The Effect of Polydrug Abuse on Neuropsychological Functions

This dissertation, "The Effect of Polydrug Abuse on Neuropsychological Functions" by Keens, Cheng Hiu-wan, 鄭曉韻, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis titled The Effect of Polydrug Abuse on Neuropsychological Functions Submitted by Cheng Hiu Wan, Keens For the degree of Master of Social Sciences At the University of Hong Kong in June 2006 Individuals with histories of drug abuse more often exhibit deficits in neurocognitive processing than those without such histories (Bolla, Cadet, & London, 1998; Bolla, Rothman, & Cadet, 1999). Of particular interest is the greater incidence of impaired executive cognitive functions among drug abusers. Poly-substance abuse is becoming an increasingly common phenomenon in Hong Kong. In particular, the concomitant uses of ecstasy (MDMA) and ketamine (EK) became more and more popular among the youth (under the age of 21), especially with the emergence of the rave culture. Among the variety of illegal recreational drugs, heroin and benzodiazepines (HB) have been the most popular illegal recreational drugs in Hong Kong, especially among young adults (over the age of 21). While there is a growing body of evidence from pre-clinical, neuropsychological and brain imaging studies showing that polysubstance abuse is associated with damage to different neural circuits converging in the prefrontal cortex, research on the harmful effects of the specific patterns of polydrug use on the abusers of the Chinese origin was scarce. In view of the rapid rise of polydrug abuse in Hong Kong, the extent of these combined effects becomes an important issue for study. The present study examined neurocognitive functioning in groups of individuals who had an abused history of various psychoactive substances. Forty-six former polydrug abusers (23 EK users, 23 HB users) were compared to 2 46 matched non-drug abusing controls. Neuropsychological assessments of attention, inhibition and cognitive flexibility were conducted. Results showed that polydrug users exhibited greater magnitude of impairments in switching attention, verbal fluency and figural fluency, but not on attentional control and selective attention relative to their non-user counterparts. EK and HB users made significantly more omission errors in mental processing task than non-users, which reflected their lower impulsive control. Within polydrug users, HB group were more impaired in attentional control and switching attention compared with EK group. Their impairments in these domains were positively correlated with their years of drug addiction. Canonical discriminant analysis yielded figural fluency and verbal fluency as potential core neuropsychological variables for differentiating EK users from non-users. Secondly, verbal fluency, speed of mental processing and total omission errors successfully classify HB users from non-users. Finally, measures of mental processing speed and attentional control could accurately classify HB users from EK users. Although conclusions are somewhat limited by the small sample size, performance of the non-drug users were still significantly better than that of the poly-drug abusers on many measures, suggesting that a history of polydrug abuse impairs neuropsychological functions. Further research is necessary to explore the factors underlying performance impairment in these specific patterns of drug use and to determine the clinical significance of the observed impairment for general performance or functioning in the natural environment. Longitudinal and