Dawn M. Marsh

Laboratory behavioral measures of impulsivity

Previous research and theory have conceptualized impulsivity as a multifaceted construct that requires multiple modes of measurement for accurate assessment. This article describes a software package that includes four paradigms for measuring multiple and unique aspects of impulsivity. Specifically, four tasks are described: (1) the two choice impulsivity paradigm, (2) the single key impulsivity paradigm, (3) the GoStop impulsivity paradigm, and (4) the time paradigm. These tasks measure processes related to the capacity to tolerate delay for reward, to inhibit an already initiated response, and to estimate the passage of time. These processes have been found to be important to the understanding of impulsive behaviors. The programs are flexible and allow the experimenter to manipulate a number of parameters related to delay-reward contingencies, timing, performance feedback/payment, and data output variables. Manipulation of these parameters makes the paradigms scalable to a wide range of ability levels and appropriate for samples ranging from children to adults. The four paradigms in this software package are available at no cost and can be obtained by contacting the corresponding author.

Behavioral impulsivity paradigms: a comparison in hospitalized adolescents with disruptive behavior disorders.

BACKGROUND Behavioral impulsivity paradigms vary widely and studies using these measures have typically relied on a single measure used in isolation. As a result, comparisons between measures are difficult, with little consensus regarding which method may be most sensitive to individual impulsivity differences of different populations. METHOD A single testing session of each of four different impulsivity tasks was completed by two groups of adolescents aged 13-17: hospitalized inpatients with disruptive behavior disorders (DBD; n = 22) and controls (n = 22). Tasks included two rapid-decision (IMT/DMT and GoStop) and two reward-directed (TC and SKIP) impulsivity paradigms. Behavioral testing took place within 3 days of hospitalization for the adolescents with DBD. RESULTS Compared to controls, the DBD group exhibited higher commission error rates, lower inhibited response rates after a stop-signal, and twice as many reward-directed responses even after IQ differences between the groups were taken into account. When the four paradigms were compared, effect-size calculations indicated that the two rapid-decision paradigms were more sensitive to group differences than the reward-directed tasks. CONCLUSIONS Despite the initiation of pharmacotherapy within the first 3 days of hospitalization, in contrast to the control group, the adolescents with DBD performed consistently with what has been operationally defined as impulsivity. Based on these results, these tasks appear to measure similar, but unique components of the impulsivity construct. With further study, laboratory behavioral paradigms may prove to be useful additions to current clinical diagnostic and treatment procedures in a variety of psychiatric populations.

Immediate and delayed memory tasks: A computerized behavioral measure of memory, attention, and impulsivity

The Immediate and Delayed Memory Task (IMT/DMT), a variant of the Continuous Performance Test (CPT), is a new software package designed to be a flexible research tool for the study of attention, memory, and impulsivity. This package allows researchers to determine the design to be used during a testing session and to manipulate many of the parameters. It features two components: the IMT and the DMT, both of which present sequential 2- to 7-digit stimuli with variable presentation rates and intertrial intervals. Subjects respond to identically matched stimuli presented consecutively, spanning a brief period of time (IMT), or to stimuli spanning a greater period of time (during which intervening stimuli to be ignored appear; DMT). Task complexity can be adjusted to suit applications for both children and adults. Preliminary studies have demonstrated that these laboratory tasks are sensitive to group differences, produce stable baselines of performance, and are sensitive to drug-induced performance decrements.

Comparisons of women with high and low trait impulsivity using behavioral models of response-disinhibition and reward-choice

Two types of behavioral models of impulsive behavior, response-disinhibition/attentional and reward-choice response models, were used to compare women grouped by high (Impulse+, n=43) and low (Impulse−, n=43) self-reported impulsive behavior on the Eysenck I7 Questionnaire. Two of the four different tasks tested were response-disinhibition/attentional models; these included the Immediate and Delayed Memory Task and the GoStop Task. The other two tasks were based on the reward-choice model of impulsivity and included the Single Key Impulsivity Paradigm and the Two-Choice Reward Task. Of particular interest was whether commission errors (response-disinhibition/attentional paradigms) or a preference for smaller–sooner rewards over larger–later rewards (reward-choice) would differ between the groups. Participants completed one session of each task in a single day. The most significant findings were that the Impulse+ group had: (1) elevated commission errors; (2) lower stimulus discriminability (between target and catch stimuli); and (3) poorer response inhibition to a stop signal. Responding on the response-disinhibition/attentional tasks distinguished between the impulsivity groups while the reward-choice tasks did not. These results demonstrate that women who report higher levels of trait impulsivity respond in a manner consistent with previous studies examining impulsive behavior.

A comparison between adults with conduct disorder and normal controls on a continuous performance test: Differences in impulsive response characteristics

Continuous Performance Test (CPT) responding was compared between 15 adults with a history (childhood/adolescent) of Conduct Disorder (CD) and 15 normal controls. Of particular interest was whether response latencies and commission errors, which have been suggested to be measures of impulsivity, would differ between the groups. The CPT procedure used included two conditions: Immediate Memory Task and Delayed Memory Task (IMT/DMT; Dougherty et al., 1998). Both the IMT (0.5-s delay) and DMT (3.5-s delay with distracter stimuli at 0.5-s intervals) required the subject to respond if a briefly displayed number was identical to the one presented before it. Stimuli included target (identical match), catch (four of five digits matched), and novel (no match). Participants completed six 22-min testing sessions scheduled across a single day. The most significant findings were that the CD group (compared to the control group) had (a) elevated commission errors (responses to catch stimuli); (b) lower stimulus discriminability (between target and catch stimuli); and (c) shorter response latencies. These results are consistent with the few previous studies indicating that these parameters are related to impulsive behaviors.

