The control of responsiveness in ADHD by catecholamines: evidence for dopaminergic, noradrenergic and interactive roles

We explore the neurobiological bases of attention deficit hyperactivity disorder (ADHD) from the viewpoint of the neurochemistry and psychopharmacology of the catecholamine-based behavioural systems. The contributions of dopamine (DA) and noradrenaline (NA) neurotransmission to the motor and cognitive symptoms of ADHD (e.g. hyperactivity, variable and impulsive responses) are studied in rodent and primate models. These models represent elements of the behavioural units observed in subjects with ADHD clinically, or in laboratory settings (e.g. locomotion, changed sensitivity/responsivity to novelty/reinforcement and measures of executive processing). In particular, the models selected emphasize traits that are strongly influenced by mesocorticolimbic DA in the spontaneously hypertensive (SHR) and the Naples high excitability (NHE) rat lines. In this context, the mode of action of methylphenidate treatment is discussed. We also describe current views on the altered control by mesolimbic catecholamines of appropriate and inappropriate goal-directed behaviour, and the tolerance or intolerance of delayed reinforcement in ADHD children and animal models. Recent insights into the previously underestimated role of the NA system in the control of mesocortical DA function, and the frontal role in processing information are elaborated.     

Oxidative stress in university students during examinations

Mental stress in psychiatric disease and in daily life contributes to oxidative stress in the body. In this study we investigated a connection between possible psychological stress caused by university undergraduate examinations and oxidative stress experienced by our test subjects. Some parameters of oxidative stress (single strand breaks of DNA in lymphocytes, sensitivity to lipid oxidation and antioxidant status) were studied in medical students on the day of the examination (stress condition) and compared with the same parameters obtained from the same students during the term between two examination periods (non-stress condition). The results show that in the stress condition oxidative damage to DNA and sensitivity to lipid oxidation were significantly increased (p<0.05) when compared with the same parameters in "non-stress" conditions. A significant decrease in plasma antioxidant activity (p<0.05) in students that were under stress was observed. These results suggest that during university examinations students are under increased oxidative stress.     

The role of affordances in inhibition of return

Inhibition of return (IOR) is a response delay that occurs when the target is preceded by an irrelevant stimulus (cue) at the same location. IOR can be object based, as well as location based. The aim of the present study was to investigate the role of the pragmatic features of a visually presented object in causing IOR. Two experiments were carried out using different objects as stimuli, for which the graspable part (affordance) was clearly defined. The presentation of a whole object, with the part commonly used to grasp it located below, served as a cue. The presentation of either the graspable or the ungraspable part of the cued or uncued object served as the target Results showed that responses were slower when the graspable part was shown in the cued location than when the ungraspable part was shown in the same location. The effect was apparently linked to the kind of action necessary to grasp an object.     

Dissociating the influence of familiarity and meaningfulness from word frequency in naming and lexical decision performance

Performance in two experiments was compared on a list of words of high and low frequency in which familiarity/meaningfulness (FM) was balanced and on a list of high- and low-frequency words in which FM was confounded with frequency (i.e., high frequency--high familiarity vs. low frequency--low familiarity). Both repetition and task (lexical decision and naming) were investigated. In the lexical decision task of Experiment 1, both frequency and repetition effects were larger in the list with FM confounded than in the list with FM matched. In the naming task, frequency and repetition effects and their interaction were significant, but there was no influence of FM list context. In Experiment 2, in which the repetitions occurred across blocks, as opposed to randomly intermixed within a list, similar results were found; however, there was no interaction between list and repetition. The results suggest that an evaluation of items in terms of their meaning and familiarity explains a large part of the variance, only in lexical decision. These dimensions may be cued both by subjective feelings of familiarity and the extent to which semantic information is available and by episodic traces due to recent encounters with the item.     

