Biomedical subjects

Peter D Balsam

Publications and source records attributed to Peter D Balsam.

8 recordsLinked to original sources

PubMed2006

Amphetamine affects the start of responding in the peak interval timing task.

In this paper we investigate how amphetamine affects performance in a PI task by comparing two analyses of responding during peak trials. After training on 24 s fixed interval (FI-24) with 96 s peak trials, rats were given amphetamine for 4 consecutive days at doses of .5 and 1.0 mg/kg. Responses during peak trials were fitted with a Gaussian distribution to estimate the expected time of reinforcement from the peak time. A single trials analysis was also performed to determine the start time and stop time of the transition into and out of a high rate of responding on each peak trial. Amphetamine significantly decreased peak times as measured with the Gaussian curve fitting. However, in the single trials analysis, animals initiated responding significantly earlier, but did not stop responding earlier. Thus, fitting a Gaussian to the average performance across trials sometimes provides a different characterization of the timing process than does analyzing the start and stop of responding on individual trials. In the current experiment, the latter approach provided a more precise characterization of the effects of amphetamine on response timing.

Amphetamine↗

PubMed2006

Pavlovian contingencies and temporal information.

The effects of altering the contingency between the conditioned stimulus (CS) and the unconditioned stimulus (US) on the acquisition of autoshaped responding was investigated by changing the frequency of unsignaled USs during the intertrial interval. The addition of the unsignaled USs had an effect on acquisition speed comparable with that of massing trials. The effects of these manipulations can be understood in terms of their effect on the amount of information (number of bits) that the average CS conveys to the subject about the timing of the next US. The number of reinforced CSs prior to acquisition is inversely related to the information content of the CS.

Animals↗

PubMed2006

Dopamine receptor blockade and extinction differentially affect behavioral variability.

Dopamine (DA) neurons respond to unexpected food delivery and are inhibited during the omission of expected reward. DA receptor blockade mimics some, but not all, aspects of non-reward (extinction) conditions. It was therefore of interest to ask whether DA receptor blockade produces extinction-like increases in behavioral variability in addition to its well-known operant response-suppressing effects. In the current experiment, rats were trained drug-free on an operant task in which they pressed on a keyboard. Two of the keys led to food on a continuous reinforcement schedule. Both response rates and behavioral variability were measured. Test day administration of D(1) and D(2) antagonists SCH23390 and raclopride, like extinction, suppressed responding but, unlike extinction, did not lead to an increase in variability.

Analysis of Variance↗

PubMed2005

Mice with chronically elevated dopamine exhibit enhanced motivation, but not learning, for a food reward.

Dopamine has been critically implicated in learning and motivation, although its precise role remains to be determined. In order to investigate the involvement of dopamine in learning and motivation for a food reward, we used dopamine transporter knockdown mice (DAT KD) that have chronically elevated levels of extracellular dopamine. The present study demonstrates that chronically elevated dopamine enhances tendency to work for a food reward without apparent effects on Pavlovian and operant learning for this reward. The increase in dopamine is associated with elevated levels of dynorphin and Fos B expression in the dorsal caudate-putamen and the core but not the shell subregion of the nucleus accumbens. These data suggest that motivation to work, but not learning, for a food reward appears to be under the critical influence of tonic dopaminergic activity in discrete brain areas relevant for a reward-directed behavior.

Animals↗

PubMed2005

Extended habit training reduces dopamine mediation of appetitive response expression.

A wide range of behaviors is impaired after disruption of dopamine (DA) transmission, yet behaviors that are reflexive, automatic, or elicited by salient cues often remain intact. Responses triggered by strong external cues appear to be DA independent. Here, we examined the possibility that a single behavior may become DA independent as a result of extended training. Rats were trained to execute a head-entry response to a cue signaling food delivery. Vulnerability of the response to D1 or D2 receptor blockade was assessed on day 3, 7, or 17 of 28-trial-per-day training. During the early stages of training, the D1 receptor antagonist R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (SCH 23390) increased response latencies; however, the same behavior was unaffected by SCH 23390 in animals tested during the later stages of training. Other aspects of behavior such as locomotion and head-entry responses during the uncued intertrial interval remained vulnerable to SCH 23390 throughout the experiment. This D1-mediated response was unaffected by the D2 antagonist raclopride, even at a dose that strongly suppressed locomotion. The results provide strong evidence that a D1-dependent behavior becomes less dependent on DA with extended training. A number of fundamental neurobiological changes occur as behaviors become learned habits; at least for some responses, this change involves a shift from D1-mediated to D1-independent responding.

Animals↗

PubMed2005

Temporal control of conditioned responding in goldfish.

The peak procedure was used to characterize response timing during acquisition and maintenance of conditioned responding in goldfish. Subjects received light-shock pairings with a 5- or 15-s interstimulus interval. On interspersed peak trials, the conditioned stimulus light was presented for 45 s and no shock was delivered. Peaks in the conditioned response, general activity, occurred at about the time of the expected unconditioned stimulus, and variability in the activity distribution was scalar. Modeling of the changes in the activity distributions over sessions revealed that the temporal features of the conditioned response changed very little during acquisition. The data suggest that times are learned early in training, and, contrary to I. P. Pavlov's (1927/1960) concept of "inhibition of delay," that timing is learning when to respond rather than learning when not to respond.

Animals↗

PubMed2004

Temporal specificity of extinction in autoshaping.

Three experiments investigated the effects of varying the conditioned stimulus (CS) duration between training and extinction. Ring doves (Streptopelia risoria) were autoshaped on a fixed CS-unconditioned stimulus (US) interval and extinguished with CS presentations that were longer, shorter, or the same as the training duration. During a subsequent test session, the training CS duration was reintroduced. Results suggest that the cessation of responding during an extinction session is controlled by generalization of excitation between the training and extinction CSs and by the number of nonreinforced CS presentations. Transfer of extinction to the training CS is controlled by the similarity between the extinction and training CSs. Extinction learning is temporally specific.

Animals↗

PubMed2003

Effects of dopamine antagonists on the timing of two intervals.

Rats were trained on a two-interval (12 and 36 s) temporal production task (the peak procedure). Test sessions were conducted in which either the D(1) antagonist SCH-23390 (SCH; 0.02, 0.04, 0.06 mg/kg) or the D(2) antagonist haloperidol (HAL; 0.05, 0.1, 0.2 mg/kg) were injected prior to testing. Both drugs affected the amount of responding, but only HAL affected timing. Under HAL, both intervals were overestimated, consistent with a HAL-induced decrease in clock speed. Drug-induced decreases in response output were more profound for the long interval than the short. In addition, there was evidence of HAL- and SCH-induced delays in response initiation that were more severe for the long interval, perhaps owing to its status as a weaker conditioned stimulus.

Acoustic Stimulation↗