Cognitive and neuroplasticity mechanisms by which congenital or early blindness may confer a protective effect against schizophrenia

"Love looks not with the eyes": supranormal processing of emotional speech in individuals with late-blindness versus preserved processing in individuals with congenital-blindness

Processing of emotional speech in the absence of visual information relies on two auditory channels: semantics and prosody. No study to date has investigated how blindness impacts this process. Two theories, Perceptual Deficit, and Sensory Compensation, yiled different expectations about the role of visual experience (or its lack thereof) in processing emotional speech. To test the effect of vision and early visual experience on processing of emotional speech, we compared individuals with congenital blindness (CB, n = 17), individuals with late blindness (LB, n = 15), and sighted controls (SC, n = 21) on identification and selective-attention of semantic and prosodic spoken-emotions. Results showed that individuals with blindness performed at least as well as SC, supporting Sensory Compensation and the role of cortical reorganisation. Individuals with LB outperformed individuals with CB, in accordance with Perceptual Deficit, supporting the role of early visual experience. The LB advantage was moderated by executive functions (working-memory). Namely, the advantage was erased for individuals with CB who showed higher levels of executive functions. Results suggest that vision is not necessary for processing of emotional speech, but early visual experience could improve it. The findings support a combination of the two aforementioned theories and reject a dichotomous view of deficiencies/enhancements of blindness.

Eyes, the window on psychosis?

Much has been written on the theory that congenital blindness might protect against schizophrenia, but proof remains elusive. It has been suggested that visual ability might be associated with schizophrenia in a bell-shaped distribution, with both lifelong absent and perfect vision being protective. Alternatively, ocular aberrations and schizophrenia may share an aetiology. Any neuronal pathology implicated in schizophrenia could affect the retina, since it is an embryological extension of the brain. The retina is more amenable to direct imaging than other parts of the central nervous system and may give unique insights into schizophrenia-associated neuropathology. It is also possible that psychosis causes visual impairment: people with psychotic illnesses are probably not accessing optical care optimally and have higher levels of risk factors for visual loss.

Phenotypic Trade-Offs: Deciphering the Impact of Neurodiversity on Drug Development in Fragile X Syndrome

Fragile X syndrome (FXS) is the most common single-gene cause of intellectual disability and autism spectrum disorder. Individuals with FXS present with a wide range of severity in multiple phenotypes including cognitive delay, behavioral challenges, sleep issues, epilepsy, and anxiety. These symptoms are also shared by many individuals with other neurodevelopmental disorders (NDDs). Since the discovery of the FXS gene, FMR1, FXS has been the focus of intense preclinical investigation and is placed at the forefront of clinical trials in the field of NDDs. So far, most studies have aimed to translate the rescue of specific phenotypes in animal models, for example, learning, or improving general cognitive or behavioral functioning in individuals with FXS. Trial design, selection of outcome measures, and interpretation of results of recent trials have shown limitations in this type of approach. We propose a new paradigm in which all phenotypes involved in individuals with FXS would be considered and, more importantly, the possible interactions between these phenotypes. This approach would be implemented both at the baseline, meaning when entering a trial or when studying a patient population, and also after the intervention when the study subjects have been exposed to the investigational product. This approach would allow us to further understand potential trade-offs underlying the varying effects of the treatment on different individuals in clinical trials, and to connect the results to individual genetic differences. To better understand the interplay between different phenotypes, we emphasize the need for preclinical studies to investigate various interrelated biological and behavioral outcomes when assessing a specific treatment. In this paper, we present how such a conceptual shift in preclinical design could shed new light on clinical trial results. Future clinical studies should take into account the rich neurodiversity of individuals with FXS specifically and NDDs in general, and incorporate the idea of trade-offs in their designs.

