Anticipatory oculomotor responses in parents of children with attention deficit hyperactivity disorder.

OBJECTIVE: Diminished inhibitory control has been proposed as a core characteristic and potential endophenotype of attention deficit hyperactivity disorder (ADHD). If this is the case, one would expect to find this trait among first-degree relatives of individuals with ADHD. The aim of this study, therefore, was to determine whether the oculomotor measures typically related to inhibitory control failures in individuals with ADHD are also observed among those relatives. METHODS: Using prosaccadic and antisaccadic tasks in gap and overlap conditions, we assessed a group of unaffected parents of children with ADHD symptoms and compared them to a group of unaffected parents of children with typical development. Direction errors, anticipatory errors and saccadic reaction times were analyzed. We also determined the presence of ADHD behaviors (in adulthood and childhood) in all participants. RESULTS: No between-group differences were observed for the antisaccadic measures, but the group of parents of children with ADHD made more anticipatory responses on the prosaccadic-gap task than the parents of controls. A moderate association between these anticipatory errors and dimensional inattention scores was also found. CONCLUSIONS: Saccadic performance differed between the two groups of parents, as those with children with ADHD showed a failure to withhold the initiation of responses in the absence of external control references (gap condition) on tasks with low cognitive load (prosaccadic). These anticipatory responses were related to inattention traits. Our results support the familial compound of ADHD as a multifactorial disorder.

Volitional eye movement control and ADHD traits: a twin study.

BACKGROUND: Top-down volitional command of eye movements may serve as a candidate endophenotype of ADHD, an important function underlying goal-directed action in everyday life. In this twin study, we examined the relation between performance on a response inhibition eye-tracking paradigm and parent-rated ADHD traits in a population-based twin sample. We hypothesized that altered eye movement control is associated with the severity of ADHD traits and that this association is attributable to genetic factors. METHODS: A total of 640 twins (320 pairs, 50% monozygotic) aged 9-14 years) from the Child and Adolescent Twin Study in Sweden (CATSS) participated. Twins performed the antisaccade task indexing inhibitory alterations as either direction errors (following exogenous cues rather than instructions) or premature anticipatory eye movements (failure to wait for cues). We calculated the associations of eye movement control and ADHD traits using linear regression mixed-effects models and genetic and environmental influences with multivariate twin models. RESULTS: Premature anticipatory eye movements were positively associated with inattentive traits (ß = .17; 95% CI: 0.04, 0.31), while controlling for hyperactive behaviors and other covariates. Both premature anticipatory eye movements and inattention were heritable (h2  = 0.40, 95% CI: 0.22, 0.56; h2  = 0.55; 95% CI: 0.42, 0.65; respectively), and their genetic correlation was small but statistically significant (r = .19, 95% CI: 0.02, 0.36). However, the genetic correlation did not remain significant after adjusting for covariates (age, sex, hyperactivity traits, IQ). No link was found between direction errors and ADHD traits. CONCLUSIONS: This study indicates that there is a specific, genetically influenced, relation between top-down eye movement control and the inattentive traits typical of ADHD.

Zebrafish dscaml1 Deficiency Impairs Retinal Patterning and Oculomotor Function.

Down syndrome cell adhesion molecules (dscam and dscaml1) are essential regulators of neural circuit assembly, but their roles in vertebrate neural circuit function are still mostly unexplored. We investigated the functional consequences of dscaml1 deficiency in the larval zebrafish (sexually undifferentiated) oculomotor system, where behavior, circuit function, and neuronal activity can be precisely quantified. Genetic perturbation of dscaml1 resulted in deficits in retinal patterning and light adaptation, consistent with its known roles in mammals. Oculomotor analyses revealed specific deficits related to the dscaml1 mutation, including severe fatigue during gaze stabilization, reduced saccade amplitude and velocity in the light, greater disconjugacy, and impaired fixation. Two-photon calcium imaging of abducens neurons in control and dscaml1 mutant animals confirmed deficits in saccade-command signals (indicative of an impairment in the saccadic premotor pathway), whereas abducens activation by the pretectum-vestibular pathway was not affected. Together, we show that loss of dscaml1 resulted in impairments in specific oculomotor circuits, providing a new animal model to investigate the development of oculomotor premotor pathways and their associated human ocular disorders.SIGNIFICANCE STATEMENTDscaml1 is a neural developmental gene with unknown behavioral significance. Using the zebrafish model, this study shows that dscaml1 mutants have a host of oculomotor (eye movement) deficits. Notably, the oculomotor phenotypes in dscaml1 mutants are reminiscent of human ocular motor apraxia, a neurodevelopmental disorder characterized by reduced saccade amplitude and gaze stabilization deficits. Population-level recording of neuronal activity further revealed potential subcircuit-specific requirements for dscaml1 during oculomotor behavior. These findings underscore the importance of dscaml1 in the development of visuomotor function and characterize a new model to investigate potential circuit deficits underlying human oculomotor disorders.

