Reinforcer Magnitude Research Articles

Using a brief experimental analysis for writing speed intervention identification

AbstractThe Brief Experimental Analysis (BEA) is an effective method for identifying interventions to improve academic skills but rarely been applied to individuals with writing deficits and individuals with intellectual disabilities. This study extends the BEA literature by identifying effective writing interventions to increase writing speed for a 16‐year‐old female with an intellectual disability. A BEA was used to evaluate four interventions (i.e., tracing, oral instruction, fixed ratio reinforcement, and response dependent reinforcer magnitude) for writing speed. Results identified fixed ratio reinforcement and response dependent reinforcer magnitude as most effective in increasing writing speed; results maintained over an extended treatment evaluation.

Characterization and utilization of cacao shell powder as a biofiller in natural rubber composite

The cacao shell, a by-product of the chocolate industry, is considered a waste and is normally discarded. This work aims to study the feasibility of using cacao shell powder (CSP) as a biofiller in rubber applications. The CSP was initially prepared, characterized, and incorporated into natural rubber (NR) at different loadings. Its reinforcement was compared with calcium carbonate (CaCO3) and carbon black (CB). The results showed that CSP had a relatively large average particle size (∼152 μm) and, thus, a very small specific surface area (4.5 m2/g). It mostly consisted of organic substances like cellulose, hemicellulose, lignin, proteins, etc. When incorporated into NR, both scorch time and optimal cure time decreased due to the existence of nitrogen-containing compounds, whereas hardness and modulus increased gradually with increasing CSP loading due to the dilution effect. At a given loading, CSP showed shorter scorch and cure times with greater hardness and modulus than CaCO3, indicating its greater cure activation ability and higher reinforcement magnitude. However, its reinforcement was far lower than that of carbon black. The maximum tensile strength was found at 30 phr of CSP loading, with a value of approximately 19.2 MPa, which was about 3% higher than that of CaCO3 but approximately 19% lower than CB. The findings suggest that, like other inert fillers, CSP can be employed for cost-reduction purposes in many applications where exceptionally high strengths are not essential, such as rubber bands, rubber flooring, rubber mats for livestock, etc.

Autoshaped impulsivity: Some explorations with a neural network model

This study evaluated the effect of delay and magnitude of reinforcement in Pavlovian contingencies, extending the understanding of the phenomenon of autoshaped impulsivity as described in Alcalá's thesis (2017) and Burgos and García-Leal (2015). The effects of adding a trace interval were analyzed on the maintained responses of impulsive choice, seen as the preference of a small and immediate reinforcer over a larger and delayed one, and the role of the contextual unit, as well as the inhibitory units according to the Diffuse Discrepancy Model. In the Simulation, the model with inhibitory units was used, trained in two signals with different delays and reinforcement magnitudes, and subsequently presented concurrently in choice tasks without reinforcement nor learning, using an ABA within-subject design. In general, the DD model successfully simulated the phenomenon of autoshaped impulsivity, consistent with studies from Alcalá's thesis (2017), Burgos and García-Leal (2015), and Picker and Poling (1982). It also predicted the elimination of this effect (autoshaped impulsivity) after introducing a trace interval. The observed results and their implications are discussed, as well as possible future studies with animals and humans.

Methamphetamine increases risky choice in rats, but only when magnitude and probability of reinforcement are manipulated within a session

