People with Parkinson's disease (PD) tend to slow down and decrease the intensity of their movements even though many retain the ability to move quickly and forcefully. Now, scientists report evidence that the slowdown likely arises from the brain's 'cost/benefit analysis,' which gets skewed by the loss of dopamine in people with PD. In addition, their small study demonstrated that noninvasive electrical stimulation of the brain corrected temporarily improved some patients' motor symptoms.