Dopaminergic genotype biases spatial attention in healthy children

Dopamine influences attentional rate modulation in Macaque posterior parietal cortex

Cognitive neuroscience has made great strides in understanding the neural substrates of attention, but our understanding of its neuropharmacology remains incomplete. Although dopamine has historically been studied in relation to frontal functioning, emerging evidence suggests important dopaminergic influences in parietal cortex. We recorded single- and multi-unit activity whilst iontophoretically administering dopaminergic agonists and antagonists while rhesus macaques performed a spatial attention task. Out of 88 units, 50 revealed activity modulation by drug administration. Dopamine inhibited firing rates according to an inverted-U shaped dose-response curve and increased gain variability. D1 receptor antagonists diminished firing rates according to a monotonic function and interacted with attention modulating gain variability. Finally, both drugs decreased the pupil light reflex. These data show that dopamine shapes neuronal responses and modulates aspects of attentional processing in parietal cortex.

Lateralization of attention in adults with ADHD: Evidence of pseudoneglect

Background.

We investigated whether adults with attention-deficit/hyperactivity disorder (ADHD) show pseudoneglect—preferential allocation of attention to the left visual field (LVF) and a resulting slowing of mean reaction times (MRTs) in the right visual field (RVF), characteristic of neurotypical (NT) individuals —and whether lateralization of attention is modulated by presentation speed and incentives.

Method.

Fast Task, a four-choice reaction-time task where stimuli were presented in LVF or RVF, was used to investigate differences in MRT and reaction time variability (RTV) in adults with ADHD (n = 43) and NT adults (n = 46) between a slow/no-incentive and fast/incentive condition. In the lateralization analyses, pseudoneglect was assessed based on MRT, which was calculated separately for the LVF and RVF for each condition and each study participant.

Results.

Adults with ADHD had overall slower MRT and increased RTV relative to NT. MRT and RTV improved under the fast/incentive condition. Both groups showed RVF-slowing with no between-group or between-conditions differences in RVF-slowing.

Conclusion.

Adults with ADHD exhibited pseudoneglect, a NT pattern of lateralization of attention, which was not attenuated by presentation speed and incentives.

Children's DAT1 Polymorphism Moderates the Relationship Between Parents' Psychological Profiles, Children's DAT Methylation, and Their Emotional/Behavioral Functioning in a Normative Sample

Parental psychopathological risk is considered as one of the most crucial features associated with epigenetic modifications in offspring, which in turn are thought to be related to their emotional/behavioral profiles. The dopamine active transporter (DAT) gene is suggested to play a significant role in affective/behavioral regulation. On the basis of the previous literature, we aimed at verifying whether children’s DAT1 polymorphisms moderated the relationship between parents’ psychological profiles, children’s emotional/behavioral functioning, and DAT1 methylation in a normative sample of 79 families with school-age children (Ntot = 237). Children’s biological samples were collected through buccal swabs, while Symptom Check-List-90 item Revised, Adult Self Report, and Child Behavior Check-List/6–18 was administered to assess parental and children’s psychological functioning. We found that higher maternal externalizing problems predicted the following: higher levels of children’s DAT1 methylation at M1, but only among children with 10/10 genotype; higher levels of methylation at M2 among children with 10/10 genotype; while lower levels for children with a 9-repeat allele. There was also a positive relationship between fathers’ externalizing problems and children’s externalizing problems, only for children with a 9-repeat allele. Our findings support emerging evidence of the complex interplay between genetic and environmental factors in shaping children’ emotional/behavioral functioning, contributing to the knowledge of risk variables for a child’s development and psychological well-being.

Dissociable Catecholaminergic Modulation of Visual Attention: Differential Effects of Catechol-O-Methyltransferase and Dopamine Beta-Hydroxylase Genes on Visual Attention

Visual attention enables us to prioritise behaviourally relevant visual information while ignoring distraction. The neural networks supporting attention are modulated by two catecholamines, dopamine and noradrenaline. The current study investigated the effects of single nucleotide polymorphisms in two catecholaminergic genes – COMT (Val¹⁵⁸Met) and DBH (444 G/A) – on individual differences in attention functions. Participants (n = 125) were recruited from the Oxford Biobank by genotype-based recall. They were tested on a continuous performance task (sustained attention), a Go/No-Go task (response inhibition), and a task assessing attentional selection in accordance with the Theory of Visual Attention (TVA). We found a significant effect of DBH genotype status on the capacity to maintain attention over time (sustained attention) as measured by the continuous performance task. Furthermore, we demonstrated a significant association between COMT genotype status and effective threshold of visual perception in attentional selection as estimated based on the TVA task performance. No other group differences in attention function were found with respect to the studied genotypes. Overall, our findings provide novel experimental evidence that: (i) dopaminergic and noradrenergic genotypes have dissociable effects on visual attention; (ii) either insufficient or excessive catecholaminergic activity may have equally detrimental effects on sustained attention.

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Catecholaminergic genotypes have dissociative cognitive effects on visual attention.

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DBH (444 G/A) polymorphism affects sustained attention.

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COMT Val¹⁵⁸Met polymorphism affects perceptual threshold in visual attention.