Risky choice is associated with maladaptive behaviors, particularly substance use disorders. Current animal models of risky choice are often confounded by other constructs like behavioral flexibility and suboptimal choice. The purpose of the current experiment was to determine if the psychostimulant methamphetamine, a drug whose popularity has increased in recent years, increases risky choice in an equivalent expected value (EEV) task. In the EEV task, rats are given a choice between two reinforcer alternatives that differ in magnitude and probability of delivery, but have equivalent expected value. Forty-eight Sprague Dawley rats were tested in three versions of the EEV task. In the first version of the EEV task, both reinforcer magnitude and probability were adjusted across blocks of trials for both alternatives. In the second and the third versions of the EEV task, reinforcer magnitude was held constant across each block of trials (either 1 vs. 2 pellets or 4 vs. 5 pellets). We found that male rats preferred the “riskier” option, except when reinforcer magnitudes were held constant at 4 and 5 pellets across each block of trials. Methamphetamine (0.5 mg/kg) increased preference for the risky option in both males and females, but only when both reinforcer magnitude and probability were manipulated across blocks of trials for each alternative. The current results demonstrate that both magnitude of reinforcement and probability of reinforcement interact to influence risky choice. Overall, this study provides additional support for using reinforcers with expected value to measure risky choice.

Resurgence Following Higher or Lower Quality Alternative Reinforcement.

Resurgence is a temporary increase in a previously suppressed target behavior following a worsening in reinforcement conditions. Previous studies have examined how higher rates or magnitudes of alternative reinforcement affect suppression of the target behavior and subsequent resurgence. However, there has been no investigation of the effects of higher versus lower qualities of alternative reinforcement on resurgence. Using a three-phase resurgence preparation with rats, the present experiments examined the effects of an alternative reinforcer that was of higher (Experiment 1) or lower (Experiment 2) quality than the reinforcer that had previously maintained the target behavior. The results of both experiments showed greater reductions in target behavior with a higher quality alternative reinforcer and larger increases in target responding when a higher quality alternative reinforcer was removed. Along with prior findings with higher rates and magnitudes of alternative reinforcement, these findings suggest that variations in reinforcer dimensions that increase the efficacy of alternative reinforcement also tend to increase resurgence when alternative reinforcement is removed. The results are discussed in terms of the resurgence as choice in context model and in terms of potential clinical implications.

Psychic trauma causes increased impulsivity in a model of gambling addiction by altering dopamine and serotonin metabolism in the prefrontal cortex

BACKGROUND: Gambling addiction (gambling) involves frequently repeated episodes of gambling that are detrimental to social, professional, material, and family values. Gambling addiction is often combined with posttraumatic stress disorder.
 AIM: This study aimed to examine the effect of predator presentation stress on the manifestations of gambling addiction in an animal model in a test of probability and magnitude of reinforcement in the Iowa gambling task and monoamine metabolism in the prefrontal cortex of rats.
 MATERIALS AND METHODS: Rats were trained in a test of probability and magnitude of reinforcement in the Iowa gambling task in a 3-beam maze. Each run in arm 1 of the maze was reinforced with one sunflower seed, each second run in arm 2 with two seeds, and each third run in arm 3 with three seeds. Correspondingly, half of the runs in arm 2 and 2/3 of the runs in arm 3 were left unreinforced. After training, the animals were placed in a terrarium with a tiger python, one of which was victimized for its food requirements. On day 14 after predator presentation, dopamine and serotonin metabolism in the prefrontal cortex was determined using high-performance liquid chromatography with electrochemical detection.
 RESULTS: The levels of the dopamine metabolite dioxyphenylacetic acid and the ratio of dioxyphenylacetic acid to dopamine in the prefrontal cortex decreased. The levels of serotonin, its metabolite 5-hydroxyindoleacetic acid, and the ratio of 5-hydroxyindoleacetic acid to serotonin in the prefrontal cortex were also decreased in rats after exposure to a predator. Moreover, predator presentation induced significant behavioral changes in rats, increasing impulsivity in making choices in a test of probability and magnitude of reinforcement in the Iowa gambling task. The acute vital stress of predator presentation increased the number of escapes to arm 3 of the maze, suggesting that the animals exhibited more risky behavior when choosing reinforcements of different strengths and probability.
 CONCLUSIONS: The animal model showed that the depletion of the dopaminergic and serotoninergic systems of the prefrontal cortex underlies pathological gambling addiction and inadequate decision-making caused by posttraumatic stress disorder.