Cortical connectivity in the face of congenital structural changes-A case of homozygous LAMC3 mutation

The homozygous LAMC3 gene mutation is associated with severe bilateral smoothening and thickening of the lateral occipital cortex . Despite this and further significant changes in gray matter structure, a patient harboring this mutation exhibited a range of remarkably intact perceptual abilities . One possible explanation of this perceptual sparing could be that the white matter structural integrity and functional connectivity in relevant pathways remained intact. To test this idea, we used diffusion tensor and functional magnetic resonance imaging to investigate functional connectivity in resting-state networks in major structural pathways involved in object perception and visual attention and corresponding microstructural integrity in a patient with homozygous LAMC3 mutation and sex, age, education, and socioeconomically matched healthy control group. White matter microstructural integrity results indicated widespread disruptions in both intra- and interhemispheric structural connections except inferior longitudinal fasciculus. With a few exceptions, the functional connectivity between the patient's adjacent gray matter regions of major white matter tracts of interest was conserved. In addition, functional localizers for face, object, and place areas showed similar results with a representative control, providing an explanation for the patient's intact face, place, and object recognition abilities. To generalize this finding, we also compared functional connectivity between early visual areas and face, place, and object category-selective areas, and we found that the functional connectivity of the patient was not different from the control group. Overall, our results provided complementary information about the effects of LAMC3 gene mutation on the human brain including intact temporo-occipital structural and functional connectivity that are compatible with preserved perceptual abilities.

Patients with first-episode untreated schizophrenia who experience concomitant visual disturbances and auditory hallucinations exhibit co-impairment of the brain and retinas-a pilot study

There are limited structural brain and retina alteration data from schizophrenia patients who experience visual disturbances (VDs) with or without auditory hallucinations (AHs). We compared brain and retina alterations between first-episode untreated schizophrenia patients with VDs (FUSCH-VDs) with versus without AHs, and between patients and healthy controls (HCs)(N = 30/group). VDs, AHs, gray matter volumes (GMVs), and retinal thicknesses were evaluated with the Bonn Scale for Assessment of Basic Symptoms (BSABS) scale, the Auditory Hallucinations Rating Scale (AHRS), magnetic resonance imaging (MRI), and optical coherence tomography (OCT), respectively. Compared to HCs, FUSCH-VDs had reduced GMVs, mainly in dorsal V3/V3A and V5 regions, the fusiform gyrus, and ventral V4 and V8 regions. Most FUSCH-VDs (85.0%; 51/60) had primary visual cortex-retina co-impairments. FUSCH-VDs with AHs had more serious and larger scope GMV reductions than FUSCH-VDs without AHs. FUSCH-VDs with AHs had significant retinal thickness reductions compared to HCs. Primary visual cortex-retina co-impairments were found to be more common, and more pronounced when present, in FUSCH-VDs with AHs than in FUSCH-VDs without AHs. The present findings support the notion that VDs and AHs may have reciprocal deteriorating actions in patients with schizophrenia.

Brain Entropy During Aging Through a Free Energy Principle Approach

Neural complexity and brain entropy (BEN) have gained greater interest in recent years. The dynamics of neural signals and their relations with information processing continue to be investigated through different measures in a variety of noteworthy studies. The BEN of spontaneous neural activity decreases during states of reduced consciousness. This evidence has been showed in primary consciousness states, such as psychedelic states, under the name of "the entropic brain hypothesis." In this manuscript we propose an extension of this hypothesis to physiological and pathological aging. We review this particular facet of the complexity of the brain, mentioning studies that have investigated BEN in primary consciousness states, and extending this view to the field of neuroaging with a focus on resting-state functional Magnetic Resonance Imaging. We first introduce historic and conceptual ideas about entropy and neural complexity, treating the mindbrain as a complex nonlinear dynamic adaptive system, in light of the free energy principle. Then, we review the studies in this field, analyzing the idea that the aim of the neurocognitive system is to maintain a dynamic state of balance between order and chaos, both in terms of dynamics of neural signals and functional connectivity. In our exploration we will review studies both on acute psychedelic states and more chronic psychotic states and traits, such as those in schizophrenia, in order to show the increase of entropy in those states. Then we extend our exploration to physiological and pathological aging, where BEN is reduced. Finally, we propose an interpretation of these results, defining a general trend of BEN in primary states and cognitive aging.