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Both too little and too much catecholamines may detrimentally impact sustained attention.

Dopamine signaling tunes spatial pattern selectivity in C. elegans

Animals with complex brains can discriminate the spatial arrangement of physical features in the environment. It is unknown whether such sensitivity to spatial patterns can be accomplished in simpler nervous systems that lack long-range sensory modalities such as vision and hearing. Here we show that the nematode Caenorhabditis elegans can discriminate spatial patterns in its surroundings, despite having a nervous system of only 302 neurons. This spatial pattern selectivity requires touch-dependent dopamine signaling, including the mechanosensory TRP-4 channel in dopaminergic neurons and the D2-like dopamine receptor DOP-3. We find that spatial pattern selectivity varies significantly among C. elegans wild isolates. Electrophysiological recordings show that natural variations in TRP-4 reduce the mechanosensitivity of dopaminergic neurons. Polymorphic substitutions in either TRP-4 or DOP-3 alter the selectivity of spatial patterns. Together, these results demonstrate an ancestral role for dopamine signaling in tuning spatial pattern preferences in a simple nervous system.

Visuospatial Asymmetries Arise from Differences in the Onset Time of Perceptual Evidence Accumulation

Healthy subjects tend to exhibit a bias of visual attention whereby left hemifield stimuli are processed more quickly and accurately than stimuli appearing in the right hemifield. It has long been held that this phenomenon arises from the dominant role of the right cerebral hemisphere in regulating attention. However, methods that would enable more precise understanding of the mechanisms underpinning visuospatial bias have remained elusive. We sought to finely trace the temporal evolution of spatial biases by leveraging a novel bilateral dot motion detection paradigm. In combination with electroencephalography, this paradigm enables researchers to isolate discrete neural signals reflecting the key neural processes needed for making these detection decisions. These include signals for spatial attention, early target selection, evidence accumulation, and motor preparation. Using this method, we established that three key neural markers accounted for unique between-subject variation in visuospatial bias: hemispheric asymmetry in posterior α power measured before target onset, which is related to the distribution of preparatory attention across the visual field; asymmetry in the peak latency of the early N2c target-selection signal; and, finally, asymmetry in the onset time of the subsequent neural evidence-accumulation process with earlier onsets for left hemifield targets. Our development of a single paradigm to dissociate distinct processing components that track the temporal evolution of spatial biases not only advances our understanding of the neural mechanisms underpinning normal visuospatial attention bias, but may also in the future aid differential diagnoses in disorders of spatial attention.SIGNIFICANCE STATEMENT The significance of this research is twofold. First, it shows that individual differences in how humans direct their attention between left and right space reflects physiological differences in how early the brain starts to accumulate evidence for the existence of a visual target. Second, the novel methods developed here may have particular relevance to disorders of attention, such as unilateral spatial neglect. In the case of spatial neglect, pathological inattention to left space could have multiple underlying causes, including biased attention, impaired decision formation, or a motor deficit related to one side of space. Our development of a single paradigm to dissociate each of these components may aid in supporting more precise differential diagnosis in such heterogeneous disorders.

MAOA Influences the Trajectory of Attentional Development

Attention is vital to success in all aspects of life (Meck and Benson, 2002; Erickson et al., 2015), hence it is important to identify biomarkers of later attentional problems early enough to intervene. Our objective was to determine if any of 11 genes (APOE, BDNF, HTR4, CHRNA4, COMT, DRD4, IGF2, MAOA, SLC5A7, SLC6A3, and SNAP25) predicted the trajectory of attentional development within the same group of children between infancy and childhood. We recruited follow up participants from children who participated as infants in visual attention studies and used a similar task at both time points. Using multilevel modeling, we associated changes in the participant’s position in the distribution of scores in infancy to his/her position in childhood with genetic markers on each of 11 genes. While all 11 genes predicted reaction time (RT) residual scores, only Monoamine oxidase A (MAOA) had a significant interaction including time point. We conclude that the MAOA single nucleotide polymorphism (SNP) rs1137070 is useful in predicting which girls are likely to develop slower RTs on an attention task between infancy and childhood. This early identification is likely to be helpful in early intervention.

Anticlockwise or clockwise? A dynamic Perception-Action-Laterality model for directionality bias in visuospatial functioning

Orientation bias and directionality bias are two fundamental functional characteristics of the visual system. Reviewing the relevant literature in visual psychophysics and visual neuroscience we propose here a three-stage model of directionality bias in visuospatial functioning. We call this model the 'Perception-Action-Laterality' (PAL) hypothesis. We analyzed the research findings for a wide range of visuospatial tasks, showing that there are two major directionality trends in perceptual preference: clockwise versus anticlockwise. It appears these preferences are combinatorial, such that a majority of people fall in the first category demonstrating a preference for stimuli/objects arranged from left-to-right rather than from right-to-left, while people in the second category show an opposite trend. These perceptual biases can guide sensorimotor integration and action, creating two corresponding turner groups in the population. In support of PAL, we propose another model explaining the origins of the biases - how the neurogenetic factors and the cultural factors interact in a biased competition framework to determine the direction and extent of biases. This dynamic model can explain not only the two major categories of biases in terms of direction and strength, but also the unbiased, unreliably biased or mildly biased cases in visuosptial functioning.

