Stimulus-dependent dopamine release in attention-deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) is related to an attenuated and dysfunctional dopamine system. Normally, a high extracellular dopamine level yields a tonic dopaminergic input that down-regulates stimuli-evoked phasic dopamine responses through autoreceptors. Abnormally low tonic extracellular dopamine in ADHD up-regulates the autoreceptors so that stimuli-evoked phasic dopamine is boosted. The authors propose that these boosted phasic responses yield hypersensitivity to environmental stimuli in ADHD. Stimuli evoking moderate brain arousal lead to well-functioning performance, whereas either too little or too much stimuli attenuate cognitive performance. Strong, salient stimuli may easily disrupt attention, whereas an environment with impoverished stimuli causes low arousal, which is typically compensated for by hyperactivity. Stochastic resonance is the phenomenon that makes a moderate noise facilitate stimulus discrimination and cognitive performance. Computational modeling shows that more noise is required for stochastic resonance to occur in dopamine-deprived neural systems in ADHD. This prediction is supported by empirical data.     

Facets of psychopathy, heart rate variability and cognitive function

The aim of the present study was to investigate whether the four facets of Hare's Psychopathy Checklist-Revised (PCL-R; Hare, 1991; Bolt, Hare, Vitale, & Newman, 2004) were related to physiological and cognitive mechanisms. Fifty-three male prisoners participated in this study. Physiological responses were measured as heart rate variability (HRV) and heart rate (HR). Cognitive functions were measured using a continuous performance test (CPT; California Computerized Assessment Package, Abbreviated version) and a working memory test (WMT); based on Baddeley & Hitch (1974). The regression analysis of the HRV revealed that the interpersonal facet explained most of the variance during baseline (28%), CPT (16%), and WMT (12%). This was also true for the HR data during baseline (28%), CPT (20%), WMT (10%), and recovery (13%). The antisocial facet explained 10% of the variance only during baseline. Subjects scoring high compared to low on the interpersonal facet also showed better cognitive functioning. The study suggests that the different facets were differently associated with both physiological and cognitive functions.     

Perspective effects in repeated reading: An eye movement study

The present study examined the influence of perspective instructions on online processing of expository text during repeated reading. Sixty-two participants read either a high or a low prior knowledge (HPK vs. LPK) text twice from a given perspective while their eye movements were recorded. They switched perspective before a third reading. Reading perspective affected the first-pass reading and also increased sentence wrap-up processing time in the perspective-relevant sentences. Prior knowledge facilitated the recognition of the (ir)relevance of text information and resulted in relatively earlier perspective effects in the HPK versus LPK text. Repeated reading facilitated processing, as indicated by all eye movement measures. After the perspective switch, a repetition benefit was observed for the previously relevant text information, whereas a repetition cost was found for the previously irrelevant text information. These results indicate that reading perspective and prior knowledge have a significant influence on how readers allocate visual attention during reading.     

Family perception of interpersonal behavior as a predictor in eating disorders: a prospective, six-year followup study

This study assessed family perception patterns of interpersonal behavior in families with a daughter diagnosed with an eating disorder 6 years after treatment that used a prospective design. Family perception patterns of patients found to have a poor outcome at followup (n = 15) were compared with patients with a good outcome (n = 23), as well as a control group (n = 36). Using the system of multiple level observation of groups (SYMLOG), all 238 family members evaluated themselves and each other. The index patients with a poor outcome perceived themselves as friendlier and more positive than they were perceived by their families. In comparison to parents of daughters with a good outcome and the control group, parents of daughters in the poor outcome group perceived themselves to be less friendly than their partners perceived them to be. A rigid polarization of the perception of the index patient by family members and a discrepancy in this perception between the index patient and the rest of the family were found to be indicative of a poor prognosis. Implications for treatment based on family perception patterns of interpersonal behavior are discussed.     

Dimensional complexity and power spectral measures of the EEG during functional versus predicative problem solving

Electroencephalograms were recorded in 22 men while solving tasks of visual-pattern completion and during mental relaxation. They were primed (by foregoing trials) to solve these tasks either in a predicative or functional mode of thinking. Predicative thinking required that in order to complete the pattern the subject had to get involved with the logic of the static structure of the pattern and therefore had to recognize the recurrence of certain features of the elements (e.g., shape, color, and size). Functional thinking required involvement in a dynamic reading of the logic of the pattern and therefore to search for operations and actions to be performed on the pattern elements (e.g., pushing, mirroring, and rotating). The EEG complexity during predicative thinking decreased in comparison to functional thinking and mental relaxation, with this reduction being most pronounced over the right parietal cortex. A reduction in dimensional complexity during functional thinking as compared to mental relaxation, which was concentrated over the left central cortex, although significant, was less clear. The reduced EEG complexity during predicative thought, dominant over the right hemisphere, could reflect increased competitive inhibition among respective cortical neuron assemblies in association with the visual analysis of static element features, converging upon those predicates relevant for the solution.     

Anxiety and Threat Perception Abnormalities in Normal Children

The current study examined the relationship between childhood anxiety and threat perception abnormalities. Children (N = 105) were exposed to stories reflecting three types of anxiety: social anxiety, separation anxiety, and generalized anxiety. From children's reactions to the stories, a number of threat perception indices were derived. Children's level of anxiety was assessed by means of questionnaires and a structured diagnostic interview. Results indicated that high levels of anxiety, as measured by questionnaires and interview, were accompanied by a high frequency of threat perception, high ratings of threat, a high frequency of threatening interpretations, high levels of negative feelings and cognitions, and an early detection of threat. Furthermore, results seemed to suggest that threat perception abnormalities were mediated by children's general level of anxiety rather than by levels of specific anxiety symptoms.     

Implicit and explicit learning of event sequences: evidence for distinct coding of perceptual and motor representations

Event-related brain potentials (ERPs) of 21 subjects were recorded in a choice reaction time task with a repeating eight-element long stimulus sequence. The regular event sequence was sometimes interrupted by 'perceptual' or by 'motor deviants' which both replaced an expected stimulus but either preserved or violated the sequence of motor responses. Response times confirmed that all subjects had acquired some knowledge of the sequential dependencies. By means of a post-experimental free recall and recognition test, subjects were classified as having either explicit or implicit knowledge of the event sequence. The ERPs showed different effects for different types of stimuli and the two groups. In the group of explicit learners, a larger N200 component was evoked by both types of deviants and a larger P300 by motor deviants only. In the group of implicit learners these 'perceptual components' remained unaffected. In contrast, in both groups of subjects the lateralized readiness potential (LRP) which accompanied motor deviants revealed a partial activation of the to be expected but incorrect response, i.e. motor learning. These results suggest that explicit learners acquire knowledge about both, stimulus and response dependencies while implicit learners acquire knowledge about response dependencies only.