Executive attention in schizophrenic males and the impact of COMT Val108/158Met genotype on performance on the attention network test

Modulation of hemispheric asymmetry in executive control of attention in schizophrenia with atypical antipsychotic treatment: Potential benefits of olanzapine

Deficits in executive control of attention have been reported in schizophrenia patients, but can be ameliorated by treatment of atypical antipsychotics along with the symptoms. However, it remains unclear whether this effect is related to a modulation of hemispheric asymmetry in executive control by the medicine. In this behavioral study, we employed a lateralized version of the attention network test to examine the hemispheric asymmetry of executive control in schizophrenia patients before and after olanzapine treatment, compared to matched healthy controls. Executive control was measured as a conflict effect, indexed as the response time (RT) difference between incongruent versus congruent flanker conditions, and was compared between stimuli presented in the left and the right visual field (i.e., processed by right versus left hemisphere of the brain). Results showed that pre-treatment schizophrenia patients revealed a right hemisphere superiority in conflict effect (i.e., a smaller effect in the right hemisphere than in the left hemisphere), driven by the incongruent condition. Olanzapine treatment reduced this right hemisphere superiority by improving the efficiency of the left hemisphere in the incongruent condition. These results suggested that olanzapine treatment may improve the efficiency of executive control in the left hemisphere in schizophrenia patients.

The effects of catechol-O-methyltransferase single nucleotide polymorphisms on positive and negative symptoms of schizophrenia: A systematic review and meta-analysis

The catechol-O-methyltransferase (COMT) gene is thought to have an important role in the etiopathogenesis of schizophrenia, but there are conflicting results regarding its role in clinical presentation. We aimed to elucidate the relationship between the single nucleotide polymorphisms (SNPs) in the COMT gene and the severity of positive and negative symptoms. In order to investigate the relationship, the PubMed, PubMed Central, Scopus, and Cochrane CENTRAL databases were screened for eligible articles. Thirty-eight studies, including 4443 adult patients with schizophrenia, were included in the quantitative analyses, and four studies were qualitatively assessed. Quantitative analyses were performed for acutely ill and clinically stable patient subgroups regarding the different genotypes of rs4680 SNP. Our results showed that the severity of negative symptoms was higher in patients who were rs4680 Met homozygous compared to Val/Met heterozygotes only in acutely ill samples. There was no other significant difference between genotypes. Meta-regression did not reveal any significant moderator effect on the difference in negative symptoms. General psychopathology, positive, negative, and total psychotic symptom levels also were similar between Val homozygotes and Met carriers. Nonetheless, there are some limitations in the study. First, SNPs except for rs4680 were under-researched because of the limited number of studies. Second, high heterogeneity across studies was the main concern. Our results suggested that the COMT rs4680 Met allele was associated with higher levels of negative symptoms within acutely ill patients. Future studies should focus on specific patient subgroups to reveal the moderating effects of SNPs.

Gene polymorphisms and response to transcranial direct current stimulation for auditory verbal hallucinations in schizophrenia

OBJECTIVE

Recent observations demonstrate a significant ameliorative effect of add-on transcranial direct current stimulation (tDCS) on auditory verbal hallucinations (AVHs) in schizophrenia. Of the many SNPs, NRG1 rs35753505 and catechol-o-methyl transferase (COMT) rs4680 polymorphisms have shown to have a strong association with neuroplasticity effect in schizophrenia.

METHODS

Schizophrenia patients (n=32) with treatment resistant auditory hallucinations were administered with an add-on tDCS. The COMT (rs4680) and NRG1 (rs35753505) genotypes were determined. The COMT genotypes were categorised into Val group (GG; n=15) and Met group (GG/AG; n=17) and NRG1 genotypes were categorised into AA group (n=12) and AG/GG group (n=20).

RESULTS

The reduction in auditory hallucination sub-scale score was significantly affected by COMT-GG genotype [Time×COMT interaction: F(1,28)=10.55, p=0.003, ɳ2=0.27]. Further, COMT-GG effect was epistatically influenced by the co-occurrence of NRG1-AA genotype [Time×COMT×NRG1 interaction: F(1,28)=8.09, p=0.008, ɳ2=0.22]. Irrespective of genotype, females showed better tDCS response than males [Time×Sex interaction: F(1,21)=4.67, p=0.04, ɳ2=0.18].

CONCLUSION

COMT-GG and NRG1-AA genotypes aid the tDCS-induced improvement in AVHs in schizophrenia patients. Our preliminary observations need replication and further systematic research to understand the neuroplastic gene determinants that modulate the effect of tDCS.

Deficit of supramodal executive control of attention in schizophrenia

Although a deficit in executive control of attention is one of the hallmarks in schizophrenia that has significant impact on everyday functioning due to its relationship with thought processing, whether this deficit occurs across modalities, i.e., is supramodal, remains unclear. To investigate the supramodal mechanism in SZ, we examined cross-modal correlations between visual and auditory executive control of attention in a group of patients with schizophrenia (SZ, n = 55) compared to neurotypical controls (NC, n = 55). While the executive control effects were significantly correlated between the two modalities in the NC group, these effects were not correlated in the SZ group, with a significant group difference in the correlation. Further, the inconsistency and magnitude of the cross-modal executive control effects were significantly larger in the SZ group compared to the NC group. Together, these results suggest that there is a disruption of a common supramodal executive control mechanism in patients with schizophrenia, which may be related to the thought processing disorder characterizing the disorder.

