Stimulant-induced adaptations in neostriatal matrix and striosome systems: transiting from instrumental responding to habitual behavior in drug addiction

Converging evidence indicates that repeated exposure to motor stimulants such as cocaine and amphetamine produces marked alterations in network responsiveness of striatal neurons to subsequent challenge with the same stimulant drug. Such alterations, which correlate with persistent patterns of repetitive behavior, associate with distinct compartmental changes in the neostriatum. Striatal matrix system neurons undergo "silencing" following repeated drug challenges, allowing striosome system neurons to exhibit preferential activation. Matrix neurons are innervated by sensory and motor areas of neocortex and are activated in the course of on-going, adaptive behavior. Inactivation of matrix neurons by chronic stimulant exposure may therefore constrain sensorimotor and cognitive processing. In turn, the striosomes are anatomically connected through re-entrant loops with limbic prefrontal and allocortical structures, such as anterior cingulate cortex, orbital frontal cortex, and basolateral amygdala, all of which play a part in stimulant-induced reinforcement and relapse to drug-taking. Moreover, functional evidence links striosome system neurons, which are responsible for providing inhibitory regulatory feedback to midbrain dopamine neurons, with reinforcement-based processes. In considering such evidence, we postulate that recurrent matrix inactivation and recruitment of striosome-based pathways by chronic stimulant exposure represent neural end-points of the transit from action-outcome associative behavior to conditioned habitual responding. Within this theoretical framework, habitual behavior can be elicited by both interoceptive cues and exteroceptive conditioned stimuli to promote the automatic execution of learned responses.     

Brain potentials to native and non-native speech contrasts in 7- and 11-month-old American infants

Abstract Behavioral data establish a dramatic change in infants' phonetic perception between 6 and 12 months of age. Foreign-language phonetic discrimination significantly declines with increasing age. Using a longitudinal design, we examined the electrophysiological responses of 7- and 11-month-old American infants to native and non-native consonant contrasts. Analyses of the event-related potentials (ERP) of the group data at 7 and at 11 months of age demonstrated that infants' discriminatory ERP responses to the non-native contrast are present at 7 months of age but disappear by 11 months of age, consistent with the behavioral data reported in the literature. However, when the same infants were divided into subgroups based on individual ERP components, we found evidence that the infant brain remains sensitive to the non-native contrast at 11 months of age, showing differences in either the P150-250 or the N250-550 time window, depending upon the subgroup. Moreover, we observed an increase in infants' responsiveness to native language consonant contrasts over time. We describe distinct neural patterns in two groups of infants and suggest that their developmental differences may have an impact on language development.     

Visual behavior and perception of trajectories of moving objects with visual occlusion

Experienced athletes in sports with moving objects have shown greater skill when using visual information to anticipate the direction of a moving object than nonexperienced athletes of those sports. Studies have shown that expert athletes are more effective than novices in occlusion situations in the first stages of the sports sequence. In this study, 12 athletes with different competitive experience in sports with moving objects viewed a sequence of tennis ball launches with and without visual occlusion, launched by a ball-shooting machine toward different areas with respect to the participant's position. The relation among visual behavior, occlusion time, and the precision of the task is reviewed. The spot where the balls bounced was analysed by a digital camera and visual behavior by an Eye Tracking System. Analysis showed that the nonexperienced athletes made significantly more errors and were more variable in visual occlusion conditions. Participants had a stable visual search strategy.     

Perception without awareness: further evidence from a Stroop priming task

In the present research, we examined the influence of prime-target stimulus onset asynchrony (SOA) on Stroop-priming effects from masked words. Participants indicated the color of a central target, which was preceded by a 33-msec prime word followed either immediately or after a variable delay by a pattern mask. The prime word was incongruent or congruent with the target color on 75% and 25% of the trials, respectively. The words followed by an immediate mask produced reliable Stroop interference at SOAs of 300 and 400 msec but not at SOAs of 500 and 700 msec. The words followed by a delayed mask produced a reversed (i.e., facilitatory) Stroop effect, which reached significance at an SOA of 400 msec or longer, but never at the shorter 300-msec SOA. Such an differential time course of both types of Stroop priming effects provides further evidence for the existence of qualitative differences between conscious and nonconscious perceptual processes.     

Mental models in deductive reasoning

We report research investigating the role of mental models in deduction. The first study deals with conjunctive inferences (from one conjunction and two conditional premises) and disjunctive inferences (from one disjunction and the same two conditionals). The second study examines reasoning from multiple conditionals such as: If e then b; If a then b; If b then c; What follows between a and c? The third study addresses reasoning from different sorts of conditional assertions, including conditionals based on if then, only if, and unless. The paper also presents research on figural effects in syllogistic reasoning, on the effects of structure and believability in reasoning from double conditionals, and on reasoning from factual, counterfactual, and semifactual conditionals. The findings of these studies support the model theory, pose some difficulties for rule theories, and show the influence on reasoning of the linguistic structure and the semantic content of problems.     

Motivational versus volitional mediation of passivity in institutionalized older people

The relationship between perceived loss of control and passivity in social activities in a non-handicapped institutionalized elderly population was assessed. Perceived loss of control was assessed from three different types of expectancies: low action-outcome expectancies, high situation-outcome expectancies, and low efficacy expectancies. Passivity scores were reported by the staff. The effect of these three types of expectancies on passivity was analyzed in terms of motivation and volition, which were treated as mediating variables. Overall analysis of the structural equations, as well as partial hierarchical regression analyses, showed that efficacy expectancies were good predictors of passivity, but this was not the case for the action-outcome and situation-outcome expectancies. These results lend more support to a volitional rather than to a motivational interpretation of the effect of control on passivity. The implications of these results for intervention and for a differentiated conception of expectancies are discussed.     

Neuropsychological Findings in Congenital and Acquired Childhood Hydrocephalus

Hydrocephalus is an increase in cerebrospinal fluid volume that can be caused by a variety of etiologies. The most common connatal and acquired causes of hydrocephalus are spina bifida, aqueduct stenosis, and preterm low birthweight infants with ventricular hemorrhage. In general, the literature suggests mild neuropsychological deficits associated with hydrocephalus, which are predominant in visuospatial and motor functions, and other nonlanguage skills. Although the precise nature of the neuropsychological deficits in hydrocephalus are not completely known, several factors such as etiology, raised intracranial pressure, ventricular size, and changes in gray and white matter tissue composition as well as shunt treatment complications have been shown to influence cognition. In fact, the presence of complications and other brain abnormalities in addition to hydrocephalus such as infections, trauma, intraventricular hemorrhage, low birthweight, and asphyxia are important determinants of the ultimate cognitive status, placing the child at a high risk of cognitive impairment.     

Patterns of hemispheric perceptual asymmetries: left hemispatial biases predict changes in anxiety and positive affect in undergraduate women

Consistent with the tripartite model of anxiety and depression, hemispheric asymmetries may be differentially associated with depressive and anxious symptoms. Indeed, research has demonstrated that asymmetries do exist when examining hemispatial biases in both anxious and depressed individuals; however, the magnitude and direction of these asymmetries has been variable. The Chimeric Faces Task was used here to measure these asymmetries, along with measures for current and future levels of anxiety and depression. Results indicated that (a) increased left hemispatial biases at Time 1 predict increased anxiety (i.e., physiological hyperarousal) at Time 2 among female undergraduate students and (b) decreased left hemispatial biases at Time 1 predict decreased positive affectivity at Time 2 among the same participants. The possibility that hemispatial biases represent a vulnerability to future anxiety and depression is discussed.