Response expectancies affect the acquisition and display of behavioral tolerance to alcohol

Drug Abuse as a Problem of Impaired Control: Current Approaches and Findings

The author presents a selective and integrative overview of cur-rent research examining acute effects of abused drugs on aspects of behavioral control in humans. The review discusses the concept of behavioral control and reviews research models that examine inhibitory influences as a central mechanism of control. Evidence for drug-induced impairment of inhibitory mechanisms is reviewed from current neuroanatomical, neuropharmacological, and behavioral perspectives. Model-based laboratory assessments of behavioral control are described in terms of their application to behavioral pharmacology and evidence for alcohol and psychostimulant effects on basic inhibitory mechanisms is reviewed. Drug effects on inhibitory mechanisms are also discussed in terms of their relevance to higher-order cognitive and behavioral functions, and in relation to impulsive behaviors, such as drug abuse. The review concludes by identifying important drug-related phenomenon (e.g., drug tolerance, cue reactivity) that might also be studied in behavioral control frameworks in future research.

Tolerance to the beneficial effects of prophylactic migraine drugs: a systematic review of causes and mechanisms

Loss of benefit of a previously effective treatment regimen, also known as tolerance, can be an important barrier to the successful preventive treatment of migraine. We undertook a systematic review of the literature to identify the prevalence and possible mechanisms of drug tolerance in migraine prophylaxis. Results demonstrate that the frequency of tolerance to prophylactic migraine treatment is unknown, but available data support an estimate that it occurs in 1-8% of patients receiving prophylaxis. Four broad types of tolerance were identified that are likely to be relevant to migraine prophylaxis. These are pharmacokinetic, pharmacodynamic, behavioral, and cross tolerance. The mechanisms that underlie these types of tolerance determine whether their effects can be overcome or minimized. For example, certain forms of tolerance may be affected by manipulation of environmental cues associated with drug administration, by the order in which drugs are used, and by the concomitant use of other medications. Many medications used for migraine prophylaxis exert their effects through the endogenous opioid system. The implications of this finding are explored, particularly the parallels between medication overuse headache and tolerance to migraine prophylaxis. Given the many ways in which tolerance to migraine medications may develop, in some ways it is not surprising that migraine-preventive drugs stop working; it is more surprising that in many cases they do not.

Transfer of learning to compensate for impairment by alcohol and visual degradation

RATIONALE

Past research on social drinkers shows that prior experience performing a task in a visually degraded environment results in the reduction of alcohol-induced impairment. It is possible that task experience under alcohol might similarly carry over to reduce impairment from visual degradation.

OBJECTIVES

The purpose of this study was to test the symmetry of the transfer of learning between two distinct sources of impairment, visual degradation and alcohol.

MATERIALS AND METHODS

Psychomotor impairment was measured by a pursuit rotor tracking task. Forty two participants were randomly assigned to one of six treatment groups. Two groups were tested under alcohol after having prior task experience performing with or without visual degradation. Two groups were tested under visual degradation after having prior task experience performing under active (0.65 g/kg) or inactive (placebo) doses of alcohol. The remaining two groups served as controls that tested the learning effects of repeating each active treatment.

RESULTS

Clear evidence for asymmetrical transfer of learning was observed. Prior task experience with visual degradation reduced the impairing effects of alcohol. By contrast, prior task experience under alcohol had no effect on impairment produced by visual degradation.

CONCLUSIONS

Evidence for differential transfer of learning to compensate for alcohol- and visual-degradation-induced impairment is of practical interest, given that the two disturbances commonly co-occur outside the laboratory. Reasons for the asymmetry are unclear, and likely involve differences in mechanisms by which each treatment impairs psychomotor function.

Compensating for alcohol-induced impairment of control: effects on inhibition and activation of behavior

RATIONALE

Studies have shown that expectations of alcohol-induced impairment can produce adaptive responses to alcohol that reduce the degree of behavioral impairment displayed. However, compensatory effects have been variable for cognitive and psychomotor tasks.

OBJECTIVES

Using a model-driven approach to understanding behavioral control, the present study examined compensatory and impairment effects following the expectation and actual administration of alcohol on the ability to inhibit and activate behavior.

METHODS

Social drinkers (N=17) performed a cued go/no-go task that required quick responses to go targets and inhibition of responses to no-go targets under four conditions: no treatment, alcohol expectancy (placebo), 0.45 g/kg alcohol, and 0.65 g/kg alcohol.

RESULTS

Inhibitory and activational aspects of behavioral control were impaired by both active doses of alcohol. Alcohol slowed response activation and increased failures to inhibit responses in a dose-dependent manner. Subjects also displayed a small, but statistically significant, compensatory improvement in inhibitory control in response to the expectation of alcohol. Moreover, individual differences in the compensatory response were related to differences in alcohol impairment. Those who displayed greater compensatory responses to placebo displayed the least impairment in response to alcohol.

CONCLUSIONS

By modeling behavioral control as the net effect of countervailing activational and inhibitory influences, the study suggests that fundamental mechanisms of control might not display uniform compensatory reactions to alcohol-related cues. Greater consideration of how alcohol-related expectancies shape behaviors under the drug should lead to a better understanding of individual differences with respect to risk for alcohol abuse.

