Psychomotor activity is one of the traits we most immediately perceive in others. Psychomotor slowing, which can be easily noticed on a first medical examination, is a symptom which may be prodromal of psychic disturbances.

Historically, psychomotor retardation is a characteristic attached to depression, especially melancholia. Some studies show that psychomotor retardation is associated with good therapeutic prognosis, including positive response to electro-convulsivo-therapy. The cluster of non-verbal symptoms includes both basic aspects related to motor behavior such as attitudes and movements and more complex aspects such as goal-directed behaviors. We will see that this intuitive and fundamental dimension of clinical depression is not homogeneous. From a motor point of view, hypo-bradykinesia in depression may be compared to the one found in cortico-subcortical syndromes such as Parkinson's disease. This comparison suggests that key brain structures such as the basal ganglia could be involved in depression.

Moreover, the loss of vital energy is the dominant psychopathological explanation linked to psychomotor retardation. From a phenomenological point of view, this interpretation seems to be relevant but appears disappointing as an experimental variable. However, motivation, understood as the factor that energizes the behavior seems to be an interesting and promising concept.

Experimentally, it is possible to measure how much an individual is able to invest energy in order to achieve a goal.

The impact of depression on the process of incentive motivation will be analyzed before turning to a description of therapeutic interventions related to psychomotor field such as sports or sensorimotor stimulations that appear to be promising tracks for clinical improvement.

Food uncertainty has the effect of invigorating food-related responses. Psychologists have noted that mammals and birds respond more to a conditioned stimulus that unreliably predicts food delivery, and ecologists have shown that animals (especially small passerines) consume and/or hoard more food and can get fatter when access to that resource is unpredictable. Are these phenomena related? We think they are. Psychologists have proposed several mechanistic interpretations, while ecologists have suggested a functional interpretation: The effect of unpredictability on fat reserves and hoarding behavior is an evolutionary strategy acting against the risk of starvation when food is in short supply. Both perspectives are complementary, and we argue that the psychology of incentive motivational processes can shed some light on the causal mechanisms leading animals to seek and consume more food under uncertainty in the wild. Our theoretical approach is in agreement with neuroscientific data relating to the role of dopamine, a neurotransmitter strongly involved in incentive motivation, and its plausibility has received some explanatory and predictive value with respect to Pavlovian phenomena. Overall, we argue that the occasional and unavoidable absence of food rewards has motivational effects (called incentive hope) that facilitate foraging effort. We show that this hypothesis is computationally tenable, leading foragers in an unpredictable environment to consume more food items and to have higher long-term energy storage than foragers in a predictable environment.

Serotonin 2C receptor (5-HT2CR) agonists attenuate reinstatement of cocaine-seeking behavior. These receptors are found throughout the limbic system, including the basolateral amygdala (BlA), which is involved in forming associations between emotional stimuli and environmental cues, and the central amygdala (CeA), which is implicated in the expression of conditioned responding to emotional stimuli. This study investigated whether 5-HT2CRs in the amygdala are involved in cue and cocaine-primed reinstatement of cocaine-seeking behavior. Rats were trained to self-administer cocaine (0.75 mg/kg, i.v.) which that was paired with light and tone cues, and then subsequently they underwent daily extinction training. Rats then received bilateral microinfusions of the 5-HT2CR agonist CP809101 (0.01–1.0 μg/0.2 μl/side) into either the BlA or CeA prior to tests for cue or cocaine-primed (10 mg/kg, i.p.) reinstatement. Rats were also tested for CP809101 effects on anxiety-like behavior on the elevated plus-maze (EPM). Surprisingly, intra-BlA CP809101 had no effect on cue reinstatement, though it did increase anxiety-like behavior on the EPM. Intra-CeA infusions of CP809101 attenuated cocaine-primed reinstatement, an effect that was prevented with concurrent administration of the 5-HT2CR antagonist SB242084 (0.1 μg/0.2 μl/side). CP809101 had no effect on cue reinstatement or anxiety-like behavior on the EPM. These findings suggest that 5-HT2CRs in the BlA modulate anxiety, whereas those in the CeA modulate incentive motivational effects induced by cocaine priming injections.