Atypical behaviour and connectivity in SHANK3-mutant macaques.

Mutation or disruption of the SH3 and ankyrin repeat domains 3 (SHANK3) gene represents a highly penetrant, monogenic risk factor for autism spectrum disorder, and is a cause of Phelan-McDermid syndrome. Recent advances in gene editing have enabled the creation of genetically engineered non-human-primate models, which might better approximate the behavioural and neural phenotypes of autism spectrum disorder than do rodent models, and may lead to more effective treatments. Here we report CRISPR-Cas9-mediated generation of germline-transmissible mutations of SHANK3 in cynomolgus macaques (Macaca fascicularis) and their F1 offspring. Genotyping of somatic cells as well as brain biopsies confirmed mutations in the SHANK3 gene and reduced levels of SHANK3 protein in these macaques. Analysis of data from functional magnetic resonance imaging revealed altered local and global connectivity patterns that were indicative of circuit abnormalities. The founder mutants exhibited sleep disturbances, motor deficits and increased repetitive behaviours, as well as social and learning impairments. Together, these results parallel some aspects of the dysfunctions in the SHANK3 gene and circuits, as well as the behavioural phenotypes, that characterize autism spectrum disorder and Phelan-McDermid syndrome.

Comparing Eye-tracking Data of Children with High-functioning ASD, Comorbid ADHD, and of a Control Watching Social Videos.

Children with autism spectrum disorders (ASD) are known to have sensory-perceptual processing deficits that weaken their abilities to attend and perceive social stimuli in daily living contexts. Since daily social episodes consist of subtle dynamic changes in social information, any failure to attend to or process subtle human nonverbal cues, such as facial expression, postures, and gestures, might lead to inappropriate social interaction. Traditional behavioral rating scales or assessment tools based on static social scenes have limitations in capturing the moment-to-moment changes in social scenarios. An eye-tracking assessment, which can be administered in a video-based mode, is therefore preferred, to augment clinical observation. In this study, using the single-case comparison design, the eye-tracking data of three participants, a child with autism spectrum disorder (ASD), another with comorbid attention deficit-hyperactive disorder (ADHD), and a neurotypical control, are captured while they view a video of social scenarios. The eye-tracking experiment has helped answer the research question: How does social attention differ between the three participants? By predefining areas of interest (AOIs), their visual attention on relevant or irrelevant social stimuli, how fast each participant attends to the first social stimuli appearing in the videos, for how long each participant continues to attend to those stimuli within the AOIs, and the gaze shifts between multiple social stimuli appearing concurrently in the same social scene are captured, compared, and analyzed in a video-based eye-tracking experiment.

Infant neural sensitivity to eye gaze depends on early experience of gaze communication.

A fundamental question in functional brain development is how the brain acquires specialised processing optimised for its individual environment. The current study is the first to demonstrate that distinct experience of eye gaze communication, due to the visual impairment of a parent, affects the specificity of brain responses to dynamic gaze shifts in infants. Event-related potentials (ERPs) from 6 to 10 months old sighted infants with blind parents (SIBP group) and control infants with sighted parents (CTRL group) were recorded while they observed a face with gaze shifting Toward or Away from them. Unlike the CTRL group, ERPs of the SIBP group did not differentiate between the two directions of gaze shift. Thus, selective brain responses to perceived gaze shifts in infants may depend on their eye gaze communication experience with the primary caregiver. This finding highlights the critical role of early communicative experience in the emerging functional specialisation of the human brain.

