ReviewInvestigating the neurocognitive deficits associated with chronic drug misuse
Introduction
Cognitive impairments may contribute to drug misuse and addiction in at least two ways. First, they may increase the likelihood of drug-seeking behaviour through various kinds of cognitive deficits including, for example, failures of impulse control mechanisms. Second, they may interfere with users’ capacity to assimilate and participate in rehabilitation programs that often have an educative and cognitive emphasis [1].
The nature and extent of cognitive deficits in drug abusers, and their relationship to hypothesised neurochemical and morphological pathology, is now a burgeoning area of research that capitalises on advances on all fronts of cognitive neuroscience. These include advances in neuroanatomy and molecular pharmacology 2., 3., psychological theory relating to the nature of motivated action and reinforcement mechanisms for drugs of abuse [4], and sophisticated imaging techniques for studying the physiological correlates of cognitive activity in the brain, including positron emission tomography (PET) and functional magnetic resonance imaging modalities 5., 6., 7., as well as event-based electroencephalography [8].
Despite the growth of this research and its ability to use such impressive technical resources, however, the study of the neuropsychology of human drug abuse also faces formidable clinical, methodological and theoretical obstacles. In this review, we first describe briefly these obstacles and then consider how recent studies investigating neurocognitive deficits associated with different kinds of drugs have coped with these problems. In separate sections, we consider the neurocognitive correlates of the ‘illicit’ use of cannabis, stimulants and opiates. We do not discuss the well-documented neurocognitive correlates of prolonged alcohol or nicotine abuse, or the more commonly prescribed drugs liable to abuse such as the benzodiazepines. Relevant reviews have been published elsewhere 9., 10.. However, we do refer to the neuropsychological correlates of alcohol abuse in connection with selected stimulant-abuse studies discussed below.
Section snippets
Theoretical and methodological issues
Most of the neurotransmitters affected by drugs of abuse exert their effects through relatively diffuse patterns of innervation across the whole of the forebrain and wider cortical areas. It is therefore unsurprising that there have been relatively few, if any, convincing demonstrations of differences in neurocognitive performance between abusers of different classes of drug (e.g. stimulants versus hypnotics/sedatives).
The chronic use of illicit drugs may be associated with a rather generalized
Cannabis
Previous reviews have concluded that early studies into the effects of prolonged cannabis use provided only very weak evidence that neurocognitive deficits persisted beyond the residual effects of drug taken within the previous 12–24 hours [13]. However, Block and Ghoneim [14] have found that, relative to a matched group of healthy, non-drug-using controls, heavy marijuana use is associated with small but significant impairments in memory retrieval, verbal expression and mathematical reasoning,
Stimulants
Reflecting the massive increase in cocaine use during the early 1980s, research into the cognitive effects of prolonged stimulant abuse has been dominated by the search for characteristic patterns of deficits following chronic cocaine abuse, highlighting problems in visuo-motor performance, attention and verbal memory 25., 26., 27.. Length of abstinence has been a common theme with some claims that residual deficits persist over months of abstinence 28., 29.. The issue of whether or not cocaine
Opiates
In comparison with cannabis and stimulants, there has been substantially less research into neuropsychological deficits in chronic abusers of opiates. Early studies found some evidence that opiate abusers are more likely to be impaired on batteries of traditional neuropsychological tests such as the Halstead battery, and the Wechsler Adult Intelligence Scale (WAIS) and aphasia tests [64], whereas Hill and Mikhael [65] found evidence of impairment in some measures of memory but relatively few
Conclusions
Progress in preventing and treating drug misuse and addiction requires a fuller understanding of the significance of cognitive dysfunction in the onset and maintenance of drug-seeking behaviour. At the clinical level, diagnostic systems need to be refined to characterize further the nature of substance abuse disorders at various stages of pathology so that the clinical impact of cognitive dysfunction can be more fully appreciated. Neuropsychological deficits associated with drug abuse involving
References and recommended reading
Papers of particular interest, published within the annual period of review, have been highlighted as:
• of special interest
•• of outstanding interest
References (73)
- et al.
Distribution of dopamine D3 receptor expressing neurons in the human forebrain: comparison with D2 receptor expressing neurons
Neuropsychopharmacology
(1999) - et al.
Acute effects of cocaine on human brain activity and emotion
Neuron
(1997) - et al.
Event-related potential indices of auditory selective attention in dependent amphetamine users
Biol Psychiatry
(1999) - et al.
The residual neuropsychological effects of cannabis: the current status of research
Drug Alcohol Depend
(1995) - et al.
Differential impairments of selective attention due to frequency and duration of cannabis use
Biol Psychiatry
(1995) Do cognitive impairments recover following cessation of cannabis use?
Life Sci
(1995)- et al.
Brain glucose metabolism in chronic marijuana users at baseline and during marijuana intoxication
Psychiatry Res
(1996) - et al.
Repeated exposure to Δ9-tetrahydrocannabinol reduces prefrontal cortical dopamine in the rat
Neurosci Lett
(1998) - et al.
Neuropsychological performance of recently abstinent alcoholics and cocaine abusers
Drug Alcohol Depend
(1995) - et al.
Neuropsychological deficits in abstinent cocaine abusers: preliminary findings after two weeks of abstinence
Drug Alcohol Depend
(1993)