Genetic associations with reflexive visual attention in infancy and childhood

This study elucidates genetic influences on reflexive (as opposed to sustained) attention in children (aged 9-16 years; N = 332) who previously participated as infants in visual attention studies using orienting to a moving bar (Dannemiller, 2004). We investigated genetic associations with reflexive attention measures in infancy and childhood in the same group of children. The genetic markers (single nucleotide polymorphisms and variable number tandem repeats on the genes APOE, BDNF, CHRNA4, COMT, DRD4, HTR4, IGF2, MAOA, SLC5A7, SLC6A3, and SNAP25) are related to brain development and/or to the availability of neurotransmitters such as acetylcholine, dopamine, or serotonin. This study shows that typically developing children have differences in reflexive attention associated with their genes, as we found in adults (Lundwall, Guo & Dannemiller, 2012). This effort to extend our previous findings to outcomes in infancy and childhood was necessary because genetic influence may differ over the course of development. Although two of the genes that were tested in our adult study (Lundwall et al., 2012) were significant in either our infant study (SLC6A3) or child study (DRD4), the specific markers tested differed. Performance on the infant task was associated with SLC6A3. In addition, several genetic associations with an analogous child task occurred with markers on CHRNA4, COMT, and DRD4. Interestingly, the child version of the task involved an interaction such that which genotype group performed poorer on the child task depended on whether we were examining the higher or lower infant scoring group. These findings are discussed in terms of genetic influences on reflexive attention in infancy and childhood.

Genetic contributions to attentional response time slopes across repeated trials

Background

Attention provides vital contribution to everyday functioning, and deficits in attention feature in many psychological disorders. Improved understanding of attention may eventually be critical to early identification and treatment of attentional deficits. One step in that direction is to acquire a better understanding of genetic associations with performance on a task measuring reflexive (exogenous) visual attention. Reflexive attention is an important component of overall attention because (along with voluntary selective attention) it participates in determining where attention is allocated and how susceptible to distractors the subject might be. The task that we used involves the presentation of a target that is preceded by one of several different types of cues (none, double, or single, either ipsilateral or contralateral to where the target subsequently appears). We used several different outcome measures depending on the cue presented. We have previously studied the relationship between selected genes and mean response time (RT). Here we report on the contributions of genetic markers to RT increases or decreases over the course of the task (linear trend in RT slope).

Results

Specifically, we find that RT slope for a variety of reflexive attention outcome measures is dependent on DAT1 genotype. DRD4 was near significant for one outcome measure in the final (best) model. APOE, COMT, and DBH were not significant in any models.

Conclusions

It is especially interesting that genotype predicts linear changes in RT across trials (and not just mean differences or moment-to-moment variability). DAT1 is a gene that produces a protein involved in the transport of dopamine from the synapse. To our knowledge, this is the first study that has associated neurotransmitter genotypes with RT slope on a reflexive attention experiment. The direction of these effects is consistent with genetic risk for attention deficit hyperactivity disorder (ADHD). That is, those with two risk alleles for ADHD (6R/6R on the DAT1 intron 8 VNTR) either got slower as the task progressed or had the least improvement. Those with no risk alleles (5R/5R) had the most improvement in RT as the task progressed.

An association between a dopamine transporter gene (SLC6A3) haplotype and ADHD symptom measures in nonclinical adults

Previous genetic studies have postulated that attention deficit hyperactivity disorder (ADHD) should be regarded as the extreme end of a set of behavioural traits that can be continuously measured in the general population. The current study adopted a quantitative trait approach to examine the relationship between dopamine gene variants and self-reported ADHD symptoms in 517 nonclinical adults. Although genetic associations with variants of both the dopamine transporter (DAT1; SLC6A3) and D4 receptor (DRD4) genes have been reliably reported in children, results in adults are less consistent. We probed two potentially functional variable number of tandem repeat (VNTR) polymorphisms in the 3'UTR and intron 8 of DAT1, the 10-repeat and 6-repeat alleles of which respectively form a haplotype (10/6 DAT1 haplotype) that is associated with childhood ADHD. We also genotyped the exon 3 VNTR of DRD4, the 7-repeat allele of which is also an established risk factor for childhood ADHD. Permutation analysis showed an influence of the 10/6 DAT1 haplotype on both CAARS-G and CAARS-H (DSM-IV ADHD Symptoms Total and ADHD Index respectively), such that ADHD symptom scores increased with each additional copy of the 10/6 DAT1 haplotype. This result survived corrections for multiple comparisons both at the level of genotype and phenotype. A nominal association with CAARS-G was also found for the 7-repeat allele of the DRD4 VNTR however this did not survive multiple comparison correction. Our results provide further support for the influence of variation in the 10/6 DAT1 haplotype and individual differences in ADHD symptoms in adults.

