John and Made it Up, please try this test. I read about it in a terrific review article about bradykinesia.

Using your writing hand draw an outline on a picture. Then try it again while squeezing a ball with your other hand.

When I do it, I immediately have trouble with my right writing hand and it's a huge effort to draw the outline, and I'm very slow.

Squeezing a ball is not a complicated action. Yet, my brain cannot accomodate it. Can yours?

I have trouble with repetitive movements. Like brushing my teeth.

The article is:

Brain, Vol. 124, No. 11, 2131-2146, November 2001
© 2001 Oxford University Press

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Review article

Pathophysiology of bradykinesia in Parkinson's disease
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A. Berardelli1, J. C. Rothwell2, P. D. Thompson3 and M. Hallett4

I have the PDF on my computer if this link isn't accessible to you:

http://brain.oxfordjournals.org/cgi/...ll/124/11/2131

I found it:

"Simultaneous, sequential or repetitive movements

If any additional complexity is added to a simple movement, either by repeating the movement or by combining it with other tasks, bradykinesia becomes more prominent. Clinical tests of bradykinesia often make use of this phenomenon. Repetitive sequential movement involving isolated finger movements, hand opening/closing or wrist pronation/supination become smaller (hypokinesia) and slower with repetition of the movement (`fatigue') (Agostino et al., 1998Go). Schwab and colleagues asked patients to squeeze a sphygmomanometer bulb in one hand and outline a drawing with the other (Schwab et al., 1954Go). They had much more difficulty if they had to do both tasks together than if each one was performed alone. Indeed, in most cases, patients tended to alternate between the tasks rather than perform them at the same time."

Experimental studies have analysed these features of bradykinesia in some detail. In essence, they show that bradykinesia is more than the slowness seen in simple single movements. There are additional problems in combining or sustaining complex movements. Benecke and colleagues examined rapid elbow flexion movements combined with a simultaneous or sequential hand movement performed with either the same or the opposite arm (Benecke et al., 1986Go, 1987Go). In contrast to normal subjects, in whom there was no decrement of performance when two tasks were combined, patients with Parkinson's disease showed (i) a marked slowing of movement over and above that seen in each task alone when both had to be performed together, and (ii) a longer pause between each element of a sequential task. Indeed, these two extra deficits correlated better with clinical measures of bradykinesia than the slowness in each simple movement.

Similar problems in performing simultaneous movements have been described in bilateral reaching (Stelmach and Worringham, 1988Go; Castiello and Bennett, 1997Go) and cranking tasks (Johnson et al., 1998Go). In sequential movements, prolonged pauses between each element have been observed in everyday movements, such as rising from a chair to pick up an object or drinking from a cup (Bennett et al., 1995Go). Elements of fatigue have also been reported in longer-lasting sequences of movements (Berardelli et al., 1986aGo; Agostino et al., 1992Go, 1994Go).


What is the nature of the extra deficits in performance of complex movements?

The problem of combining tasks or switching from one task to another is not confined to movement. It can be observed in cognitive tasks or combined cognitive and motor tasks (Brown and Marsden, 1991Go; Oliveira et al., 1998Go). Such observations are important since they indicate that the extra deficit seen in complex movements is not necessarily a purely motor problem. They raise the possibility that global processing mechanisms, perhaps involving attention, are also a factor. Brown and Marsden suggested that patients either have a limited processing resource that interferes with their ability to run more than one task at the same time, or that they have difficulty in switching this resource between tasks (Brown and Marsden, 1991Go). An alternative is that the global resource is the same in patients, but that tasks are performed less automatically than in normal subjects. In this case, each task would consume more of the processing resource, and lead to difficulties in performing several tasks at once, or in switching between tasks. Effectively, patients may be trying to compensate for lack of basal ganglia input by devoting more resources to each single task they perform. When required to perform more than one task at once, this becomes a limiting factor.