COMT Val108/158Met genotype modulates human sensory gating

The Use of Event-Related Potentials in the Study of Schizophrenia: An Overview

Event-related potentials (ERPs) are small voltage changes in the brain that reliably occur in response to auditory or visual stimuli. ERPs have been extensively studied in both humans and animals to identify biomarkers, test pharmacological agents, and generate testable hypotheses about the physiological and genetic basis of schizophrenia. In this chapter, we discuss how ERPs are generated and recorded as well as review canonical ERP components in the context of schizophrenia research in humans. We then discuss what is known about rodent homologs of these components and how they are altered in common pharmacologic and genetic manipulations used in preclinical schizophrenia research. This chapter will also explore the relationship of ERPs to leading hypotheses about the pathophysiology of schizophrenia. We conclude with an evaluation of both the utility and limitations of ERPs in schizophrenia research and offer recommendations of future directions that may be beneficial to the field.

Catechol-O-methyltransferase (COMT) Val158Met Polymorphism and Prepulse Inhibition of the Change-related Cerebral Response

Change-related potentials elicited by an abrupt sound feature's change are attenuated by a leading weak sound (prepulse inhibition: PPI). We investigated whether the PPI index is associated with the catechol-methyltransferase (COMT) Val158Met polymorphism (rs4680), which is involved in the metabolism of dopamine in the prefrontal cortex. Healthy subjects with normal hearing were recruited (n = 70). A train of 100-Hz clicks 650 ms in duration was used. The test stimulus was an abrupt increase in sound intensity (+10 dB) from the baseline (70 dB) provided at 400 ms after the sound onset. Three consecutive clicks at 30, 40, and 50 ms before the change's onset were greater (+3 or +5 dB) from the baseline as a prepulse. The targeting auditory evoked potential component was Change-N1 peaking approx. 130 ms after the change onset. We calculated the inhibition level as the% inhibition of the Change-N1 amplitude by a prepulse. The %PPI in the Met-carriers was significantly greater than that in the Val/Val-individuals. Our results suggest that dopamine might play a role in the PPI of the change-related response. We propose that this index has the potential to identify an intermediate phenotype in psychiatric disorders such as schizophrenia.

Comparative Analysis of Dopaminergic and Cholinergic Mechanisms of Sensory and Sensorimotor Gating in Healthy Individuals and in Patients With Schizophrenia

Sensory and sensorimotor gating provide the early processing of information under conditions of rapid presentation of multiple stimuli. Gating deficiency is observed in various psychopathologies, in particular, in schizophrenia. However, there is also a significant proportion of people in the general population with low filtration rates who do not show any noticeable cognitive decline. The review article presents a comparative analysis of existing data on the peculiarities of cholinergic and dopaminergic mechanisms associated with lowering gating in healthy individuals and in patients with schizophrenia. The differences in gating mechanisms in cohorts of healthy individuals and those with schizophrenia are discussed.

Symptom dimensions to address heterogeneity in tinnitus

Tinnitus, the auditory phantom percept, is a well-known heterogenous disorder with multiple subtypes. Researchers and clinicians have tried to classify these subtypes according to clinical profiles, aetiologies, and response to treatment with little success. The occurrence of overlapping tinnitus subtypes suggests that the disorder exists along a continuum of severity, with no clear distinct boundaries. In this perspective, we propose a neuro-mechanical framework, viewing tinnitus as a dimensional disorder which is a complex interplay of its behavioural, biological and neurophysiological phenotypes. Moreover, we explore the potential of these dimensions as interacting networks without a common existing cause, giving rise to tinnitus. Considering tinnitus as partially overlapping, dynamically changing, interacting networks, each representing a different aspect of the unified tinnitus percept, suggests that the interaction of these networks determines the phenomenology of the tinnitus, ultimately leading to a dimensional spectrum, rather than a categorical subtyping. A combination of a robust theoretical framework and strong empirical evidence can advance our understanding of the functional mechanisms underlying tinnitus and ultimately, improve treatment strategies.