The influence of CHRNA4, COMT, and maternal sensitivity on orienting and executive attention in 6-month-old infants

Despite claims concerning biological mechanisms sub-serving infant attention, little experimental work examines its underpinnings. This study examines how candidate polymorphisms from the cholinergic (CHRNA4 rs1044396) and dopaminergic (COMT rs4680) systems, respectively indicative of parietal and prefrontal/anterior cingulate involvement, are related to 6-month-olds' (n=217) performance during a visual expectation eye-tracking paradigm. As previous studies suggest that both cholinergic and dopaminergic genes may influence susceptibility to the influence of other genetic and environmental factors, we further examined whether these candidate genes interact with one another and/or with early caregiving experience in predicting infants' visual attention. We detected an interaction between CHRNA4 genotype and observed maternal sensitivity upon infants' orienting to random stimuli and a CHRNA4-COMT interaction effect upon infants' orienting to patterned stimuli. Consistent with adult research, we observed a direct effect of COMT genotype on anticipatory looking to patterned stimuli. Findings suggest that CHRNA4 genotype may influence susceptibility to other attention-related factors in infancy. These interactions may account for the inability to establish a link between CHRNA4 and orienting in infant research to date, despite developmental theorizing suggesting otherwise. Moreover, findings suggest that by 6months, dopamine, and relatedly, the prefrontal cortex/anterior cingulate, may be important to infant attention.

Differential impairments across attentional networks in binge drinking

RATIONALE

The cognitive deficits observed in young binge drinkers have been largely documented during the last decade. Yet, these earlier studies have mainly focused on high-level cognitive abilities (particularly memory and executive functions), and uncertainty thus still abounds regarding the integrity of less complex cognitive processes in binge drinking. This is particularly true for attentional abilities, which play a crucial role in behavior regulation and are impaired in other alcohol-related disorders.

OBJECTIVES AND METHODS

To specify the attentional deficits associated with binge drinking, two groups of university students (40 binge drinkers and 40 matched controls) performed the Attention Network Task, a theoretically grounded test assessing three independent attentional networks: alerting, orienting, and executive control.

RESULTS

Binge drinkers displayed preserved orienting performance but impaired alerting and executive control. Binge drinking is thus not related to a general attentional impairment but rather to specific impairments of the alerting and executive control networks.

CONCLUSIONS

These results underline that, beyond the already explored high-level deficits, binge drinking is also related to impairments for attentional abilities. In view of the role played by attentional impairments in alcohol dependence, the present data also suggest that rehabilitation programs should be developed to improve attentional abilities at the early stages of alcohol-related disorders.

Impact of DRD2/ANKK1 and COMT Polymorphisms on Attention and Cognitive Functions in Schizophrenia

BACKGROUND

Cognitive deficits such as poor selective attention and executive functions decline have been reported in patients with schizophrenia. Many studies have emphasized the role of dopamine in regulating cognitive functions in the general population as well as in schizophrenia. However, the relationship between cognitive processes, schizophrenia and dopaminergic candidate genes is an original approach given interesting results. The purpose of the current exploratory study was to examine the interaction of dopaminergic genes (coding for dopamine receptor D2, DRD2, and for Catecholamine-O-Methyl-Transferase, COMT) with the diagnostic of schizophrenia in (i) the executive control of attention, (ii) selective attention, and (iii) executive functions.

METHODS AND RESULTS

We recruited 52 patients with schizophrenia and 53 healthy controls who performed the Stroop Color-Word Test, the Attention Network Test and the Wisconsin Card Sorting test. Four single nucleotide polymorphisms (SNPs) in the DRD2 gene (rs6275, rs6277, rs2242592 and rs1800497) and two SNPs in the COMT gene (rs4680 and rs165599) have been genotyped. Patients with schizophrenia performed significantly worse than controls in all cognitive performance, taking into account demographic variables. A significant gene by disease interaction was found for the Stroop interference (p = 0.002) for rs6275 of the DRD2 gene. The COMT Val/Val genotype and schizophrenia were associated with increased number of perseverative errors (p = 0.01).

CONCLUSIONS

In our study, the DRD2 gene is involved in attention while the COMT gene is implicated in executive functions in patients with schizophrenia.

Network-Dependent Modulation of COMT and DRD2 Polymorphisms in Healthy Young Adults

Nonlinear modulation of the dopamine signaling on brain functions can be estimated by the interaction effects of dopamine-related genetic variations. We aimed to explore the interaction effects of COMT rs4680 and DRD2 rs1076560 on intra-network connectivity using independent component analysis. In 250 young healthy adults, we identified 11 meaningful resting-state networks (RSNs), including the salience, visual, auditory, default-mode, sensorimotor, attention and frontoparietal networks. A two-way analysis of covariance was used to investigate COMT×DRD2 interactions on intra-network connectivity in each network, controlling for age, gender and education. Significant COMT×DRD2 interaction was found in intra-network connectivity in the left medial prefrontal cortex of the anterior default-mode network, in the right dorsolateral frontal cortex of the right dorsal attention network, and in the left dorsal anterior cingulate cortex of the salience network. Post hoc tests revealed that these interactions were driven by the differential effects of DRD2 genotypes on intra-network connectivity in different COMT genotypic subgroups. Moreover, even in the same COMT subgroup, the modulation effects of DRD2 on intra-network connectivity were different across RSNs. These findings suggest a network-dependent modulation of the DA-related genetic variations on intra-network connectivity.

