Brain response in heavy drinkers during cross-commodity alcohol and money discounting with potentially real rewards: A preliminary study

Background

Alcohol use disorder (AUD) is associated with exaggerated preference for immediate rewards, a candidate endophenotype for use disorders. Addiction symptomology is often well-described by the preference for immediate intoxication over other delayed prosocial rewards. We measured brain activation in AUD-implicated regions during a cross-commodity delay discounting (CCD) task with choices for immediate alcohol and delayed money.

Methods

Heavy drinkers (n=24) experienced a brief intravenous alcohol infusion prime, regained sobriety, then chose between 'One Shot' and delayed money in an adjusting delay CCD task (sober and intoxicated); also during fMRI (sober). Participants also performed a behavioral sensation seeking task and completed self-report inventories of other risk factors. We assessed brain activation to choices representing immediate intoxication versus delayed money rewards in a priori regions of interest defined within the framework of Addictions NeuroImaging Assessment.

Results

Activation to CCD choice versus control trials activated paralimbic and ventral frontal cortical regions, including orbital and medial prefrontal cortex, posterior cingulate/retrosplenial cortex, angular and superior frontal gyri. We detected no differences between immediate or delayed choices. Left medial orbitofrontal cortex activation correlated with alcohol-induced wanting for alcohol; females showed greater activation than males. Behavioral sensation seeking correlated with right nucleus accumbens task engagement.

Conclusions

Alcohol decision-making elicited activation in regions governing reward, introspection, and executive decision-making in heavy drinkers, demonstrating the utility of laboratory tasks designed to better model real-world choice. Our findings suggest that the brain processes subserving immediate and delayed choices are mostly overlapping, even with varied commodities.

Task parameters influence operant response variability in mice

RATIONALE

During operant conditioning, animals associate actions with outcomes. However, patterns and rates of operant responding change over learning, which makes it difficult to distinguish changes in learning from general changes in performance or movement. Thus, understanding how task parameters influence movement execution is essential.

OBJECTIVES

To understand how specific operant task parameters influenced the repetition of future operant responses, we investigated the ability of operant conditioning schedules and contingencies to promote reproducible bouts of five lever presses in mice.

METHODS

Mice were trained on one of the four operant tasks to test three distinct hypotheses: (1) whether a cue presented concurrently with sucrose delivery influenced the pattern of lever pressing; (2) whether requiring animals to collect earned sucrose promoted the organization of responses into bouts; and (3) whether only reinforcing bouts where interresponse time (IRT) variances were below a target promoted reproducible patterns of operant behavior.

RESULTS

(1) Signaling reinforcer delivery with a cue increased learning rates but resulted in mice pressing the lever in fast succession until the cue turned on, rather than executing discrete bouts. (2) Requiring mice to collect the reinforcer between bouts had little effect on behavior. (3) A training strategy that directly reinforced bouts with low variance IRTs was not more effective than a traditional fixed ratio schedule at promoting reproducible action execution.

CONCLUSIONS

Together, our findings provide insights into the parameters of behavioral training that promote reproducible actions and that should be carefully selected when designing operant conditioning experiments.

Choosing a future from a murky past: A generalization-based model of behavior

Remembering the past appears critical in allowing organisms to detect order in an environment, and hence to behave in accordance with likely future events. Yet the shortcomings of remembering and perceiving typically mean that the remembered past differs from the actual past, and hence that behavior does not perfectly track the structure of the environment. Here, we outline how the process of generalization might be used to understand differences between what an organism does, and the structure of the past and potential structure of the environment. We explore how different sources of generalization - both from within the same stimulus situation, and from different stimulus situations - might be modeled quantitatively, and how predictions made by this modeling approach are supported by research. Finally, we discuss how generalization from multiple stimulus situations, longer-term experience, and from stimulus situations in the past that are not identical to the stimulus situation in the present, might contribute to our understanding of how an organism's experience translates into behavior.

The reinforcing value of food and non-food alternative: Associations with BMI z-score and percent fat mass

There is growing evidence of an association between the relative reinforcing value of food (RRVF; how hard a child is willing to work for a food versus a non-food reinforcer) and weight across many life stages, but few studies have examined this association among preschool age children. This study investigated the association between the RRVF (measured as the food reinforcing ratio (FRR)) and body mass index (BMI) z-score and percent fat mass (%FM), in 3 year-old children. The sample was comprised of 33 children who were 3 years of age (36-47 months). Children selected their favourite food reinforcer (cookie) and non-food (audiobook) reinforcer to be used in the FRR task, which was delivered using a sequential progressive fixed ratio reward schedule. Child height, weight and percent body fat using bioelectrical impedance analysis were assessed by trained research staff. Linear regression analyses showed that FRR was significantly and positively associated with BMI z-scores. FRR was not significantly associated with %FM. Findings from this study support the RRVF as a potential risk factor in the development of childhood obesity. Longitudinal research involving larger sample sizes would strengthen future research exploring associations between RRVF and body composition in preschool age children.