Effect of new coumarin derivatives on the impulsive and compulsive components of gambling addiction in rats

BACKGROUND: The search for new neuroactive compounds that selectively affect the mechanisms of emotional reinforcement in gambling addiction is of interest. No previous studies have examined the effects of coumarins on gambling addiction.
 AIM: This study aimed to investigate the effect of new coumarin derivatives on the impulsive and compulsive components of gambling addiction in rats.
 MATERIALS AND METHODS: The effects of drugs on elements of gambling addiction were assessed in rats in the “marble burying” test and “probability and magnitude of reinforcement” in the three-arm maze, a version of the Iowa test. The effects of the following six coumarin derivatives were assessed: LVM-091, LVM-092, LVM-096, LVM-099, LVM-S144, and IEM-2886.
 RESULTS: In the “burrowing balls” test, substances synthesized based on coumarins LVM-092, LVM-099, LVM-S144, and IEM-2886 reduced the level of compulsivity, reducing the number of buried balls compared with the control and diazepam groups (p ≤ 0.05). In the “probability and magnitude of reinforcement” test, after the administration of drugs LVM-091, LVM-099, LVM-S144, and IEM-2886, the level of impulsivity and risk behavior decreased, reducing the number of animals entering the sleeve with the greatest reinforcement and its low probability.
 CONCLUSIONS: New coumarin derivatives cause an anticompulsive effect and reduce the impulsivity level in rats, which in the future can be used for treating obsessive–compulsive disorders and addictive conditions, such as Internet addiction and gaming addiction.

Behavioral mechanisms of oxycodone's effects in female and male rats: Reinforcement delay and impulsive choice.

μ-Opioid agonists (e.g., morphine) typically increase impulsive choice, which has been interpreted as an opioid-induced increase in sensitivity to reinforcement delay. Relatively little research has been done with opioids other than morphine (e.g., oxycodone), or on sex differences in opioid effects, on impulsive choice. The present study investigated the effects of acute (0.1-1.0 mg/kg) and chronic (1.0 mg/kg twice/day) administration of oxycodone on choice controlled by reinforcement delay, a primary mechanism implicated in impulsive choice, in female and male rats. Rats responded under a concurrent-chains procedure designed to quantify the effects of reinforcement delay on choice within each session. For both sexes, choice was sensitive to delay under this procedure. Sensitivity to delay under baseline was slightly higher for males than females, suggesting more impulsive choice with males. When given acutely, intermediate and higher doses of oxycodone decreased sensitivity to delay; this effect was larger and more reliable in males than females. When given chronically, sex differences were also observed: tolerance developed to the sensitivity-decreasing effects in females, whereas sensitization developed in males. These data suggest that reinforcement delay may play an important role in sex differences in impulsive choice, as well as in the effects of acute and chronic administration of opioids in impulsive choice. However, drug-induced changes in impulsive choice could be related to at least two potential behavioral mechanisms: reinforcement delay and/or reinforcement magnitude. Effects of oxycodone on sensitivity to reinforcement magnitude remain to be fully characterized. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Effects of methamphetamine on probability discounting in rats using concurrent chains

How stimulant drugs affect risky choice and the role of reinforcement magnitude has been an important question for research on impulsivity. This study investigated rats’ responding on a rapid acquisition, concurrent chains, probability discounting task under methamphetamine administration. In each block of four sessions, probability of reinforcement delivery was unequal (0.5/1.0, 1.0/0.5) or equal, (1.0/1.0, 0.5/0.5) while amount of reinforcement was constant and unequal. This allowed for an estimate of probability discounting and the magnitude effect (where larger reinforcers are discounted at a greater rate) in each block. Baseline, acute and chronic methamphetamine administration, and re-establish baseline phases were completed. Rats showed sensitivity to probability and magnitude in baseline, as well as a magnitude effect whereby preference for the larger reinforcement was greater with 100% than 50% reinforcement probability. Acute methamphetamine dose-dependently reduced the probability effect. There were no effects of chronic administration and only probability discounting was maintained in the re-establish baseline phase. This was the first procedure to find a magnitude effect with rats in a probability discounting procedure and demonstrates that acute methamphetamine reduces both the probability and magnitude effects which increases propensity for risky choice.