Attentional alterations in alcohol dependence are underpinned by specific executive control deficits

BACKGROUND

Attentional biases and deficits play a central role in the development and maintenance of alcohol dependence, but the underlying attentional processes accounting for these deficits have been very little explored. Importantly, the differential alterations across the 3 attentional networks (alerting, orienting, and executive control) remain unclear in this pathology.

METHODS

Thirty recently detoxified alcohol-dependent individuals and 30 paired controls completed the Attention Network Test, which allow exploring the attentional alterations specifically related to the 3 attentional networks.

RESULTS

Alcohol-dependent individuals presented globally delayed reaction times compared to controls. More centrally, they showed a differential deficit across attention networks, with a preserved performance for alerting and orienting networks but impaired executive control (p < 0.001). This deficit was not related to psychopathological comorbidities but was positively correlated with the duration of alcohol-dependence habits, the number of previous detoxification treatments and the mean alcohol consumption before detoxification.

CONCLUSIONS

These results suggest that attentional alterations in alcohol dependence are centrally due to a specific alteration of executive control. Intervention programs focusing on executive components of attention should be promoted, and these results support the frontal lobe hypothesis.

Gene-sex interactions in schizophrenia: focus on dopamine neurotransmission

Schizophrenia is a severe mental disorder, with a highly complex and heterogenous clinical presentation. Our current perspectives posit that the pathogenic mechanisms of this illness lie in complex arrays of gene × environment interactions. Furthermore, several findings indicate that males have a higher susceptibility for schizophrenia, with earlier age of onset and overall poorer clinical prognosis. Based on these premises, several authors have recently begun exploring the possibility that the greater schizophrenia vulnerability in males may reflect specific gene × sex (G×S) interactions. Our knowledge on such G×S interactions in schizophrenia is still rudimentary; nevertheless, the bulk of preclinical evidence suggests that the molecular mechanisms for such interactions are likely contributed by the neurobiological effects of sex steroids on dopamine (DA) neurotransmission. Accordingly, several recent studies suggest a gender-specific association of certain DAergic genes with schizophrenia. These G×S interactions have been particularly documented for catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO), the main enzymes catalyzing DA metabolism. In the present review, we will outline the current evidence on the interactions of DA-related genes and sex-related factors, and discuss the potential molecular substrates that may mediate their cooperative actions in schizophrenia pathogenesis.

COMT, neuropsychological function and brain structure in schizophrenia: a systematic review and neurobiological interpretation

BACKGROUND

Endophenotypes in genetic psychiatry may increase our understanding of the molecular mechanisms underlying disease risk and its manifestations. We sought to investigate the link between neuropsychological impairments and brain structural abnormalities associated with the COMT Val(158)Met polymorphism in patients with schizophrenia to improve understanding of the pathophysiology of this disorder.

METHODS

We performed a systematic review using studies identified in PubMed and MEDLINE (from the date of the first available article to July 2012). Our review examined evidence of an association between the COMT Val(158)Met polymorphism and both neuropsychological performance and brain structure in patients with psychosis, in their relatives and in healthy individuals (step 1). The review also explored whether the neuropsychological tasks and brain structures identified in step 1 met the criteria for an endophenotype (step 2). Then we evaluated evidence that the neuropsychological endophenotypes identified in step 2 are associated with the brain structure endophenotypes identified in that step (step 3). Finally, we propose a neurobiological interpretation for this evidence.

RESULTS

A poorer performance on the n-back task and the Continuous Performance Test (CPT) and smaller temporal and frontal brain areas were associated with the COMT Val allele in patients with schizophrenia and their relatives and met most of the criteria for an endophenotype. It is possible that the COMT Val(158)Met polymorphism therefore contributes to the development of these neuropsychological and brain structural endophenotypes of schizophrenia, in which the prefrontal cortex may represent the neural substrate underlying both n-back and CPT performances.

LIMITATIONS

The association between a single genetic variant and an endophenotype does not necessarily imply a causal relationship between them.

CONCLUSION

This evidence and the proposed interpretation contribute to explain, at least in part, the biological substrate of 4 important endophenotypes that characterize schizophrenia.

The DOPA decarboxylase (DDC) gene is associated with alerting attention

DOPA decarboxylase (DDC) is involved in the synthesis of dopamine, norepinephrine and serotonin. It has been suggested that genes involved in the dopamine, norepinephrine, and cholinergic systems play an essential role in the efficiency of human attention networks. Attention refers to the cognitive process of obtaining and maintaining the alert state, orienting to sensory events, and regulating the conflicts of thoughts and behavior. The present study tested seven single nucleotide polymorphisms (SNPs) within the DDC gene for association with attention, which was assessed by the Attention Network Test to detect three networks of attention, including alerting, orienting, and executive attention, in a healthy Han Chinese sample (N=451). Association analysis for individual SNPs indicated that four of the seven SNPs (rs3887825, rs7786398, rs10499695, and rs6969081) were significantly associated with alerting attention. Haplotype-based association analysis revealed that alerting was associated with the haplotype G-A-T for SNPs rs7786398-rs10499695-rs6969081. These associations remained significant after correcting for multiple testing by max(T) permutation. No association was found for orienting and executive attention. This study provides the first evidence for the involvement of the DDC gene in alerting attention. A better understanding of the genetic basis of distinct attention networks would allow us to develop more effective diagnosis, treatment, and prevention of deficient or underdeveloped alerting attention as well as its related prevalent neuropsychiatric disorders.

