Avoiding pitfalls: Bayes factors can be a reliable tool for post hoc data selection in implicit learning.

Research on implicit processes has revealed problems with awareness categorizations based on nonsignificant results. Moreover, post hoc categorizations result in regression to the mean (RTM), by which aware participants are wrongly categorized as unaware. Using Bayes factors to obtain sensitive evidence for participants' lack of knowledge may deal with nonsignificance being nonevidential, but also may prevent regression-to-the-mean effects. Here, we examine the reliability of a novel Bayesian awareness categorization procedure. Participants completed a reward learning task followed by a flanker task measuring attention towards conditioned stimuli. They were categorized as B_Aware and B_Unaware of stimulus-outcome contingencies, and those with insensitive Bayes factors were deemed B_Insensitive. We found that performance for B_Unaware participants was below chance level using unbiased tests. This was further confirmed using a resampling procedure with multiple iterations, contrary to the prediction of RTM effects. Conversely, when categorizing participants using t tests, t_Unaware participants showed RTM effects. We also propose a group boundary optimization procedure to determine the threshold at which regression to the mean is observed. Using Bayes factors instead of t tests as a post hoc categorization tool allows evaluating evidence of unawareness, which in turn helps avoid RTM. The reliability of the Bayesian awareness categorization procedure strengthens previous evidence for implicit reward conditioning. The toolbox used for the categorization procedure is detailed and made available. Post hoc group selection can provide evidence for implicit processes; the relevance of RTM needs to be considered for each study and cannot simply be assumed to be a problem.

GABAA receptor subtype involvement in addictive behaviour.

GABAA receptors form the major class of inhibitory neurotransmitter receptors in the mammalian brain. This review sets out to summarize the evidence that variations in genes encoding GABAA receptor isoforms are associated with aspects of addictive behaviour in humans, while animal models of addictive behaviour also implicate certain subtypes of GABAA receptor. In addition to outlining the evidence for the involvement of specific subtypes in addiction, we summarize the particular contributions of these isoforms in control over the functioning of brain circuits, especially the mesolimbic system, and make a first attempt to bring together evidence from several fields to understanding potential involvement of GABAA receptor subtypes in addictive behaviour. While the weight of the published literature is on alcohol dependency, the underlying principles outlined are relevant across a number of different aspects of addictive behaviour.

Impulsivity as a Multifaceted Construct Related to Excessive Drinking Among UK Students.

AIMS: A substantial number of university students exceed alcohol guidelines. Impulsivity has been repeatedly implicated in heavy alcohol use, yet despite knowledge that impulsivity is multifaceted, there have previously been few studies applying multiple measures of self-report and behavioural impulsivity to examine the relationship with excessive student drinking. This results in a limited understanding of the relationship of various facets of impulsivity to student drinking. METHODS: Participants completed a comprehensive battery of impulsivity measures: the Barratt Impulsiveness Scale as a self-report index and the Stop Signal Task, Information Sampling Task and Monetary Choice Questionnaire as behavioural measures of three facets of impulsivity. Participants who exceeded UK drinking guidelines were compared to those who did not on measures of impulsivity. Hierarchical linear regression was then employed to test whether indices of impulsivity were associated with the average units consumed per week. RESULTS: Participants who exceeded UK guidelines reported increased impulsivity in facets of self-report impulsivity. They also displayed performance deficits in normal adjustment of Go responses on the Stop Signal Task. In the regression model, nonplanning impulsivity on the Barratt Impulsiveness Scale was seen to predict quantity of alcohol consumed per month. CONCLUSIONS: The study applies a comprehensive selection of behavioural and self-report measures of impulsivity and indicates that excessive drinkers are more impulsive in some but not all aspects. The results indicate that the wide range of deficits apparent in alcohol-dependent individuals are not evident in this younger, heavy drinking population, but that specific performance and self-identified deficits are already apparent.

Effect of varenicline on aspects of inhibitory control in smokers.

