Psychomotor performance in Alzheimer disease

The clinical course of Alzheimer disease (AD) is primarily characterized by a progressive decline in intellectual functioning. Motor behavior is generally considered to remain intact until late in the course of the disease. Nevertheless, preliminary studies of AD patients indicate that compromised psychomotor performance may be an important clinical and functional characteristic. To date, there has not appeared in the AD literature a systematic investigation of either the extent of elementary motor deficits, or the possibility of an interactive effect between task complexity and degree of psychomotor dysfunction. The present study was designed to ascertain the presence and degree of psychomotor impairment in a sample of AD patients carefully screened for absence of other psychiatric or neurologic disorders. Laboratory measures of strength, coordination, manipulative dexterity, visual scanning, visuomotor tracking, graphomotor coding, writing speed, and reaction time were utilized. The selection of tests and experimental design allowed for interpretation of psychomotor performance relative to the degree of cognitive involvement. It was predicted that the performance of AD patients would not significantly differ from that of controls on simple motor tasks. However, AD patients were predicted to perform significantly worse than controls on complex motor tasks involving increased cognitive load. Data were submitted to Principal Components Analysis, from which three principal factors emerged: Simple Motor, Complex Motor, and Cognitive Motor. Between-group comparisons supported the above hypotheses. AD patients were found to be significantly impaired relative to controls on Complex Motor and Cognitive Motor tasks. There were, however, no significant group differences on measures of Simple Motor abilities. The presence of psychomotor deficit in AD is discussed in terms of a generalized slowing of processing speed, and associated inability to generate and execute rapid responses to motor tasks with high cognitive demands.