The neuropsychology of amphetamine and opiate dependence: implications for treatment

Abstract

Chronic use of amphetamines and/or opiates has been associated with a wide range of cognitive deficits, involving domains of attention, inhibitory control, planning, decision-making, learning and memory. Although both amphetamine and opiate users show marked impairment in various aspects of cognitive function, the impairment profile is distinctly different according to the substance of abuse. In light of evidence showing that cognitive impairment in drug users has a negative impact on treatment engagement and efficacy, we review substance-specific deficits on executive and memory function, and discuss possibilities to address these during treatment intervention.

Figures

Fig. 1

a In the Wisconsin Card Sorting Test, participants are presented with a deck of cards, showing stimuli that differ along the dimensions of color, shape and number. Participants are asked to match each of the cards of the deck to one of the stimulus cards A–D displayed in front of them. Feedback informs participants of the correctness of their choices. Successful matching requires the learning of a sorting rule and the adaptation of the matching strategy when the sorting rule changes. b In the CANTAB 2D-IDED task, participants are trained to discriminate stimuli that differ along the dimensions of shapes and lines. Feedback teaches participants which stimulus is correct, and after six correct responses, the stimuli and/or rules are changed. Shapes remain the relevant dimension (i.e., shifts are intra-dimensional within the same dimension) until stage 8, when the new dimension, the white lines, become the relevant dimension (i.e., extra-dimensional shift)

Fig. 2

a In the Stop-Signal task, participants are presented with a series of stimuli and are instructed to press the button on the left of the response panel when the arrow on the screen is pointing to the left, and to press the button on the right when the arrow is pointing to the right. After a practice session of 16 ‘go’ trials, participants are instructed to withhold their responses when they hear a stop-signal (which occurs in 25% of the trials in the form of an auditory ‘beep’ sound-a 300 Hz tone). b In the Go-Nogo task, participants are presented with a series of letters, and are instructed to press a button as quickly and accurately as possible in response to any letter presented except to the letter X

Fig. 3

a In the Iowa Gambling task, participants are presented with four card decks and asked to make series of card selections concerning winning and losing monetary rewards. Participants are not told that there are ‘safe’ and ‘risky’ decks. Over the course of the task, participants generally develop a preference for the ‘safe’ decks (C and D) over the risky decks (A and B). The net-score, which is calculated from the total number of cards selected from ‘safe’ minus ‘risky’ decks, reflects the decision-making strategy across the task. b The Risk Task requires participants to choose between two mutually exclusive options with different probabilities of reward and punishment. On each trial, an array of six boxes is presented on the screen, with a ratio of red and blue boxes that varies from trial to trial (5:1, 4:2, 3:3 boxes). Participants are told that the computer had hidden a yellow token, at random, behind one of the six boxes and they need to decide whether the token is hidden behind a red or blue box. Their decision on each trial is shaped by a fixed bet, associated with each alternative, regarding the magnitude of potential gain or loss (90:10, 80:20, 70:30; 60:40, 50:50 points). Feedback is provided by the way of gain or loss of points following each trial. Since the least likely option is always associated with the large reward value, participants are facing a reward–conflict situation

Fig. 4

The graph shows how feedback modulates ongoing decision-making differentially in current and former users of amphetamine and opiates on the Risk Task. Individual difference scores (computed by subtracting likely choices following a win from likely choices following a loss) reflect whether the likely option was chosen preferably following positive or negative feedback. As can be seen in the graph, negative feedback induced greater risk-taking than positive feedback in the methadone group but not in any of the other groups. This differential effect of task feedback on decision-making was significantly greater in methadone maintained opiate users than in controls (p=0.003) and street heroin users (p=0.010); (see Ersche et al. 2005b), printed with permission from the nature publishing group