Brain predictive coding processes are associated to COMT gene Val158Met polymorphism

Predicting events in the ever-changing environment is a fundamental survival function intrinsic to the physiology of sensory systems, whose efficiency varies among the population. Even though it is established that a major source of such variations is genetic heritage, there are no studies tracking down auditory predicting processes to genetic mutations. Thus, we examined the neurophysiological responses to deviant stimuli recorded with magnetoencephalography (MEG) in 108 healthy participants carrying different variants of Val158Met single-nucleotide polymorphism (SNP) within the catechol-O-methyltransferase (COMT) gene, responsible for the majority of catecholamines degradation in the prefrontal cortex. Our results showed significant amplitude enhancement of prediction error responses originating from the inferior frontal gyrus, superior and middle temporal cortices in heterozygous genotype carriers (Val/Met) vs homozygous (Val/Val and Met/Met) carriers. Integrating neurophysiology and genetics, this study shows how the neural mechanisms underlying optimal deviant detection vary according to the gene-determined cathecolamine levels in the brain.

Genetic underpinnings of schizophrenia-related electroencephalographical intermediate phenotypes: A systematic review and meta-analysis

Although substantial research into genetics of psychotic disorders has been conducted, a large proportion of their genetic architecture has remained unresolved. Electroencephalographical intermediate phenotypes (EIP) have the potential to constitute a valuable tool when studying genetic risk loci for schizophrenia, in particular P3b amplitude, P50 suppression, mismatch negativity (MMN) and resting state power spectra of the electroencephalogram (EEG). Here, we systematically reviewed studies investigating the association of single nucleotide polymorphisms (SNPs) with these EIPs and meta-analysed them when appropriate. We retrieved 45 studies (N = 34,971 study participants). Four SNPs investigated in more than one study were genome-wide significant for an association with schizophrenia and three were genome-wide suggestive, based on a lookup in the influential 2014 GWAS (Ripke et al., 2014). However, in our meta-analyses, rs1625579 failed to reach a statistically significant association with p3b amplitude decrease and rs4680 risk allele carrier status was not associated with p3b amplitude decrease or with impaired p50 suppression. In conclusion, evidence for SNP associations with EIPs remains limited to individual studies. Careful selection of EIPs and SNPs, combined with consistent reporting of effect sizes, directions of effect and p-values would aid future meta-analyses.

Genetic Determinants of Gating Functions: Do We Get Closer to Understanding Schizophrenia Etiopathogenesis?

Deficits in the gating of sensory stimuli, i.e., the ability to suppress the processing of irrelevant sensory input, are considered to play an important role in the pathogenesis of several neuropsychiatric disorders, in particular schizophrenia. Gating is disrupted both in schizophrenia patients and their unaffected relatives, suggesting that gating deficit may represent a biomarker associated with a genetic liability to the disorder. To assess the strength of the evidence for the etiopathogenetic links between genetic variation, gating efficiency, and schizophrenia, we carried out a systematic review of human genetic association studies of sensory gating (suppression of the P50 component of the auditory event-related brain potential) and sensorimotor gating (prepulse inhibition of the acoustic startle response). Sixty-three full-text articles met the eligibility criteria for inclusion in the review. In total, 117 genetic variants were reported to be associated with gating functions: 33 variants for sensory gating, 80 variants for sensorimotor gating, and four variants for both sensory and sensorimotor gating. However, only five of these associations (four for prepulse inhibition-CHRNA3 rs1317286, COMT rs4680, HTR2A rs6311, and TCF4 rs9960767, and one for P50 suppression-CHRNA7 rs67158670) were consistently replicated in independent samples. Although these variants and genes were all implicated in schizophrenia in research studies, only two polymorphisms (HTR2A rs6311 and TCF4 rs9960767) were also reported to be associated with schizophrenia at a meta-analytic or genome-wide level of evidence. Thus, although gating is widely considered as an important endophenotype of schizophrenia, these findings demonstrate that evidence for a common genetic etiology of impaired gating functions and schizophrenia is yet unsatisfactory, warranting further studies in this field.