RATIONALE: Varenicline, a partial agonist at α4ß2 nicotinic receptors (nAChRs) aids smoking cessation by reducing craving. Successful quitting may be associated with greater inhibitory control but the effectiveness of varenicline in this regard is unknown. OBJECTIVES: This study aimed to investigate the effect of varenicline on aspects of inhibitory control in smokers. METHODS: A double-blind, placebo-controlled study investigating the effect of varenicline 1 mg (or matched placebo) in satiated and abstinent smokers. Tests included Rapid Visual Information Processing (RVIP), Stop-Signal (SS), Prospective Memory (PM) and the Cambridge Gambling Task (CGT). RESULTS: Smoking enhanced RVIP accuracy and latency to respond. Varenicline did not alter RVIP performance, nor the effect of smoking, suggesting that these effects were unrelated to α4ß2 nAChRs. Smoking increased the number of errors during SS and increased the stop latency, indicating that smoking decreased inhibitory control. Varenicline partially mimicked this effect of smoking but also reduced the smoking-induced increase, indicating a role for α4ß2 nAChRs. Likewise, smoking increased the number of points bet following a win during CGT and varenicline blocked this effect. There was no effect of smoking or varenicline on PM target detection per se. However, smoking protected the target detection rate in the ongoing task when a concurrent intention was introduced. Varenicline improved response speed in both satiated and abstinent smokers. CONCLUSIONS: Some aspects of inhibitory control may be mediated by α4ß2-related mechanisms and blockade of smoking-induced disinhibition may contribute towards the action of varenicline as an aid to smoking cessation.

Mechanisms of attention to conditioned stimuli predictive of a cigarette outcome.

Attention to stimuli associated with a rewarding outcome may be mediated by the incentive motivational properties that the stimulus acquires during conditioning. Other theories of attention state that the prediction error (the discrepancy between the expected and the actual outcome) during conditioning guides attention; once the outcome is fully predicted, attention should be abolished for the conditioned stimulus. The current study examined which of these mechanisms is dominant in conditioning when the outcome is highly rewarding. Allocation of attention to stimuli associated with cigarettes (the rewarding outcome) was tested in 16 smokers, who underwent a classical conditioning paradigm, where abstract visual stimuli were paired with a tobacco outcome. Stimuli were associated with 100% (stimulus A), 50% (stimulus B), or 0% (stimulus C) probability of receiving tobacco. Attention was measured using an eye-tracker device, and the appetitive value of the stimuli was measured with subjective pleasantness ratings during the conditioning process. Dwell time bias (duration of eye gaze) was greatest overall for the A stimulus, and increased over conditioning. Attention to stimulus A was dependent on the ratings of pleasantness that the stimulus evoked, and on the desire to smoke. These findings appear to support the theory that attention for conditioned stimuli is dominated by the incentive motivational qualities of the outcome they predict, and implicate a role for attention in the maintenance of addictive behaviours like smoking.

The effects of micronutrient supplementation on vasomotor symptoms in postmenopausal women.

OBJECTIVE: Estrogen is the most effective treatment for vasomotor symptoms. Given its potential risks, herbal preparations and nutritional supplements have been developed as alternative remedies. The main aim of this double-blind, randomized, placebo-controlled trial was to assess any impact of a nutritional supplement containing 12 vitamins and nine minerals on the frequency and severity of hot flushes in postmenopausal women over a 3-month period. SUBJECTS AND METHODS: Ninety-one postmenopausal women were randomized to either the placebo (n = 45) or the treatment arm (n = 46). Seventy out of the 91 women completed the study (36 from the treatment group and 34 from the placebo group). At baseline and the 14-week post-intervention assessments, study participants completed questionnaires on the frequency and severity of hot flushes and night sweats, the Profile of Mood State questionnaire, the World Health Organization Quality of Life Questionnaire, the National Adult Reading Test and the Rey Auditory-Verbal Learning Test. Between assessments, the women also completed hot flush diaries. RESULTS: There was a significant decrease (p < 0.01) in the number (±standard error of the mean) of hot flushes experienced per week for treatment (pre 31.3 ± 4.7; post 23.1 ± 4.8) and placebo groups (pre 28.1 ± 4.7; post 17.3 ± 4.0). A significant decrease (p < 0.001) in the number of night sweats experienced per week was also observed in the treatment (pre 6.1 ± 1.0; post 4.2 ± 0.7) and placebo groups (pre 5.9 ± 0.7; post 3.7 ± 0.7). CONCLUSIONS: This study demonstrates a significant placebo effect on hot flushes and night sweats, as consistent with other studies. The micronutrient supplement containing 21 vitamins and minerals was not superior over placebo in effects on hot flushes and night sweat experiences.

A role for glutamate in subjective response to smoking and its action on inhibitory control.