TUBB3 E410K syndrome with osteoporosis and cough syncope in a patient previously diagnosed with atypical Moebius syndrome.

BACKGROUND: A heterozygous c.1228G > A p.E410K mutation in TUBB3 encoding neuronal-specific ß-tubulin isotype 3 causes TUBB3 E410K syndrome, which exhibits a wide range of neurological and endocrinological abnormalities. CASE DESCRIPTION: The patient is a 31-year-old Japanese woman who was diagnosed with atypical Moebius syndrome because of congenital facial weakness and extraocular ophthalmoplegia sparing abduction. She suffered a femoral neck fracture at 23 years of age, and radiological and endocrinological studies revealed osteoporosis because of hypogonadotropic hypogonadism. She also had borderline intellectual disability, cyclic vomiting, syncope with cough, and decreased sense of smell since childhood. Brain magnetic resonance imaging revealed abnormal morphology of the corpus callosum and pontine. Hypoplastic bilateral oculomotor and facial nerves were evident. Based on these symptoms, we analyzed the TUBB3 gene and identified a heterozygous c.1228G > A (p.E410K) mutation that confirmed the diagnosis of TUBB3 E410K syndrome. CONCLUSION: TUBB3 E410K syndrome may be diagnosed as atypical Moebius syndrome because of overlapping clinical symptoms. Genetic analysis of c.1228G > A in TUBB3 is useful to differentiate TUBB3 E410K syndrome from other disorders presenting congenital external ophthalmoplegia and facial nerve palsy.

Genetic Influence on Eye Movements to Complex Scenes at Short Timescales.

Where one looks within their environment constrains one's visual experiences, directly affects cognitive, emotional, and social processing [1-4], influences learning opportunities [5], and ultimately shapes one's developmental path. While there is a high degree of similarity across individuals with regard to which features of a scene are fixated [6-8], large individual differences are also present, especially in disorders of development [9-13], and clarifying the origins of these differences is essential to understand the processes by which individuals develop within the complex environments in which they exist and interact. Toward this end, a recent paper [14] found that "social visual engagement"-namely, gaze to eyes and mouths of faces-is strongly influenced by genetic factors. However, whether genetic factors influence gaze to complex visual scenes more broadly, impacting how both social and non-social scene content are fixated, as well as general visual exploration strategies, has yet to be determined. Using a behavioral genetic approach and eye tracking data from a large sample of 11-year-old human twins (233 same-sex twin pairs; 51% monozygotic, 49% dizygotic), we demonstrate that genetic factors do indeed contribute strongly to eye movement patterns, influencing both one's general tendency for visual exploration of scene content, as well as the precise moment-to-moment spatiotemporal pattern of fixations during viewing of complex social and non-social scenes alike. This study adds to a now growing set of results that together illustrate how genetics may broadly influence the process by which individuals actively shape and create their own visual experiences.

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.

Association of DISC1, BDNF, and COMT polymorphisms with exploratory eye movement of schizophrenia in a Chinese Han population.

BACKGROUND: Previous studies suggested that exploratory eye movement (EEM) dysfunction appears to be a biological marker specific to schizophrenia, with an unknown molecular mechanism. Genetic studies indicate that disrupted-in-schizophrenia-1 (DISC1), brain-derived neurotrophic factor (BDNF), and catechol-O-methyl transferase (COMT) genes might be implicated in the etiology of schizophrenia, but not in all populations. OBJECTIVES: The present study aimed to explore associations between these candidate genes and EEM endophenotypes for schizophrenia in a Chinese Han population. METHODS: EEM recordings were examined in 139 patients with schizophrenia and 143 healthy control participants. RESULTS: All five EEM parameters, responsive search score, cognitive search score, number of eye fixations, total eye scanning length, and mean eye scanning length, of schizophrenic patients differed significantly from those of healthy controls (P<0.001). The DISC1 SerCys, BDNF ValMet, and COMT ValMet were genotyped in a total sample of 818 schizophrenic patients and 827 healthy control participants, including the above EEM samples. We found that DISC1 Cys and BDNF Met were associated with an increased risk of developing schizophrenia (P<0.001). Furthermore, responsive search score scores of BDNF Met/Met carriers were significantly lower than those of Val allele carriers (P=0.022), which remained modest after Bonferroni correction. CONCLUSION: The BDNF MetMet polymorphism might be associated with the EEM dysfunction of schizophrenia.

