In a choice among assured, familiar outcomes of behavior, impulsiveness is the choice of less rewarding over more rewarding alternatives. Discussions of impulsiveness in the literature of economics, sociology, social psychology, dynamic psychology and psychiatry, behavioral psychology, and \"behavior therapy\" are reviewed. 'Impulsiveness seems to be best accounted for by the hyberbolic curves that have been found to describe the decline in effectiveness of rewards as the rewards are delayed from the time of choice. Such curves predict a reliable change of choice between some alternative rewards as a function of time. This change of choice provides a rationale for the known kinds of impulse control and relates them to several hitherto perplexing phenomena: behavioral rigidity, time-out from positive reinforcement, willpower, self-reward, compulsive traits, projection, boredom, and the capacity of punishing stimuli to attract attention.

Specious reward: a behavioral theory of impulsiveness and impulse control.

The study of pain in awake animals raises ethical, philosophical, and technical problems. We review the ethical standards for studying pain in animals and emphasize that there are scientific as well as moral reasons for keeping to them. Philosophically, there is the problem that pain cannot be monitored directly in animals but can only be estimated by examining their responses to nociceptive stimuli; however, such responses do not necessarily mean that there is a concomitant sensation. The types of nociceptive stimuli (electrical, thermal, mechanical, or chemical) that have been used in different pain models are reviewed with the conclusion that none is ideal, although chemical stimuli probably most closely mimic acute clinical pain. The monitored reactions are almost always motor responses ranging from spinal reflexes to complex behaviors. Most have the weakness that they may be associated with, or modulated by, other physiological functions. The main tests are critically reviewed in terms of their sensitivity, specificity, and predictiveness. Weaknesses are highlighted, including 1) that in most tests responses are monitored around a nociceptive threshold, whereas clinical pain is almost always more severe; 2) differences in the fashion whereby responses are evoked from healthy and inflamed tissues; and 3) problems in assessing threshold responses to stimuli, which continue to increase in intensity. It is concluded that although the neural basis of the most used tests is poorly understood, their use will be more profitable if pain is considered within, rather than apart from, the body's homeostatic mechanisms.

Animal Models of Nociception

Attention-deficit/hyperactivity disorder (ADHD) is currently defined as a cognitive/behavioral developmental disorder where all clinical criteria are behavioral. Inattentiveness, overactivity, and impulsiveness are presently regarded as the main clinical symptoms. The dynamic developmental behavioral theory is based on the hypothesis that altered dopaminergic function plays a pivotal role by failing to modulate nondopaminergic (primarily glutamate and GABA) signal transmission appropriately. A hypofunctioning mesolimbic dopamine branch produces altered reinforcement of behavior and deficient extinction of previously reinforced behavior. This gives rise to delay aversion, development of hyperactivity in novel situations, impulsiveness, deficient sustained attention, increased behavioral variability, and failure to "inhibit" responses ("disinhibition"). A hypofunctioning mesocortical dopamine branch will cause attention response deficiencies (deficient orienting responses, impaired saccadic eye movements, and poorer attention responses toward a target) and poor behavioral planning (poor executive functions). A hypofunctioning nigrostriatal dopamine branch will cause impaired modulation of motor functions and deficient nondeclarative habit learning and memory. These impairments will give rise to apparent developmental delay, clumsiness, neurological "soft signs," and a "failure to inhibit" responses when quick reactions are required. Hypofunctioning dopamine branches represent the main individual predispositions in the present theory. The theory predicts that behavior and symptoms in ADHD result from the interplay between individual predispositions and the surroundings. The exact ADHD symptoms at a particular time in life will vary and be influenced by factors having positive or negative effects on symptom development. Altered or deficient learning and motor functions will produce special needs for optimal parenting and societal styles. Medication will to some degree normalize the underlying dopamine dysfunction and reduce the special needs of these children. The theory describes how individual predispositions interact with these conditions to produce behavioral, emotional, and cognitive effects that can turn into relatively stable behavioral patterns.

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A dynamic developmental theory of attention-deficit/hyperactivity disorder (ADHD) predominantly hyperactive/impulsive and combined subtypes.

Intensification of the central serotoninergic processes as a possible determinant of the thymoleptic effect.

The involvement of nucleus accumbens dopamine in appetitive and aversive motivation

Behavioral responses developed in rats have been employed in the evaluation of the comparative effects of several central nervous system (CNS) active pharmacological agents. Differentiation has been made between those CNS active materials that have a specific effect on a conditioned response (chlorpromazine, reserpine, morphine), and those that have a somewhat nonspecific effect on a conditioned response (barbital, pentobarbital, methylparafynol, meprobamate). The interrelationships between reserpine and serotonin in the CNS have been described by Pletscher et al.’ The effect of serotonin itself upon a conditioned response has also been examined in this study. Lysergic acid diethylamide (LSD) has been reported to antagonize certain properties of serotonin (Gaddum,2 Shore et ~ l . , ~ Costa4) and reserpine (Shore et ~ 1 . ~ ) . We have utilized the conditioned response to examine the interactions of lysergic acid diethylamide with reserpine and serotonin, as well as chlorpromazine, morphine, and meprobamate. Mescaline was also studied, in a manner similar to LSD-25, for possible interaction with conditioned-response blocking agents.

