Vocate: More on PD rehab

The dominance of the cortical level over the sub-cortical level is adduced by Luria's research with Parkinson's disease patients ( 1959b, 1960b, 1961a, 1967d), which demonstrated that it is possible to transfer the control of defective involuntary (sub-cortical) motor behaviors to the voluntary (cortical) motor areas so that the subject can still perform the desired action because the pathology has left the cortical areas intact.
In Parkinson's disease patients:
The injured subcortical apparatus excites repeated tonic responses, and the pathologically perseverating tension of all muscles is an obstacle to the execution of the instruction. It is easy to imagine such a difficulty in carrying out a voluntary movement if one briefly tenses all the muscles of one hand and then tries to move it without relaxing the tension. ( Luria, 1959b, p. 455)
However, if the origin of the motor act is shifted from the automatic movement realm governed by the sub-cortical motor apparatus to the conscious movement domain of the cortical motor areas, the patient is able to carry out the required movements. This may be accomplished by
attaching a symbolic function to his movements. He is asked to reply to the experimenter's questions by beating out the necessary numbers with his finger. If we then ask him, "How many wheels on a car?" or "How many points on a compass?" we see that the same patient who had failed in the previous experiment and could not automatically strike the table with his fingers even two or three times, easily begins to do so, switching his movements into his speech system and subordinating them to the complex dynamic constellation of cortical connections. ( Luria, 1959b, p. 455)
Similarly, the Parkinson's disease patient who is unable to walk more than one or two steps will find that his difficulties
in successive automatic movements may be compensated for temporarily if they are transferred to the cortical level, and if the continuous movement is superseded by a cycle of isolated responses to individual stimuli. Such a patient cannot take several steps on a smooth floor but can easily cross several lines marked on the floor or several objects placed on the floor. ( Luria, 1967d, p. 417)
Such mechanisms force the control of the normally automatic components of walking to the conscious, voluntary control of the cortical level by separating them into individual responses to individual stimuli, thus requiring cortical level processing.