Effects of alcohol and performance incentives on immediate working memory

RATIONALE AND OBJECTIVES

The Sternberg Memory Scanning task was used to test the hypotheses that immediate working memory (WM) would be impaired during moderate rising blood alcohol concentrations (BACs), and provision of a rewarding incentive for good performance under alcohol would counteract this impairment.

METHODS

Two groups (n=18) of social drinkers received either 0.62 g/kg alcohol (A) or a placebo (P). Reward (verbal feedback and money) for good performance was provided to another pair of alcohol and placebo groups (n=18) (AR and PR). All participants completed two tests when BACs in the alcohol groups were rising (68 and 80 mg/100 ml) and two tests during declining BACs (73 and 64 mg/100 ml).

RESULTS

Comparisons of A and P groups showed that rising BACs impaired immediate WM [increased errors, slowed rate of mental scanning, slowed reaction time (RT) when a larger number of items had to be held in WM]. Comparisons of AR and PR groups showed that reward for good performance during rising BACs counteracted impairment in scanning rate and RT but did not reduce errors. Tests during declining BACs of 73 mg/100 ml indicated some symptoms of impairment abated before others. When BAC declined to 64 mg/106 ml, the groups no longer differed on any measure of WM.

CONCLUSIONS

An acute dose of alcohol can impair aspects of immediate WM performance while BACs are rising, and some of these effects can be reversed when incentives to perform well are provided.

Effects of information on the reinforcing, subjective, and psychomotor effects of nitrous oxide in healthy volunteers

The purpose of this study was to characterize the reinforcing, subjective, and psychomotor effects of nitrous oxide (N2O) in healthy volunteers who were given different amounts of information regarding the drugs they were being administered in the experiment. A choice procedure was used in which subjects first sampled a placebo and a given concentration of N2O and then chose between the two. N2O concentration varied across the four-session experiment from 10-40%. Besides choice, subjective and psychomotor effects served as dependent measures. In the INFORMED group (n = 11), subjects were told at the beginning of each sampling trial what concentration of N2O they were inhaling or whether they were inhaling 100% oxygen (placebo). They were also informed about the prototypic effects of N2O (e.g. tingling or numbing, euphoria, dysphoria) and oxygen (e.g. no discernible effects). In the NON-INFORMED group (n = 11), subjects were only told at the beginning of each sampling trial that the drugs they would be inhaling came from one of six classes of drugs. Thirty percent N2O was chosen by a significantly higher proportion of subjects than expected by chance in the INFORMED group, but not in the NON-INFORMED group. Further, the probability of choosing 20-40% N2O was higher in the INFORMED group than in the NON-INFORMED group. Subjective effects of N2O were not affected by the information manipulation. Psychomotor performance at the highest N2O concentration tested (40%) was impaired to a greater extent in the NON-INFORMED than in the INFORMED group. We conclude that the reinforcing effects of N2O, and perhaps the impairing effects, can be modulated by telling subjects beforehand that they are inhaling N2O and what effects they might be expected to experience from the drug.

Impairment and recovery under repeated doses of alcohol: effects of response-outcomes

This research examined the behavioral effect of alcohol during rising and declining blood alcohol concentrations (BACs) when the dose was repeated three times (mean peak BAC = 78 mg/100 ml). A total of 36 male social drinkers learned a complex psychomotor task and subsequently performed it at intervals after alcohol was received. Subjects performed under one of two conditions: an experimental (E) treatment associated drug-compensatory (nonimpaired) task performance with a positively reinforcing outcome or a control (C) treatment associated no environmental consequence with performance. E treatment diminished impairment at all positions on the BAC curve and carried over to result in progressively less impairment when the dose was repeated. In contrast, C treatment tended to increase impairment around the BAC curve with repeated doses. The rate of recovery during declining BACs remained stable across sessions and was not altered by the treatments. The results imply that impairment under a dose of alcohol is governed by two processes: response-outcome associations that determine the amount of impairment displayed under a dose and some adaptive process that determines the rate of recovery with time during exposure to a dose.

Response outcomes affect the retention of behavioral tolerance to alcohol: information and incentive

Twenty-four male undergraduates acquired tolerance during three sessions where they received moderate doses of alcohol (0.62 g/kg) and repeatedly performed a motor skill task with immediate knowledge of results (KR) on each trial. Subjects were assigned to one of four groups (n = 6) before a retention test session where two groups received alcohol and two expected alcohol but received a placebo. The effect on tolerance retention of withholding KR was tested in alcohol group A. The effect of an incentive in the absence of KR was examined in the other alcohol group (AM) that was offered a delayed monetary reward for nonimpaired performance. Both alcohol groups failed to retain tolerance and their impairment did not differ. The effect of substituting the incentive for KR on a drug-compensatory response to placebo was examined in group PM by comparing its performance to group PC where KR was continued. A compensatory response (i.e., performance superior to drug-free baseline) was displayed by the PC group but not by group PM. Thus, despite a monetary incentive to perform well, tolerance to alcohol and a compensatory response to placebo were both disrupted by withholding KR. The results were interpreted in terms of the information about performance conveyed by KR.