868 HANDBOOK OF PHYSIOLOGY ^ NEUROPHYSIOLOGY II 



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FIG. 3. Torsion dystonia during intention to reach out the left hand. The movement is retarded 

 by spasmodic contractions of the trunk muscles and by torsion of the left arm. The fingers show 

 athetoid movements. The dystonia is augmented during voluntary movement. [Redrawn from 

 motion pictures made by Jung; from Hassler (84).] 



ing much more like \-oluntary mo\-ements than do 

 the genuine myoclonic phenomena (yawning tics, 

 snorting tics). Even more complex stereotyped move- 

 inents of the limb and speech inuscles, like palilalia, 

 are known. Lesions of the striatum are most com- 

 monly considered as the substrate for these motor dis- 

 orders. 



g) The hypokinetic-rigicl parkinsonian syndrome 

 differs from all hyperkinetic syndromes because of the 

 absence of spontaneous, reactive and automatic move- 

 ments. Motor stiffness, loss of congenital or acquired 

 automatisms (akinesia) and a tenacious increase of 

 muscle tone (rigidity) are its major characteristics. 



Tremor at rest, is often present although not obligatory 

 when the patient is at rest. Impairment of voluntary 

 activity due to the loss of automatic movements and 

 the difficulty of initiating and performing mo\ements 

 rnay be even more pronounced than in many hyper- 

 kinetic disorders. Rigidity is not accompanied by 

 irradiation and enhancement of the phasic stretch 

 reflexes. \'oluntary movements inhifiit the resting 

 tremor. Autonomic symptoms such as salivation, 

 exaggerated sweating and seborrhea adiposa are 

 aspects of the parkinsonian syndrome. The anatomical 

 defect is destruction of nerve cells in the substantia 

 nis;ra. 



