Effects of delays on human performance on a temporal discrimination procedure: evidence of a choose-short effect.

Studies of temporal discrimination in non-human subjects have reliably shown a choose-short effect: higher matching accuracy on short-duration-sample trials than on long-duration-sample trials. This effect occurs as a function of increasing the delay between the onset of sample and comparison stimuli in a delayed matching-to-sample procedure. The present experiment investigated whether the choose-short effect could be demonstrated in human subjects under conditions which paralleled those used with non-human subjects. Subjects responded under a discrete-trial procedure in which they were required to push one of two buttons depending on the duration of a sample stimulus (a blue square on a computer monitor). Delays (0, 8, 16, and 32s) separated sample and comparison stimuli (two white boxes) and were tested both within and across several sessions. Intermediate durations (probe stimuli between 2 and 4s) were also presented. The addition of a delay between the sample and comparison stimuli produced a bias to judge intervals as short when the 8 and 32-s delays were tested across sessions and when the 0, 16, and 32-s delays were tested within the same session. Thus, the choose-short effect was produced in human subjects using the interval bisection procedure regardless of delay length.

Acute effects of lorazepam on laboratory measures of aggressive and escape responses of adult male parolees.

Acute benzodiazepine administrations typically decrease aggressive responding, but increases in aggression have been reported in some studies. The benzodiazepine lorazepam has been studied less frequently than other benzodiazepines in aggression research, although it is often used to suppress violent aggression in patients. The present study was designed to investigate the effects of acute administrations of lorazepam on aggressive responding in adult humans on a laboratory aggression task. Eight adult males participated in experimental sessions on the Point Subtraction Aggression Paradigm (PSAP), which provided subjects with aggressive, escape and monetary-reinforced response options. Acute oral doses (1, 2 and 4 mg) of lorazepam decreased both aggressive responding and monetary-reinforced responding in seven of eight subjects. In one subject, lorazepam produced dose-dependent increases in aggressive responding. The effects of lorazepam on escape responding were the same as the effects on aggressive responding. The results are consistent with prior research using the PSAP and clinical data showing that benzodiazepines generally decrease aggression, and contrast with other studies that have shown that benzodiazepines can increase aggression. Since lorazepam affected both aggressive and escape responding, it is suggested that while lorazepam often produces sedation, it also modifies human aggressive responding, in part, by suppressing reactions to aversive stimuli.

Acute marijuana effects on response-reinforcer relations under multiple variable-interval schedules.

Acute marijuana administration may alter response-reinforcer relationships via a change in reinforcer efficacy, but may also impair coordination and motor function. One approach to evaluating drug effects on both motor function and reinforcer efficacy involves fitting the matching law equation to data obtained under multiple variable interval (VI) schedules. The present report describes an experiment that examined the effects of acute marijuana on response properties using this approach. Six human subjects responded under a multiple VI schedule for monetary reinforcers after smoking placebo and two active doses of marijuana. The low marijuana dose produced unsystematic changes in responding. As measured by the matching law equation parameters (k and rB), at the high dose five subjects showed a decrease-motor-related properties of response rate and four subjects' responding indicated a decrease in reinforcer efficacy. These data raise the possibility that, at high doses, marijuana administration alters both motor function and reinforcer efficacy.

Acute effects of D-fenfluramine on simultaneous measures of aggressive escape and impulsive responses of adult males with and without a history of conduct disorder.

RATIONALE: The role of serotonin in human aggression was evaluated by administering D-fenfluramine and comparing the effects on laboratory measures of aggression, escape and impulsivity among subjects with and without a history of conduct disorder. METHODS: Ten male subjects with a history of criminal behavior participated in experimental sessions that measured aggressive and impulsive responses. Five subjects had a history of childhood conduct disorder (CD+) and five control subjects did not. Aggression was measured using the Point Subtraction Aggression Paradigm (PSAP), which provides subjects with an aggressive, escape 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 long delays. RESULTS: Acute doses (0.1, 0.2 and 0.4 mg/kg) of D-fenfluramine produced significant decreases in aggressive responses in CD+ subjects and large decreases in escape responses for CD+ subjects and smaller decreases for control subjects. Impulsive responses were decreased slightly and monetary reinforced responses were not changed in either group. Decreases in aggressive responses were not selective, since escape responses were also decreased, but such effects could not be attributed to a non-specific sedative action because monetary reinforced responses were increased and reaction times were decreased, indicative of central nervous system stimulation. CONCLUSIONS: Release of serotonin by D-fenfluramine is the possible mechanism for reductions in aggressive responses. These results are consistent with a large body of data linking reduced serotonin function and aggressive behavior.

Risk taking by adolescents with maladaptive behavior histories.