Cue-induced reinstatement of seeking behavior in male rats is independent from the rewarding value of the primary reinforcer: Effect of mGluR5 blockade

Environmental conditioning factors have a profound impact on alcohol-seeking behavior and the maintenance of alcohol use in individuals with alcohol dependence. Cues associated with alcohol, depending on the perceived value of the primary reinforcer, gain salience and can trigger relapse.This study investigates the correlation between the reward magnitude of the primary reinforcer and the reinstatement evoked by cues predictive of their availability in male rats. Rat self-administration procedures were used to test reinstatement, with reinforcers consisting of 10% alcohol, 10% sucrose, or 2% sodium chloride (NaCl) experienced under need-state conditions. The effect of MTEP ([(2-methyl-1,3-thiazol-4-yl) ethynyl] pyridine), a selective metabotropic glutamate receptor 5 (mGluR5) antagonist, on motivation and reinstatement behaviors was also evaluated. Resultsdemonstrate that under Fixed Ratio 1 (FR1) schedule, the three reinforcers maintain operant responding with the following order of magnitude 10% sucrose >2% NaCl >10% alcohol > water. Under a progressive ratio (PR) schedule of reinforcement, rats exhibit a significantly higher breakpoint for 2% NaCl (under Na-depletion), followed by 10% sucrose and 10% alcohol. After extinction, a significant reinstatement is observed with the magnitude order of 10% sucrose >10% alcohol >2% NaCl. However, only re-exposure to alcohol-paired cues induced significant reinstatement of alcohol-seeking after 4 and 8 months. Treatment with MTEP significantly reduces reinstatement of responding across all reinforcers, with the strongest effect observed on alcohol-seeking. These findings suggest that mGluR5 plays a general role in controlling cue-reactivity, but the effect is prominent in the case of alcohol compared to natural rewards.In conclusion, the results demonstrate a remarkable dissociation between the rewarding magnitude of the primary reinforcer and its ability to trigger relapse upon presentation of a cue previously associated with it. Importantly, alcohol, despite having lower intrinsic motivational value compared to a natural reward (sucrose) or a consummatory stimulus experienced under need state conditions (NaCl), can elicit more robust and longer-term reinstatement of seeking responses. Finally, our data demonstrate a significant involvement of the mGluR5 system in the regulation of seeking behavior.

An assessment of token value and effectiveness: A replication.

The purpose of the current study was to conduct a systematic replication of Fiske et al. (2015) to extend the behavior-analytic literature on token reinforcement. Specifically, the researchers addressed several of the limitations of Fiske et al. by including specific conditioning procedures, creating a controlled history of reinforcement with the token system, including participants with and without disabilities to extend the generality of the findings, and equating the magnitude of reinforcement across the primary and paired-token conditions. The current study evaluated the reinforcing value of tokens by using progressive-ratio schedules to compare the efficacy of primary reinforcement, paired tokens, and unpaired tokens. The results suggest that paired tokens may function as reinforcers, but they were not as consistently effective as primary reinforcers.

Effects of environmental and pharmacological manipulations on cocaine-vs-negative reinforcer choice in male and female rats.

