THE GENERAL PRINCIPLES OF MOTOR INTEGRATION 



789 



an indication that the function is released, presum- 

 ably from cortical control. 



The part played by the hypothalamus in the de- 

 termination of motor behavior is difficult to assess. 

 From various anatomical points in the posterior 

 hypothalamus poorly restricted effects on pupils, 

 heart, arterial pressure, gastric and intestinal motil- 

 ity, with various motor responses, can be obtained 

 by stimulation; this field has been reviewed by Ran- 

 son & Magoun (81), by Beattie (8) and others, and 

 by Hess (49, 50). It remains to be shown what par- 

 ticular elaboration of any one of these transmitted 

 effects is served ijy their hypothalamic connections. 

 The outstanding functional significance of the region 

 would appear to be the general integration of these 

 various effects into the patterns of sleep and wake- 

 fulness, apathy and attention, pleasure and fear. The 

 mofe appropriate regulation of emotion and visceral 

 activity in relation to the environment recjuires the 

 functional activity of specific areas of the cerebral 

 cortex. The extent to which these general hypo- 

 thalamic motor functions are also subject to endo- 

 crine control is not yet clear. 



Thalamic {Decorlicate) Animal 



Of the many reactions pos.sessed by the thalamic 

 or decorticate animal that are absent in the de- 

 cerebrate, we have already seen how the righting 

 reflexes have been attributed to the activity of the 

 midbrain, and emotional and visceral responses to 

 the hypothalamus. It is questionable whether the 

 thalamus per se adds further to motor behavior, 

 other than by its reciprocal relationship to the cortex. 

 The subthalamus, including the subthalamic nucleus 

 and the upward extensions of the red nucleus and 

 substantia nigra, and the important fiber tracts inter- 

 relating these with the basal ganglia and brain-stem 

 reticular formation, are important for the elabora- 

 tion of righting reflexes and of piogression (54, 55, 

 82). In higher mammals it is not yet certain which 

 of these structures makes possible the intensification 

 of kinetic activity that distinguishes the thalamic 

 animal from the decerebrate. All that can be con- 

 cluded on present information is that whereas the 

 posterior hypothalamus contributes behavioral drive, 

 the subthalamus endows more perfect integration of 

 motor response. 



The thalamic and decorticate cat (6) and dog 

 (78) present a nearly natural distribution of posture. 

 It is notable that when the limbs are suspended in 

 space an extension posture appears which disappears 



immediately the limb makes contact with the ground 

 (6). The tactile placing reactions are absent, and a 

 limb hanging over, the edge of a table remains ex- 

 tended. Yet by asymmetry of broad contact with 

 body surface the animal can right itself, and with 

 marked displacement a limb posture will be cor- 

 rected. The extended posture has elements of spastic- 

 ity and is contralateral to a unilateral decortication. 

 The decorticate monkey also shows spasticity which 

 is strongly influenced by asymmetrical body con- 

 tact, being an extension of the under limbs when 

 the animal is lying on one side. The uppermost arm 

 and foot are then more flexed, and traction upon 

 them elicits stronger flexion (the traction reaction). 

 When the animal is sitting, the arms are flexed, the 

 lower limbs extended, and the traction reaction is 

 present in both upper limbs. If he is leaned forward 

 in sitting posture, the arms extend; if leaned back, 

 they flex more; if supported on hands and feet, all 

 limbs show a positive supporting reaction. The kinetic 

 body-on-l)ody righting reflexes, as well as the labyrin- 

 thine righting reflexes, make gradual recovery from 

 decortication and are the basis for the somewhat 

 stiff and awkward automatic behavior of the chronic 

 'thalamic' animal. All the elements of these re- 

 sponses can be demonstrated in man following some 

 types of capsular hemiplegia (100) but are limited 

 tonic types of reaction without kinetic effectiveness. 

 The intense spasticity of many cases of capsular 

 hemiplegia in man presents motor effects that can- 

 not be directly compared with the motor status of 

 the thalamic or decorticate animal. The hand may 

 be tightly clasped in a fist, trapping the thumb under 

 the other fingers, or the wrist may be flexed but 

 strongly pronated with extended fingers. An inter- 

 mediate type presents extension of the wrist with 

 overextended metacarpophalangeal joints and 

 strongly flexed (clawed) interphalangeal joints. In 

 all these different postures the traction reaction is 

 intensely overactive, and in the last variety clonus of 

 the finger flexors is prominent. The two extremes of 

 postures of the hand can occur without spasticity 

 or increased tendon reflexes in the conditions of 

 dystonia and athetosis. When they appear in com- 

 bination with spasticity as a result of capsular lesions, 

 a more general rigidity of all muscles in the cor- 

 responding limbs is also present. It is therefore as- 

 sumed that such intense spastic states are a com- 

 bination of released spastic traction reaction of the 

 type produced by cortical lesions with a superimposed 

 facilitation of either avoiding or grasping extrapy- 

 ramidal mechanism of the type that is called dystonia. 



