Conditioned tolerance to the effects of alcohol on inhibitory control in humans

Understanding How Acute Alcohol Impacts Neural Encoding in the Rodent Brain

Alcohol impacts neural circuitry throughout the brain and has wide-ranging effects on the biophysical properties of neurons in these circuits. Articulating how these wide-ranging effects might eventually result in altered computational properties has the potential to provide a tractable working model of how alcohol alters neural encoding. This chapter reviews what is currently known about how acute alcohol influences neural activity in cortical, hippocampal, and dopaminergic circuits as these have been the primary focus of understanding how alcohol alters neural computation. While other neural systems have been the focus of exhaustive work on this topic, these brain regions are the ones where in vivo neural recordings are available, thus optimally suited to make the link between changes in neural activity and behavior. Rodent models have been key in developing an understanding of how alcohol impacts the function of these circuits, and this chapter therefore focuses on work from mice and rats. While progress has been made, it is critical to understand the challenges and caveats associated with experimental procedures, especially when performed in vivo, which are designed to answer this question and if/how to translate these data to humans. The hypothesis is discussed that alcohol impairs the ability of neural circuits to acquire states of neural activity that are transiently elevated and characterized by increased complexity. It is hypothesized that these changes are distinct from the traditional view of alcohol being a depressant of neural activity in the forebrain.

Meta-analysis of acute alcohol effects on response inhibition

Alcohol intoxication impairs response inhibition; however, discrepant findings have been reported regarding the magnitude and moderators of this effect. This meta-analysis of human laboratory studies aimed to quantify acute effects of alcohol on response inhibition and evaluate moderators of this effect. Eligible studies examined alcohol's effects on response inhibition with the Go/No-Go (GNG) task (n = 1616 participants) or Stop Signal Task (SST) (n = 1310 participants). Results revealed a detrimental effect of acute alcohol on response inhibition overall (g = 0.411, 95 % CI [0.350, 0.471]), with similar effects in studies using GNG (g = 0.431, SE = 0.031) and SST (g = 0.366, SE = 0.063). Effect sizes were larger in studies involving higher breath alcohol concentration levels and under GNG conditions that established a prepotent response set. These findings establish the magnitude, precision, and potential moderators of alcohol's effects on inhibitory control, furthering understanding of a key neurobehavioral mechanism proposed to underlie alcohol-related impulsivity and impaired control over consumption.

The Naturalistic Cannabis Administration Protocol (NCAP): A Proof-of-Concept Study

Lab-based studies examining the effects of cannabis administration on human behavior compromise ecological validity due to the influence of set and setting. Contextual factors of clinical settings have long been recognized as producing measurable changes in physiology, emotionality, and cognition. Among people who use drugs, these settings may be associated with higher levels of perceived stigma and stereotype threat which may meaningfully confound the effects of cannabis on outcomes of interest. Recent liberalization of cannabis regulation may allow novel and more ecologically valid approaches to assessing the acute effects of cannabis. The Naturalistic Cannabis Administration Protocol (NCAP) is a novel paradigm for the study of acute cannabis effects in an ecologically valid manner. Two independent studies demonstrated the safety and feasibility of the NCAP. Participants (N= 79; Mage = 25.44, SD = 5.67) self-administered the cannabis of their choice in their home and then (Study 1; n= 47) engaged in a leisure activity or (Study 2; n= 32) underwent cognitive assessment remotely via videoconference following cannabis administration. The NCAP was well tolerated across samples with no reported adverse events. These findings provide a rationale for the adoption of the NCAP to reduce research barriers and develop our research capabilities to fit the landscape of cannabis use today.

Alcohol use during pregnancy and motherhood: Attitudes and experiences of pregnant women, mothers, and healthcare professionals

Alcohol is the most used substance by women of childbearing age. Alcohol exposed pregnancies can have serious consequences to the fetus, and the UK has one of the highest rates of drinking during pregnancy. Alcohol use during motherhood is also a public health concern, linked with potential harms to the woman and child. This qualitative study investigated the attitudes and experiences of pregnant/parenting women and healthcare professionals regarding maternal drinking. A semi-structured focus group and interviews were conducted in the North West of England with pregnant women, mothers, and healthcare professionals. Quantitative measures captured demographics, alcohol use, and screened for mental ill-health for pregnant women and mothers. Reflexive thematic analysis was used to analyse narratives. Findings revealed that most participants believed avoiding alcohol during pregnancy is the safest option. However, some pregnant women and mothers stated that there was insufficient evidence to demonstrate the harms of low-level drinking and that abstinence guidelines were patronising. All participants reported that low-level drinking during motherhood was acceptable. Heavy drinking was believed to pose serious harm during pregnancy and motherhood to the baby and mother, in addition to damaging relationships. Strong motives were revealed for choosing and avoiding to drink, such as coping with the difficulties of motherhood and parental responsibilities, respectively. Contradictions were found across quantitative and qualitative self-reports of consumption, reflecting potential underreporting of alcohol use. Additionally, drinking levels were discussed in extremes only (low/heavy) without considering 'grey area' drinking. Clear, consistent advice and guidelines are needed to support women in reducing their alcohol use during pregnancy and motherhood. These should include the unique potential risks regarding maternal drinking, and the harm attributable to non-clinically dependent alcohol use. The maternal participants in this study were middle-class, therefore, research is needed to capture the views and experiences of women of all socioeconomic backgrounds.