Laboratory-Measured Aggressive Behavior of Women: Acute Tryptophan Depletion and Augmentation

Plasma L-tryptophan (Trp) reductions have been related to aggression increases in men. Impairment of serotonin synthesis and neurotransmission is one explanation. Using repeated-measures, this Trp manipulation study measured laboratory-induced aggression in 12 women after Trp augmentation (T+), depletion (T−), and food-restricted (fasting control) conditions. Participants were provoked with periodic subtraction of money from their task earnings by a (fictitious) partner. Aggression was defined as the number of point subtractions participants made from their fictitious partner. Participants completed five testing sessions under each condition. T+ decreased aggressive responses and T− increased aggressive responses. Post-hoc analyses showed changes in aggressive behavior were specific to women with higher fasting control plasma Trp, which is consistent with research demonstrating that men with higher levels of baseline Trp are more aggressive. These findings indicate that both T+ and T− can influence aggressive behavior and that certain subgroups of women may be more susceptible to serotonin manipulation.

Influence of trait hostility on tryptophan depletion-induced laboratory aggression

Previous research has indicated that laboratory aggression in men increases after temporarily reducing the synthesis and neurotransmission of serotonin (5-HT) in the brain using the plasma L-tryptophan (Trp) depletion technique. Further research indicates that male subjects selected for high trait hostility are particularly prone to increased aggression following plasma Trp depletion. In a recent study of laboratory aggression in male control subjects, we demonstrated that laboratory aggression increased following ingestion of a Trp-depleting beverage, but not after ingestion of a Trp-containing beverage nor under food-restricted conditions. We report here that the increases in aggression under Trp-depleted conditions were specific to men who scored the highest on the Buss-Perry Aggression Questionnaire. These preliminary data support earlier findings that compared to non-hostile men, hostile men may be more prone to behavior change induced by the perturbation of the 5-HT neurotransmitter system.

Characterizing aggressive behavior with the Impulsive/Premeditated Aggression Scale among adolescents with conduct disorder.

This study extends the use of the Impulsive/Premeditated Aggression Scale for subtyping aggressive behavior among adolescents with Conduct Disorder. Of the Conduct Disorder symptoms, aggression has the strongest prognostic and treatment implications. While aggression is a complex construct, convergent evidence supports a dichotomy of impulsive and premeditated aggressive subtypes that are qualitatively different from one another in terms of phenomenology and neurobiology. Previous attempts at measuring subtypes of aggression in children and adults are not clearly generalizable to adolescents. Sixty-six adolescents completed a questionnaire for characterizing aggression (Impulsive/Premeditated Aggression Scale), along with standard measures of personality and general functioning. Principal components analysis demonstrated two stable factors of aggression with good internal consistency and construct validity. Compared to the premeditated aggression factor, the impulsive aggression factor was associated with a broader range of personality, thought, emotional, and social problems. As in the adult and child literature, characterization of aggressive behavior into two subtypes appears to be relevant to understanding individual differences among adolescents with Conduct Disorder.

Validation of the Immediate and Delayed Memory Tasks in Hospitalized Adolescents With Disruptive Behavior Disorders

This study explores concurrent and criterion validity of a Continuous Performance Test, the Immediate and Delayed Memory Tasks (IMT/DMT). Concurrent validity was examined through comparison with collateral measures of impulsivity, while criterion validity was assessed by comparison of groups with differing levels of impulsive behavior, those with and without disruptive behavior disorders (DBD). DBDs in the DSM-IV include conduct disorder and oppositional defiant disorder, which are both largely characterized by impulsive behaviors. We compared group performance on the IMT/DMT and several collateral measures of impulsivity between adolescent controls (n = 22) and psychiatric inpatients with a DBD diagnosis (n = 22). Data collected indicated that (1) DBD patients emitted more commission errors; (2) commission errors, but not correct detections, were significantly correlated with collateral measures of impulsivity, and (3) in posthoc comparisons, those DBD patients with histories of physical fighting emitted the greatest number of commission errors, followed by DBD nonfighters, and then controls. Similar group performance differences were observed for collateral impulsivity measures. This study supports the use of commission error rates on the Immediate and Delayed Memory Tasks as a behavioral measure of impulsivity. With further development, objective measures like these may prove useful in clinical assessment procedures and in monitoring treatment outcome.

Familial Transmission of Continuous Performance Test Behavior: Attentional and Impulsive Response Characteristics

Abstract Continuous Performance Tests (CPTs) provide information on attentional processing and impulsive behavior. The results of previous research that used self-report measures have provided evidence for familial transmission (through genetic and/or environmental influences) of impulsive characteristics. The authors of the present study examined whether the impulsive behavioral parameters that are measured by the CPT also share familial relationships. The researchers asked 26 healthy parent-adolescent pairs to complete the Immediate and Delayed Memory Tasks (IMT/DMT; D. M. Dougherty, 1999; D. M. Dougherty, D. M. Marsh, & C. W. Mathias, 2002), a modified CPT (B. A. Cornblatt, N. J. Risch, G. Faris, D. Friedman, & L. Erlenmeyer-Kimling, 1988; H. E. Rosvold, A. Mirsky, I. Sarason, E. D. Breansome, Jr., & L. H. Beck, 1956), and the Barratt Impulsiveness Scale (BIS; J. H. Patton, M. S. Stanford, & E. S. Barratt, 1995), a self-report measure. The main findings can be summarized as follows: (a) commission errors (but not correct detections) on the IMT and DMT were correlated between parents and their adolescent children, (b) adolescents emitted a higher proportion of commission errors than did their parents, and (c) self-reported impulsivity (i.e., BIS) was correlated with commission errors for parents, but not for adolescents. The findings of this study support the use of an objective behavioral measure of impulsivity to assess familial relationships of impulsivity.