The adverse consequences of human addictive drug use could be the result of either addictive drug consumption resulting in punishment (e.g., incarceration) or failure to engage in negative-reinforced behaviors that might compete with drug-maintained behaviors (e.g., contingency management strategies that reset payment amounts for drug free urines). The goal of the present study was to establish a discrete-trial cocaine-vs-negative reinforcer (SNR) choice procedure where rats were presented with a simplified model of this conflict: choose negative reinforcement (i.e., escape or avoid foot shock) or choose an intravenous (IV) cocaine infusion followed by an inescapable shock. Responding was maintained in male and female rats by IV cocaine infusions (0.32-1.8 mg/kg/inf) and a SNR (0.1-0.7 mA shock) under a discrete-trial concurrent"choice" schedule during daily sessions. Following parametric reinforcer magnitude and response requirement experiments, the effects of 12 h extended access cocaine self-administration and acute diazepam (0.32-10 mg/kg, IP) pretreatment were determined on cocaine-vs-SNR choice. Negative reinforcement was chosen over all cocaine doses. Lowering shock magnitude or increasing SNR response requirement failed to promote behavioral reallocation towards cocaine. Extended access cocaine self-administration sessions resulted in high daily cocaine intakes but failed to significantly increase cocaine choice in all (19) but one rat. Acute diazepam pretreatment also did not alter choice behavior up to doses that produced behavioral depression. These results suggest that SNRs may be a source of reinforcement that effectively compete with and mitigate maladaptive addictive drug-maintained behaviors in the general population.

Rich-lean transitions produced by stimuli associated with accurate and inaccurate responding by pigeons.

Discriminable transitions from relatively favorable schedules of reinforcement to unfavorable schedules (rich-lean transitions) can produce disruptions in operant behavior. A prior evaluation in our laboratory (Toegel et al., 2021) found that placing a border around a key displayed on a resistive touchscreen increased pigeons' response accuracy relative to conditions without the border. We sought to evaluate (a) whether effects of the key border on accuracy could be replicated in a within-session comparison and (b) whether transitions from a response alternative associated with accurate responding to one associated with inaccurate responding functioned as rich-lean transitions. Pigeons' key pecks were reinforced according to a two-component multiple schedule with identical fixed-ratio (FR) requirements and reinforcer magnitudes. The components differed based on whether the virtual key was displayed behind a border or with no border. In line with prior research, within-session comparisons yielded higher response accuracy in components with the key border than in components without the border. Furthermore, transitions from the border component to the no border component functioned as rich-lean transitions for pigeons whose obtained FRs in no border components were substantially larger than the FR programmed in that component.

A quantitative analysis of resurgence following downshifts in alternative-reinforcer magnitude.

Resurgence is the increase in a previously reinforced and then extinguished target response due to changes in reinforcement conditions for an alternative response, including reductions in the rate or magnitude of reinforcement for the alternative response. Research with nonhumans suggests that reductions in both alternative-reinforcer rate and magnitude produce resurgence, but the present study was the first to examine effects of downshifts in alternative-reinforcer magnitude on humans' resurgence. Moreover, it was the first to evaluate whether the quantitative framework, resurgence as choice in context (RaC2 ), could account for those effects. Consistent with predictions of RaC2 , resurgence of a target button press occurred with reductions in point gain for an alternative response, with greater reductions producing higher levels of resurgence. However, the model consistently underpredicted and then overpredicted resurgence during tests with low-magnitude reinforcement and extinction. Systematic deviations in model predictions of alternative responding were also evident and consistent with previous fits of RaC2 to nonhuman data. Overall, our findings suggest that RaC2 could be a useful quantitative theoretical framework for understanding processes contributing to resurgence in humans, but further theoretical development is needed to account for the apparent divergent effects of extinction versus downshifts in reinforcer magnitude.

"Distractor" effects in delay discounting of probability by pigeons.

Impulsive behavior can be measured by performance on a successive delay-discounting task, in which a response to a stimulus provides a small reinforcer sooner (SS), but in the absence of a response, a larger reinforcer later (LL). Previous research suggests that the presence of a concurrent "distractor" stimulus, to which responding has no programed consequence, can result in increased LL reinforcers. In the present experiments, we used differences in the probability of reinforcement between SS and LL (rather than magnitude of reinforcement) and tested the hypothesis that the concurrent stimulus may become a Pavlovian conditioned stimulus. For the Red-Only group, a response to the SS stimulus resulted in a reinforcer with a low probability (SS), whereas the absence of a response resulted in a reinforcer with a high probability (LL). For the Red-Green group, (analogous to the more typical simultaneous choice between an SS and LL stimulus) the absence of a response to the SS stimulus replaced the SS stimulus with the LL stimulus and a response to the LL stimulus resulted in the reinforcer. Thus, for the Red-Green group, the concurrent stimulus should have been less effective because responding to the concurrent stimulus was not immediately followed by the reinforcer. In Experiment 1, the concurrent stimulus was a yellow key-light; in Experiment 2, it was a houselight. In both experiments, the concurrent stimulus was effective in increasing the number of LL reinforcers and the effect was larger for the Red-Only group than for the Red-Green group.

