Biomedical subjects

Cynthia J Pietras

Publications and source records attributed to Cynthia J Pietras.

8 recordsLinked to original sources

PubMed2005

Response-cost punishment via token loss with pigeons.

Two experiments were conducted to investigate punishment via response-contingent removal of conditioned token reinforcers (response cost) with pigeons. In Experiment 1, key pecking was maintained on a two-component multiple second-order schedule of token delivery, with light emitting diodes (LEDs) serving as token reinforcers. In both components, responding produced tokens according to a random-interval 20-s schedule and exchange periods according to a variable-ratio schedule. During exchange periods, each token was exchangeable for 2.5-s access to grain. In one component, responses were conjointly punished according to fixed-ratio schedules of token removal. Response rates in this punishment component decreased to low levels while response rates in the alternate (no-punishment) component were unaffected. Responding was eliminated when it produced neither tokens nor exchange periods (Extinction), but was maintained at moderate levels when it produced tokens in the signaled absence of food reinforcement, suggesting that tokens served as effective conditioned reinforcers. In Experiment 2, the effect of the response-cost punishment contingency was separated from changes in the density of food reinforcement. This was accomplished by yoking either the number of food deliveries per component (Yoked Food) or the temporal placement of all stimulus events (tokens, exchanges, food deliveries) (Yoked Complete), from the punishment to the no-punishment component. Response rates decreased in both components, but decreased more rapidly and were generally maintained at lower levels in the punishment component than in the yoked component. In showing that the response-cost contingency had a suppressive effect on responding in addition to that produced by reductions in reinforcement density, the present results suggest that response-cost punishment shares important features with other forms of punishment.

Animals↗

PubMed2005

Performance of heavy marijuana-smoking adolescents on a laboratory measure of motivation.

Marijuana smoking produces effects that may persist for hours or days beyond the period of acute intoxication. Despite evidence that adolescence represents a period of heightened exposure to marijuana, little research exists regarding possible impairment in adolescents who smoke marijuana regularly, and none exists regarding basic behavioral processes. In the present study, adolescents who smoked marijuana on a regular basis (near daily) were compared to a control group of adolescents on a two-option experimental task designed to measure motivation. The contingencies were arranged such that one option (work), which required systematically increasing response output, initially produced greater rates of monetary reinforcement than an alternative option (non-work) that required no response output to earn money. Switching to the non-work option was interpreted as a measure of reduced motivation. Significant differences were found between the groups: the marijuana-smoking participants switched earlier to the non-work option, and derived a greater percentage of their earnings from the non-work option. These differences existed when controlling for differences in cognitive aptitude, gender, and the presence of conduct disorder. A significant correlation between cannabinoid levels and percent of earnings derived from the non-work option suggests that these effects could be associated with the presence of cannabinoids in the marijuana-smoking group.

Adaptation, Psychological↗

PubMed2003

Alcohol effects on human risk taking.

RATIONALE: Despite a well-established relationship between alcohol and risky behavior in the natural environment, laboratory investigations have not reliably shown acute alcohol effects on human risk-taking. OBJECTIVES: The present study was designed to demonstrate a dose-response relationship between acute alcohol administration and human risk taking. Further, this investigation sought to delineate behavioral mechanisms that may be involved in alcohol-induced changes in the probability of risky behavior. METHODS: Using a laboratory measure of risk taking designed to address acute drug effects, 16 adults were administered placebo, 0.2, 0.4, and 0.8 g/kg alcohol in a within-subject repeated measures experimental design. The risk-taking task presented subjects with a choice between two response options operationally defined as risky and non-risky. Data analyses examined: breath alcohol level (BAL), subjective effects, response rates, distribution of choices between the risky and non-risky option, and trial-by-trial probabilities of making losing and winning risky responses. RESULTS: The alcohol administration produced the expected changes in BAL, subjective effects, and response rate. Alcohol dose-dependently increased selection of the risky response option, and at the 0.8 g/kg dose, increased the probability of making consecutive losing risky responses following a gain on the risky response option. CONCLUSIONS: Acute alcohol administration can produce measurable changes in human risk-taking under laboratory conditions. Shifts in trial-by-trial response probabilities suggest insensitivity to past rewards and more recent losses when intoxicated, an outcome consistent with previous studies. This shift in sensitivity to consequences is a possible mechanism in alcohol-induced changes in risk taking.