Dopamine transporter genotype is associated with a lateralized resistance to distraction during attention selection

Although lateral asymmetries in orienting behavior are evident across species and have been linked to interhemispheric asymmetries in dopamine signaling, the relative contribution of attentional versus motoric processes remains unclear. Here we took a cognitive genetic approach to adjudicate between roles for dopamine in attentional versus response selection. A sample of nonclinical adult humans (N = 518) performed three cognitive tasks (spatial attentional competition, spatial cueing, and flanker tasks) that varied in the degree to which they required participants to resolve attentional or response competition. All participants were genotyped for two putatively functional tandem repeat polymorphisms of the dopamine transporter gene (DAT1; SLC6A3), which are argued to influence the level of available synaptic dopamine and confer risk to disorders of inattention. DAT1 genotype modulated the task-specific effects of the various task-irrelevant stimuli across both the spatial competition and spatial cueing but not flanker tasks. Specifically, compared with individuals carrying one or two copies of the 10-repeat DAT1 allele, individuals without this allele demonstrated an immunity to distraction, such that response times were unaffected by increases in the number of distractor stimuli, particularly when these were presented predominantly in the left hemifield. All three genotype groups exhibited uniform costs of resolving leftward response selection in a standard flanker task. None of these significant effects could be explained by speed-accuracy trade-offs, suggesting that participants without the 10-repeat allele of the DAT1 tandem repeat polymorphism possess an enhanced attentional ability to suppress task-irrelevant stimuli in the left hemifield.

Dopamine transporter SLC6A3 genotype affects cortico-striatal activity of set-shifts in Parkinson's disease

Parkinson's disease is a neurodegenerative condition that affects motor function along with a wide range of cognitive domains, including executive function. The hallmark of the pathology is its significant loss of nigrostriatal dopamine, which is necessary for the cortico-striatal interactions that underlie executive control. Striatal dopamine reuptake is mediated by the SLC6A3 gene (formerly named DAT1) and its polymorphisms, which have been largely overlooked in Parkinson's disease. Thirty patients (ages 53-68 years; 19 males, 11 females) at early stages of Parkinson's disease, were genotyped according to a 9-repeat (9R) or 10-repeat (10R) allele on the SLC6A3/DAT1 gene. They underwent neuropsychological assessment and functional magnetic resonance imaging while performing a set-shifting task (a computerized Wisconsin Card Sorting Task) that relies on fronto-striatal interactions. Patients homozygous on the 10R allele performed significantly better on working memory tasks than 9R-carrier patients. Most importantly, patients carrying a 9R allele exhibited less activation than their 10R homozygous counterparts in the prefrontal cortex, premotor cortex and caudate nucleus, when planning and executing a set-shift. This pattern was exacerbated for conditions that usually recruit the striatum compared to those that do not. This is the first study indicating that the SLC6A3/DAT1 genotype has a significant effect on fronto-striatal activation and performance in Parkinson's disease. This effect is stronger for conditions that engage the striatum. Longitudinal studies are warranted to assess this polymorphism's effect on the clinical evolution of patients with Parkinson's disease, especially with cognitive decline.

Dopamine system genes are associated with orienting bias among healthy individuals

Healthy individuals display subtle orienting bias, manifested as a tendency to direct greater attention toward one hemispace, and evidence suggests that this bias reflects an individual trait, which may be modulated by asymmetric dopamine signaling in striatal and frontal regions. The current study examined the hypothesis that functional genetic variants within dopaminergic genes (DAT1 3' VNTR, dopamine D2 receptor Taq1A (rs1800497) and COMT Val158Met (rs4680)) contribute to individual differences in orienting bias, as measured by the greyscales paradigm, in a sample of 197 young healthy Israeli Jewish participants. For the Taq1A variant, homozygous carriers of the A2 allele displayed significantly increased leftward orienting bias compared to the carriers of the A1 allele. Additionally, and as previously reported by others, we found that bias towards leftward orienting of attention was significantly greater among carriers of the 9-repeat allele of the DAT1 3' VNTR as compared to the individuals who were homozygous for the 10-repeat allele. No significant effect of the COMT Val158Met on orienting bias was found. Taken together, our findings support the potential influence of genetic variants on inter-individual differences in orienting bias, a phenotype relevant to both normal and impaired cognitive processes.

Spatial attention: differential shifts in pseudoneglect direction with time-on-task and initial bias support the idea of observer subtypes

Asymmetry in human spatial attention has long been documented. In the general population the majority of individuals tend to misbisect horizontal lines to the left of veridical centre. Nonetheless in virtually all previously reported studies on healthy participants, there have been subsets of people displaying rightward biases. In this study, we report differential time-on task effects depending on participants' initial pseudoneglect bias: participants with an initial left bias in a landmark task (in which they had to judge whether a transection mark appeared closer to the right or left end of a line) showed a significant rightward shift over the course of the experimental session, whereas participants with an initial right bias shifted leftwards. We argue that these differences in initial biases as well as the differential shifts with time-on task reflect genuine observer subtypes displaying diverging behavioural patterns. These observer subtypes could be driven by differences in brain organisation and/or lateralisation such as varying anatomical pathway asymmetries (Thiebaut de Schotten et al., 2011).

Do dopamine gene variants and prenatal smoking interactively predict youth externalizing behavior?