Reversibility of neuropathology and motor deficits in an inducible mouse model for FXTAS.

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset neurodegenerative disorder affecting carriers of the fragile X-premutation, who have an expanded CGG repeat in the 5'-UTR of the FMR1 gene. FXTAS is characterized by progressive development of intention tremor, ataxia, parkinsonism and neuropsychological problems. The disease is thought to be caused by a toxic RNA gain-of-function mechanism, and the major hallmark of the disease is ubiquitin-positive intranuclear inclusions in neurons and astrocytes. We have developed a new transgenic mouse model in which we can induce expression of an expanded repeat in the brain upon doxycycline (dox) exposure (i.e. Tet-On mice). This Tet-On model makes use of the PrP-rtTA driver and allows us to study disease progression and possibilities of reversibility. In these mice, 8 weeks of dox exposure was sufficient to induce the formation of ubiquitin-positive intranuclear inclusions, which also stain positive for the RAN translation product FMRpolyG. Formation of these inclusions is reversible after stopping expression of the expanded CGG RNA at an early developmental stage. Furthermore, we observed a deficit in the compensatory eye movements of mice with inclusions, a functional phenotype that could be reduced by stopping expression of the expanded CGG RNA early in the disease development. Taken together, this study shows, for the first time, the potential of disease reversibility and suggests that early intervention might be beneficial for FXTAS patients.

Síndrome de Kearns-Sayre: manifestaciones oftalmológicas / Kearns-Sayre syndrome: Ophthalmic manifestations

Presentamos el caso de una paciente joven con diagnóstico clínico y genético de síndrome de Kearns-Sayre (SKS). Como hallazgos, destacaban blefaroptosis, limitación de la motilidad extrínseca ocular, retinopatía en sal y pimienta así como insuficiencia mitral leve. La anatomía patológica indicaba citopatía mitocondrial y el estudio genético detectó deleción y duplicación en heteroplasmia del ADN mitocondrial. El SKS es un raro trastorno neuromuscular, caracterizado por la tríada oftalmoplejía externa progresiva, retinopatía pigmentaria y bloqueo cardíaco. La detección temprana del SKS es clave para evitar potenciales complicaciones cardíacas

The clinical case and genetic diagnosis of Kearns-Sayre syndrome (KSS) is described in a young patient. The findings included: ptosis, ocular motility disturbances, pigmentary retinopathy, as well as mitral insufficiency. A muscle biopsy revealed mitochondrial cytopathyand heteroplasmic mitochondrial DNA deletions. KSS is a rare neuromuscular disorder defined by a characteristic triad of progressive external ophthalmoplegia, pigmentary retinopathy and atrioventricular block. Early detection is essential to avoid potential cardiac complications

Genome-wide scans of genetic variants for psychophysiological endophenotypes: introduction to this special issue of Psychophysiology.

This special issue addresses the heritability and molecular genetic basis of 17 putative endophenotypes involving resting EEG power, P300 event-related potential amplitude, electrodermal orienting and habituation, antisaccade eye tracking, and affective modulation of the startle eye blink. These measures were collected from approximately 4,900 twins and parents who provided DNA samples through their participation in the Minnesota Twin Family Study. Included are papers that detail the methodology followed, genome-wide association analyses of single nucleotide polymorphisms and genes, analysis of rare variants in the human exome, and a whole genome sequencing study. Also included are 11 articles by leading experts in psychophysiology and genetics that provide perspective and commentary. A final integrative report summarizes findings and addresses issues raised. This introduction provides an overview of the aims and rationale behind these studies.