Antipsychotic medications and cognitive functioning in bipolar disorder: moderating effects of COMT Val108/158 Met genotype

BACKGROUND

There is a negative association between the use of antipsychotics and cognitive functioning in bipolar patients, which may be mediated by altered dopamine signaling in selected brain areas, and moderation thereof by genetic sequence variation such as COMT Val108/158Met. The interaction between antipsychotic drug use and the COMT Val108/158Met genotype on two-year cognitive functioning in bipolar patients was examined.

METHODS

Interaction between the COMT Val108/158Met and antipsychotics on a composite cognitive measure was examined in 51 bipolar patients who were assessed 12 times at two-monthly intervals over a period of two years (379 observations).

RESULTS

There was a significant negative effect of the interaction between antipsychotic medications and Val allele load on the composite cognitive measure in bipolar patients (p < 0.001).

CONCLUSIONS

The negative effects of antipsychotics on cognitive functioning in bipolar disorder may be moderated by the COMT Val 108/158 Met genotype, with a negative effect of Val allele load. If replicated, the results may be indicative of pharmacogenetic interactions in bipolar disorder.

Unaffected control of distractor interference in schizophrenia: a meta-analysis of incompatibility slowing in flanker tasks

In schizophrenia research executive functions have been frequently reported to be impaired on a global level, largely ignoring the fact that the term executive functions refers to a collection of cognitive functions, which may be affected independently of each other. In the present meta-analysis we were able to show that an aspect of interference control, the ability to resist to distracting information, is not substantially affected in schizophrenia. Summarizing the results of 21 studies using a flanker task, we did not find an increased incompatibility slowing (relative to a compatible flanker condition). The mean effect size, integrating the data of 1029 schizophrenia and 848 controls, was with M(g) = 0.037 (95% confidence interval: -0.05 to 0.13) small and the test power was with 1-β = 0.991 sufficiently high to exclude even small population effects. A similar result was obtained when analyzing the incompatibility slowing relative to a neutral flanker condition (8 studies, M(g) = -0.032, 95% confidence interval: -0.16 to 0.09). In not being substantially affected in schizophrenia, the ability to resist distractor interference could serve as "scaffold function", which used by cognitive remediation programs, would allow to build up general functions, such as vigilance and attention, before the affected executive abilities would be addressed.

Executive attention impairment in first-episode schizophrenia

BACKGROUND

We compared the attention abilities of a group of first-episode schizophrenia (FES) patients and a group of healthy participants using the Attention Network Test (ANT), a standard procedure that estimates the functional state of three neural networks controlling the efficiency of three different attentional behaviors, i.e., alerting (achieving and maintaining a state of high sensitivity to incoming stimuli), orienting (ability to select information from sensory input), and executive attention (mechanisms for resolving conflict among thoughts, feelings, and actions).

METHODS

We evaluated 22 FES patients from 17 to 29 years of age with a recent history of a single psychotic episode treated only with atypical neuroleptics, and 20 healthy persons matched with FES patients by sex, age, and educational level as the control group. Attention was estimated using the ANT in which participants indicate whether a central horizontal arrow is pointing to the left or the right. The central arrow may be preceded by spatial or temporal cues denoting where and when the arrow will appear, and may be flanked by other arrows (hereafter, flankers) pointing in the same or the opposite direction.

RESULTS

The efficiency of the alerting, orienting, and executive networks was estimated by measuring how reaction time was influenced by congruency between temporal, spatial, and flanker cues. We found that the control group only demonstrated significantly greater attention efficiency than FES patients in the executive attention network.

CONCLUSIONS

FES patients are impaired in executive attention but not in alerting or orienting attention, suggesting that executive attention deficit may be a primary impairment during the progression of the disease.

Evidence of IQ-modulated association between ZNF804A gene polymorphism and cognitive function in schizophrenia patients

ZNF804A gene polymorphism rs1344706 has been suggested as the most compelling case of a candidate gene for schizophrenia by a genome-wide association study and several replication studies. The current study of 570 schizophrenia patients and 448 controls again found significantly different genotype frequencies of rs1344706 between patients and controls. More important, we found that this association was modulated by IQ, with a stronger association among individuals with relatively high IQ, which replicated results of Walters et al, 2010. We further examined whether this IQ-modulated association also existed between the SNP and the intermediate phenotypes (working memory and executive functions) of schizophrenia. Data were available from an N-back task (366 patients and 414 controls) and the attention network task (361 patients and 416 controls). We found that the SNP and IQ had significant interaction effects on the intermediate phenotypes for patients, but not for controls. The disease risk allele was associated with poorer cognitive function in patients with high IQ, but better cognitive function in patients with low IQ. Together, these results indicated that IQ may modulate the role of rs1344706 in the etiology of both schizophrenia and its cognitive impairments, and pointed to the necessity of considering general cognitive function as indexed by IQ in the future studies of genetic bases of schizophrenia.

The effects of CACNA1C gene polymorphism on spatial working memory in both healthy controls and patients with schizophrenia or bipolar disorder

CACNA1C gene polymorphism (rs1006737) is a susceptibility factor for both schizophrenia (SCZ) and bipolar disorder (BP). However, its role in working memory, a cognitive function that is impaired in both diseases, is not clear. Using three samples, including healthy controls, patients with SCZ, and patients currently in manic episodes of BP, this study tested the association between the SNP rs1006737 and spatial working memory as measured by an N-back task and a dot pattern expectancy (DPX) task. Among SCZ patients and healthy controls, the clinical risk allele was associated with impaired working memory, but the association was either in opposite direction or non-significant in patients with BP. These results indicated that rs1006737 may have differential effects on working memory in different disease populations and pointed to the necessity for more studies in different patient populations.

