 

 are unusually \iolent in proportion to the stimulus, 



