Analysis of apraxia in Alzheimer's disease

Abstract

The studies in this text were designed so as to explore some aspect of the presence of apraxia, in Alzheimer's Disease, as measured by the Waterloo Apraxia Battery (WatAB) (Roy, 1996). In the first four studies, we confirmed Benke's (1993) suggestion that two forms of apraxia were present and dissociable in AD. The majority of participants were apraxic in both imitation and pantomime conditions and a few were impaired on only one. In all of this work impairment was greater when tasks require analysis of visual gestural information than when a gesture must be generated from memory. the pattern of no difference in performance in Imitation as in Pantomime continued throughout the work herein.

Ochipa et al. (1992) suggest that apraxia in AD is conceptual in nature such findings as reported above are unexpected and contradictory. Of all the patterns predicted by Roy's (1996) model the most prevalent found was that where AD participants were impaired on Concurrent Imitation, Delayed Imitation, Pantomime and gesture- tool-object recognition (Conceptual) tests. According to Roy such a pattern suggests an impaired knowledge of action and tool/object function along with impairment in response organization and control (sensory-perceptual, conceptual and production systems). This pattern suggests that in AD, participants cannot make use of cues to assist their motoric performance as they cannot recognize a gesture, provide it when asked or when asked to copy someone else.

Another purpose of this work was to review the relationship between cognition and praxis via the DRS and the WatAB. First a correlation matrix indicated that many of the tests used, both motoric and conceptual, were highly correlated with the DRS. Many of the WatAB sub tests were also highly correlated with each other. Our findings are perhaps best considered an indication that the WatAB will be a useful tool for future research and ultimately for clinical use.

The fifth study in this series was designed to test for apraxia under more naturalistic conditions. The Tool Selection Task (TST) was used, allowing an opportunity to manipulate the conditions under which the Concurrent Imitation tasks on the WatAB have been presented. The latter was in response to our consistent finding that the AD group performed praxis tasks with more error when using Transitive (Tool Use) gestures. We had hypothesized that presenting the tasks while sitting directly across from participant was too demanding and leading to difficulties with left and right. The use of a mirror for presenting the task did not eliminate error. We then used a broad measurement of visuo-spatial skills. The results do not determine whether Transitive gestures are particularly sensitive to changes in visuo-spatial changes during AD. We recommend including such a broad measure in future research.

In the WatAB TST the items such as eating are specific and the presentation of each task provides more cues as to the action required. We hypothesized that the presence of more cues would increase performance (reduce error). We report that as the number of cues increase the amount of error decreases in AD. Additionally, the TST is a measure of creativity as each task is presented twice (correct tool present or a reasonable alternative as one of the four choices). We report that using a method of measuring creativity can determine group differences and that the AD group spent more time selecting the correct tool in the alternate condition.