RATIONALE: Our previous study using memantine in smokers suggests that there may be a differential role for N-methyl-D-aspartate (NMDA) receptors in the subjective and cognitive effects of smoking. OBJECTIVES: This study was designed to investigate if D-cycloserine (DCS) would modulate the subjective and cognitive effects of limited smoking. METHODS: Forty-eight habitual smokers abstinent for a minimum of 2 h were randomly allocated to receive either placebo or 50 mg DCS (double-blind) and were subsequently required either to smoke half of one cigarette or to remain abstinent. Subjective and physiological effects of DCS were measured at baseline, 90 min postcapsule, and again after the partial-smoking manipulation, while the effects on sustained attention (rapid visual information processing test--RVIP) and cognitive flexibility (intra-extra dimensional set-shift test--IED) were evaluated only after the partial-smoking manipulation. RESULTS: DCS alone did not produce significant subjective effects other than an increase in ratings of "Stimulated". In combination with partial smoking, however, DCS blocked the smoking-induced increase in "Stimulated" and the decrease in "Relaxed" ratings. Furthermore, in combination with smoking, DCS reduced the number of false alarms during the RVIP test (an index of inhibitory control) and produced a small increase in diastolic blood pressure. DCS failed to modulate IED performance. CONCLUSIONS: These findings provide further evidence of a role for glutamate release in the subjective effects of smoking but not the effects on attention and cognitive flexibility. Furthermore, our results indicate that glutamate release may also be involved in the effect of smoking on inhibitory control.

Degree of dependence influences the effect of smoking on cognitive flexibility.

Pre-frontal cortical (PFC) dysfunction has been put forward as the basis for development and maintenance of addiction. To explore this relationship, the present study investigated the effects of smoking on PFC-mediated cognitive flexibility and subjective states in low- (LD) and high-dependent (HD) smokers. Twenty-four LD and 24 HD smokers (Fagerström dependence scores ≤ 4 and ≥ 5, respectively) were randomly allocated to non-smoking or smoking condition (12 LD and 12 HD participants per condition). After abstaining from smoking for a minimum of two hours volunteers completed a battery of questionnaires [nicotine-specific Visual Analogue Scales (Nic-VAS), Questionnaire of Smoking Urges (QSU) and Profile of Mood States (POMS)] at baseline [T1] and again after smoking one cigarette or remaining abstinent [T2]. Cognitive flexibility was evaluated at T2 using the Intra-Extra Dimensional Set-Shift test. The Rapid Visual Information Processing test was performed as a control nicotine-sensitive task at several time points during the experiment. Compared to LD smokers, HD smokers had higher salivary cotinine and breath CO levels at baseline and reported more craving (QSU) and felt less stimulated (Nic-VAS), vigorous, friendly and elated (POMS) throughout the experiment. Smoking increased Nic-VAS ratings of 'Buzzed' and 'Dizzy' and decreased craving in all participants. Smoking selectively impaired cognitive flexibility in HD smokers since HD smokers allocated to the smoking condition made significantly more errors with the intra-dimensional set-shift than their counterparts in the abstinent condition. No effect of smoking on RVIP test was observed, most likely due to the practice effect which was significant in both groups of smokers. The practice effect, however, was more pronounced in LD smokers. This study demonstrates that PFC-mediated cognitive effects of smoking as well as subjective reports vary according to the degree of nicotine dependence.

Mechanisms of attention for appetitive and aversive outcomes in Pavlovian conditioning.

Different mechanisms of attention controlling learning have been proposed in appetitive and aversive conditioning. The aim of the present study was to compare attention and learning in a Pavlovian conditioning paradigm using visual stimuli of varying predictive value of either monetary reward (appetitive conditioning; 10p or 50p) or blast of white noise (aversive conditioning; 97 dB or 102 dB). Outcome values were matched across the two conditions with regard to their emotional significance. Sixty-four participants were allocated to one of the four conditions matched for age and gender. All participants underwent a discriminative learning task using pairs of visual stimuli that signalled a 100%, 50%, or 0% probability of receiving an outcome. Learning was measured using a 9-point Likert scale of expectancy of the outcome, while attention using an eyetracker device. Arousal and emotional conditioning were also evaluated. Dwell time was greatest for the full predictor in the noise groups, while in the money groups attention was greatest for the partial predictor over the other two predictors. The progression of learning was the same for both groups. These findings suggest that in aversive conditioning attention is driven by the predictive salience of the stimulus while in appetitive conditioning attention is error-driven, when emotional value of the outcome is comparable.

Behavioural measures of frontal lobe function in a population of young social drinkers with binge drinking pattern.

