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After an interesting description and discussion of many cases, the author advances an original conception of the mechanism of voluntary motor activity. "Kinésie paradoxale," commonly observed in Parkinson's syndrome, has never received sufficient attention from neurologists. All theories that are offered to explain the mechanism of motor trouble in Parkinson's disease, which fail to explain the phenomenon of paradoxic kinesis, must be considered as unsatisfactory. The author's conception can be summarized as follows:
1. Voluntary motility is the result of collaboration of two functionally opposed motor systems: (a) expansive system (systéme expansif), through which the individual takes part in the external world, and (b) executive system (systéme executif ou frenateur) inhibiting the first, and having for its function the learned motor acts—execution of isolated movements for definite purposes. The first system bears on the quantitative aspect of motor activity. Its lesion does not produce paralysis, but lack of