Drug-behavior interaction history: modification of the effects of morphine on punished behavior.

Squirrel monkeys were trained to respond under a multiple fixed-interval, fixed-interval schedule in which the first response after 5 min terminated a visual stimulus in the presence of which electric shocks could occur. During one component of the schedule, correlated with one color of stimulus lights, every 30th response also produced electric shock; responding was suppressed during this component to approximately 10 to 12% of that occurring in the alternate component in which responding was not punished. In contrast to previous research, morphine (0.03 to 1.0 mg/kg) increased punished responding. Unpunished responding, however, was either not affected or decreased at doses of morphine that increased punished responding. Increases in rate of punished responding also occurred when the single-schedule punishment condition was studied alone in these animals. Subsequent experimentation, which systematically analyzed the development of the rate-enhancing effects of morphine on punished responding, involved the study of drug effects in additional monkeys trained initially under a single-schedule punishment condition. The effects of morphine on punished responding were studied before, after, and then during exposure to the multiple schedule that included a component in which responding was not punished. Increases in response rate with morphine did not occur until it was administered during exposure to the multiple schedule that included a component in which responding was not punished. As with the other monkeys, once the rate increases in punished responding occurred under the multiple schedule, these effects of morphine persisted, even when the multiple schedule was removed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Working memory and behavioral inhibition in children with attention-deficit/hyperactivity disorder (ADHD): an examination of varied central executive demands,construct overlap,and task impurity

The stop-signal paradigm is the premier metric of behavioral inhibition in contemporary attention-deficit/hyperactivity disorder (ADHD) research. The stop-signal paradigm’s choice-reaction time component, however, arguably places greater demands on working memory processes (e.g., controlled-focused attention) relative to alternative inhibition metrics (i.e., go/no-go (GNG) tasks), and consequently obscures conclusions about inhibition and working memory deficits in affected children. The current study, therefore, aimed to determine whether shared variance between stop-signal behavioral inhibition and working memory performance in children with ADHD reflects overlap between the working memory and inhibition constructs or insufficient specificity of the stop-signal paradigm. Fifty-five children (8–12 years) with and without ADHD were administered established phonological (PH) and visuospatial (VS) working memory measures, as well as stop-signal and GNG tasks that vary with respect to demands on controlled-focused attention. Although working memory and GNG performance each uniquely predicted children’s inattention, stop-signal task performance was not a significant predictor of unique variance in inattention, above and beyond variance associated with working memory. Collectively, these findings suggest that performance on the stop-signal task, compared to the GNG task, is confounded by greater demands associated with working memory and consequently reflects an impure estimate of the inhibition construct.     

Matching, maximizing, and the behavioral unit: concurrent reinforcement of response sequences.

Pigeons pecked two keys in a probability matching situation in which four two-peck sequences were intermittently reinforced: left-left, left-right, right-left and right-right. In Phase 1, relative reinforcement rate was varied with respect to the first response of a sequence: reinforcers were differentially assigned for left-left and left-right sequences as opposed to right-left and right-right sequences. The second response of reinforced sequences occurred equally on the left and right keys across conditions. In Phase II, relative reinforcement rate was varied for sequences that involve an alternation as opposed to those that did not. The relative outputs of the different sequences matched the relative reinforcement rates for the different sequences in both phases. Relative response rates for key pecks did not always match relative reinforcement rates. The intertrial interval separating responses was varied in both phases; increases in the intertrial interval affected the relative frequency of different sequences. The results demonstrate that response sequences acted as functional units influencing choice and thus support a structural account of choice. At the same time, the matching of relative sequence proportion and relative reinforcement rate supports a matching account.     

Repeated diazepam administration: effects on the acquisition and performance of response chains in humans.

The effects of repeated diazepam administration (80 mg) were assessed across a 12-hr time course with humans responding under a two-component multiple schedule of repeated acquisition and performance of response sequences. Subjects resided in an inpatient clinical research ward for the duration of the study. In each component of the multiple schedule, subjects completed sequences of 10 responses in a predetermined order using three keys of a numeric keypad. In the acquisition component, a new response sequence was to be acquired each session. In the performance component, the response sequence always remained the same. After stable responding was obtained and the effects of the placebo assessed, diazepam was administered for 3 consecutive days. The effects of repeated diazepam administration on overall percentage of errors across the two components of the multiple schedule were selective. In the acquisition component, the first dose of diazepam increased percentage errors with the magnitude of effects decreasing across the second and third days of diazepam administration. In the performance component, the percentage of errors was either minimally affected across all 3 days of diazepam administration or substantively increased on Day 1 with subsequent diazepam administrations having minimal effects. Effects on response rate were not selective. Diazepam decreased rates of responding in both schedule components, with the magnitude of effects decreasing across successive administrations. These results replicate previous findings in humans and nonhumans on the selective effects of diazepam on acquisition versus performance baselines. Also, the results suggest that the selective effects do not result from differences in reinforcement rate. Finally, the present results demonstrate that the selective recovery from repeated drug administration previously demonstrated in nonhumans using a repeated acquisition arrangement has generality to human behavior.