CONTROL OF STROKE SIZE, PEAK ACCELERATION, AND STROKE DURATION IN PARKINSONIAN HANDWRITING

The aim of this study was to quantify handwriting deficits in Parkinson's disease patients through use of signal-to-noise analyses. Six idiopathic Parkinson's disease subjects and six age-matched controls performed normal handwriting patterns; in addition they wrote larger, slower, faster, and with reduced sensory feedback. Results showed that Parkinsonians, as well as normals, generally were able to modify stroke size, peak accelerations, or force amplitudes, and stroke durations as they wrote the required patterns. However, the signal-to-noise analyses suggested that the movement deficits, often noted in Parkinsonians, were primarily due to an impaired force-amplitude component rather than to an impaired stroke-duration component. Reduction of sensory feedback did not alter Parkinsonian handwriting relative to that of controls, suggesting that Parkinsonians do not rely more on sensory feedback during handwriting than do normals. The dysfunctioning of force amplitude is assumed to occur at a relatively low level of the motor-system hierarchy, as no corrections appeared in the readjustment of stroke duration. The observed, increased variability of force amplitude is discussed in terms of impaired muscle-firing patterns in the Parkinsonians.