Loss of α-calcitonin gene-related peptide (αCGRP) reduces the efficacy of the Vestibulo-ocular Reflex (VOR).

The neuroactive peptide calcitonin-gene related peptide (CGRP) is known to act at efferent synapses and their targets in hair cell organs, including the cochlea and lateral line. CGRP is also expressed in vestibular efferent neurons as well as a number of central vestibular neurons. Although CGRP-null (-/-) mice demonstrate a significant reduction in cochlear nerve sound-evoked activity compared with wild-type mice, it is unknown whether and how the loss of CGRP influence vestibular system function. Vestibular function was assessed by quantifying the vestibulo-ocular reflex (VOR) in alert mice. The loss of CGRP in (-/-) mice was associated with a reduction of the VOR gain of ≈50% without a concomitant change in phase. Using immunohistochemistry, we confirmed that, although CGRP staining was absent in the vestibular end-organs of null (-/-) mice, cholinergic staining appeared normal, suggesting that the overall gross development of vestibular efferent innervation was unaltered. We further confirmed that the observed deficit in vestibular function of null (-/-) mice was not the result of nontargeted effects at the level of the extraocular motor neurons and/or their innervation of extraocular muscles. Analysis of the relationship between vestibular quick phase amplitude and peak velocity revealed that extraocular motor function was unchanged, and immunohistochemistry revealed no abnormalities in motor endplates. Together, our findings show that the neurotransmitter CGRP plays a key role in ensuring VOR efficacy.

Development of oculomotor circuitry independent of hox3 genes.

Hox genes have been shown to be essential in vertebrate neural circuit formation and their depletion has resulted in homeotic transformations with neuron loss and miswiring. Here we quantifiy four eye movements in the zebrafish mutant valentino and hox3 knockdowns, and find that contrary to the classical model, oculomotor circuits in hindbrain rhombomeres 5-6 develop and function independently of hox3 genes. All subgroups of oculomotor neurons are present, as well as their input and output connections. Ectopic connections are also established, targeting two specific subsets of horizontal neurons, and the resultant novel eye movements coexists with baseline behaviours. We conclude that the high expression of hox3 genes in rhombomeres 5-6 serves to prevent aberrant neuronal identity and behaviours, but does not appear to be necessary for a comprehensive assembly of functional oculomotor circuits.

A cerebellar learning model of vestibulo-ocular reflex adaptation in wild-type and mutant mice.

Mechanisms of cerebellar motor learning are still poorly understood. The standard Marr-Albus-Ito theory posits that learning involves plasticity at the parallel fiber to Purkinje cell synapses under control of the climbing fiber input, which provides an error signal as in classical supervised learning paradigms. However, a growing body of evidence challenges this theory, in that additional sites of plasticity appear to contribute to motor adaptation. Here, we consider phase-reversal training of the vestibulo-ocular reflex (VOR), a simple form of motor learning for which a large body of experimental data is available in wild-type and mutant mice, in which the excitability of granule cells or inhibition of Purkinje cells was affected in a cell-specific fashion. We present novel electrophysiological recordings of Purkinje cell activity measured in naive wild-type mice subjected to this VOR adaptation task. We then introduce a minimal model that consists of learning at the parallel fibers to Purkinje cells with the help of the climbing fibers. Although the minimal model reproduces the behavior of the wild-type animals and is analytically tractable, it fails at reproducing the behavior of mutant mice and the electrophysiology data. Therefore, we build a detailed model involving plasticity at the parallel fibers to Purkinje cells' synapse guided by climbing fibers, feedforward inhibition of Purkinje cells, and plasticity at the mossy fiber to vestibular nuclei neuron synapse. The detailed model reproduces both the behavioral and electrophysiological data of both the wild-type and mutant mice and allows for experimentally testable predictions.

Human CFEOM1 mutations attenuate KIF21A autoinhibition and cause oculomotor axon stalling.