[Schizophrenia, genetics and cognition]

Schizophrenia is a complex and heritable disorder. Nevertheless, molecular genetics of schizophrenia remains inconclusive. By developing the concept of endophenotype for the disorder, it is easier to define an association between a phenotype and genetic variants or physiopathological processes. Cognitive disorders could be useful endophenotypes for schizophrenia. For example, the val(158)/met COMT polymorphism has been associated with executive function or working memory. Therefore, several cognitive dysfunctions were proposed as endophenotypes and were investigated in the context of different genetic polymorphisms. Genome-wide association studies and epistatic studies demonstrated the complexity of the mechanisms underlying cognitive disturbance. However, meta-analysis remains inconclusive. Altogether, the study of endophenotypes is an attractive approach to solve the complex mechanisms causing schizophrenia vulnerability. Nevertheless, several limitations exist and include the lack of reproducibility, the discordant results between healthy subjects and patients, the exclusion of the many rare variants.

S100B gene polymorphisms predict prefrontal spatial function in both schizophrenia patients and healthy individuals

Animal studies have strongly implicated a role of S100B in spatial ability and our recent study of humans found that S100B gene polymorphisms (rs9722, rs1051169, and rs2839357) were associated with schizophrenia patients' spatial ability (as assessed by a block design task and a mental rotation task). In this study, we explored the associations between these and three additional SNPs in S100B and prefrontal functions (working memory and executive control) among 434 schizophrenia patients and 412 healthy controls. Results showed that, for both schizophrenia patients and healthy controls, two SNPs were significantly associated with prefrontal functions in the spatial domain (P value threshold was set at 0.014 after correcting for multiple comparisons), with the AA genotype of rs9722 and the GG genotype of rs2839357 linked to poorer performance. No SNP was associated with prefontal functions in the verbal domain (all Ps >0.05). These results extend our previous study and further confirm the important roles of the S100B gene in spatial abilities.

COMT and ALDH2 polymorphisms moderate associations of implicit drinking motives with alcohol use

Dual process models of addiction emphasize the importance of implicit (automatic) cognitive processes in the development and maintenance of substance use behavior. Although genetic influences are presumed to be relevant for dual process models, few studies have evaluated this possibility. The current study examined two polymorphisms with functional significance for alcohol use behavior (COMT Val158Met and ALDH2*2) in relation to automatic alcohol cognitions and tested additive and interactive effects of genotype and implicit cognitions on drinking behavior. Participants were college students (n = 69) who completed Implicit Association Tasks (IATs) designed to assess two classes of automatic drinking motives (enhancement motives and coping motives). Genetic factors did not show direct associations with IAT measures; however, COMT and ALDH2 moderated associations of implicit coping motives with drinking outcomes. Interaction effects indicated that associations of implicit motives with drinking outcomes were strongest in the context of genetic variants associated with relatively higher risk for alcohol use (COMT Met and ALDH2*1). Associations of genotype with drinking behavior were observed for ALDH2 but not COMT. These findings are consistent with the possibility that genetic risk or protective factors could potentiate or mitigate the influence of reflexive cognitive processes on drinking behavior, providing support for the evaluation of genetic influences in the context of dual process models of addiction.

Test-retest reliability of Attention Network Test measures in schizophrenia

BACKGROUND

The Attention Network Test (ANT) is a well established behavioral measure in neuropsychological research to assess three different facets of selective attention, i.e., alerting, orienting, and conflict processing. Although the ANT has been applied in healthy individuals and various clinical populations, data on retest reliability are scarce in healthy samples and lacking for clinical populations. The objective of the present study was a longitudinal assessment of relevant ANT network measures in healthy controls and schizophrenic patients.

METHODS

Forty-five schizophrenic patients and 55 healthy controls were tested with ANT in a test-retest design with an average interval of 7.4 months between test sessions. Test-retest reliability was analyzed with Pearson and Intra-class correlations.

RESULTS

Healthy controls revealed moderate to high test-retest correlations for mean reaction time, mean accuracy, conflict effect, and conflict error rates. In schizophrenic patients, moderate test-retest correlations for mean reaction time, orienting effect, and conflict effect were found. The analysis of error rates in schizophrenic patients revealed very low test-retest correlations.

CONCLUSIONS

The current study provides converging statistical evidence that the conflict effect and mean reaction time of ANT yield acceptable test-retest reliabilities in healthy controls and, investigated longitudinally for the first time, also in schizophrenia. Obtained differences of alerting and orienting effects in schizophrenia case-control studies should be considered more carefully. The analysis of error rates revealed heterogeneous results and therefore is not recommended for case control studies in schizophrenia.