Social media sites users' choice between utilitarian and informational reinforcers assessed using temporal discounting.

This study provides a first approach to the use of the Multiple-Choice Procedure in social media networks use, as well as empirical evidence for the application of the Behavioral Perspective Model to digital consumption behavior in young users in conjunction with a methodology based on behavioral economics. The participants were part of a large university in Bogotá, Colombia, and they received an academic credit once they completed the online questionnaire. A total of 311 participants completed the experiment. Of the participants, 49% were men with a mean age of 20.6 years (SD = 3.10, Range = 15-30); 51% were women with a mean age of 20.2 years (SD = 2.84, Range = 15-29). Among the total participants, 40% reported that they used social networks between 1 and 2 h a day, 38% between 2 and 3 h, 16% for 4 h or more, and the remaining 9% used them for 1 h or less per day. The factorial analysis of variance (ANOVA) allowed us to identify a statistically significant effect of the delay of the alternative reinforcer, that is, the average crossover points were higher when the monetary reinforcer was delayed 1 week, compared to the immediate delivery of the monetary reinforcer. There was no statistically significant effect of the interaction between the magnitude of the reinforcer and the delay time of the alternative reinforcer. This study supports the relative reinforcing value of an informational reinforcement consequence such as social media use, which is sensitive to both the magnitude of reinforcement and the delay in delivery as individual factors. The findings on reinforcer magnitude and delay effects are consistent with previous research that have applied behavioral economics to the study of non-substance-related addictions.

Evaluating Different Magnitudes of Reinforcement Within the Caught Being Good Game

The Caught Being Good Game (CBGG) is an evidence-based practice used in classrooms to reduce disruptive classroom behavior. This approach to classwide intervention has been implemented and its effectiveness demonstrated across grade levels and types of disruptive behavior. Teachers report that the CBGG is an easy classroom management strategy to implement. Although several studies have been published demonstrating its utility, less research has examined how variations in the contingencies employed impact outcomes. In the current study, the CBGG was implemented across three classrooms in an effort to replicate previous findings. As well, the magnitude of reward/reinforcement was manipulated to determine whether this parameter affected intervention efficacy. Results of the study demonstrated appropriate classroom behavior increased across three elementary classrooms. The impact of magnitude of reward/reinforcement was idiosyncratic across the three classrooms, with no uniform impact of magnitude on intervention outcomes. Reasons why magnitude of reinforcement may not have impacted the efficacy of the CBGG are discussed.

Examining resurgence and repetition with the evolutionary theory of behavior dynamics

Recently, Redner et al. (2022) examined the nature of resurgence across repeated iterations of the traditional three-phase resurgence procedure with four pigeons. Although extant research findings in this area are mixed, Redner et al. found that resurgence generally increased in magnitude with repetition. These findings provide a baseline against which future research examining resurgence using this three-phase procedure can be compared and contrasted. The purpose of the present investigation was to examine resurgence via concurrent schedule arrangements similar to those described by Redner et al. with 30 artificial organisms (AOs) animated by the Evolutionary Theory of Behavior Dynamics (McDowell, 2004). We quantified the prevalence of resurgence across iterations and found that resurgence occurred in 86.7 % (156 of 180) iterations across all 30 AOs. This is strikingly similar to the resurgence prevalence estimates of 87.5 % reported by both Redner et al. (2022). However, we also found that the magnitude of target responding generally did not change significantly with repetition. This finding is inconsistent with Redner et al. but is consistent with the predictions of prominent quantitative models of behavioral persistence and a number of relevant studies (Volkert et al., 2009; Gratz et al., 2019). We also conducted exploratory analyses to examine how several variables (e.g., sensitivity to reinforcement, reinforcer magnitude, number of sessions of exposure to various phases) affect the prevalence and magnitude of resurgence among AOs.