Externalizing behaviors (encompassing antisocial, impulsive, and substance use behaviors) are pervasive and impairing across a multitude of settings and developmental contexts. These behaviors, though often investigated separately, are highly comorbid. Prenatal tobacco exposure in interaction with various genetic influences has predicted later externalizing behavior, and recent evidence supports investigating sex differences in these patterns. In the current study, we extend this work by (a) examining two functional genetic markers in the dopamine system: the transporter gene (DAT1) and the dopamine receptor D4 gene (DRD4) in interaction with prenatal tobacco exposure to predict a latent composite of externalizing behavior and (b) testing whether these patterns differ by sex of youth in a community sample of adolescents (n=176). The relatively small sample is partially offset by high quality, multi-method prospective measurement. We assessed prenatal tobacco exposure using prospective repeated cotinine-corrected reports and externalizing behaviors were assessed utilizing multiple measures across three waves. The interaction between DAT1 (but not DRD4) and prenatal tobacco exposure was statistically significant in boys, and patterns appeared to differ by sex. Risk for externalizing behaviors for exposed boys increased linearly as a function of the 10r DAT1 allele. For exposed girls, there was a trend such that DAT1 heterozygotes had a marginally higher risk than homozygotes. This pattern was not explained by passive gene-environment correlation. Elucidating sex-specific pathways through which early adverse exposures and genetic susceptibilities contribute to externalizing behavior can inform early targeted prevention efforts for those children at highest risk.

Behavioral consequences of aberrant alpha lateralization in attention-deficit/hyperactivity disorder

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) is characterized by problems in directing and sustaining attention. Recent findings suggest that alpha oscillations (8-12 Hz) are crucially involved in gating information between brain regions when allocating attention. The current study investigates whether aberrant modulation of alpha oscillations contributes to attention problems in ADHD patients.

METHODS

Magnetoencephalographic signals were recorded in adults with ADHD (n = 17) and healthy control subjects (n = 18) while they performed a visuospatial attention task. Cues directed attention to the left or right visual hemifield with an 80% validity with respect to the upcoming target.

RESULTS

Unlike the control group, subjects with ADHD showed a higher accuracy for invalidly cued right targets compared with invalidly cued left targets (p = .04). This coincided with an inability of the ADHD subjects to sustain the posterior hemispheric alpha lateralization in the period before the target for the left cue condition (p = .011). Furthermore, the control group showed a strong correlation between the degree of alpha lateralization and the magnitude of the cueing effect assessed in terms of accuracy (rs = .71, p = .001) and reaction times (rs =-.81, p<.001). These correlations were absent in the ADHD group.

CONCLUSIONS

Our results demonstrate that subjects with ADHD have a failure in sustaining hemispheric alpha lateralization when cued to the left, resulting in an attentional bias to the right visual hemifield. These findings suggest that aberrant modulations of alpha oscillations reflect attention problems in ADHD and might be related to the neurophysiological substrate of the disorder.

Dopamine transporter genotype predicts attentional asymmetry in healthy adults

A number of recent studies suggest that DNA variation in the dopamine transporter gene (DAT1) influences spatial attention asymmetry in clinical populations such as ADHD, but confirmation in non-clinical samples is required. Since non-spatial factors such as attentional load have been shown to influence spatial biases in clinical conditions, here we sought to determine whether any association between DAT1 genotype and spatial bias might be moderated by non-spatial attentional load. Healthy adults were asked to react to sudden onset peripheral targets while demand on non-spatial attention was manipulated via a central task. Participants were genotyped for a DAT1 variable number of tandem repeat (VNTR) polymorphism. The 10-repeat allele of this variant is a replicated susceptibility allele for ADHD and has been shown to associate with spatial bias. As expected, an overall leftward asymmetry/pseudoneglect was observed when the data were averaged across the entire sample. When data were stratified by DAT1 genotype, individuals lacking homozygosity for the 10-repeat DAT1 allele (non-10/10) showed a pronounced leftward bias that was significantly different from zero. In line with past reports from children with ADHD, this leftward bias was attenuated in individuals who were homozygous for the DAT1 10-repeat allele (10/10), suggestive of relatively weaker right hemisphere dominance for spatial attention. This effect of DAT1 genotype on spatial bias was not modulated by non-spatial attention load. These data confirm in healthy adult participants both the existence and the direction of the relationship previously reported between DAT1 genotype and spatial bias in children with ADHD. These data add to a growing body of evidence showing that spatial attentional asymmetry is a stable quantitative trait, with individual differences in this trait significantly predicted by common DNA variation in the DAT1 gene.

Attentional asymmetries in a visual orienting task are related to temperament

Spatial asymmetries are an intriguing feature of directed attention. Recent observations indicate an influence of temperament upon the direction of these asymmetries. It is unknown whether this influence generalises to visual orienting behaviour. The aim of the current study was therefore to explore the relationship between temperament and measures of spatial orienting as a function of target hemifield. An exogenous cueing task was administered to 92 healthy participants. Temperament was assessed using Carver and White's (1994) Behavioural Inhibition System and Behavioural Activation System (BIS/BAS) scales. Individuals with high sensitivity to punishment and low sensitivity to reward showed a leftward asymmetry of directed attention when there was no informative spatial cue provided. This asymmetry was not present when targets were preceded by spatial cues that were either valid or invalid. The findings support the notion that individual variations in temperament influence spatial asymmetries in visual orienting, but only when lateral targets are preceded by a non-directional (neutral) cue. The results are discussed in terms of hemispheric asymmetries and dopamine activity.