BACKGROUND: Binge drinking may lead to brain damage. The aim of the present study was to compare the cognitive abilities of binge and non-binge drinkers in tasks which test functions linked to discrete areas of the prefrontal cortex. METHODS: Non-binge and binge drinkers were identified according to their binge score derived from the Alcohol Use Questionnaire. Cognitive performance was tested with the Spatial Working Memory task (SWM) linked to the dorsolateral prefrontal cortex, Intra/Extradimensional Shift and reversal task (IED) linked to dorsolateral prefrontal cortex (shift) and to orbitofrontal cortex (reversal), Paired Associates Learning task (PAL) linked to temporal cortex, and Reaction Time Task (RTI) a task measuring motor impulsivity (Inferior frontal gyrus). Personality traits, alcohol outcome expectancies and mood were also evaluated. RESULTS: Binge drinkers recorded a significantly shorter movement time to target in the RTI, and completed fewer stages on first trial in the PAL, compared with non-bingers. In the IED as well as in the SWM, only female binge drinkers were more impaired than non-binge drinkers. CONCLUSIONS: Functions linked to dorsolateral prefrontal cortex may be more impaired in female, whereas functions linked with the temporal lobe may be impaired in both male and female binge drinkers compared to non-binge drinkers. Functions linked to orbitofrontal cortex were not impaired. The increased speed of response in the RTI in binge drinkers may indicate an increased motor impulsivity in binge drinkers.

Differential involvement of glutamatergic mechanisms in the cognitive and subjective effects of smoking.

There is growing preclinical evidence for the involvement of glutamate in the behavioral actions of nicotine. The aim of this study, was to investigate the role of N-methyl-D-aspartate (NMDA) receptors in the cognitive and subjective effects of smoking in humans. Sixty regular smokers took part in this double-blind placebo controlled study, that investigated the effect of the NMDA-antagonist memantine (40 mg) and the nicotinic-receptor antagonist mecamylamine (10 mg) on smoking-induced improvement in performance of a task of sustained attention and on smoking-induced changes in subjective effects and craving. Increases in subjective ratings of 'buzzed' following smoking were reversed by memantine, but not by mecamylamine. In contrast, improvement on a Rapid Visual Information Processing task by smoking was opposed by mecamylamine, but not by memantine. Smoking reduced craving for cigarettes, but neither drug altered this effect. Our results suggest that glutamatergic mechanisms may have differential involvement in the subjective and cognitive actions of smoking. Further investigations using different ligands are warranted to fully characterize the role of glutamate underlying the consequences of smoking behavior.

First evidence of a functional interaction between DNA quadruplexes and poly(ADP-ribose) polymerase-1.

We discovered that the abundant human nuclear protein poly(ADP-ribose) polymerase-1 (hPARP-1) binds to intramolecular DNA quadruplexes in vitro with high affinity and with a stoichiometry of two proteins for one quadruplex. Using an enzymatic assay, we have shown that hPARP-1 gets catalytically activated upon binding to G-quadruplexes localized at the c-kit promoter and human telomere regions. This is the first example of a truly functional quadruplex-protein interaction, which has possible implications in understanding hPARP-1 mediated mechanisms of transcription regulation and telomere end protection.

Effects of stress on emotional reactivity in hostile heavy social drinkers following dietary tryptophan enhancement.

AIM: Because individuals high on hostility may be at risk for alcohol abuse due to serotonergic dysfunction and greater reactivity to stress, we examined the effects of acute dietary tryptophan enhancement and stress on mood and craving for alcohol in low-hostile (LoH) and high-hostile (HiH) individuals. METHODS: Thirty-four LoH and 33 HiH heavy social drinkers [selection based on the Hostility scale from the Buss and Perry Aggression Questionnaire (1992)] received either tryptophan-enriched or control diet and underwent a stress-induction procedure. Trait differences between the two hostile groups were explored using personality, anxiety, and depression questionnaires. Mood, craving for alcohol, and salivary cortisol levels (CORT) were measured before and after tryptophan and after stress-induction. Heart rate (HR) was measured during stress-induction. RESULTS: HiHs compared to LoHs scored higher on the depression and anxiety trait scales as well in the character dimension Harm Avoidance and reported more of stress exposure over the past month. They also showed more negative mood and higher craving for alcohol. Diet alone did not produce any subjective or physiological effects. Stress increased CORT, HR, negative mood, and craving for alcohol. HiHs displayed higher CORT increase and lower cardiovascular reactivity in response to stress compared to LoHs. Opposite to the predictions, tryptophan enhancement selectively facilitated stress-induced increase in craving in the HiHs. CONCLUSION: Among heavy drinkers HiHs report higher craving for alcohol and show greater reactivity to stress as measured by CORT and negative mood. The effects of stress on craving in HiHs may be mediated by a serotonergic mechanism.