Development and Evaluation of a Visual Remediation Intervention for People with Schizophrenia

It is now well documented that schizophrenia is associated with impairments in visual processing at all levels of vision, and that these disturbances are related to deficits in multiple higher-level cognitive and social cognitive functions. Visual remediation methods have been slow to appear in the literature as a potential treatment strategy to target these impairments, however, in contrast to interventions that aim to improve auditory and higher cognitive functions in schizophrenia. In this report, we describe a National Institute of Mental Health (NIMH)-funded R61/R33 grant that uses a phased approach to optimize and evaluate a novel visual remediation intervention for people with schizophrenia. The goals of this project are: (1) in the R61 phase, to establish the optimal components and dose (number of sessions) of a visual remediation intervention from among two specific visual training strategies (and their combination) for improving low and mid-level visual functions in schizophrenia; and (2) in the R33 phase, to determine the extent to which the optimal intervention improves not only visual processing but also higher-level cognitive and role functions. Here we present the scientific background for and innovation of the study, along with our methods, hypotheses, and preliminary data. The results of this study will help determine the utility of this novel intervention approach for targeting visual perceptual, cognitive, and functional impairments in schizophrenia.

Blindness, Psychosis, and the Visual Construction of the World

The relationship between visual loss and psychosis is complex: congenital visual loss appears to be protective against the development of a psychotic disorder, particularly schizophrenia. In later life, however, visual deprivation or visual loss can give rise to hallucinosis, disorders of visual insight such as blindsight or Anton syndrome, or, in the context of neurodegenerative disorders, more complex psychotic presentations. We draw on a computational psychiatric approach to consider the foundational role of vision in the construction of representations of the world and the effects of visual loss at different developmental stages. Using a Bayesian prediction error minimization model, we describe how congenital visual loss may be protective against the development of the kind of computational deficits postulated to underlie schizophrenia, by increasing the precision (and consequent stability) of higher-level (including supramodal) priors, focusing on visual loss-induced changes in NMDA receptor structure and function as a possible mechanistic substrate. In simple terms, we argue that when people cannot see from birth, they rely more heavily on the context they extract from the other senses, and the resulting model of the world is more impervious to the false inferences, made in the face of inevitably noisy perceptual input, that characterize schizophrenia. We show how a Bayesian prediction error minimization framework can also explain the relationship between later visual loss and other psychotic symptoms, as well as the effects of visual deprivation and hallucinogenic drugs, and outline experimentally testable hypotheses generated by this approach.

Comparative psychopharmacology of autism and psychotic-affective disorders suggests new targets for treatment

The first treatments showing effectiveness for some psychiatric disorders, such as lithium for bipolar disorder and chlorpromazine for schizophrenia, were discovered by accident. Currently, psychiatric drug design is seen as a scientific enterprise, limited though it remains by the complexity of brain development and function. Relatively few novel and effective drugs have, however, been developed for many years. The purpose of this article is to demonstrate how evolutionary biology can provide a useful framework for psychiatric drug development. The framework is based on a diametrical nature of autism, compared with psychotic-affective disorders (mainly schizophrenia, bipolar disorder and depression). This paradigm follows from two inferences: (i) risks and phenotypes of human psychiatric disorders derive from phenotypes that have evolved along the human lineage and (ii) biological variation is bidirectional (e.g. higher vs lower, faster vs slower, etc.), such that dysregulation of psychological traits varies in two opposite ways. In this context, the author review the evidence salient to the hypothesis that autism and psychotic-affective disorders represent diametrical disorders in terms of current, proposed and potential psychopharmacological treatments. Studies of brain-derived neurotrophic factor, the PI3K pathway, the NMDA receptor, kynurenic acid metabolism, agmatine metabolism, levels of the endocannabinoid anandamide, antidepressants, anticonvulsants, antipsychotics, and other treatments, demonstrate evidence of diametric effects in autism spectrum disorders and phenotypes compared with psychotic-affective disorders and phenotypes. These findings yield insights into treatment mechanisms and the development of new pharmacological therapies, as well as providing an explanation for the longstanding puzzle of antagonism between epilepsy and psychosis. Lay Summary: Consideration of autism and schizophrenia as caused by opposite alterations to brain development and function leads to novel suggestions for pharmacological treatments.