Inferior frontal white matter asymmetry correlates with executive control of attention

White matter (WM) asymmetries of the human brain have been well documented using diffusion tensor imaging (DTI). However, the relationship between WM asymmetry pattern and cognitive performance is poorly understood. By means of tract-based spatial statistics (TBSS) and voxel-based analyses of whole brain, this study examined the WM asymmetries and the correlations between WM integrity/asymmetries and three distinct components of attention, namely alerting, orienting, and executive control (EC), which were assessed by attention network test (ANT). We revealed a number of WM anisotropy asymmetries, including leftward asymmetry of cingulum, corticospinal tract and cerebral peduncle, rightward asymmetry of internal capsule, superior longitudinal fasciculus and posterior corona radiata, as well as heterogeneous asymmetries in anterior corpus callosum and anterior corona radiata (ACR). Moreover, specific correlation was found between asymmetric pattern of inferior frontal ACR and EC performance. Additionally, this study also proposed that there were no significant relationships of WM anisotropy asymmetries to alerting and orienting functions. Further clusters of interest analyses and probabilistic fiber tracking validated our findings. In conclusion, there are a number of differences in WM integrity between human brain hemispheres. Specially, the anisotropy asymmetry in inferior frontal ACR plays a crucial role in EC function. Our finding is supportive of the functional studies of inferior frontal regions and in keeping with the theory of the brain lateralization on human ventral attention system.

Neural correlates of the attention network test in schizophrenia

Attentional deficits are prominent in schizophrenia, affecting nearly all cognitive functions. Human attention comprises three essential components: alerting, orienting and executive control. For the assessment of these functions, the attention network test (ANT) has been proposed and used in healthy controls and patients. In schizophrenia, the ANT has revealed behavioral deficits; however, the corresponding neural correlates have not been examined. In the present study, neural correlates of attention were investigated in 17 schizophrenia patients and 17 healthy controls using the ANT with fMRI. Behavioral deficits emerged in the alertness system with a reduced efficiency for temporal cues. In fMRI, changes were observed for all three domains-alerting, orienting and conflict-and revealed hyper- as well as hypoactivation in patients. Affected regions during alerting comprised a broad fronto-temporo-parieto-occipito-cerebellar network, while differences during orienting mainly tapped fronto-parietal regions and during conflict processing a thalamo-frontal-temporal occipital network including the postcentral regions. In general, hyperactivations were positively correlated with more severe psychopathologial symptoms.

Visual P3 amplitude modulation deficit in schizophrenia is independent of duration of illness

BACKGROUND

In the search for markers of schizophrenia, functional deficits during inhibition have been a major focus. In previous studies, we found a reduced amplitude modulation of the visual P3 component of the event-related potential (ERP) in schizophrenic patients during inhibition in the Attention Network Test (ANT). The objective of the present study was to explore whether this deficit exhibits properties of a trait or state marker of schizophrenia.

METHODS

Eighteen recent onset inpatients and eighteen chronic schizophrenic outpatients as well as 36 healthy controls, including a young adult and an old adult group to match recent onset and chronic illness groups for age and sex, were included. Participants were tested with ANT while 32-channel electroencephalogram was recorded and visual P3 amplitudes were analyzed. Amplitude modulation was defined as the variation of P3 amplitude at Pz as a function of ANT flanker conditions.

RESULTS

There were no significant behavioral between-group differences in terms of alerting, orienting, and inhibition. Mean visual P3 was significantly lower in schizophrenic patients than in healthy controls. Parietal P3 amplitude was significantly less modulated in both recent onset (-0.035) and chronic schizophrenic patients (-0.081) compared with young (-0.588; p<0.05) and older healthy controls, respectively (-0.556; p<0.05). No correlations were obtained between P3 modulation and clinical or demographic variables.

CONCLUSION

The results provide evidence that the observed deficit of visual P3 amplitude modulation is independent of duration of illness and age and may contain properties of a trait marker of schizophrenia.

Effects of a CACNA1C genotype on attention networks in healthy individuals

BACKGROUND

Recent genetic studies found the A allele of the variant rs1006737 in the alpha 1C subunit of the L-type voltage-gated calcium channel (CACNA1C) gene to be over-represented in patients with psychosis, including schizophrenia, bipolar disorder and major depressive disorder. In these disorders, attention deficits are among the main cognitive symptoms and have been related to altered neural activity in cerebral attention networks. The particular effect of CACNA1C on neural function, such as attention networks, remains to be elucidated.

METHOD

The current event-related functional magnetic resonance imaging (fMRI) study investigated the effect of the CACNA1C gene on brain activity in 80 subjects while performing a scanner-adapted version of the Attention Network Test (ANT). Three domains of attention were probed simultaneously: alerting, orienting and executive control of attention.

RESULTS

Risk allele carriers showed impaired performance in alerting and orienting in addition to reduced neural activity in the right inferior parietal lobule [Brodmann area (BA) 40] during orienting and in the medial frontal gyrus (BA 8) during executive control of attention. These areas belong to networks that have been related to impaired orienting and executive control mechanisms in neuropsychiatric disorders.

CONCLUSIONS

Our results suggest that CACNA1C plays a role in the development of specific attention deficits in psychiatric disorders by modulation of neural attention networks.