Adult↗

PubMed2003

Effects of methylphenidate on impulsive choice in adult humans.

RATIONALE: Several studies with nonhumans and humans have shown that stimulants decrease impulsive choices on delay-to-reinforcement (self-control) procedures. Little is known, however, about the effects of the stimulant methylphenidate on choice for delayed reinforcers in humans. OBJECTIVES: The present study was designed to investigate the effects of acute methylphenidate administrations on impulsive responding in adult humans on a delay-to-reinforcement task. METHODS: Eleven adult males with a history of criminal behavior but no history of attention-deficit hyperactivity disorder (ADHD) participated. Impulsive responding was measured using an adjusting-delay procedure in which subjects were presented with repeated choices between a small amount of money delivered after a short delay and a larger amount of money delivered after a delay that adjusted as a function of previous choices. Subjects were exposed to four experimental sessions each day of participation and 60 min prior to the first daily session received placebo or 0.15, 0.30, or 0.60 mg/kg methylphenidate. Stable choice patterns were re-established between each methylphenidate dose. RESULTS: Individuals differed in their sensitivity to methylphenidate, but in over half of the subjects methylphenidate decreased impulsive (i.e., increased the number of self-control choices) and increased the delay to the large reinforcer. The largest increases in self-control choices tended to occur at the 0.30-mg/kg and 0.60-mg/kg doses, and the effects often persisted across multiple daily sessions. In six subjects, under at least one methylphenidate dose, the number of impulsive choices decreased to zero. CONCLUSIONS: Acute methylphenidate administrations tended to decrease the number of impulsive choices in adult humans on an adjusting-delay procedure, although there were substantial individual differences in the sensitivity of choice to methylphenidate. In no case, however, did methylphenidate increase impulsive choices. These results are consistent with several recent laboratory studies with nonhumans and humans showing that stimulants increase preference for large, delayed reinforcers.

Adolescent↗

PubMed2003

Acute effects of gabapentin on laboratory measures of aggressive and escape responses of adult parolees with and without a history of conduct disorder.

RATIONALE: The possible role of GABA in human aggression was evaluated by administering gabapentin to subjects with and without a history of conduct disorder and comparing the effects on laboratory measures of aggression and escape. METHODS: Eighteen male and two female subjects with a history of criminal behavior participated in experimental sessions, which measured aggressive and escape responses. Ten subjects had a history of childhood conduct disorder (CD+) and ten subjects with no history (non-CD controls). Aggression was measured using the Point Subtraction Aggression Paradigm (PSAP), which provided subjects aggressive, escape and monetary reinforced response options. RESULTS: Acute doses (200, 400 and 800 mg) of gabapentin had similar effects on aggressive responses among CD+ subjects compared to non-CD control subjects. Aggressive responses of CD+ and non-CD control subjects increased at lower gabapentin doses, and decreased at the highest 800 mg gabapentin dose. Gabapentin increased escape responses for both CD+ and non-CD controls CD- subjects at the lowest dose, but then produced dose-related decreases at the two higher doses in both groups. No changes in monetary reinforced responses were observed, indicative of no CNS stimulation or sedation. CONCLUSIONS: Gabapentin produced similar bitonic effects upon aggressive and escape responses in subjects with and without a history of childhood conduct disorder. This is in marked contrast to prior differential effects of baclofen on aggressive responses between CD+ and non-CD control subjects in a previous study.

Acetates↗

PubMed2003

Human risky choice under temporal constraints: tests of an energy-budget model.