"High-risk" adolescents with maladaptive behavior histories and control adolescents (15-17 years of age) participated in a laboratory experiment that measured aspects of risk-taking behavior. High-risk adolescents had behavioral profiles entailing combinations of past substance use disorder, early onset substance use, conduct disorder, criminal history, and dropping out of school. A risk-taking task presented participants with "risky" and nonrisky response options. The risky response option offered a low probability of a large monetary reward or a high probability of a smaller monetary loss and resulted in a net loss of monetary earnings. The nonrisky option protected current earnings. High-risk adolescents chose the risky option more often, had lower overall earnings, and were more likely to persist in making (losing) risky responses following a single gain on the risky option. The data replicate previous findings with high-risk adults.

Executive cognitive functioning, alcohol, and aggression: comment on Giancola (2000).

P. R. Giancola (2000) postulated executive cognitive functioning (ECF) as a mechanism to explain the association between alcohol consumption and aggression. Alcohol intoxication disrupts ECF, which heightens the probability of aggression. This is most likely to occur in individuals with low ECF. These propositions are found lacking. The disruption in ECF by alcohol would be greatest among individuals with high ECF, and low-ECF individuals presumably would not experience much further disruption as result of low baseline functioning. These 2 premises appear to be inconsistent. The concept of ECF suffers from the problems associated with hypothetical constructs. Patterns of aggression emerge in young children before the development of cognitive skills associated with ECF, and the association of aggression and low ECF occur as results of environmental risk factors. ECF is neither a necessary nor a sufficient condition to explain aggression following alcohol drinking.

Fenfluramine effects on impulsivity in a sample of adults with and without history of conduct disorder.

RATIONALE: The role of serotonin in impulsivity was examined by administering the serotonin-releasing drug, d,l-fenfluramine, and measuring effects on impulsive responding of male subjects with and without a history of conduct disorder (CD) under controlled laboratory conditions. METHODS: Five adult male subjects with a history of CD and five matched controls were recruited into a study to determine the acute effects of d,l-fenfluramine on a laboratory measure of impulsive behavior. This laboratory measure, based upon delay of gratification, presented subjects with choices between a small reward after a short delay and a larger reward after a longer delay. Impulsive behavior was indicated by frequent choices for the smaller reward. RESULTS: Acute oral doses of d,l-fenfluramine (0.21, 0.42, and 0.85 mg/kg) produced decreases in the number of impulsive choices in all subjects with a history of CD, but had no effect on the control subjects. CONCLUSIONS: This data suggests that a deficit in serotonin and/or dopamine may play a role in impulsivity in CD subjects, and drugs which act to reduce this biological deficit can reduce impulsiveness.

Analysis of risk taking in adults with a history of high risk behavior.

Antisocial behavior often involves frequent risk-taking, e.g. excessive substance use and criminality, which may lead to destructive consequences. In the present study, adults with a history of high-risk behavior (primarily drug dependence and conduct disorder) and matched controls worked on a novel laboratory task designed to measure risk-taking. The contingencies of the task were such that choosing a 'risky' response option resulted in a net loss of monetary earnings compared to a safer, more conservative response alternative. The risky option offered a low probability of a large monetary reward or a high probability of a smaller monetary loss. The non-risky option protected current earnings. High-risk history subjects chose the risky option more often, had lower overall earnings, and were more likely to persist in making (losing) risky responses following a single gain on the risky option. The data support theories of maladaptive behavior focused on hypersensitivity to reward and insensitivity to aversive events.

Effects of d,l-fenfluramine on aggressive and impulsive responding in adult males with a history of conduct disorder.

RATIONALE: The role of serotonin in aggression and impulsivity was examined by administering the serotonin-releasing drug, d, l-fenfluramine and measuring effects on aggressive and impulsive responding under controlled laboratory conditions. METHODS: Ten male subjects with a history of conduct disorder and criminal behavior participated in experimental sessions, which measured aggressive and impulsive responses. Aggression was measured using the Point subtraction Aggression paradigm (PSAP), which provides subjects with an aggressive, escape and monetary reinforced response options. Impulsive responses were measured using a paradigm which provided subjects with choices between small rewards after short delays versus larger rewards have long delays. RESULTS: Acute challenge doses (0.2,0.4 and 0.8 mg/kg) of d,l-fenfluramine produced significant dose-dependent decreases in aggressive and impulsive responses. Escape and monetary reinforced responses were not significantly changed. Decreases in aggressive responses were therefore selective, because escape responses were not affected, and could not be attributed to a non-specific sedative action because monetary reinforced responses were slightly increased. CONCLUSIONS: Release of serotonin and/or reuptake blockade by d,l-fenfluramine is the possible mechanism for reductions in aggression and impulsivity. These results are consistent with a large body of data linking reduced serotonin function and aggressive behavior and impulsivity.

Laboratory and psychometric measurements of impulsivity among violent and nonviolent female parolees.