Perception in attention deficit hyperactivity disorder

A large body of research demonstrated that individuals with attention deficit hyperactivity disorder (ADHD) suffer from various neuropsychological deficits. In contrast, less is known and only divergent evidence exists on perceptual functions of individuals with ADHD. This is problematic as neuropsychological and perceptual functions are closely interrelated and are often difficult to disentangle in behavioral assessments. This study presents the conduct and results of a systematic literature review on perceptual functions in children and adults with ADHD. This review considers studies using psychophysical methods (objective measurements) and self- and informant reports (subjective measurements). Results indicate that individuals with ADHD have altered perceptual functions in various domains as compared to typically developing individuals. Increased perceptual functions in individuals with ADHD were found with regard to olfactory detection thresholds, whereas reduced perceptual functions were evident for aspects of visual and speech perception. Moreover, individuals with ADHD were found to experience discomfort to sensory stimuli at a lower level than typically developing individuals. Alterations of perceptual functions in individuals with ADHD were shown to be moderated by various factors, such as pharmacological treatment, cognitive functions, and symptom severity. We conclude by giving implications for daily life functioning and clinical practice.

Does COMT val158met polymorphism influence P50 sensory gating, eye tracking or saccadic inhibition dysfunctions in schizophrenia?

Three electrophysiological endophenotypes are routinely studied in schizophrenia (SCZ): smooth pursuit eye movement (SPEM) dysfunction, deficits in P50 auditory-evoked potential inhibition, and saccadic inhibition deficits. The current study aimed to investigate the relationship between the COMT val158met polymorphism and these three endophenotypes. One hundred four SCZ patients (DSM-IV-R criteria) and 89 healthy controls were included in this study. P50 auditory-evoked potential inhibition, antisaccade paradigm and SPEM were analyzed. All individuals were genotyped for the COMT val158met. SCZ patients showed a higher rate of deficits measured by the SPEM, antisaccade and P50 inhibition paradigms without association with COMT val158met. However, in our control group, we have found an association between the Val polymorphism and the smoking status. More importantly, we have found a higher accuracy of saccades during the predictive pursuit task associated to the Met polymorphism in controls but not in SCZ patients who were receiving antidopaminergic medications. This result is in line with the hypothesis of the relationship between the Met polymorphism of the COMT gene, a higher level of dopamine in the prefrontal cortex and the role of the fronto-cerebellar loop in smooth predictive pursuit.

Multivariate Genetic Correlates of the Auditory Paired Stimuli-Based P2 Event-Related Potential in the Psychosis Dimension From the BSNIP Study

OBJECTIVE

The complex molecular etiology of psychosis in schizophrenia (SZ) and psychotic bipolar disorder (PBP) is not well defined, presumably due to their multifactorial genetic architecture. Neurobiological correlates of psychosis can be identified through genetic associations of intermediate phenotypes such as event-related potential (ERP) from auditory paired stimulus processing (APSP). Various ERP components of APSP are heritable and aberrant in SZ, PBP and their relatives, but their multivariate genetic factors are less explored.

METHODS

We investigated the multivariate polygenic association of ERP from 64-sensor auditory paired stimulus data in 149 SZ, 209 PBP probands, and 99 healthy individuals from the multisite Bipolar-Schizophrenia Network on Intermediate Phenotypes study. Multivariate association of 64-channel APSP waveforms with a subset of 16 999 single nucleotide polymorphisms (SNPs) (reduced from 1 million SNP array) was examined using parallel independent component analysis (Para-ICA). Biological pathways associated with the genes were assessed using enrichment-based analysis tools.

