“Hold Test” Use in Environmental Epidemiologic Studies On Behavioral Toxicology: Which Tasks Should Be Used?

Abstract

ISEE-544 Objective: Neuropsychological testing has become a widely accepted methodology for assessing neurotoxicity in environmental and occupational exposure studies. These tools allow quantification of a continuum of functional effects ranging from subtle deficits to clinical diagnosis; a dose-response pattern can be explored. Neuropsychological performance is a dynamic process requiring a full grasp of all the potential covariates associated with performance. One variable associated with performance on neuropsychological test in adults is premorbid intelligence (an individual's intellectual abilities before exposure). Premorbid abilities are usually estimated through the use of one of more “hold tests,” tasks that are thought to be resistant to neurotoxic effects. The single word reading subtest of the Wide Range Achievement Test-3 (WRAT-R/3) is a widely used hold test in neuropsychological research, but its utility and validity have been questioned (Johnstone et al., 1996; Michelsen et al., 1996). This project assessed its utility with adult neurological and occupational groups. Materials and Methods: A pilot study examining visuospatial functioning in neurological patients (Parkinson's disease or multiple sclerosis diagnosis), lead-exposed workers, and normal controls was conducted using the WRAT-R/3 and 8 visuospatial tasks. Results: Performance on the WRAT reading subtest was a poor predictor of performance on the visuospatial tests in the battery (Spearman correlation coefficients of 0.02–0.23; P=0.14–0.74). The Wechsler Adult Intelligence Scale-III (WAIS-III) Picture Completion subtest, a task that requires identification of missing details in drawings, was significantly correlated with all but one of the visuospatial tests (Spearman correlation coefficient ranged from 0.32 to 0.60; P < 0.001–0.05). This test is generally resistant to the effects of neurotoxicant exposure in adults. Conclusions: Studies using neuropsychological tests to examine the impact of neurotoxic substances should include hold tests for both verbal and nonverbal functioning. The WAIS-III Picture Completion subtest is a strong candidate for measurement of premorbid visuospatial abilities.