The ocular motility disorder "Congenital fibrosis of the extraocular muscles type 1" (CFEOM1) results from heterozygous mutations altering the motor and third coiled-coil stalk of the anterograde kinesin, KIF21A. We demonstrate that Kif21a knockin mice harboring the most common human mutation develop CFEOM. The developing axons of the oculomotor nerve's superior division stall in the proximal nerve; the growth cones enlarge, extend excessive filopodia, and assume random trajectories. Inferior division axons reach the orbit but branch ectopically. We establish a gain-of-function mechanism and find that human motor or stalk mutations attenuate Kif21a autoinhibition, providing in vivo evidence for mammalian kinesin autoregulation. We identify Map1b as a Kif21a-interacting protein and report that Map1b⁻/⁻ mice develop CFEOM. The interaction between Kif21a and Map1b is likely to play a critical role in the pathogenesis of CFEOM1 and highlights a selective vulnerability of the developing oculomotor nerve to perturbations of the axon cytoskeleton.

Relating dopaminergic and cholinergic polymorphisms to spatial attention in infancy.

Early selective attention skills are a crucial building block for cognitive development, as attention orienting serves as a primary means by which infants interact with and learn from the environment. Although several studies have examined infants' attention orienting using the spatial cueing task, relatively few studies have examined neurodevelopmental factors associated with attention orienting during infancy. The present study examined the relationship between normative genetic polymorphisms affecting dopamine and acetylcholine signaling and attention orienting in 7-month-old infants during a spatial cueing task. We focused on 3 genes, including the CHRNA4 C¹545T SNP (rs10344946), DAT1 3'UTR VNTR, and COMT Val¹58Met SNP (rs4680), as previous adult research has linked spatial attention skills to these polymorphisms. Behavioral measures included both facilitation of orienting at the cued location as well as inhibition of return (IOR), in which attention orienting is suppressed at the cued location. Results indicated that COMT Val carriers showed robust IOR relative to infants with the Met/Met genotype. However, COMT was unrelated to infants' facilitation responses, and there were no effects of CHRNA4 or DAT1 on either facilitation or IOR. Overall, this study suggests that variations in dopamine signaling, likely in prefrontal cortex, contribute to individual differences in orienting during early development.

Identifcation of a novel mutation p.I240T in the FRMD7 gene in a family with congenital nystagmus.

Congenital Nystagmus (CN) is a genetically heterogeneous ocular disease, which causes a significant proportion of childhood visual impairment. To identify the underlying genetic defect of a CN family, twenty-two members were recruited. Genotype analysis showed that affected individuals shared a common haplotype with markers flanking FRMD7 locus. Sequencing FRMD7 revealed a T > C transition in exon 8, causing a conservative substitution of Isoleucine to Tyrosine at codon 240. By protein structural modeling, we found the mutation may disrupt the hydrophobic core and destabilize the protein structure. We reviewed the literature and found that exons 2, 8, and 9 (11.4% of the sequence of FRMD7 mRNA) represent the majority (55.3%) of the reported FRMD7 mutations. In summary, we identified a novel mutation in FRMD7, showed its molecular consequence, and revealed the mutation-rich exons of the FRMD7 gene. Collectively, this provides molecular insights for future CN clinical genetic diagnosis and treatment.

The influence of dopamine-related genes on perceptual stability.

Bistable perception is the spontaneous and automatic alternation between two different perceptual states that occurs when sensory information is ambiguous. Perceptual alternation rates are robust within individuals but vary substantially between individuals. Slowed perceptual switching has been consistently reported in patients with bipolar disorder (BPD) and has been suggested as a trait marker for this disease. Although genetic factors have been implicated in both BPD and bistable perception, the underlying biological mechanisms that mediate the observed perceptual stability in BPD remain elusive. Here, we tested the effect of two variable number tandem repeat (VNTR) polymorphisms in DRD4 and DAT1 (SLC6A3), both candidate genes for BPD with functional impact on dopaminergic neurotransmission, on bistable perception in a cohort of 108 healthy human subjects. The BPD risk allele DRD4-2R was significantly associated with slow perceptual switching. There was no effect of DAT1 genotype on bistable perception. Our findings indicate that genetic differences in dopaminergic neurotransmission linked to BPD also account for interindividual variability in bistable perception, thus providing a genetic basis for perceptual stability as a trait marker of BPD.