Consistency of handwriting movements in dementia of the Alzheimer's type: A comparison with Huntington's and Parkinson's diseases

Patients with dementia of the Alzheimer's type (DAT) and their matched cont rols wrote, an a computer graphics tablet, 4 consecutive, cursive letter 'l 's, with varying levels of visual feedback: noninking pen and blank paper s o that only the hand movements could be seen, noninking pen and lined paper to constrain their writing, goggles to occlude the lower visual field and eliminate all relevant visual feedback, and inking pen with full vision. Th e kinematic measures of stroke length, duration, and peak velocity were exp ressed in terms of consistency via a signal-to-noise ratio (M value of each parameter divided by its SD). Irrespective of medication or severity, DAT patients had writing strokes of significantly less consistent lengths than controls', and were disproportionately impaired by reduced visual feedback. Again irrespective of medication or severity, patients' strokes were of si gnificantly less consistent duration, and significantly less consistent pea k velocity than controls', independent of feedback conditions. Patients. un like controls, frequently perseverated, producing more than 4 'l's, or mult iple sets of responses, which was not differentially affected by level of v isual feedback. The more variable performance of patients supports a degrad ation of the base motor program, and resembles that of Huntington's rather than Parkinson's disease patients. It may indeed reflect frontal rather tha n basal ganglia dysfunction.