No association between the Catechol-O-Methyltransferase (COMT) val158met polymorphism and cognitive improvement following cognitive remediation therapy (CRT) in schizophrenia

Cognitive deficits are rate limiters on recovery in schizophrenia that respond poorly to pharmacotherapy. Cognitive remediation therapy (CRT), a novel psychological therapy, has produced promising outcomes for cognition. However, little is known about the biological mechanisms that might underlie individual differences in CRT response. Catechol-O-Methyltransferase (COMT) is associated specifically with prefrontal cognition. The COMT Val158Met polymorphism is known to have a functional effect on the rate of dopamine degradation, which may be related to cognitive treatment response. This study aimed to determine whether COMT genotype influences cognitive improvement following CRT in schizophrenia. Participants with schizophrenia were recruited from three randomised controlled trials of CRT compared to treatment as usual, and one CRT treatment only trial, each providing 40 CRT sessions. Eighty-seven participants (40%) agreed to participate in the genetic study, and provided DNA for COMT genotyping. Cognitive function and psychopathology were assessed at baseline, post-treatment and 3-6-month follow-up. People with the COMT Val/Met genotype performed more poorly on categories achieved at baseline on the Wisconsin Card Sorting Test (WCST) than those homozygous for the Val or Met allele. Cognitive function improved with CRT but there was no association between this cognitive improvement and COMT genotype, either in the CRT group or in the total sample. The COMT val158Met polymorphism does not appear to be a clinically useful biomarker of cognitive improvement following CRT in schizophrenia. A complex set of factors may influence cognitive change, however, such that the COMT genotype might still have a subtle effect on response to CRT or similar interventions.

Single-subject classification of schizophrenia by event-related potentials during selective attention

BACKGROUND

Executive dysfunction has repeatedly been proposed as a robust and promising substrate of analytical approaches in the research of neurocognitive markers of schizophrenia. Here, we present a mixed model- and data-driven classification approach by applying a task that targets executive dysfunction in schizophrenia and by investigating relevant event-related potential (ERP) features with machine learning classifiers.

METHODS

Forty schizophrenic patients and forty matched healthy controls completed the Attention Network Test while an electroencephalogram was recorded. Target-locked N1 and P3 ERP components were constructed and submitted to different classification analyses without a priori hypotheses. Standardized source localization was applied to estimate neural sources of N1 and P3 deficits in schizophrenia.

RESULTS

We obtained a classification accuracy of 79% using only very few ERP components. Central P3 components following compatible and incompatible trials and right parietal N1 latencies averaged across targets and were sufficient for classification. P3 deficits were associated with anterior cingulate cortex dysfunction, while right posterior current density deficits were observed in schizophrenia during the N1 time frame.

CONCLUSIONS

The data exemplarily show how automated inference may be applied to classify a pathological state in single subjects without prior knowledge of their diagnoses. While classification accuracy may be optimized by application of other executive paradigms, this approach illustrates the potential of machine learning algorithms for the identification of biomarkers that are independent of clinical assessments. Conversely, data suggest a pathophysiological mechanism that includes early visual and late executive deficits during response inhibition in schizophrenia.

Evidence of specificity of a visual P3 amplitude modulation deficit in schizophrenia

BACKGROUND

In a previous study, we found a reduced amplitude modulation of the visual P3 component of the event-related potential (ERP) in schizophrenic patients compared with healthy controls during inhibition in the Attention Network Test (ANT). The objective of the present study was to replicate this finding and to explore whether this cortical processing deficit is specific to schizophrenia.

METHODS

Sixteen schizophrenic patients, sixteen depressive patients, and sixteen healthy controls matched for age, sex, and education were included. Participants were tested with the ANT, a test of selective attention that provides behavioral estimates for alerting, orienting, and inhibition. 32-Channel electroencephalogram was recorded and visual P3 amplitudes were topographically analyzed and compared between groups.

RESULTS

There were no significant behavioral between-group differences in terms of mean reaction time, accuracy, and ANT effects alerting, orienting, and inhibition. Absolute visual P3 amplitude was not reduced in schizophrenia or depression. P3 amplitude modulation was defined as P3 amplitude at Pz as a function of ANT flanker conditions. We found a parietal P3 amplitude modulation deficit in schizophrenic patients (-.015) that was absent in both healthy controls (-.705; p = .002) and depressive patients (-1.022; p = .001).

CONCLUSION

The results provide evidence that a deficit of visual P3 amplitude modulation distinguishes schizophrenia from healthy and disease controls and provides greater discriminative power than absolute visual P3 amplitude.

COMT Val158Met polymorphism, cognitive stability and cognitive flexibility: an experimental examination

Background

Dopamine in prefrontal cortex (PFC) modulates core cognitive processes, notably working memory and executive control. Dopamine regulating genes and polymorphisms affecting PFC - including Catechol-O-Methyltransferase (COMT) Val158Met - are crucial to understanding the molecular genetics of cognitive function and dysfunction. A mechanistic account of the COMT Val158Met effect associates the Met allele with increased tonic dopamine transmission underlying maintenance of relevant information, and the Val allele with increased phasic dopamine transmission underlying the flexibility of updating new information. Thus, consistent with some earlier work, we predicted that Val carriers would display poorer performance when the maintenance component was taxed, while Met carriers would be less efficient when rapid updating was required.

Methods

Using a Stroop task that manipulated level of required cognitive stability and flexibility, we examined reaction time performance of patients with schizophrenia (n = 67) and healthy controls (n = 186) genotyped for the Val/Met variation.

Results

In both groups we found a Met advantage for tasks requiring cognitive stability, but no COMT effect when a moderate level of cognitive flexibility was required, or when a conflict cost measure was calculated.

Conclusions

Our results do not support a simple stability/flexibility model of dopamine COMT Val/Met effects and suggest a somewhat different conceptualization and experimental operationalization of these cognitive components.