Risk-sensitive foraging models predict that choice between fixed and variable food delays should be influenced by an organism's energy budget. To investigate whether the predictions of these models could be extended to choice in humans, risk sensitivity in 4 adults was investigated under laboratory conditions designed to model positive and negative energy budgets. Subjects chose between fixed and variable trial durations with the same mean value. An energy requirement was modeled by requiring that five trials be completed within a limited time period for points delivered at the end of the period (block of trials) to be exchanged later for money. Manipulating the duration of this time period generated positive and negative earnings budgets (or, alternatively, "time budgets"). Choices were consistent with the predictions of energy-budget models: The fixed-delay option was strongly preferred under positive earnings-budget conditions and the variable-delay option was strongly preferred under negative earnings-budget conditions. Within-block (or trial-by-trial) choices were also frequently consistent with the predictions of a dynamic optimization model, indicating that choice was simultaneously sensitive to the temporal requirements, delays associated with fixed and variable choices on the upcoming trial, cumulative delays within the block of trials, and trial position within a block.

Adult↗

PubMed2002

Acute effects of baclofen, a gamma-aminobutyric acid-B agonist, on laboratory measures of aggressive and escape responses of adult male parolees with and without a history of conduct disorder.

RATIONALE: The possible role of gamma-aminobutyric acid (GABA) in human aggression was evaluated by administering baclofen, a GABA-B agonist and comparing the effects on laboratory measures of aggression and escape among subjects with and without a history of conduct disorder. METHODS: Twenty male subjects with a history of criminal behavior participated in experimental sessions, which measured aggressive and escape responses. Ten subjects had a history of childhood conduct disorder (CD+) and ten control subjects had no history of CD. Aggression was measured using the point subtraction aggression paradigm (PSAP), which provides subjects with aggressive, escape, and monetary-reinforced response options. RESULTS: Acute doses (0.07, 0.14 and 0.28 mg/kg) of baclofen had remarkably different effects on aggressive responses among CD+ subjects relative to control subjects. Aggressive responses of CD+ subjects decreased, while aggressive responses of control subjects increased following baclofen administration. Baclofen decreased escape responses for both CD+ and control subjects. No changes in monetary-reinforced responses were observed, indicative of no central nervous system stimulation or sedation. CONCLUSIONS: The GABA-B agonist baclofen suppressed aggressive responses in subjects with a history of childhood CD, while producing the opposite effect in control subjects. These suggest a possible unique role for GABA in the regulation of aggression in CD+ population.

Adult↗

PubMed2001

Effects of chronic paroxetine administration on measures of aggressive and impulsive responses of adult males with a history of conduct disorder.

RATIONALE: The role of serotonin in human aggression and impulsivity was evaluated by administering paroxetine or placebo for 3 weeks and comparing the effects on laboratory measures of aggression and impulsivity among male subjects with a history of conduct disorder. METHODS: Twelve male subjects with a history of criminal behavior participated in experimental sessions, which measured aggressive and impulsive responses. Six subjects were assigned to placebo treatment and six subjects to placebo and paroxetine treatment. Aggression was measured using the point subtraction aggression paradigm (PSAP), which provides subjects with an aggressive and monetary reinforced response options. Impulsive responses were measured using a paradigm that gives subjects choices between small rewards after short delays versus larger rewards after longer delays. RESULTS: Chronic administration of paroxetine (20 mg/day) for 21 days produced significant decreases in impulsive responses. Decreases in aggressive responses were evident only at the end of paroxetine treatment. Decreases in impulsive and aggressive responses could not be attributed to a non-specific sedative action because monetary reinforced responses were not decreased as has been observed following CNS sedation. CONCLUSIONS: Inhibition of serotonin reuptake by paroxetine is the possible mechanism for reductions in aggressive and impulsive responses. These results support other data linking serotonin function and aggression and impulsivity.

Administration, Oral↗