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.

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.

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.

The purpose of this study was to examine the relationship between laboratory behavioral measured impulsivity (using the Immediate and Delayed Memory Tasks) and suicidal attempt histories. Three groups of adults were recruited, those with either: no previous suicide attempts (Control, n = 20), only a single suicide attempt (Single, n = 20), or multiple suicidal attempts (Multiple, n = 10). As hypothesized, impulsive responses increased with the number of suicide attempts (Control < Single < Multiple). This study helps to demonstrate how laboratory behavioral measures of impulsivity can be used to discriminate groups based on suicidal histories among samples not currently exhibiting significant suicidal behaviors.

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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 aI., 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.A number of different approaches have been used to study impulsive responding in the laboratory. One of the most popular methods is the operant model, which defines impulsive responding as a choice for a smaller immediate reinforcer over a larger delayed reinforcer. The advantages of this approach are its rich history from which comparisons can be made and the clearly defined responses that are amenable to statistical and theoretical analyses (see Anslie, 1975, for a review). As a result, the operant conditioning perspective remains a popular model for investigating impulsive choice behavior in both humans and nonhumans

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 ϩ ), depletion (T Ϫ ), 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 ϩ decreased aggressive responses and T Ϫ 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 ϩ and T Ϫ can influence aggressive behavior and that certain subgroups of womenA number of psychobiological syndromes characterized by poor impulse control have been associated with low concentrations of the major serotonin (5-HT) metabolite 5-hydroxyindoleacetic acid (5-HIAA) in cerebrospinal fluid (CSF). Serotonin dysfunction has been correlated with impulsive and violent criminal behaviors (Brown et al. , 1982Lidberg et al. 1985;Limson et al., 1991;Virkkunen and Närvänen 1987;Virkkunen et al. 1994aVirkkunen et al. , 1994b, alcohol abuse and dependence (Badawy et al. 1995;Ballenger et al. 1979;Banki 1981;Borg et al. 1985;Moss 1987;Roy and Linnoila 1989), Gilles de la Tourette's syndrome (Butler et al. 1979;Cohen et al. 1978Cohen et al. , 1979, bulimia (Jimerson et al. 1990(Jimerson et al. , 1992, and suicide attempts (Asberg et al. 1976(Asberg et al. , 1986Banki and Arato 1983;López-Ibor et al. 1985), as well as with children institutionalized for aggressive behavior (Kruesi 1989;Kruesi et al. 1990Kruesi et al. , 1992.Direct experimental manipulation of 5-HT levels and the measurement of resultant behavior have provided stronger evidence for the connection between central nervous system (CNS) 5-HT and impulsive/aggressive behaviors. Serotonin synthesis depends on the availability of the essential amino acid tryptophan (Trp). Thus, manipulation of 5-HT can be accomplished through increases or decreases in dietary Trp, which in turn increases or decreases plasma Trp and ultimately 5-HT in the CNS Gessa et al. 1974; Online publication: 9/14/01 at www.acnp.org/citations/ Npp091401176. N EUROPSYCHOPHARMACOLOGY 2002 -VOL . 26 , NO . 5 Tryptophan and Aggression 661 Young et al. 1989). This manipulation is postulated to affect brain 5-HT because 5-HT synthesis depends primarily on Trp availability (Fernstrom 1983 (Carpenter et al. 1998;Young and Gauthier 1981), rate reductions of 5-HT synthesis in the human brain (Nishizawa et al. 1997), and blunted release of 5-HT from serotonergic neurons in vivo (Stancampiano et al. 1997). As a res...

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