The influence of alcohol on basic motoric and cognitive disinhibition.

It has been proposed that alcohol weakens control processes, which in turn supports the occurrence of disinhibited behaviours. Two studies were run, in parallel (both with 32 participants) using a between-subject design to investigate any disinhibiting effects of a moderate dose of alcohol (0.6 g/kg compared to placebo), previously found to trigger increased desire for alcohol. Disinhibiting effects were tested on basic motoric and cognitive control processes, using a go/no-go (GNG) and the Stroop task (ST) respectively. Although a higher proportion of participants wanted more alcohol under the alcohol preload (priming effect), this effect was not found to be significant. In the GNG task, correct response latency (RL) decreased from baseline [P = 0.008] while number of incorrect hits increased [P = 0.030] irrespective of treatment, indicating the formation of a habit-like response and motoric disinhibition. Although error rate did not differ between groups, an interaction occurred with regard to erroneous RL: participants under alcohol became quicker, while those under placebo became slower [P = 0.014]. In the ST, those preloaded with alcohol made significantly more errors [P = 0.021] and were quicker to complete the task [P = 0.044] compared with those preloaded with placebo, indicating a strong alcohol effect on cognitive disinhibition. The data suggest that a moderate dose of alcohol, which induces priming to want more alcohol, had disinhibiting effects both on a basic motoric and a cognitive inhibitory task. Thus the idea that priming may be mediated by the disinhibitory effects of alcohol is supported.

Avoidance of alcohol-related stimuli in alcohol-dependent inpatients.

BACKGROUND: Previous research has shown an attentional bias toward drug-related stimuli in heavy social drinkers. Attentional orientation to drug-related cues may lead to increased craving and preoccupation with the drug and impaired ability to focus attention on nondrug-related activities, resulting in renewed drug taking or relapse from drug abstinence. OBJECTIVE: The aim of this study was to investigate whether alcohol-dependent inpatients would differ in their selective attention toward alcohol-related stimuli in comparison with a group of social drinking controls. METHOD: Thirty-five alcohol-dependent inpatients were compared with a group of 39 social drinking controls matched for age, sex, and verbal IQ. Attentional bias was assessed using alcohol-related pictures in a dot probe detection task. Questionnaires were used to examine outcome expectancies after alcohol consumption, anxiety, mood, and craving. RESULTS: The alcoholic inpatients showed a bias away from the alcohol-related stimuli, scored higher on alcohol outcome expectancies, and on anxiety measures (both state and trait). They also presented with more negative mood compared with the control group. Craving was higher in the alcoholic group for the factor "loss of control over drinking." CONCLUSIONS: Alcoholic inpatients undergoing treatment based on the 12-step treatment of Alcoholics Anonymous (Minnesota model), which includes counseling, and intensive group, individual, and family psychotherapy, show an avoidance for drug-related stimuli and a perception of loss of control over drinking. We suggest that their increased perception of loss of control over drinking produces the avoidance from the drug-related stimuli.

The effect of alcohol and repetition at encoding on implicit and explicit false memories.

RATIONALE: Alcohol impairs explicit memory, whilst leaving implicit memory relatively intact. Less is known about its effects on false memories. AIM: The present study examines the effects of alcohol on explicit and implicit false memories using study list repetition as a tool for modulating learning at encoding. METHODS: Thirty-two participants were given either an alcohol (0.6 g/kg) or placebo beverage before undergoing an encoding phase consisting of 10 lists of nine associated words (veridical items). Each list was associated to a word, which was not presented at encoding (semantically associated non-studied lure; critical item), serving as the measure for false memory. Half of the lists were presented once, and half were repeated three times. The next day, participants underwent an implicit (stem completion and post hoc awareness measurements), and an explicit (free recall) task. RESULTS: Alcohol decreased veridical and false explicit memory for singularly presented lists compared to placebo; no group difference existed for repeated lists. Implicit veridical memory was not affected by alcohol. Awareness memory measures demonstrated in placebo participants an increased ability with repetition in rejecting false memories. The reverse was found in intoxicated participants who with repetition accepted more false memories. CONCLUSION: Alcohol appears to decrease semantic activation leading to a decline in false memories. Increased learning with repetition, which increases the rejection of false memories under placebo, is reversed under alcohol leading to a decrease in rejection of false memories. The latter effect of alcohol may be due to its ability to impair monitoring processes established at encoding.