Optimisation of cognitive performance in rodent operant (touchscreen) testing: Evaluation and effects of reinforcer strength

Operant testing is a widely used and highly effective method of studying cognition in rodents. Performance on such tasks is sensitive to reinforcer strength. It is therefore advantageous to select effective reinforcers to minimize training times and maximize experimental throughput. To quantitatively investigate the control of behavior by different reinforcers, performance of mice was tested with either strawberry milkshake or a known powerful reinforcer, super saccharin (1.5% or 2% (w/v) saccharin/1.5% (w/v) glucose/water mixture). Mice were tested on fixed (FR)- and progressive-ratio (PR) schedules in the touchscreen-operant testing system. Under an FR schedule, both the rate of responding and number of trials completed were higher in animals responding for strawberry milkshake versus super saccharin. Under a PR schedule, mice were willing to emit similar numbers of responses for strawberry milkshake and super saccharin; however, analysis of the rate of responding revealed a significantly higher rate of responding by animals reinforced with milkshake versus super saccharin. To determine the impact of reinforcer strength on cognitive performance, strawberry milkshake and super saccharin-reinforced animals were compared on a touchscreen visual discrimination task. Animals reinforced by strawberry milkshake were significantly faster to acquire the discrimination than animals reinforced by super saccharin. Taken together, these results suggest that strawberry milkshake is superior to super saccharin for operant behavioral testing and further confirms that the application of response rate analysis to multiple ratio tasks is a highly sensitive method for the detection of behavioral differences relevant to learning and motivation.

Optimizing reproducibility of operant testing through reinforcer standardization: identification of key nutritional constituents determining reward strength in touchscreens

Reliable and reproducible assessment of animal learning and behavior is a central aim of basic and translational neuroscience research. Recent developments in automated operant chamber technology have led to the possibility of universal standard protocols, in addition to increased translational potential, reliability and accuracy. However, the impact of regional and national differences in the supplies of available reinforcers in this system on behavioural performance and inter-laboratory variability is an unknown and at present uncontrolled variable. Therefore, we aimed to identify which constituent(s) of the reward determines reinforcer strength to enable improved standardization of this parameter across laboratories. Male C57BL/6 mice were examined in the touchscreen-based fixed ratio (FR) and progressive ratio (PR) schedules, reinforced with different kinds of milk-based reinforcers to directly compare the incentive values of plain milk (PM, high-calorie: high-fat/low-sugar), strawberry-flavored milk (SM, high-calorie: low-fat/high-sugar), and semi-skimmed low-fat milk (LM, low-calorie: low-fat/low-sugar) on the basis of differences in caloric content, sugar/fat content, and flavor. Use of a higher caloric content reward was effective in increasing operant training acquisition rate. Total trial number completed in FR and breakpoint in PR were higher using the two isocaloric milk products (PM and SM) than the lower caloric LM, with comparable outcomes between PM and SM conditions, suggesting that total caloric content determines reward strength. Analysis of within-session changes in response rate revealed that overall outputs in FR and PR primarily depend on the response rate at the initial phase of a session, which itself was dependent on reinforcer caloric content. Interestingly, the rate of satiation, indicated by decay in response rate within a FR session, was highest when reinforced with SM, suggesting a rapid satiating effect of sugar. The key contribution of reward caloric content to operant performance was confirmed in a multi-laboratory study using the touchscreen 5-choice serial reaction time task (5-CSRTT) reinforced by two isocaloric milk-based liquid rewards with different countries of origin, which yielded consistent performance parameters across sites. Our results indicate that milk-based liquid reinforcer standardization can be facilitated by matching caloric content across laboratories despite regional or national differences in other non-caloric aspects of the reinforcers.

Using Computer Tablets to Assess Preference for Videos in Children with Autism

Using computer tablets, we assessed preference for videos in five children with autism spectrum disorder (ASD). Then, we provided access to most preferred and less preferred videos contingent on sitting on one of two chairs within a concurrent schedule design. All participants spent consistently more time sitting on the chair associated with the video selected the most often during the preference assessment, indicating that practitioners may use the tablet-based assessment procedure to identify potential video reinforcers for children with ASD in applied settings.

A preclinical evaluation of the discriminative and reinforcing properties of lisdexamfetamine in comparison to D-amfetamine, methylphenidate and modafinil

Lisdexamfetamine dimesylate, which consists of L-lysine covalently bound to D-amfetamine, is the first prodrug for treating ADHD. Its metabolic conversion to yield D-amfetamine by rate-limited, enzymatic hydrolysis is unusual because it is performed by peptidases associated with red blood cells. Other stimulants shown to be effective in managing ADHD include D-amfetamine, methylphenidate and modafinil. All have the potential for misuse or recreational abuse. The discriminative and reinforcing effects of these compounds were determined in rats using a 2-choice, D-amfetamine (0.5 mg/kg, i.p.)-cued drug-discrimination test, and by substitution for intravenous cocaine in self-administration. Lisdexamfetamine (0.5-1.5 mg/kg [D-amfetamine base], p.o.) generalised to saline when tested 15 min post-dosing, but dose-dependently generalised to d-amfetamine at 60 min. At 120 min, its D-amfetamine-like effects were substantially diminished. At 15 min, methylphenidate (3.0-10 mg/kg, p.o.) and D-amfetamine (0.1-1.5 mg/kg, p.o.) dose-dependently generalised to the intraperitoneal D-amfetamine cue. Switching to the intraperitoneal route reduced the interval required for lisdexamfetamine to be recognised as D-amfetamine-like, but did not alter its potency. Switching to intraperitoneal injection increased the potency of methylphenidate and D-amfetamine by 3.4× and 2.2×, respectively. Modafinil (50-200 mg/kg, i.p.) generalised partially, but not fully, to d-amfetamine. Methylphenidate (0.1, 0.3, 1.0 mg/kg/injection, i.v.) maintained robust self-administration at the 2 highest doses. Neither lisdexamfetamine (0.05, 0.15 or 0.5 mg/kg/injection [D-amfetamine base], i.v.) nor modafinil (0.166, 0.498 or 1.66 mg/kg/injection, i.v.) served as reinforcers. The results reveal important differences between the profiles of these stimulants. Lisdexamfetamine did not serve as a positive reinforcer in cocaine-trained rats, and although it generalised fully to D-amfetamine, its discriminative effects were markedly influenced by its unusual pharmacokinetics.