Soil moisture and hysteresis affect both magnitude and efficiency of root reinforcement

Plant roots can protect soil against shallow landslides. The mechanics of rooted soil failure under varying soil water content remain poorly understood. The aim of our study was to characterize the impact of soil water content on root mechanical traits and reinforcement to soil. One-year-old Symplocos setchuensis trees were replanted in shear boxes (0.4 × 0.4 × 0.5 m3), which were placed in a canopy gap on Jinyun Mountain, Chongqing, China. After three years of vegetation growth, root mechanical measurements and soil direct shear tests were performed at five levels of volumetric soil water content varying from 14.9 to 44.4 %, by either wetting or drying the soil. For each shear box, we measured soil shear strength, root area ratio, root tensile force, root water content, and root failure mode (slippage versus breakage) during or after the shearing process. Root area ratio and root failure modes were examined for different root diameter classes. With increasing volumetric soil water content, we found a persistent decrease in root tensile strength (ca. 15 %) and an increase in root water content (ca. 11 %), although the dependence on volumetric soil water content was not statistically significant for certain soil water content levels. We found that both additional shear strength of rooted soil and proportion of root failure in breakage increased first and then decreased, with peak values occurring at a soil water content of ca. 22 %. Altered root tensile force (68.0 % contribution to root reinforcement variation) and the change in proportion of root failure modes (breakage or slippage; 8.4 % contribution to root reinforcement variation) jointly contribute to the negative impact of soil water on observed root reinforcement. Soil shear strength was positively correlated with root area ratio and their relationship was linear. At high soil water content (>28 %), the slope of the linear relationship decreased rapidly with increasing soil water content, suggesting that increasing root biomass is not effective for enhancing root reinforcement in very wet soil conditions. Regarding hysteresis, root reinforcement magnitude and efficiency were higher in the drying process than in the wetting process when soil moisture was low. Our results highlight the vital role of soil water features in affecting soil-root mechanical interactions and such effects should be taken into account in future root reinforcement modelling and assessment

Effects of environmental manipulations on cocaine-vs-social choice in male and female rats

Cocaine use disorder occurs in an environment where cocaine and other nondrug commodities are concurrently available. Preclinical drug-vs-nondrug choice procedures are one simplified method of modeling this complex clinical environment. The present study established a discrete-trial cocaine-vs-social interaction choice procedure in male and female rats and determined sensitivity of choice behavior to manipulations of reinforcer magnitude and non-contingent “sample” reinforcer presentation. Rats could make up to nine discrete choices between an intravenous cocaine infusion (0.1–1.0 mg/kg/inf) and social interaction with a same-sex social “Partner” rat. Cocaine infusions were available under a progressive-ratio (PR) schedule of reinforcement, and social interaction was available under a fixed-ratio (FR) 3 schedule. Social interaction was chosen over no or small cocaine doses (saline, 0.01 mg/kg/inf) and behavior was reallocated away from social and towards cocaine at larger cocaine doses (1.0 mg/kg/inf). Manipulating social interaction time as one method to alter social reinforcer magnitude did not significantly alter cocaine-vs-social choice. Removing the non-contingent reinforcer presentations before the discrete choice trials also failed to affect cocaine-vs-social choice, suggesting the time interval was sufficient to minimize any potential influence of the non-contingent cocaine infusions on subsequent choice behavior. Overall, the present results were consistent with previous drug-vs-social choice studies and extend our knowledge of environmental factors impacting drug-vs-social choice. Future studies determining the pharmacological sensitivity of cocaine-vs-social choice will be important in expanding the preclinical utility of these procedures for candidate medication drug development.