Autism and psychosis as diametrical disorders of embodiment

Humans have evolved an elaborate system of self-consciousness, self-identity, self-agency, and self-embodiment that is grounded in specific neurological structures including an expanded insula. Instantiation of the bodily self has been most-extensively studied via the 'rubber hand illusion', whereby parallel stimulation of a hidden true hand, and a viewed false hand, leads to the felt belief that the false hand is one's own. Autism and schizophrenia have both long been regarded as conditions centrally involving altered development of the self, but they have yet to be compared directly with regard to the self and embodiment. Here, we synthesize the embodied cognition literature for these and related conditions, and describe evidence that these two sets of disorders exhibit opposite susceptibilities from typical individuals to the rubber hand illusion: reduced on the autism spectrum and increased in schizophrenia and other psychotic-affective conditions. Moreover, the opposite illusion effects are mediated by a consilient set of associated phenomena, including empathy, interoception, anorexia risk and phenotypes, and patterns of genetic correlation. Taken together, these findings: (i) support the diametric model of autism and psychotic-affective disorders, (ii) implicate the adaptive human system of self-embodiment, and its neural bases, in neurodevelopmental disorders, and suggest new therapies and (iii) experimentally ground Bayesian predictive coding models with regard to autism compared with psychosis. Lay summary: Humans have evolved a highly developed sense of self and perception of one's own body. The 'rubber hand illusion' can be used to test individual variation in sense of self, relative to connection with others. We show that this illusion is reduced in autism spectrum disorders, and increased in psychotic and mood disorders. These findings have important implications for understanding and treatment of mental disorders.

A possible key role of vision in the development of schizophrenia

Based on a brief overview of the various aspects of schizophrenia reported by numerous studies, here we hypothesize that schizophrenia may originate (and in part be performed) from visual areas. In other words, it seems that a normal visual system or at least an evanescent visual perception may be an essential prerequisite for the development of schizophrenia as well as of various types of hallucinations. Our study focuses on auditory and visual hallucinations, as they are the most prominent features of schizophrenic hallucinations (and also the most studied types of hallucinations). Here, we evaluate the possible key role of the visual system in the development of schizophrenia.

Visual Acuity in Late Adolescence and Future Psychosis Risk in a Cohort of 1 Million Men

BACKGROUND

We aimed to determine whether late adolescent visual impairment is associated with later psychosis.

METHODS

We conducted a longitudinal cohort study of Swedish male military conscripts aged 18 or 19 years from January 1, 1974, through December 31, 1997 (N = 1140710). At conscription, uncorrected and optometry-lens-corrected distance visual acuity was measured. Participants were then followed up to see if they received an inpatient diagnosis of non-affective psychotic disorder, including schizophrenia (N = 10769). Multivariable Cox modeling was used to estimate differences between groups.

RESULTS

After adjustment for confounders, those with severe impairment before optical correction in their best eye (decimal fraction <0.3) had an increased psychosis rate compared to those with normal uncorrected vision (decimal fraction 1.0) (hazard ratio [HR] 1.26, 95% CI 1.16-1.37). Larger interocular visual acuity difference was associated with an increased psychosis rate (adjusted HR 1.49, 95% CI 1.37-1.63 in those with differences >0.5 compared to those with no between eye acuity difference). Individuals with impaired vision that could not be corrected to normal with lenses had highest rates of psychosis (best eye adjusted HR 1.56; 95% CI 1.33-1.82), those with imperfect, but correctable vision also had elevated rates (best eye adjusted HR 1.21; 95% CI 1.15-1.28). Individuals with visual impairment had higher rates of psychosis than their full siblings with normal vision (adjusted HR 1.20, 95% CI 1.07-1.35).

CONCLUSIONS

Impaired visual acuity is associated with non-affective psychosis. Visual impairment as a phenotype in psychosis requires further consideration.

