Neurocognitive deficits in cocaine users: a quantitative review of the evidence

Studies on the neurocognitive effects of cocaine abuse are equivocal with respect to the specific types of deficits observed, although the vast majority of studies indicate that at least some deficits in certain broad functions such as attention, learning and memory, executive functions, and response speed exist. All of these studies based their results on null hypothesis statistical significance testing (NHSST). It is argued that effect size analysis, which provides information about the magnitude of difference, offers a more valid index of cognitive impairments in a population when compared to NHSST. Accordingly, the objective of the current study was to conduct an effect size analysis (or a meta-analysis in cases where the same test measure was utilized in more than one study) to determine the type and the magnitude of the specific cognitive deficits found as a result of cocaine use. Effect sizes were calculated for each test variable across 15 empirical studies that met inclusion criteria. The results from 481 cocaine users and 586 healthy normal controls revealed that cocaine use had the largest effect on several measures of attention (0.40 < d < 1.10). Moderate to large effect sizes (d > 0.50) were also obtained on tests of visual memory and working memory. Minimal effect sizes (d < 0.30) were obtained on tests of verbal fluency and other language functions and sensory-perceptual functions. Tests of executive functioning produced mixed findings and were interpreted in terms of degree rather than nature of impairment. The results are consistent with findings from neuroimaging and neurochemical studies that have found cocaine use to be associated with dysfunctions in the anterior cingulate gyrus and orbitofrontal cortex; these regions are highly implicated in the mediation of attentional and executive functions, respectively. Methodological limitations of the empirical studies included in the analysis are discussed.