BACKGROUND: Female parolees participated in a study to determine the relationship between behavioral and psychometric measures of impulsivity and their previous criminal history. METHODS: Subjects were assigned to a violent (n = 10) or nonviolent group (n = 20) based upon their criminal history. Subjects were given two response options defined as: 1) an impulsive choice--small monetary reward (5 cents) after a short fixed delay of 5 sec, and 2) a self-control choice--a larger monetary reward (15 cents) after a variable longer delay initially set at 15 sec. The measure of impulsivity in this behavioral choice procedure was the number of trials on which the subject selected the impulsive option. This definition of impulsivity is based upon an extensive experimental literature in nonhumans and humans related to delay of gratification, that is, the ability to tolerate long delays imposed between the initiation of behavior and the presentation of a reinforcer. RESULTS: Our results indicated that the violent female subjects selected the impulsive option significantly more often than the nonviolent female parolees. CONCLUSIONS: The correlation between impulsive and aggressive responses among the female parolees was nonsignificant and negative, in contrast to a significant positive correlation previously reported among male parolees.

Prolactin response to buspirone was reduced in violent compared to nonviolent parolees.

A neuroendocrine challenge procedure was carried out in male and female parolees. The parolees were divided into violent and non-violent groups based upon their criminal history. Buspirone (0.4 mg/kg), a 5-HT1a agonist, was used as the challenge agent and plasma prolactin levels were determined. The violent parolees had a blunted prolactin response compared to the non-violent parolees. While reduced serotonergic activity may account for this difference, the pharmacology of buspirone and control of prolactin release suggest a role for dopamine. A reduced serotonergic response would be consistent with a large body of data linking reduced serotonin function and aggressive behavior. While the mechanism is not definite, these data clearly provide evidence for an altered and blunted biological response in parolees with a history of violence.

The effects of tryptophan depletion and loading on laboratory aggression in men: time course and a food-restricted control.

Some studies have shown that sharp reduction of L-tryptophan (Trp) concentration in plasma results in increases in laboratory-measured aggression. Conversely, raising plasma Trp has blunted aggression. These effects are presumably due to impaired or enhanced serotonin synthesis and neurotransmission in the brain. In this study, the laboratory-measured aggressive behavior of eight men under both Trp depletion (T-) and Trp loading (T+) conditions was compared to their aggressive behavior under food-restricted control conditions (overnight fast without an amino acid beverage). Subjects were provoked by periodic subtraction of money which was attributed to a fictitious other participant, and aggression was defined as the number of retaliatory responses the subject made ostensibly to reduce the earnings of the (fictitious) other participant. Following ingestion of the T- beverage, aggressive responding was significantly elevated relative to the food-restricted control condition, and this increased aggressive behavior became more pronounced across behavioral testing sessions on a time-course which paralleled previously documented decreases in plasma Trp concentrations. In contrast, no changes were observed in aggressive responding under T+ conditions relative to food-restricted conditions. These within-subject behavioral changes under depleted plasma Trp conditions support earlier indications of a role of serotonin in regulating aggression.

Laboratory measurement of aggression in high school age athletes: provocation in a nonsporting context.

This study investigated the relationship between aggression and type of sports involvement in high school age boys. Athletes (16 boys), ages 15 to 18 years, were separated into two groups, one of 8 athletes who participated in sports with high physical contact, e.g., football and basketball, and the other of 8 athletes who participated in low contact sports, e.g., track and baseball. Students participated in six 25-min. Point Subtraction Aggression Paradigm sessions. The paradigm is an established laboratory model of aggression with three response options: (1) a point-maintained response, (2) an aggressive response, and (3) an escape response. Analysis indicated that the only difference between the groups was that individuals who participated in high contact sports emitted significantly more aggressive responses than individuals who participated in low contact sports. Similarly, psychometric measures of aggression indicated that individuals in the former group self-reported more behavioral incidents of aggression than those in the latter group.

Ipsapirone neuroendocrine challenge: relationship to aggression as measured in the human laboratory.

Thirty-one human subjects were administered a neuroendocrine challenge with the 5-HT1a agonist ipsapirone after completing six sessions of a laboratory measure of aggression, the Point Subtraction Aggression Paradigm (PSAP), in order to determine if a laboratory measure of aggression was related to serotonin function. Subjects who showed more aggressive responding on the PSAP (n = 11) had a significantly blunted temperature response to ipsapirone compared to those with less aggressive responding (n = 20). There was no difference between the two groups on the cortisol response to ipsapirone. This study supports a relationship between serotonin function and aggression as measured in the human laboratory, similar to the well-documented association between self-reported aggression and serotonin.

Laboratory measurement of adaptive behavior change in humans with a history of substance dependence.

