Introduction Movement-Related Potentials in Parkinson’s Disease:External Cues and Attentional Strategies R. Cunnington, R. Iansek, J.L. Bradshaw. Movement Disorders Vol. 14, No. 1, 1999, pp. 63–68 1 Hypokinetic movement can be greatly improved in Parkinson’s disease patients by the provision of external cues to guide movement. It has recently been reported, however, that movement performance in parkinsonian patients can be similarly improved in the absence of external cues by using attentional strategies, whereby patients are instructed to consciously attend to particular aspects of the movement which would normally be controlled automatically.

2 External cues: Attentional strategy: Providing horizontal lines set at an appropriate stride length can greatly improve gait performance. Providing lines set at an appropriate stroke amplitude can similarly improve micrographic handwriting in parkinsonian patients. the same improvement in movement performance was also shown when external cues were removed and patients were instructed to concentrate on walking with the same large steps using attentional strategies alone. Micrographia may be improved in Parkinson’s disease patients by providing continuous verbal reminders to write ‘‘big,’’ thereby directing the patient’s attention toward producing a large amplitude. Pooya: As stated above, people are verbally reminded to write “big”. Therefore it can be equivalently assumed that people are being helped in terms of their memory. I mean that this is not an attentional strategy but it is a strategy to help memory in those patients who have forgotten what is the normal size of a hand-written text. Here, I am referring to the dichotomy of procedural/habit- learning and memory versus declarative- learning and memory (see for example Bayley et al 2005 Nature). We can say that the size of hand-writing is a habit, that in PD patients is forgotten, and giving verbal instruction is an attempt to recruit compensate declarative mechanisms. !

3 Methods EEG recorded from Cz in 24 PD patients and 24 normal subjects. Patients were on medication. Subjects performed a sequential button-pressing task using a tapping board consisting of a box containing two parallel rows of 10 buttons, one above the other. Light-emitting diodes beneath each button were initially illuminated along a pathway consisting of a particular combination of 10 top- and bottom-row buttons. During experimental trials, lights underneath the buttons were progressively extinguished from right to left. StartEnd Parkinson’s disease and control subjects were further divided into subgroups, with half receiving explicit instruction to internally generate responses and half receiving no such instruction. No Instruction: Subjects were given the instruction ‘‘Hold down each button until the light underneath goes off, then move as quickly as possible to press the next button in the sequence.’’ They were not given any instruction regarding self-timing strategies. With Instruction: Subjects were given the same initial instruction, and further instructed ‘‘The light will go off 4 sec after your previous movement. Try to time the interval for yourself and try to anticipate when the light will go off so that when the light goes off you are ready to move.’’ Therefore, subjects were instructed to internally generate responses rather than to rely on external cues, although they were still required not to move until the cue was given.

Results & Discussion By some extra instruction offered to those PD patients who are in “instructed group” the timing and predictability of the stimulus was drawn under their attention. The result shows that attention can (at least partially) solve the problems of PD patients and make their (reaction times) RTs and (movement related potentials) MRPs almost like normal people. Pooya: I can equivalently explain this effect by considering the intellectual problems of PD patients. And by intellectual problems I mean the disability of PD patients to discover the relations of successive events due to their pseudodementia as a result of, say, depression.. PD patients in “not instructed” group could not discover the regularity of GO signals so they never could predict it and show predictory activity in MRP. In contrast, normal people in “not instructed” group, could discover that there is a regularity in the GO signals and after a few trials started to predict the occurrence upcoming GO signals based on the regularity that they have discovered on their own. PD patients in “instructed” group do not have this problem because the regularity has already been explicitly described for them. ! 4

Results & Discussion Movement duration was just affected by PD. Receiving Instructions and hence attentional strategies had no effect on movement duration. Perhaps the reason for this latter effect, or I had better say lack of effect, is that this aspect of the task is not the one to which people were attending. Pooya: In a previous article by same authors (Brain. 1995;118: ) PD patients and normal subjects had no difference in their movement duration. The task was identical to that of the present article. ! Last point In “no instruction” group, because of the regular pattern of cues and responses, the task could be considered a contingent negative variation paradigm, with the previous response providing the ‘‘warning stimulus’’ for the next cue and response. On the other hand, when subjects are instructed to concentrate on anticipating presentation of the cue, movements are self-timed (although not strictly self-paced) and may be considered to reflect a Bereitschaftspotential paradigm. Pooya: to how much extent you agree? Considering the fact that the shape of MRPs (slide 4) are identical in the two groups of normal subjects, can they be considered as two different identities? ! 5