Behavioral effects of some psychopharmacological agents.

A mathematical index of performance on fixed-interval schedules of reinforcement.

Fighting episodes were produced in mice by exposing the animals to a mild footshock. This method permitted the objective measurement of the frequency of discrete fighting episodes in fighting pairs of mice. The effects of variations in stimulus intensity were studied and the optimum parameters for producing fighting episodes were determined. A quantal type assay procedure was devised in an effort to study the effects of centrally active drugs on the frequency of fighting episodes. Compounds were also studied for their effect in depressing spontaneous motor activity and protecting against maximal electroshock seizures. Reserpine and the phenothiazines that were tested suppressed fighting episodes only in doses which produced a moderate to marked degree of motor inactivation. Diphenylhydantoin and phenobarbital were more effective as anticonvulsants than in suppressing fighting episodes. Of the compounds studied in this battery of tests meprobamate exhibited a particular profile of activity which differentiated it from any of the other compounds studied. This pattern of activity was characterized by a mild degree of anticonvulsant activity, a mild depression of spontaneous motor activity and a more pronounced suppression of fighting episodes.

Effects of various centrally acting drugs on fighting behavior of mice.

Approaches to the study of behavioral effects of drugs range from observations of drug-induced symptomatology in untrained animals to objective studies of the effects of drugs on the complex behavior of highly trained animals. With the development of certain psychopharmacological principles a number of preconceptions have concurrently developed about the effects of drugs on behavior and the relevance of specific experimental techniques. The present paper analyzes principles and preconceptions that are related to several of our investigations of the effects of drugs on behavior. One of the early test procedures we employed to study the effects of drugs on behavior was a conditioned avoidance-escape response in rats. This widely used procedure is sensitive to the effects of many psychopharmacological agent^.^ Rats are conditioned to avoid an electric foot shock by climbing a pole. Three types of responses are exhibited after drug administration: (1) response to both the unconditioned stimulus (US) and conditioned stimulus (CS) ; this type of response is seen in control rats and in rats that received ineffective treatments; (2) response to the US but not to the CS; this indicates a specific block of the conditioned avoidance response; and (3) failure to respond to either the US or the CS; this indicates a nonspecific block of the conditioned avoidance r e s p o n ~ e . ~ , ~ ' ~ ~ Failure to respond to the US usually indicates an inability to climb due to motor incapacitation. Chlorpromazine, prochlorperazine, trifluoperazine, promazine, triflupromazine, perphenazine, reserpine, serotonin, and morphine are among the drugs that produced a specific block of the conditioned avoidance response. Meprobamate, barbital, pentobarbital, phenobarbital, methylparafynol, and mephenesin are among the drugs that produced nonspecific blocks of the conditioned avoidance response. Even the restricted response measured in this procedure is based upon complex mechanisms that can be altered by a variety of pharmacological effect^.^ The effects of drug interaction studies show that conditioned avoidance responses can be altered by affecting different mechanisms.3 Many of the compounds tested in the conditioned avoidance-escape procedure in rats have been used clinically in the treatment of severe mental and emotional disorders. TABLE 1 shows that the potency of a number of phenothiazines in blocking conditioned avoidance responses correlates well with their potency as used in mental and emotional disorders.G~8~10-'\"~18,20-23 28 If nonphenothiazines were included in the table, the correlation would be altered. It should not be assumed, however, that behavior maintained by aversive events is particularly relevant in the evaluation of all types of psychopharmacological agents. Recent experiments in our laboratories were designed to study the effects of positively and negatively reinforced behavior maintained concurrently in individual animals. On this concurrent avoidance fixed-ratio procedure, monkeys respond both to avoid electric shock and to obtain food. If the monkey does not respond (press a lever), it is shocked every 30 sec.;

Drug effects on the behavior of animals

Schedules of positive reinforcement were used to test the effects of meprobamate on the behavior of rats. On an FR 50 schedule, meprobamate had effects only at neurotoxic doses. On other schedules (DRL 18 LH 3, VI 1½, FI 5), meprobamate increased response rates. The effects of meprobamate were compared with effects of mephenesin, phenobarbital, chlorpromazine, prochlorperazine, and d -amphetamine on the DRL 18 LH 3 and FR 50 schedules. Mephenesin, chlorpromazine, and prochlorperazine did not increase response rates on the DRL 18 LH 3 schedule. Although there were some similarities between the effects of meprobamate and the effects of phenobarbital and d -amphetamine, qualitative differences were described.

Leonard Cook

Papers

Behavioral effects of some psychopharmacological agents.

A mathematical index of performance on fixed-interval schedules of reinforcement.

Effects of various centrally acting drugs on fighting behavior of mice.

Drug effects on the behavior of animals

Effects of meprobamate on operant behavior in rats.