Familiality and molecular genetics of attention networks in ADHD

Indices from a more elementary neuropsychological level might be useful in the search for genes for complex psychiatric disorders, such as ADHD. In this study we investigated systematically whether attentional performance as measured with the Attention Network Test (ANT) is suited for the identification of endophenotypes of ADHD. Attentional performance in affected sib pairs with ADHD (n = 181) was compared to unaffected control siblings (n = 121). Intrafamilial correlation patterns were calculated. In addition, linkage and association analyses were conducted between quantitative scores of attentional functions and dopamine receptor D4 (DRD4) and dopamine transporter (DAT1 or SLC6A3) gene variants. Only the executive attention network was significantly impaired in subjects with ADHD compared to controls (P < 0.05) and showed evidence for familiality in both affected and unaffected families. Linkage analyses revealed the highest LOD score for a severity score based on DSM-IV inattentive symptoms in the DAT1 chromosomal region (LOD score 2.6 at 15 cM). However, a SNP (rs6350) at the DAT1 locus showed a tendency for association with both alerting performance (P = 0.02) and executive attention (P = 0.01) although it did not survive alpha adjustment for multiple testing. No evidence was found for association of any of the investigated phenotypes with the VNTR in the DRD4. Thus, our data suggest that the quantitative behavioral ratings of inattentive symptoms might be more useful when searching for new genes associated with ADHD, however, among the ANT measures the executive attention network seems to be best suited for further endophenotype analyses.

Attention Network Test reveals alerting network dysfunction in multiple sclerosis

Attention is one of the cognitive domains typically affected in multiple sclerosis. The Attention Network Test was developed to measure the function of the three distinct attentional networks, alerting, orienting, and executive control. The Attention Network Test has been performed in various neuropsychiatric conditions, but not in multiple sclerosis. Our objective was to investigate functions of attentional networks in multiple sclerosis by means of the Attention Network Test. Patients with relapsing—remitting multiple sclerosis (n = 57) and healthy controls (n = 57) matched for age, sex, and education performed the Attention Network Test. Significant differences between patients and controls were detected in the alerting network (p = 0.003), in contrast to the orienting (p = 0.696) and the conflict (p = 0.114) network of visual attention. Mean reaction time in the Attention Network Test was significantly longer in multiple sclerosis patients than in controls (p = 0.032), Multiple sclerosis patients benefited less from alerting cues for conflict resolution compared with healthy controls. The Attention Network Test revealed specific alterations of the attention network in multiple sclerosis patients which were not explained by an overall cognitive slowing.

Attention network test (ANT) reveals gender-specific alterations of executive function in schizophrenia

The Attention Network Test (ANT) provides measures for three different components of visual attention: executive control (=conflict inhibition), orienting, and alerting. There is reasonable evidence that alterations of attention-mainly in the executive/conflict domain-are associated with susceptibility to psychiatric illness. Specific impairments may be a characteristic for a medical condition such as schizophrenia and thus shift our understanding from a neuropsychological endophenotype to a more precise genetic understanding of this disorder. Study subjects comprised 35 schizophrenic patients and 35 healthy controls (13 female and 22 male in both groups). The ANT was administered to all participants and rated individual responses for the three factors (alerting, orienting, and conflict) and their respective ratios relative to mean reaction times. With regard to gender differences, group comparisons were performed for schizophrenic patients vs. healthy controls. Significant differences between patients and controls could be detected for mean reaction time (639 vs. 538 ms) and for conflict ratio (0.158 vs. 0.191). The latter difference mainly resulted from gender-specific variances of the conflict network in opposite directions. The executive function as represented by the conflict network of visual attention of the ANT is affected in schizophrenia. We have detected hitherto unreported gender-specific differences between healthy controls and schizophrenic patients. Especially as regards the conflict network, the ANT offers a promising methodology to detect a neuropsychological endophenotype of schizophrenia.

Schizophrenia: genetics, prevention and rehabilitation

OBJECTIVE

Genetic factors are largely implicated in predisposing to schizophrenia. Environmental factors contribute to the onset of the disorder in individuals at increased genetic risk. Cognitive deficits have emerged as endophenotypes and potential therapeutic targets for schizophrenia because of their association with functional outcome. The aims of this review were to analyse the joint effect of genetic and environmental (G×E) factors on liability to schizophrenia and to investigate relationships between genes and cognitive endophenotypes focusing on practical applications for prevention and rehabilitation.

METHODS

Medline search of relevant studies published between 1990 and 2008.

RESULTS

In schizophrenia, examples of G×E interaction include the catechol-O-methyl transferase (COMT) (Val158Met) polymorphism, which was found to moderate the onset of psychotic manifestations in response to stress and to increase the risk for psychosis related to cannabis use, and neurodevelopmental genes such as AKT1 (serine-threonine kinase), brain-derived neurotrophic factor (BDNF), DTNBP1 (dysbindin) and GRM3 (metabotropic glutamate receptor 3), which were associated with development of schizophrenia in adulthood after exposure to perinatal obstetric complications. Neurocognitive deficits are recognised as core features of schizophrenia that facilitate the onset of the disorder and have a great impact on functional outcome. Neurocognitive deficits are also endophenotypes that have been linked to a variety of genes [COMT, neuregulin (NRG1), BDNF, Disrupted-In-Schizophrenia 1 (DISC1) and dysbindin] conferring susceptibility to schizophrenia. Recently, it has emerged that cognitive improvement during rehabilitation therapy was under control of COMT (Val158Met) polymorphism.

CONCLUSION

This review could indicate a pivotal role of psychiatric genetics in prevention and rehabilitation of schizophrenic psychoses.