Carter W. Daniels

Impulsivity affects suboptimal gambling-like choice by pigeons.

Pigeons prefer a low-probability, high-payoff but suboptimal alternative over a reliable low-payoff optimal alternative (i.e., one that results in more food). This finding is analogous to suboptimal human monetary gambling because in both cases there appears to be an overemphasis of the occurrence of the winning event (a jackpot) and an underemphasis of losing events. In the present research we found that pigeons chose suboptimally to the degree that they were impulsive as indexed by the steeper slope of the hyperbolic delay-discounting function (i.e., the shorter the delay they would accept in a smaller-sooner/larger-later procedure). These correlational findings have implications for the mechanisms underlying suboptimal choice by humans (e.g., problem gamblers) and they suggest that high baseline levels of impulsivity can enhance acquisition of a gambling habit.

Revisiting the effect of nicotine on interval timing

This paper reviews the evidence for nicotine-induced acceleration of the internal clock when timing in the seconds-to-minutes timescale, and proposes an alternative explanation to this evidence: that nicotine reduces the threshold for responses that result in more reinforcement. These two hypotheses were tested in male Wistar rats using a novel timing task. In this task, rats were trained to seek food at one location after 8s since trial onset and at a different location after 16s. Some rats received the same reward at both times (group SAME); some received a larger reward at 16s (group DIFF). Steady baseline performance was followed by 3 days of subcutaneous nicotine administration (0.3mg/kg), baseline recovery, and an antagonist challenge (mecamylamine, 1.0mg/kg). Nicotine induced a larger, immediate reduction in latencies to switch (LTS) in group DIFF than in group SAME. This effect was sustained throughout nicotine administration. Mecamylamine pretreatment and nicotine discontinuation rapidly recovered baseline performance. These results support a response-threshold account of nicotinic disruption of timing performance, possibly mediated by nicotinic acetylcholine receptors. A detailed analysis of the distribution of LTSs suggests that anomalous effects of nicotine on LTS dispersion may be due to loss of temporal control of behavior.

Nicotine-induced place conditioning and locomotor activity in an adolescent animal model of attention deficit/hyperactivity disorder (ADHD)

Attention deficit/hyperactivity disorder (ADHD) is a risk factor for tobacco use and dependence. This study examines the responsiveness to nicotine of an adolescent model of ADHD, the spontaneously hypertensive rat (SHR). The conditioned place preference (CPP) procedure was used to assess nicotine-induced locomotion and conditioned reward in SHR and the Wistar Kyoto (WKY) control strain over a range of nicotine doses (0.0, 0.1, 0.3 and 0.6 mg/kg). Prior to conditioning, SHRs were more active and less biased toward one side of the CPP chamber than WKY rats. Following conditioning, SHRs developed CPP to the highest dose of nicotine (0.6 mg/kg), whereas WKYs did not develop CPP to any nicotine dose tested. During conditioning, SHRs displayed greater locomotor activity in the nicotine-paired compartment than in the saline-paired compartment across conditioning trials. SHRs that received nicotine (0.1, 0.3, 0.6 mg/kg) in the nicotine-paired compartment showed an increase in locomotor activity between conditioning trials. Nicotine did not significantly affect WKY locomotor activity. These findings suggest that the SHR strain is a suitable model for studying ADHD-related nicotine use and dependence, but highlights potential limitations of the WKY control strain and the CPP procedure for modeling ADHD-related nicotine reward.

Less means more for pigeons but not always

When humans are asked to judge the value of a set of objects of excellent quality, they often give this set higher value than those same objects with the addition of some of lesser quality. This is an example of the affect heuristic, often referred to as the less-is-more effect. Monkeys and dogs, too, have shown this suboptimal effect. But in the present experiments, normally hungry pigeons chose optimally: a preferred food plus a less--preferred food over a more-preferred food alone. In Experiment 2, however, pigeons on a less-restricted diet showed the suboptimal less-is-more effect. Choice on control trials indicated that the effect did not result from the novelty of two food items versus one. The effect in the less-food-restricted pigeons appears to result from the devaluation of the combination of the food items by the presence of the less-preferred food item. The reversal of the effect under greater food restriction may occur because, as motivation increases, the value of the less-preferred food increases faster than the value of the more-preferred food, thus decreasing the difference in value between the two foods.