RESULTS

Para-ICA identified 2 ERP components, of which one was significantly correlated with a genetic network comprising multiple linearly coupled gene variants that explained ~4% of the ERP phenotype variance. Enrichment analysis revealed epidermal growth factor, endocannabinoid signaling, glutamatergic synapse and maltohexaose transport associated with P2 component of the N1-P2 ERP waveform. This ERP component also showed deficits in SZ and PBP.

CONCLUSIONS

Aberrant P2 component in psychosis was associated with gene networks regulating several fundamental biologic functions, either general or specific to nervous system development. The pathways and processes underlying the gene clusters play a crucial role in brain function, plausibly implicated in psychosis.

CDP-choline: effects of the procholine supplement on sensory gating and executive function in healthy volunteers stratified for low, medium and high P50 suppression

Diminished auditory sensory gating and associated neurocognitive deficits in schizophrenia have been linked to altered expression and function of the alpha-7 nicotinic acetycholinergic receptor (α7 nAChR), the targeting of which may have treatment potential. Choline is a selective α7 nAChR agonist and the aim of this study was to determine whether cytidine 5'-diphosphocholine (CDP-choline), or citicoline, a dietary source of choline, increases sensory gating and cognition in healthy volunteers stratified for gating level. In a randomized, placebo-controlled, double-blind design involving acute administration of low, moderate doses (500 mg, 1000 mg) of CDP-choline, 24 healthy volunteers were assessed for auditory gating as indexed by suppression of the P50 event-related potential (ERP) in a paired-stimulus (S1, S2) paradigm, and for executive function as measured by the Groton Maze Learning Task (GMLT) of the CogState Schizophrenia Battery. CDP-choline improved gating (1000 mg) and suppression of the S2 P50 response (500 mg, 1000 mg), with the effects being selective for individuals with low gating (suppression) levels. Tentative support was also shown for increased GMLT performance (500 mg) in low suppressors. These preliminary findings with CDP-choline in a healthy, schizophrenia-like surrogate sample are consistent with a α7 nAChR mechanism and support further trials with choline as a pro-cognitive strategy.

Beyond DSM: the role of auditory processing in attention and its disorders

This article reviews and synthesizes recent research regarding auditory processing, attention, and their roles in generating both adaptive and maladaptive behavioral responses. Research in these areas is beginning to converge on the role of polymorphisms associated with catecholamine metabolism and transport, particularly the neurotransmitter dopamine. The synthesis offered in this article appears to be the first to argue that genetic differences in dopamine metabolism may be the common factor in four disparate disorders that are often observed to be comorbid, i.e., attention-deficit hyperactivity disorder, auditory processing disorders, developmental language disorders, and reading disorders.

Reduction in phencyclidine induced sensorimotor gating deficits in the rat following increased system xc⁻ activity in the medial prefrontal cortex

RATIONALE

Aspects of schizophrenia, including deficits in sensorimotor gating, have been linked to glutamate dysfunction and/or oxidative stress in the prefrontal cortex. System xc(-), a cystine-glutamate antiporter, is a poorly understood mechanism that contributes to both cellular antioxidant capacity and glutamate homeostasis.

OBJECTIVES

Our goal was to determine whether increased system xc(-) activity within the prefrontal cortex would normalize a rodent measure of sensorimotor gating.

METHODS

In situ hybridization was used to map messenger RNA (mRNA) expression of xCT, the active subunit of system xc(-), in the prefrontal cortex. Prepulse inhibition was used to measure sensorimotor gating; deficits in prepulse inhibition were produced using phencyclidine (0.3-3 mg/kg, sc). N-Acetylcysteine (10-100 μM) and the system xc(-) inhibitor (S)-4-carboxyphenylglycine (CPG, 0.5 μM) were used to increase and decrease system xc(-) activity, respectively. The uptake of (14)C-cystine into tissue punches obtained from the prefrontal cortex was used to assay system xc(-) activity.