Stereo motion transparency processing implements an ecological smoothness constraint

Transparent motion stimuli allow us to investigate how visual motion is processed in the presence of multiple sources of information. We used stereo random-dot kinematograms to determine how motion processing is affected by the difference in direction and depth of two overlapping motion components. Observers judged whether a noise dot display contained one or two directions of motion. For all disparity differences, performance did not change among angles greater than 60 degrees, but the ability to detect transparent motion fell dramatically as the direction difference decreased below 60 degrees. When a disparity difference was added between the two motion components, detection became easier. We compared these results to an ideal-observer model limited by stimulus uncertainty and low-level sources of internal noise. The resulting measure of efficiency--the ratio of human to model performance--reflects changes in how motion stimuli are being processed. A decrease of both the direction and disparity differences had the effect of decreasing efficiency. These results suggest that the mechanism processing transparent motion may implement a smoothness constraint that tends to combine similar motions into a single percept.     

When similarity breeds content: need for closure and the allure of homogeneous and self-resembling groups

Four studies explored the relation between members' need for cognitive closure and their feelings toward groups. It was found that high (vs. low) need for closure individuals liked in-groups and out-groups more as function of the degree to which their membership was perceived as homogeneous (Studies 1-4), provided it was also self-similar (Studies 3 and 4). These results are discussed in terms of the relation between need for closure and homogeneous (vs. heterogeneous) groups' apparent potential as "closure providers."     

Multinational data show that conspiracy beliefs are associated with the perception (and reality) of poor national economic performance

While a great deal is known about the individual difference factors associated with conspiracy beliefs, much less is known about the country-level factors that shape people's willingness to believe conspiracy theories. In the current article we discuss the possibility that willingness to believe conspiracy theories might be shaped by the perception (and reality) of poor economic performance at the national level. To test this notion, we surveyed 6723 participants from 36 countries. In line with predictions, propensity to believe conspiracy theories was negatively associated with perceptions of current and future national economic vitality. Furthermore, countries with higher GDP per capita tended to have lower belief in conspiracy theories. The data suggest that conspiracy beliefs are not just caused by intrapsychic factors but are also shaped by difficult economic circumstances for which distrust might have a rational basis.     

Forgiveness,its factors,and unforgivable acts in romantic relationships: A mixed-methods study

Using a mixed-methods approach, this study investigates forgiveness, the factors of forgiveness, and unforgivable acts, and analyzes relational and gender differences in participants' qualitative answers. Open-ended questions were answered by 649 participants from Slovakia (532 dating, 117 married; 517 women, 132 men). Responses were analyzed qualitatively using the Consensual Qualitative Research-Modified method, then transformed into quantitative data in order to statistically compare the groups. The results showed that dating individuals tended to see forgiveness as working on the relationship, whereas married individuals viewed forgiveness as an emotional process. Married individuals were more likely to report that shared commitments helped them to forgive. Dating partners tended to look at the situational context. Men were more likely to report that forgiveness was key to the relationship. When forgiving their partner, men focused on internal factors, whereas women needed an apology and acts of love. Infidelity was the most common unforgivable transgression. Therapists may benefit from a more nuanced understanding of forgiveness in dating and married individuals.     

Inhibitory and facilitatory effects of cue onset and offset

The response speed to a visual target is modulated by the position of previous events (cues) even if their position is not predictive of the target position. The modulation has been considered biphasic, with an early facilitatory and a later inhibitory component. We conducted three experiments that investigated the importance of the onset and offset features of the cue for the facilitatory and inhibitory effects and estimated their separate and joint effects. The two possible target locations, one in the right and one in the left visual field, were indicated by two empty boxes, and the cue consisted of the onset and/or offset of an arrowhead located just under one of the two boxes. Different time intervals were used between cue and target. Subjects were instructed to ignore the cue and to respond to the target (a cross inside one of the two boxes). The data showed only consistent effects of inhibition (inhibition of return) with the long intervals, but the pattern was different depending on the cue type. The amount of inhibition was much greater when the onset of the cue was followed by its offset. Apparently, inhibition of return depended on the dynamic changes of the cue. Received: 23 October 1996 / Accepted: 3 June 1997