Exogenous visual orienting is associated with specific neurotransmitter genetic markers: a population-based genetic association study

Background

Currently, there is a sense that the spatial orienting of attention is related to genotypic variations in cholinergic genes but not to variations in dopaminergic genes. However, reexamination of associations with both cholinergic and dopaminergic genes is warranted because previous studies used endogenous rather than exogenous cues and costs and benefits were not analyzed separately. Examining costs (increases in response time following an invalid pre-cue) and benefits (decreases in response time following a valid pre-cue) separately could be important if dopaminergic genes (implicated in disorders such as attention deficit disorder) independently influence the different processes of orienting (e.g., disengage, move, engage).

Methodology/Principal Findings

We tested normal subjects (N = 161) between 18 and 61 years. Participants completed a computer task in which pre-cues preceded the presence of a target. Subjects responded (with a key press) to the location of the target (right versus left of fixation). The cues could be valid (i.e., appear where the target would appear) or invalid (appear contralateral to where the target would appear). DNA sequencing assays were performed on buccal cells to genotype known genetic markers and these were examined for association with task scores. Here we show significant associations between visual orienting and genetic markers (on COMT, DAT1, and APOE; R²s from 4% to 9%).

Conclusions/Significance

One measure in particular – the response time cost of a single dim, invalid cue – was associated with dopaminergic markers on COMT and DAT1. Additionally, variations of APOE genotypes based on the ε2/ε3/ε4 alleles were also associated with response time differences produced by simultaneous cues with unequal luminances. We conclude that individual differences in visual orienting are related to several dopaminergic markers as well as to a cholinergic marker. These results challenge the view that orienting is not associated with genotypic variation in dopaminergic genes.

The role of DAT1 gene on the rapid detection of task novelty

In an environment with a myriad of different stimuli, the fast detection of novel and behaviorally relevant signals becomes crucial for an adaptive behavior. The detection of task-novelty has been related to striatum-prefrontal cortex (PFC) pathways involving dopaminergic (DA) neurotransmission. Here we thus tested the hypothesis that DA regulates the detection of task novelty through the modulation of the auditory N1 potential, an auditory potential peaking at 100 ms and previously shown to be modulated by the detection of sensory novelty. Thirty-five healthy volunteers were divided in two groups according to the presence or absence of the 9-repetition allele (9R) of the SLC6A3/DAT1 gene for the dopamine transporter. Participants performed a cued task-switching paradigm that dissociated the effects of exogenous sensory novelty from those of endogenous task novelty. Individuals with the 9R allele showed an amplitude enhancement of the auditory N1 elicited to sensory changes requiring a task-set reconfiguration as compared to sensory changes with no task novelty. In contrast, individuals without the 9R allele did not have their N1 waveform modulated by task novelty. The present results suggest that individuals homozygous for the 10-repeat allele fail to detect the behavioral relevance of new stimuli at early stages.

The effects of background white noise on memory performance in inattentive school children

Background

Noise is typically conceived of as being detrimental for cognitive performance; however, a recent computational model based on the concepts of stochastic resonance and dopamine related internal noise postulates that a moderate amount of auditive noise benefit individuals in hypodopaminergic states. On the basis of this model we predicted that inattentive children would be enhanced by adding background white noise while attentive children's performance would deteriorate.

Methods

Fifty-one secondary school pupils carried out an episodic verbal free recall test in two noise conditions. In the high noise condition, verb-noun sentences were presented during auditory background noise (white noise, 78 dB), and in the low noise condition sentences were presented without noise.

Results

Exposure to background noise improved performance for inattentive children and worsened performance for attentive children and eliminated episodic memory differences between attentive and inattentive school children.

Conclusions

Consistent with the model, our data show that cognitive performance can be moderated by external background white noise stimulation in a non-clinical group of inattentive participants. This finding needs replicating in a larger sample using more noise levels but if replicated has great practical applications by offering a non-invasive way to improve school results in children with attentional problems.

Eye-blink rate predicts individual differences in pseudoneglect

Most healthy individuals display a subtle spatial attentional bias, exhibiting relative inattention for stimuli on one side of the visual field, a phenomenon known as pseudoneglect. Prior work in animals and patients has implicated dopamine in spatial attention asymmetries. The current study therefore examined - in healthy individuals - the relationship between the attentional bias and spontaneous eye-blink rate (EBR), a putative measure of central dopaminergic function. We found that those individuals, who blinked more often under resting conditions, displayed greater preference for the right side of the visual display in a subsequent attention task. This finding may support the idea that the observed attentional bias in healthy individuals reflects asymmetries in dopaminergic circuits, and corroborates previous findings implicating dopamine in spatial attention.