Neuroleptic drugs disrupt the learning and performance of operant habits motivated by a variety of positive reinforcers, including food, water, brain stimulation, intravenous opiates, stimulants, and barbiturates. This disruption has been demonstrated in several kinds of experiments with doses that do not significantly limit normal response capacity. With continuous reinforcement neuroleptics gradually cause responding to cease, as in extinction or satiation. This pattern is not due to satiation, however, because it also occurs with nonsatiating reinforcement (such as saccharin or brain stimulation). Repeated tests with neuroleptics result in earlier and earlier response cessation reminiscent of the kind of decreased resistance to extinction caused by repeated tests without the expected reward. Indeed, withholding reward can have the same effect on responding under later neuroleptic treatment as prior experience with neuroleptics themselves; this suggests that there is a transfer of learning (really unlearning) from nonreward to neuroleptic conditions. These tests under continuous reinforcement schedules suggest that neuroleptics blunt the ability of reinforcers to sustain responding at doses which largely spare the ability of the animal to initiate responding. Animals trained under partial reinforcement, however, do not respond as well during neuroleptic testing as animals trained under continuous reinforcement. Thus, neuroleptics can also impair responding (though not response capacity) that is normally sustained by environmental stimuli (and associated expectancies) in the absence of the primary reinforcer. Neuroleptics also blunt the euphoric impact of amphetamine in humans. These data suggest that the most subtle and interesting effect of neuroleptics is a selective attenuation of motivational arousal which is (a) critical for goal-directed behavior, (b) normally induced by reinforcers and associated environmental stimuli, and (c) normally accompanied by the subjective experience of pleasure. Because these drugs are used to treat schizophrenia and because they cause parkinsonian-like side effects, this action has implications for a better understanding of human pathology as well as normal motivational processes.

The sway that the response-reinforcement framework (Spencer, Thorndike, Hull, Skinner) has held on the behavioral sciences for nearly a hundred years is finally ending. The strength of this framework lay in providing concepts and methods for studying the effects of hedonic (reinforcing) stimuli on the repetition of specified responses acquired in instrumental training situations of various kinds. Its weakness lay in the invalidity of its central assumptions, stimulus-response association and response-reinforcement, which could not deal with motor-equivalence and flexibility (or “intelligence”) in behavior. To the four decades of incisive criticism on particular theoretical and empirical grounds, a more comprehensive challenge to the response-reinforcement framework is now added by the newer ideas about the nature of cognitive, motivational, and response-production processes that have emerged from the work of ethologists, neuroscientists, and cognitive psychologists. An alternative framework, incorporating the newer ideas, is clearly needed.

The particular framework proposed here is based on the ideas of perceptual learning of stimulus-stimulus correlations and of a motivational (rather than reinforcing) role of hedonic (incentive) stimuli. According to it, an act is produced when its act-assembly is activated by a pexgo (perceptual representation) of a certain eliciting stimulus complex (ES). When certain eliciting stimuli are correlated with incentive stimuli, they acquire motivational properties that serve to strengthen the pexgos generated by those eliciting stimuli and thereby increase the probability of activation of the corresponding act-assemblies. Motivation thus influences response production, not by directly instigating “existing” responses, but by modulating the strength of pexgos of eliciting stimuli for the succession of acts that comprise a response. Therefore, a response is always constructed afresh on the basis of current perceptions; not even a stable and stereotyped response occurs as a mere activation of a preformed motor program. The topography of any response that emerges is determined by the nature of the motivational state and the momentary spatiotemporal distribution of eliciting stimuli of changing motivational valence.

By suggesting that the animal learns the overlapping and nested correlations between the stimulus events that commonly occur in a given situation, and by separating what is learned from the processes of response production, the proposed perceptual-motivational framework seems capable of dealing with the problems of motor equivalence and flexibility in adaptive behavior. Some implications of this approach for further behavioral and brain research on such problems as behavior modification, learning by observation of models, analysis of causality, and search for neural substrates of learning and response production, are outlined.

Extraversion has two central characteristics: (1) interpersonal engagement, which consists of affiliation (enjoying and valuing close interpersonal bonds, being warm and affectionate) and agency (being socially dominant, enjoying leadership roles, being assertive, being exhibitionistic, and having a sense of potency in accomplishing goals) and (2) impulsivity, which emerges from the interaction of extraversion and a second, independent trait (constraint). Agency is a more general motivational disposition that includes dominance, ambition, mastery, efficacy, and achievement. Positive affect (a combination of positive feelings and motivation) is closely associated with extraversion. Extraversion is accordingly based on positive incentive motivation.

Parallels between extraversion (particularly its agency component) and a mammalian behavioral approach system based on positive incentive motivation implicate a neuroanatomical network and modulatory neurotransmitters in the processing of incentive motivation. A corticolimbic-striatal-thalamic network (1) integrates the salient incentive context in the medial orbital cortex, amygdala, and hippocampus; (2) encodes the intensity of incentive stimuli in a motive circuit composed of the nucleus accumbens, ventral pallidum, and ventral tegmental area dopamine projection system; and (3) creates an incentive motivational state that can be transmitted to the motor system.

Individual differences in the functioning of this network arise from functional variation in the ventral tegmental area dopamine projections, which are directly involved in coding the intensity of incentive motivation. The animal evidence suggests that there are three neurodevelopmental sources of individual differences in dopamine: genetic, “experience-expectant,” and “experience-dependent.” Individual differences in dopamine promote variation in the heterosynaptic plasticity that enhances the connection between incentive context and incentive motivation and behavior.

Our psychobiological threshold model explains the effects of individual differences in dopamine transmission on behavior, and their relation to personality traits is discussed.