Context-Specific Tolerance and Pharmacological Changes in the Infralimbic Cortex-Nucleus Accumbens Shell Pathway Evoked by Ketamine

Like other drugs, ketamine is abused due to its ability to act as a positive reinforcer in the control of behavior, just as natural reinforcers do. Besides, through Pavlovian conditioning, tolerance to drug effects can become conditioned to specific contextual cues showing that environmental stimuli can act as powerful mediators of craving and relapse. In the present study, we shall investigate the effects of long-term ketamine administration and withdrawal on behavioral measures and emotionality, the drug-context-specific influence on the tolerance to the sedative effects of an anesthetic dose of ketamine, and the neuropharmacological events underlying this phenomenon, in rats conditioned with 10 mg/kg of ketamine and later challenged with a dose of ketamine of 80 mg/kg in a familiar and non-familiar environment. Variations in dopamine and serotonin efflux in the infralimbic cortex-nucleus accumbens shell circuitry (IL-NAcSh) was further recorded in the same conditions. Our results highlight that besides its well-known reinforcing properties, ketamine also shares the ability to induce behavioral and pharmacological conditioned tolerance, associated with increases in cortical (IL), and decreases in striatal (NAcSh) dopamine release. To our knowledge, we are presenting the first set of behavioral and neurochemical data showing that, like other drugs of abuse, ketamine can induce learned context-specific tolerance.

Learnt effects of environmental cues on transport-related walking; disrupting habits with health promotion?

Background

In Ecological models, physical environments can be important determinants of transport-related walking. With repeated exposure to the same environment, learning of a linkage between the cues in the environment and walking should occur. Subsequent encounters with the cues can prompt the behaviour relatively automatically. No studies have experimentally tested the potential learning of this linkage between cues and behaviour. Choices between stairs and escalators in public access settings were employed to test this premise for transport-related walking.

Methods

Three studies investigated the effects of visual cues on stair/escalator choices (combined n = 115,062). In quasi-experimental, interrupted time-series designs, observers audited choices in public access settings. Design alone phases with art or coloured backgrounds were compared with design plus message phases in which verbal health promotion messages were superimposed on the visual cues. Analyses used bootstrapped logistic regression.

Results

In initial studies, the design alone phases had no effect whereas subsequent design plus message phases reduced escalator choice. In two further studies, a 5–6 week design plus message phase that reduced escalator choice preceded a design alone phase. The visual background behind the successful health promotion message was reintroduced four weeks after the intervention was removed. The visual cue of design alone reduced escalator choice after it had been paired with the verbal health promotion message. There were no differences between art and coloured backgrounds.

Conclusion

These studies demonstrate for the first time a learnt linkage between transport-related walking and environmental cues. Discussion focuses on the mechanisms that may underlie this learning and cues in the environment that are relevant to transport-related walking.

Cognitive impairment following consumption of alcohol with and without energy drinks

BACKGROUND

The aim of this study was to assess the relative effects of alcohol mixed with energy drink (AmED) versus alcohol alone on cognitive performance across the ascending and descending breath alcohol concentration (BrAC) limb using doses similar to real-world intake.

METHODS

Using a single-blind, placebo-controlled, crossover design, 19 participants completed 4 sessions where they received: (i) placebo, (ii) alcohol, (iii) AmED 500 ml energy drink (ED), and (iii) AmED 750 ml ED. Performance on measures of psychomotor function (Compensatory Tracking Task [CTT]), information processing (Digit Symbol Substitution Task [DSST]; Inspection Time Task [ITT]), and response inhibition (Brief Stop-Signal Task [Brief SST]) was assessed at ~0.05% ascending BrAC, ~0.08% peak BrAC, and ~0.05% descending BrAC.