The role of the dopamine transporter (DAT) in the development of PTSD in preschool children

Population-based association studies have supported the heritability of posttraumatic stress disorder (PTSD). This study explored the influence of genetic variation in the dopamine transporter (DAT) 3' untranslated region variable number tandem repeat on the development of PTSD in preschool children exposed to Hurricane Katrina, diagnosed using a developmentally appropriate semistructured interview. A diagnosis according to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition , (DSM-IV; American Psychiatric Association, 1994), total symptoms, and specifically Criterion D symptoms were significantly more likely to be found in children with the 9 allele. This study replicates a previous finding in adults with PTSD. The specificity of this finding to the increased arousal symptoms of Criterion D suggests that dopamine and the DAT allele may contribute to one heritable path in a multifinality model of the development of PTSD.

A genome-wide study of common SNPs and CNVs in cognitive performance in the CANTAB

Psychiatric disorders such as schizophrenia are commonly accompanied by cognitive impairments that are treatment resistant and crucial to functional outcome. There has been great interest in studying cognitive measures as endophenotypes for psychiatric disorders, with the hope that their genetic basis will be clearer. To investigate this, we performed a genome-wide association study involving 11 cognitive phenotypes from the Cambridge Neuropsychological Test Automated Battery. We showed these measures to be heritable by comparing the correlation in 100 monozygotic and 100 dizygotic twin pairs. The full battery was tested in approximately 750 subjects, and for spatial and verbal recognition memory, we investigated a further 500 individuals to search for smaller genetic effects. We were unable to find any genome-wide significant associations with either SNPs or common copy number variants. Nor could we formally replicate any polymorphism that has been previously associated with cognition, although we found a weak signal of lower than expected P-values for variants in a set of 10 candidate genes. We additionally investigated SNPs in genomic loci that have been shown to harbor rare variants that associate with neuropsychiatric disorders, to see if they showed any suggestion of association when considered as a separate set. Only NRXN1 showed evidence of significant association with cognition. These results suggest that common genetic variation does not strongly influence cognition in healthy subjects and that cognitive measures do not represent a more tractable genetic trait than clinical endpoints such as schizophrenia. We discuss a possible role for rare variation in cognitive genomics.

Pharmacogenetic treatments for drug addiction: cocaine, amphetamine and methamphetamine

BACKGROUND

Pharmacogenetics uses genetic variation to predict individual differences in response to medications and holds much promise to improve treatment of addictive disorders.

OBJECTIVES

To review how genetic variation affects responses to cocaine, amphetamine, and methamphetamine and how this information may guide pharmacotherapy.

METHODS

We performed a cross-referenced literature search on pharmacogenetics, cocaine, amphetamine, and methamphetamine.

RESULTS

We describe functional genetic variants for enzymes dopamine-beta-hydroxylase (DbetaH), catechol-O-methyltransferase (COMT), and dopamine transporter (DAT1), dopamine D4 receptor, and brain-derived neurotrophic factor (BDNF). A single nucleotide polymorphism (SNP; C-1021T) in the DbetaH gene is relevant to paranoia associated with disulfiram pharmacotherapy for cocaine addiction. Individuals with variable number tandem repeats (VNTR) of the SLC6A3 gene 3'-untranslated region polymorphism of DAT1 have altered responses to drugs. The 10/10 repeat respond poorly to methylphenidate pharmacotherapy and the 9/9 DAT1 variant show blunted euphoria and physiological response to amphetamine. COMT, D4 receptor, and BDNF polymorphisms are linked to methamphetamine abuse and psychosis.

CONCLUSIONS

Disulfiram and methylphenidate pharmacotherapies for cocaine addiction are optimized by considering polymorphisms affecting DbetaH and DAT1 respectively. Altered subjective effects for amphetamine in DAT1 VNTR variants suggest a 'protected' phenotype.

SCIENTIFIC SIGNIFICANCE

Pharmacogenetic-based treatments for psychostimulant addiction are critical for successful treatment.

Cognitive neuroscience of Attention Deficit Hyperactivity Disorder: current status and working hypotheses

Cognitive neuroscience studies of Attention Deficit Hyperactivity Disorder (ADHD) suggest multiple loci of pathology with respect to both cognitive domains and neural circuitry. Cognitive deficits extend beyond executive functioning to include spatial, temporal, and lower-level "nonexecutive" functions. Atypical functional anatomy extends beyond frontostriatal circuits to include posterior cortices, limbic regions, and the cerebellum. Pathophysiology includes dopaminergic as well as noradrenergic neurotransmitter systems. We review the major insights gained from functional brain imaging studies in ADHD and discuss working hypotheses regarding their neurochemical underpinnings.

Dopamine transporter polymorphism modulates oculomotor function and DAT1 mRNA expression in schizophrenia