About bouts: A heterogeneous tandem schedule of reinforcement reveals dissociable components of operant behavior in fischer rats

According to the biexponential refractory model (BERM) of variable-interval (VI) performance, operant behavior is organized in bouts, described by 3 dissociable components: between-bout interresponse times (IRTs), within-bout IRTs, and bout lengths. Research has shown that between-bout IRTs are sensitive to changes in rate of reinforcement and reinforcer efficacy, the length of some bouts is selectively sensitive to changes in response-reinforcer contingencies, and within-bout IRTs are relatively insensitive to both manipulations. BERM assumes that within- and between-bout IRTs are exponentially distributed, and bout lengths are described by a mixture of negative binomial and geometric distributions. To assess BERM assumptions and the interpretation of associated findings, Fischer 344/DuCrl rats were trained on a heterogeneous tandem VI fixed-ratio (FR) schedule of reinforcement intended to dissociate the components of operant behavior. Initial (VI) and terminal (FR) links were programmed on separate levers; no stimulus signaled the completion of the initial link. FR requirement, VI requirement, and deprivation level were varied. Typical performance consisted of single responses on the VI lever separated by response runs on the FR lever. It was hypothesized that (a) the interval between the end of each FR run and the first subsequent VI response (FR–VI IRTs) would constitute between-bout IRTs, and would be sensitive to changes in VI requirement and deprivation level, (b) FR runs would constitute response bouts, so the length of a fraction of them would be selectively sensitive to changes in FR requirement, and (c) intervals between consecutive FR responses (FR–FR IRTs) would constitute within-bout IRTs, and would be relatively robust to all manipulations. Findings were consistent with these expectations. The underlying distributions of FR–FR IRTs, FR–VI IRTs, and FR run lengths, however, were inconsistent with BERM assumptions. These data support the distinct components of operant performance, but challenge the simple processes assumed to underlie their generation.

The Effect of Methylphenidate on the Microstructure of Schedule-Induced Polydipsia in an animal model of ADHD

Abstract Schedule‐induced polydipsia (SIP) was established in spontaneously hypertensive rats (SHR), Wistar Kyoto rats (WKY), and Wistar rats, using a multiple fixed‐time (FT) schedule of food delivery, with 30‐ and 90‐s components. Thereafter, animals were exposed to methylphenidate (MPH; 2.5 mg/kg/d) for six consecutive SIP sessions. A test to assess possible sensitization effects was also conducted four days after termination of the drug treatment. At baseline, FT 90‐s produced longer and more frequent drinking episodes in SHR than in WKY. An analysis of the distribution of inter‐lick intervals revealed that drinking was organized in bouts, which were shorter in SHR than in WKY. Across strains and schedules, MPH shifted drinking episodes towards the beginning of inter‐food intervals, which may reflect a stimulant effect on SIP. MPH transiently reduced the frequency of drinking episodes in WKY in FT 30‐s, and more permanently reduced the frequency of licking bouts in Wistar rats. MPH also increased the length of licking bouts in Wistar rats. Overall, SHR displayed a hyperactive‐like pattern of drinking (frequent but short bouts), which 2.5 mg/kg MPH appears to reduce in WKY and Wistar but not in SHR rats. It appears that therapeutic effects of MPH on hyperactive‐like SIP require higher doses in SHR relative to control strains.

An associability decay model of paradoxical choice.

Paradoxical choices in human and nonhuman animals represent substantial deviations from rational models of behavior; such deviations often demand models that incorporate multiple perspectives, including psychology, biology, and economics. The past couple of decades have seen an increased interest in the paradoxical choice of pigeons in 2-armed bandit tasks (2ABT) developed by Zentall and colleagues. In these 2ABTs, pigeons, but not rats, systematically choose an alternative that yields less reward over multiple trials but provides more information on events within a trial, over an alternative that yields more reward over trials but provides less information on events within a trial. Although current computational models account for much of the extant data generated in studies on 2ABT choice, they do not explain, in a trial-by-trial basis, how pigeons learn to ignore some stimuli and not others in 2ABTs. To address the provenance of this differential allocation of attention, a simple model composed of Bush-Mosteller linear operators and a Pearce-Hall-like associability mechanism is proposed. This model, referred to as the Associability Decay Model (ADM) of paradoxical choice, adequately accounts for the performance of pigeons and rats in 2ABTs. The ADM yields an untested prediction that is inconsistent with other computational models of 2ABT performance, and offers potential explanations for why differences in motivation, social enrichment, and impulsivity alter the degree to which pigeons systematically choose information despite earning fewer rewards. The success of the ADM shows that a relatively simple dynamic trial-by-trial model can account for much of the extant paradoxical-choice data while identifying opportunities for further study and refinement of models of 2ABT performance. (PsycINFO Database Record