Individuals vary in their ability to adapt to changes in environmental conditions. In the present study, two laboratory experiments investigated components of adaptation in subjects with and without a history of substance dependence. In each of two experiments, the subjects were exposed to conditions that required changing response patterns between experimental days. On day 1, subjects earned monetary rewards under conditions that produced high rate responding, but on day 2 were required to wait 10 s between each response. Collectively, the two experiments demonstrated that the subjects meeting criteria for past substance dependence, and having extensive histories of substance use (> 10 years), adjusted poorly to the transition. In both studies, these subjects tended to persevere on the previously established high-rate response pattern. These data suggest a deficiency in adaptive behavior change, particularly when that change requires an abrupt slowing of response rates following a brief history of high-rate responding.

Immediate versus delayed visual memory task performance among schizophrenic patients and normal control subjects.

In an exploratory study, 10 schizophrenic patients and 10 normal control subjects performed immediate and delayed memory tasks, which were variants of previously developed continuous performance tests. Both tasks required participants to identify five-digit numbers which were repeated. Numbers were presented in series for 500 ms each and separated by a 500-ms time-out period. In the immediate memory task, subjects were to respond if a number was identical to the one that had immediately preceded it. The delayed memory task differed from the first task in that a longer delay (3.5 s) between stimuli was introduced, and during this delay distracter stimuli appeared. While normal control subjects performed accurately on both tasks (exceeding 80% correct detections), schizophrenic patients performed poorly, performing worse on the delayed memory task than on the immediate memory task. Rates of commission errors (responses made to similar, but not identical numbers) were nearly equal between groups on the immediate memory task, but on the delayed memory task normal control subjects made relatively more commission errors while schizophrenic patients made fewer commission errors. No differences in response latencies were observed between subject groups or tasks. This paradigm may prove useful in discriminating subtle differences in immediate and delayed memory capability among psychiatric populations and normal control subjects.

Impulsivity and history of drug dependence.

Impulsivity was contrasted between 32 subjects with a history of drug-dependence (DRUG+) and 26 subjects with no drug use history (DRUG-) using both behavioral and self-report measures. The hypothesis was that the DRUG+ group would be more impulsive than the DRUG- group. Subjects in the DRUG+ group self-reported more of a tendency toward impulsivity than the DRUG- group in the situations posed in questionnaires. In the behavioural paradigm involving a choice between a smaller intermediate reward and a larger but delayed reward, DRUG+ subjects selected the impulsive option more often, but these differences were not significant. The DRUG+ and DRUG- groups did differ on the mean delay interval for the larger reward, indicating less ability to tolerate longer delays for the larger reward. A frequency distribution of delay intervals for the larger reward indicated that DRUG+ subjects were more likely to maintain very short intervals and less likely to maintain longer intervals.

Antisocial personality disorder and alcohol-induced aggression.

This study compared the effects of alcohol on aggressive responding between subjects with antisocial personality disorder (ASPD) and subjects without ASPD. Eighteen alcohol drinking subjects (10 subjects without ASPD and 8 subjects with ASPD) underwent testing on a laboratory measure of aggression, the Point Subtraction Aggression Paradigm, after consumption of placebo and three doses of alcohol (0.25 g/kg, 0.5 g/kg, and 1.0 g/kg). There was a significant difference in the effect of alcohol on aggressive responding on the Point Subtraction Aggression Paradigm between subjects with ASPD and subjects without ASPD. Subjects with ASPD had a greater increase in aggressive responding after alcohol, compared with non-ASPD subjects. There was no difference between the two groups in the effect of alcohol on monetary-reinforced responding.

Subjects with a history of drug dependence are more aggressive than subjects with no drug use history.

Aggressive responding was compared between 29 subjects with a history of substance dependence and 24 subjects with no drug use history, using the Point Subtraction Aggression Paradigm. The hypothesis was that subjects from the substance dependence history group would emit more aggressive responses than subjects with no drug use history. The substance dependence history group emitted more aggressive responses per session than the non drug using group (F(1,49) = 14.867, P = 0.032). These results are consistent with previous studies that have reported an association between aggression and drug abuse or dependence.

College on problems of drug dependence meeting, Puerto Rico (June 1996) marijuana use and dependence.

Discoveries concerning an endogenous cannabinoid system and observations of dramatic increases in marijuana use among youth in the United States have fueled a recent increase in basic and clinical research to better understand and treat marijuana dependence. At the annual meeting of the College on Problems of Drug Dependence (Puerto Rico, 1996) a symposium 'Marijuana Use: Basic Mechanisms, Epidemiology, and Clinical Issues' reviewed a number of important areas of ongoing research that address marijuana dependence. Overviews and original research were presented regarding the development of dependence (preclinical and clinical research), motivational effects (laboratory models), the epidemiology of dependence and its development, clinical management of marijuana use among patients seeking treatment for other drugs of abuse, and treatment for adult marijuana dependence. This paper summarizes the symposium presentations and provides discussion of recent scientific developments concerning marijuana use and dependence.