Smooth pursuit eye movement (SPEM) deficit is an established schizophrenia endophenotype with a similar neurocognitive construct to working memory. Frontal eye field (FEF) neurons controlling SPEM maintain firing when visual sensory information is removed, and their firing rates directly correlate with SPEM velocity. We previously demonstrated a paradoxical association between a functional polymorphism of dopamine signaling (COMT gene) and SPEM. Recent evidence implicates the dopamine transporter gene (DAT1) in modulating cortical dopamine and associated neurocognitive functions. We hypothesized that DAT1 10/10 genotype, which reduces dopamine transporter expression and increases extracellular dopamine, would affect SPEM. We examined the effects of DAT1 genotype on: Clinical diagnosis in the study sample (n = 418; 190 with schizophrenia), SPEM measures in a subgroup with completed oculomotor measures (n = 200; 87 schizophrenia), and DAT1 gene expression in FEF tissue obtained from postmortem brain samples (n = 32; 16 schizophrenia). DAT1 genotype was not associated with schizophrenia. DAT1 10/10 genotype was associated with better SPEM in healthy controls, intermediate SPEM in unaffected first-degree relatives of schizophrenia subjects, and worse SPEM in schizophrenia subjects. In the gene expression study, DAT1 10/10 genotype was associated with significantly reduced DAT1 mRNA transcript in FEF tissue from healthy control donors (P < 0.05), but higher expression in schizophrenia donors. Findings suggest regulatory effects of another gene(s) or etiological factor in schizophrenia, which modulate DAT1 gene function.

A review and analysis of the relationship between neuropsychological measures and DAT1 in ADHD

Meta-analyses indicate that the gene coding for the dopamine transporter (DAT1 or SLC6A3) is associated with an increased risk for ADHD. The mechanisms of this gene for ADHD are unclear. We systematically reviewed studies linking the VNTR in the 3' UTR of the DAT1 to neurophysiological and neuropsychological measures. In addition, a broad set of executive/cognitive and motor tests was administered to 350 children (5-11 years) and adolescents (11-19 years) with ADHD and 195 non-affected siblings. Two VNTRs (in intron 8 and the 3' UTR) and four SNPs (two 5' and two 3') in DAT1 were genotyped. The effect of the polymorphisms on neuropsychological functioning was studied. The review indicated that the majority of studies did not find a relation between DAT1 and neurophysiological or neuropsychological measures. In our sample, several of the polymorphisms of DAT1 were associated with ADHD and ADHD was associated with impaired neuropsychological functioning. However, none of the DAT1 polymorphisms was convincingly associated with neuropsychological dysfunctioning. This suggests that the effect of DAT1 on ADHD was not mediated by neuropsychological performance. However, since DAT1 is mainly expressed in the striatum and not the prefrontal cortex, it may influence striatum-related functions (such as delay aversion) more heavily than prefrontal related functions (such as executive functions). Associations of DAT1 with ADHD were only found in adolescents, which may suggest that DAT1 mainly exerts its effect in adolescence, and/or that having a more persistent form of ADHD may mark a more severe or homogeneous genetic form of the disorder.

Spatial attentional bias as a marker of genetic risk, symptom severity, and stimulant response in ADHD

Attention-deficit hyperactivity disorder (ADHD) is a heritable childhood onset disorder that is marked by variability at multiple levels including clinical presentation, cognitive profile, and response to stimulant medications. It has been suggested that this variability may reflect etiological differences, particularly, at the level of underlying genetics. This study examined whether an attentional phenotype-spatial attentional bias could serve as a marker of symptom severity, genetic risk, and stimulant response in ADHD. A total of 96 children and adolescents with ADHD were assessed on the Landmark Task, which is a sensitive measure of spatial attentional bias. All children were genotyped for polymorphisms (3' untranslated (UTR) and intron 8 variable number of tandem repeats (VNTRs)) of the dopamine transporter gene (DAT1). Spatial attentional bias correlated with ADHD symptom levels and varied according to DAT1 genotype. Children who were homozygous for the 10-repeat allele of the DAT1 3'-UTR VNTR displayed a rightward attentional bias and had higher symptom levels compared to those with the low-risk genotype. A total of 26 of these children who were medication naive performed the Landmark Task at baseline and then again after 6 weeks of stimulant medication. Left-sided inattention (rightward bias) at baseline was associated with an enhanced response to stimulants at 6 weeks. Moreover, changes in spatial bias with stimulant medications, varied as a function of DAT1 genotype. This study suggests an attentional phenotype that relates to symptom severity and genetic risk for ADHD, and may have utility in predicting stimulant response in ADHD.

Attentional bias as trait: correlations with novelty seeking

Pseudoneglect is traditionally viewed as reflecting right hemisphere specialization for processing spatial information, which brings about relatively greater activation of the right hemisphere and orienting towards the contralateral space. Such interpretation implies that the leftward attentional bias is a population trait. Animal studies, however, suggest that orienting bias is a trait of the individual and individual differences in the direction and magnitude of this orienting bias reflect individual differences in asymmetry in dopaminergic brain systems, which are also reflected in other behavioral differences. The present study was designed to test the hypothesis that healthy individuals show consistent attentional bias, the direction and magnitude of which varies among individuals and is associated with the degree of novelty seeking, a temperament trait associated with dopamine asymmetry. Forty-nine right-handed participants performed the greyscales task on two separate occasions and completed the Tridimensional Personality Questionnaire. Although on average some degree of leftward attentional bias was observed on both occasions, both the direction and the magnitude of the bias differed greatly, with some individuals showing a strong leftward bias whereas others showed a strong rightward bias. A highly significant correlation was found between degree and magnitude of this bias on the two testing sessions, supporting the hypothesis that it may reflect an individual trait. As predicted, higher scores on novelty seeking were associated with rightward attentional bias, suggesting that this bias may reflect asymmetries in dopaminergic circuits in healthy individuals.