RESULTS

The expression of xCT mRNA in the prefrontal cortex was most prominent in a lateral band spanning primarily the prelimbic cortex. Although phencyclidine did not alter the uptake of (14)C-cystine in prefrontal cortical tissue punches, intraprefrontal cortical infusion of N-acetylcysteine (10-100 μM) significantly reduced phencyclidine- (1.5 mg/kg, sc) induced deficits in prepulse inhibition. N-Acetylcysteine was without effect when coinfused with CPG (0.5 μM), indicating an involvement of system xc(-).

CONCLUSIONS

These results indicate that phencyclidine disrupts sensorimotor gating through system xc(-) independent mechanisms, but that increasing cystine-glutamate exchange in the prefrontal cortex is sufficient to reduce behavioral deficits produced by phencyclidine.

Effects of COMT genotype on sensory gating and its modulation by nicotine: Differences in low and high P50 suppressors

Elevated smoking rates seen in schizophrenia populations may be an attempt to correct neuropathologies associated with deficient nicotinic acetylcholine receptors and/or dopaminergic systems using exogenous nicotine. However, nicotine's effects on cognitive processing and sensory gating have been shown to be baseline-dependent. Evidence of a restorative effect on sensory gating deficits by nicotine-like agonists has been demonstrated, however, its underlying mechanisms in the context of dopamine dysregulation are unclear. Catechol-O-methyltransferase (COMT), a key dopamine regulator in the brain, contains a co-dominant allele in which a valine-to-methionine substitution causes variations in enzymatic activity leading to reduced synaptic dopamine levels in the Val/Val genotype. Using a randomized, double-blind, placebo-controlled design with 57 non-smokers, this study examined the effects of COMT genotype on sensory gating and its modulation by nicotine in low vs. high suppressors. The results were consistent with the hypothesis that increased dopamine resulting from nicotine stimulation or Met allelic activity would benefit gating in low suppressors and impair gating in high suppressors, and that this gating improvement with nicotine would be more evident in Val carriers who were low suppressors, while the gating impairment would be more evident in Met carriers who were high suppressors. These findings reaffirm the importance of baseline-dependency and suggest a subtle relationship between COMT genotype and baseline-stratified levels of sensory gating, which may help to explain the variability of cognitive abilities in schizophrenia populations.

Functional brain networks underlying perceptual switching: auditory streaming and verbal transformations

Recent studies have shown that auditory scene analysis involves distributed neural sites below, in, and beyond the auditory cortex (AC). However, it remains unclear what role each site plays and how they interact in the formation and selection of auditory percepts. We addressed this issue through perceptual multistability phenomena, namely, spontaneous perceptual switching in auditory streaming (AS) for a sequence of repeated triplet tones, and perceptual changes for a repeated word, known as verbal transformations (VTs). An event-related fMRI analysis revealed brain activity timelocked to perceptual switching in the cerebellum for AS, in frontal areas for VT, and the AC and thalamus for both. The results suggest that motor-based prediction, produced by neural networks outside the auditory system, plays essential roles in the segmentation of acoustic sequences both in AS and VT. The frequency of perceptual switching was determined by a balance between the activation of two sites, which are proposed to be involved in exploring novel perceptual organization and stabilizing current perceptual organization. The effect of the gene polymorphism of catechol-O-methyltransferase (COMT) on individual variations in switching frequency suggests that the balance of exploration and stabilization is modulated by catecholamines such as dopamine and noradrenalin. These mechanisms would support the noteworthy flexibility of auditory scene analysis.