Between-session memory degradation accounts for within-session changes in fixed-interval performance

A common assumption in the study of fixed-interval (FI) timing is that FI performance is largely stable within sessions, once it is stable between sessions. Within-session changes in FI performance were examined in published data (Daniels and Sanabria, 2017), wherein some rats were trained on a FI 30-s schedule of food reinforcement (FI30) and others on a FI 90-s schedule (FI90). Following stability, FI90 rats were pre-fed for five sessions. Response rates declined as a function of trial, due more to latency lengthening than to run-rate reduction. Latencies were best described by a dynamic gamma-exponential mixture distribution, in which latency lengthening was driven by the growth of the criterion pulse count for a response and not by a reduction in the speed of an endogenous clock. The speed of the clock was selectively sensitive to the length of the FI; the prevalence and length of exponentially-distributed latencies were selectively sensitive to pre-feeding. These findings reveal (a) that parameters governing FI latencies are selectively sensitive to a range of manipulations, (b) a potential degradation of the criterion pulse count between consecutive sessions, and (c) a subsequent recovery of the criterion pulse count within sessions.

Suppressive and enhancing effects of nicotine on food-seeking behavior

ABSTRACT The present study examined how systemic low doses of nicotine affect the microstructure of reinforced food‐seeking behavior in rats. Rats were first given an acute saline or nicotine treatment (0.1–0.6 mg/kg, with an inter‐injection interval of at least 48 h), and then a chronic saline or nicotine treatment (0.3 mg/kg/day for 10 consecutive days). Immediately after each injection, rats were required to press a lever five times to obtain food that was available at unpredictable times (on average every 80 s) with constant probability. Acute nicotine dose‐dependently suppressed behavior prior to the delivery of the first reinforcer, but enhanced food‐reinforced behavior afterwards. These effects were primarily observed in the time it took rats to initiate food‐seeking behavior. Enhancing effects were also observed in the microstructure of food‐seeking behavior, with lower nicotine doses (0.1–0.3 mg/kg) increasing the rate at which response bouts were initiated, and higher doses (0.3–0.6 mg/kg) increasing within‐bout response rates. A pre‐feeding control suggests that changes in appetite alone cannot explain these effects. Over the course of chronic nicotine exposure, tolerance developed to the suppressive, but not to the enhancing effects of nicotine on food‐seeking behavior. These results suggest that (a) lower doses of nicotine enhance the reward value of food and/or food‐associated stimuli, (b) higher doses of nicotine enhance motoric activity, and (c) ostensive sensitization effects of nicotine on behavior partially reflect a tolerance to its transient suppressive motoric effects.

I can time with a little help from my friends: effect of social enrichment on timing processes in Pigeons (Columba livia)

There is evidence that impulsive decision-making is associated with errors in timing. However, there has been little attempt to identify the putative mechanism responsible for impulsive animals’ timing errors. One means of manipulating impulsivity in non-human animals is providing different levels of access to conspecifics. These preclinical models have revealed that social isolation increases impulsive responding across a wide range of tasks. The goal of the present study was to determine whether social isolation modulates time perception in pigeons by inducing more variability or a bias to underestimate the passage of time in temporal judgments. A temporal bisection task was used to characterize time perception. One group of pigeons performed the bisection following social enrichment, and the remaining half of the pigeons were tested following social isolation. Results revealed pigeons in the social isolation condition categorized a temporal stimulus sample as “long” at shorter durations than pigeons in the social enrichment condition. These data highlight the mechanism(s) thought to underlie timing-based interventions aimed at reducing impulsivity in humans. Future work should consider whether impulsivity is produced by misperceptions of time or a reduced threshold for a response.