RESULTS

The ITT and Brief SST showed no differential effect of AmED versus alcohol (gs < 0.30 and gs < 0.36, respectively). Moderate magnitude improvements in alcohol-induced impairment of CTT and DSST performance were observed after AmED versus alcohol on the descending BrAC limb (gs > 0.45 and gs > 0.37, respectively). A moderate magnitude decrease in DSST errors was also observed after AmED relative to alcohol at 0.050% ascending target BrAC (gs > 0.43).

CONCLUSIONS

Changes in cognitive function after AmED administration were dependent on the degree of intoxication, BrAC curve limb, and ED volume. Co-administration of ED doses which matched (500 ml) and exceeded (500 ml) maximum daily intake guidelines with alcohol decreased impairment of psychomotor function and global information processing after alcohol consumption. These results cannot be necessarily interpreted to suggest that people are less impaired after AmED, as behavior is the result of coordination of multiple cognitive functions, and reduced impairment on one aspect of cognition may not translate into global improvements.

Detecting impairment: sensitive cognitive measures of dose-related acute alcohol intoxication

The cognitive impairment that results from acute alcohol intoxication is associated with considerable safety risks. Other psychoactive substances, such as medications, pose a similar risk to road and workplace safety. However, there is currently no legal limit for operating vehicles or working while experiencing drug-related impairment. The current study sought to identify a brief cognitive task sensitive to a meaningful degree of impairment from acute alcohol intoxication to potentially stand as a reference from which to quantify impairment from other similar substances. A placebo-controlled single-blind crossover design was employed to determine the relative sensitivity of four commonly-administered cognitive tasks (Compensatory Tracking Task, Digit Symbol Substitution Test, Brief Stop Signal Task and Inspection Time Task) to alcohol-related impairment in male social drinkers at ~0.05% ascending breath alcohol concentration (BrAC), ~0.08% peak BrAC and 0.05% descending BrAC. The Inspection Time Task was identified as the most sensitive task, detecting a medium to large magnitude increase in impairment (g ≈ 0.60) at 0.05% ascending and descending BrAC, and a large magnitude effect size (g = 0.80) at 0.08% peak BrAC. The remaining tasks failed to demonstrate sensitivity to dose-dependent and limb-dependent changes in alcohol-induced impairment. The Inspection Time Task was deemed the most sensitive task for screening alcohol-related impairment based on the present results. Confirmation of equivalence with other drug-related impairment and sensitivity to alcohol-induced impairment in real-world settings should be established in future research.

Alcohol disrupts the effects of priming on the perception of ambiguous figures

Inhibitory mechanisms are thought to underpin the well-documented impairing effects of alcohol on attention. Here, we use a novel priming paradigm to investigate the effects of alcohol on inhibitory mechanisms in attention. Participants were assigned to an alcohol (N=15), or placebo (N=15) group. The dose of alcohol was 0.8 g/kg for males and 0.75 g/kg for females. Participants were asked to report figure reversals during presentation of the face-vase ambiguous figure. Prior to this, they were shown a prime that was either semantically relevant to the face-vase stimulus or was neutral. Semantic priming decreased the number of figure reversals in the first half of the test session in the placebo group but not in the alcohol group. The placebo group was also more likely than the alcohol group to report the first interpretation of the figure to be the same as the semantic prime. Prior presentation of a semantic prime had a stabilising effect on reversal rate, suggesting that the primed interpretation inhibited the alternate interpretation. The absence of an effect in the alcohol group is consistent with an alcohol-related impairment of this inhibition.

Effects of alcohol on attentional mechanisms involved in figure reversals

OBJECTIVE

The impairing effects of alcohol on attention are well documented and are thought to involve inhibitory mechanisms. We used ambiguous figures (Face-Vase and Necker cube) to test whether the intentional control mechanism is more vulnerable to the effects of alcohol than the automatic mechanism.

METHOD

Participants were assigned to an alcohol (Study 1, N = 15; Study 2, N = 18), placebo (Study 1, N = 15; Study 2, N = 20) or control (Study 1 only, N = 10) group. The doses of alcohol were 0.8 g/kg for men and 0.75 g/kg for women. Participants were shown the Face-Vase and Necker cube figures and two variants of each, which were biased in varying degrees towards one interpretation. Study 1 assessed the automatic control mechanism by asking participants to report spontaneous reversals. Study 2 assessed the intentional control mechanism by asking participants to increase reversal rate.

RESULTS

In Study 1, reversal rate was similar for all groups, whereas in Study 2, the alcohol group reported more reversals than the control group, although this was true only for the biased versions of the Face-Vase illusion.

CONCLUSIONS

The effect of alcohol on reversal rate is observed only during intentional reversals of semantically meaningful stimuli and only when the stimulus is biased.