Schizophrenia risk polymorphisms in the TCF4 gene interact with smoking in the modulation of auditory sensory gating

Several polymorphisms of the transcription factor 4 (TCF4) have been shown to increase the risk for schizophrenia, particularly TCF4 rs9960767. This polymorphism is associated with impaired sensorimotor gating measured by prepulse inhibition--an established endophenotype of schizophrenia. We therefore investigated whether TCF4 polymorphisms also affect another proposed endophenotype of schizophrenia, namely sensory gating assessed by P50 suppression of the auditory evoked potential. Although sensorimotor gating and sensory gating are not identical, recent data suggest that they share genetic fundamentals. In a multicenter study at six academic institutions throughout Germany, we applied an auditory P50 suppression paradigm to 1,821 subjects (1,023 never-smokers, 798 smokers) randomly selected from the general population. Samples were genotyped for 21 TCF4 polymorphisms. Given that smoking is highly prevalent in schizophrenia and affects sensory gating, we also assessed smoking behavior, cotinine plasma concentrations, exhaled carbon monoxide, and the Fagerström Test (FTND). P50 suppression was significantly decreased in carriers of schizophrenia risk alleles of the TCF4 polymorphisms rs9960767, rs10401120rs, rs17597926, and 17512836 (P < 0.0002-0.00005). These gene effects were modulated by smoking behavior as indicated by significant interactions of TCF4 genotype and smoking status; heavy smokers (FTND score ≥ 4) showed stronger gene effects on P50 suppression than light smokers and never-smokers. Our finding suggests that sensory gating is modulated by an interaction of TCF4 genotype with smoking, and both factors may play a role in early information processing deficits also in schizophrenia. Consequently, considering smoking behavior may facilitate the search for genetic risk factors for schizophrenia.

Separability and commonality of auditory and visual bistable perception

It is unclear what neural processes induce individual differences in perceptual organization in different modalities. To examine this issue, the present study used different forms of bistable perception: auditory streaming, verbal transformations, visual plaids, and reversible figures. We performed factor analyses on the number of perceptual switches in the tasks. A 3-factor model provided a better fit to the data than the other possible models. These factors, namely the "auditory," "shape," and "motion" factors, were separable but correlated with each other. We compared the number of perceptual switches among genotype groups to identify the effects of neurotransmitter functions on the factors. We focused on polymorphisms of catechol-O-methyltransferase (COMT) Val(158)Met and serotonin 2A receptor (HTR2A) -1438G/A genes, which are involved in the modulation of dopamine and serotonin, respectively. The number of perceptual switches in auditory streaming and verbal transformations differed among COMT genotype groups, whereas that in reversible figures differed among HTR2A genotype groups. The results indicate that the auditory and shape factors reflect the functions of the dopamine and serotonin systems, respectively. Our findings suggest that the formation and selection of percepts involve neural processes in cortical and subcortical areas.

Differential effects of chronic cannabis use on preattentional cognitive functioning in abstinent schizophrenic patients and healthy subjects

INTRODUCTION

A number of studies indicate a higher risk for psychosis as well as for neurocognitive deficits in healthy cannabis users. However, little is known about the impact of cannabis use on outcome in schizophrenia. In fact, there is growing evidence that cannabis-using schizophrenic patients may show preserved or even better neurocognitive performance compared to schizophrenic non-users.

METHODS

We measured mismatch negativity (MMN) to investigate preattentional neurocognitive functioning in long-term abstinent chronic cannabis users with (SZCA n=27) and without schizophrenia (COCA n=32) compared to schizophrenic patients (SZ n=26) and healthy controls (CO n=34) without any chronic drug use.

RESULTS

Healthy cannabis users showed reduced frontal MMN compared to controls (p=0.036). In contrast, cannabis-using schizophrenic patients showed increased frontal MMN compared to schizophrenic patients without cannabis use (p=0.038). Comparing non-cannabis users, schizophrenic patients showed reduced frontal MMN (p=0.001). No significant differences were found between CO and SZCA (p=0.27), and COCA and SZCA (p=0.50).

CONCLUSION

Results suggest that chronic cannabis use may have different effects on preattentional neurocognitive functioning in schizophrenic patients when compared to healthy subjects. This may be related to preexisting differences in the endocannabinoid system between schizophrenic patients and healthy subjects. However, due to the naturalistic design of the study, the results must be interpreted with caution.