Gender specific effects of a mild stressor on alcohol cue reactivity in heavy social drinkers.

RATIONALE: Stress plays an important role in the development and maintenance of alcohol-abuse. Some of the effects of stress on alcohol-related behaviours, however, appear to be gender-dependent. AIM: The present study set out to examine the effects of stress on feelings of desire for alcohol, skin conductance response and alcohol consumption in the presence of alcohol-related cues in relation to gender. Participants were heavy non-dependent alcohol drinkers. METHODS: Thirty-two (16 males) participants drinking more than 21 units of alcohol per week were randomly allocated to undergo the experimental stress (based on the 'Trier Social Stress' Test) or the non-stress procedure before the alcohol cue exposure procedure, during which participants handled and smelled their preferred drink. Mood and saliva cortisol level changes were used as indices of the stress effects, while alcohol craving, skin conductance and alcohol consumption were the cue reactivity measures. RESULTS: Self ratings of anxiety and tension increased and cortisol levels remained high in the stress compared to the non-stress condition; no gender differences were found. Stress induced gender-specific effects with regard to skin conductance response and alcohol consumption measurements. Stressed females did not show an increase from baseline in the skin conductance response during the alcohol cue-exposure session, which was observed in the non-stressed females; they also consumed less alcohol than males under stress. CONCLUSION: Female participants respond less to alcohol-related cues when in a negative mood state. Such a finding suggests that females when in a negative mood may be less sensitive to positive incentive processes mediating cue reactivity compared to males.

The acute effect of alcohol on decision making in social drinkers.

RATIONALE: Many studies have reported the long-term adverse effects of alcohol on executive cognitive function in chronic alcohol abusers, yet little research has investigated the acute effects of alcohol in social drinkers. Studies on acute effects report alcohol-induced deficits on tasks that require executive cognitive processes, with alcohol acting to increase preservative errors and reduce planning. AIM: The present investigation examines the acute effects of a moderate dose of alcohol on a decision-making task that involves participants making a forced choice between two simultaneously presented binary-outcome gambles. METHODS: Alcohol (0.6 g/kg) or placebo was administered to 32 social drinkers. Participants completed the task, making a total of 80 decisions about gambles that varied in the magnitude of expected gains, losses and the probability with which these outcomes were delivered. Participants also chose between gambles probing identified non-normative biases in human decision making, namely, risk aversion for choosing between gains and risk seeking for choosing between losses. RESULTS: All participants picked the experimental gamble more frequently when the probability of winning was high vs low, when the gains were large vs small and when the losses were small vs large; the alcohol group had an impaired ability to factor in the magnitude of gains and the likelihood of winning when the losses were large. Deliberation time did not differ between the groups. CONCLUSION: These data suggest that alcohol given acutely impairs risky decision making. In particular, alcohol impairs one's ability to alter responding in light of changing prospective rewards in order to make favourable decisions.

Does alcohol affect memory for emotional and non-emotional experiences in different ways?

Alcohol has been shown to have both impairing and facilitating effects on memory, depending on the sequencing of learning and ingestion of the drug. Its effects on memory for emotional material, however, have not been shown reliably. The current experiment sought to investigate the effects of alcohol on later recall of emotional and neutral events experienced before and after alcohol drinking. Using an incidental-learning paradigm, alcohol (0.65 g/kg) or placebo was administered in a double-blind randomized design to 34 participants, between two learning phases in which they viewed and rated positive, negative and neutral images. The drug's effects on memory were assessed in a surprise test of free recall. In addition, impact of alcohol on ratings of mood states, and of valence and arousal that the pictures evoked, was examined. Alcohol facilitated memory for material seen before, and impaired memory for material seen after, its administration. Furthermore, under alcohol, emotional images in the first set were more recalled over neutral than in the second set, indicating a higher retrograde facilitation for emotional than for neutral material. Alcohol improved positive mood states but had no effect on negative mood states. Evaluation of pictures with regard to valence showed an increase of the ratings for the positive and neutral images after alcohol and a decrease after placebo. No drug effects were found for arousal ratings. Whether a picture was likely to be remembered or not (tested only for set 2) was dependent on the intensity of the arousal but not of the valence that the picture evoked in the participants. Pictures that were rated high in arousal were also remembered better, and this effect was irrespective of alcohol or placebo ingestion. These data have shown that alcohol elicits retrograde facilitation and anterograde impairment for emotional materials. Furthermore, these data demonstrate that alcohol selectively facilitates memories for emotional events experienced before administration, and suggest a possible explanation for the reinforcing effects of drinking.