THE EXTRAPYRAMIDAL MOTOR SYSTEM 



903 



movements, which are primarily teleokinetic, the 

 eyes are leading, sensory anticipation and safeguard- 

 ing mechanisms being the motor accompaniments 

 of the shifting attention. By contrast, vestibular cor- 

 rection movements are mainly ereismatic mechanisms 

 to maintain normal posture. 



What we have called physiological anticipation of 

 motor action, including its attentional and sensory 

 component, is probably similar to what Auersperg 

 (8) called 'prolepsis,' coined for the regulation of eye 

 movements. It seems evident that these functions of 

 motor readiness, anticipation of action and attention 

 should work in close connection with the nonspecific 

 activation system of the brain stem. However, from 

 observations of apraxia after cortical lesions in man 

 showing defects of this anticipatory action it seems 

 probable that the human cerebral cortex and thala- 

 mocortical connections play a prominent part in 

 motor anticipation. The extrapyramidal centers, the 

 reticular formation and the spinal gamma system 

 seem to be the effector mechanisms of this function. 



posture and the different locomotor activities that 

 precede it were studied by Schaltenbrand (223) and 

 Peiper (207). When a human infant begins to raise 

 the body from the supine position by a characteristic 

 turning movement, the eyes and the head lead in a 

 manner similar to the rotatory movements of animals 

 elicited by mesodiencephalic stimulation. During the 

 2nd and 3rd year of life these iiody raising coordina- 

 tions are altered to a rotation of the pelvis and in the 

 4th and 5th year rotation is replaced by a supporting 

 action of the arms so that the trunk is brought directly 

 to a sitting position [Schaltenbrand (223)]. 



Adversive turning movements of eyes, head and 

 foretrunk, instinctive orientation movements induced 

 from various receptors and central regions, are nor- 

 mally integrated into a versatile motor behavior. 

 They appear as isolated mechanisms in infants and 

 may be released after diffuse cerebral lesions. In 

 patients with senile dementia they may be interpreted 

 as syndromes of organic regression to infantile 

 mechanisms. 



UPRIGHT POSTURE IN MAN AND ITS ONTOGENETIC 



DEVELOPMENT. The upright posture, which is peculiar 

 to the human species, is intimately related to nearly 

 all of the characteristic human aspects of motility: 

 the freedom and specialization of the hands, the 

 different position of the head, and the prominence of 

 eye movements [Straus (249)]. It seems logical to 

 assume that the extrapyramidal motor system in man 

 must be organized differently from that of other 

 animals to provide the neural substrate for the up- 

 right posture and walking. Further, the erect posture 

 requires a more elaborate regulatory process to 

 oppose gravity and to protect against falling. These 

 mechanisms are active only in the waking state and 

 require continuous support by the thalamoreticular 

 activating system. 



Erect posture and locomotion are acquired by the 

 infant during the first 2 years of life. Only in the 

 second half of the first year does sitting and standing 

 become possible. Locomotion comes later, developing 

 from crawling to walking around the 12th month. 

 These functions evidently require the regulating 

 mechanisms from various proprioceptors and a well 

 developed e.xtrapyramidal system, coordinated with 

 cerebellar and pyramidal structures and parth 

 modified by learning. 



A detailed comparison of Magnus', de Kleyn's and 

 Rademaker's findings in animals with the motor 

 behavior of normal infants at different ages is given 

 in Peiper's book (207 j. The development of erect 



MOTOR PERFORMANCES OF HUMAN ANENCEPHALI. The 



behavior of infants without cerebral cortex and with 

 various degrees of preservation of the basal ganglia 

 and brain-stem nuclei is of special interest for extra- 

 pyramidal functions. It seems safe to conclude that 

 the motor patterns and instinctive reactions observed 

 in anencephalic brain-stem creatures are mediated 

 bv lower brain-stem structures. 



In the normal huiTian newborn the cortex, the 

 striatum and their pathways are nearly unmyelinated, 

 but the pallidum and the suijthalamic nucleus are 

 well myelinated and probably can function normally 

 except for their connections with the cortex. The 

 pallidum is the highest motor center in newborn 

 human infants during the first weeks of life. Therefore, 

 they have been called Pallidiimivesen or Thalamuspalli- 

 dumwesen by Foerster (57) and have been compared 

 with pallidothalamic animals by some authors. Their 

 motor and instinctive reactions are probably coordi- 

 nated mainly by subcortical mechanisms. 



The most extensively studied human anencephalus 

 living some months without cortex and upper basal 

 ganglia and examined anatomically later in detail 

 is Camper's Mittelhirnwesen (66, 67). The brain of 

 this creature contained an intact mesencephalon, 

 pons, oblongata and cerebellum, but no cortex, 

 striatum or pallidum; only a few traces of the dien- 

 cephalon were present. Some of its instincti\e actions 

 are described in the subsequent section on attention 

 patterns. Although it showed tonic neck and labyrin- 