Seasonality of births in horizontal strabismus: comparison with birth seasonality in schizophrenia and other disease conditions

Recent work has implicated one type of horizontal strabismus (exotropia) as a risk factor for schizophrenia. This new insight raises questions about a potential common developmental origin of the two diseases. Seasonality of births is well established for schizophrenia. Seasonal factors such as light exposure affect eye growth and can cause vision abnormalities, but little is known about seasonality of births in strabismus. We examined birth seasonality in people with horizontal strabismus in a retrospective study in Washoe County, Nevada, and re-examined similar previously obtained data from Osaka, Japan. We then compared seasonal patterns of births between strabismus, refractive error, schizophrenia and congenital toxoplasmosis. Patients with esotropia had a significant seasonality of births, with a deficit in March, then increasing to an excess in September, while patients with exotropia had a distinctly different pattern, with an excess of births in July, gradually decreasing to a deficit in November. These seasonalities were statistically significant with either χ2 or Kolmogorov-Smirnov-type statistics. The birth seasonality of esotropia resembled that for hyperopia, with an increase in amplitude, while the seasonality for myopia involved a phase-shift. There was no correlation between seasonality of births between strabismus and congenital toxoplasmosis. The pattern of an excess of summer births for people with exotropia was remarkably similar to the well-established birth seasonality of one schizophrenia subtype, the deficit syndrome, but not schizophrenia as a whole. This suggests a testable hypothesis: that exotropia may be a risk factor primarily for the deficit type of schizophrenia.

Congenital blindness is protective for schizophrenia and other psychotic illness. A whole-population study

Congenital/early blindness is reportedly protective against schizophrenia. Using a whole-population cohort of 467,945 children born in Western Australia between 1980 and 2001, we examined prevalence of schizophrenia and psychotic illness in individuals with congenital/early blindness. Overall, 1870 children developed schizophrenia (0.4%) while 9120 developed a psychotic illness (1.9%). None of the 66 children with cortical blindness developed schizophrenia or psychotic illness. Eight of the 613 children with peripheral blindness developed a psychotic illness other than schizophrenia and fewer had developed schizophrenia. Our results support findings from small case studies that congenital/early cortical but not peripheral blindness is protective against schizophrenia.

Expression of schizophrenia biomarkers in extraocular muscles from patients with strabismus: an explanation for the link between exotropia and schizophrenia?

Recent studies have implicated exotropia as a risk factor for schizophrenia. We determined whether schizophrenia biomarkers have abnormal levels of expression in extraocular muscles from patients with strabismus and explored whether differences in gene expression between medial and lateral rectus muscles may explain the specific association of schizophrenia with exotropia but not esotropia. Samples from horizontal extraocular muscles were obtained during strabismus surgery and compared with age- and muscle type-matched normal muscles from organ donors. We used PCR arrays to identify differences in gene expression among 417 signaling molecules. We then focused on established schizophrenia-related growth factors, cytokines, and regulators of the extracellular matrix. Among 36 genes with significantly altered gene expression in dysfunctional horizontal rectus muscles, over one third were schizophrenia-related: CTGF, CXCR4, IL1B, IL10RA, MIF, MMP2, NPY1R, NRG1, NTRK2, SERPINA3, TIMP1, TIMP2, and TNF (adjusted p value ≤ 0.016667). By PCR array, expression of three of these genes was significantly different in medial rectus muscles, while eleven were significantly altered in lateral rectus muscles. Comparing baseline levels between muscle types, three schizophrenia-related genes (NPY1R, NTRK2, TIMP2) had lower levels of expression in medial rectus muscles. Despite the surprisingly large number of schizophrenia-related genes with altered gene expression levels in dysfunctional muscles, the lack of specificity for medial rectus muscles undermines a model of shared, region-specific gene expression abnormalities between exotropia and schizophrenia, but rather suggests consideration of the alternative model: that exotropia-induced aberrant early visual experiences may enable and/or contribute as a causative factor to the development of schizophrenia.

Visual and non-visual motion information processing during pursuit eye tracking in schizophrenia and bipolar disorder

Despite many reports on visual processing deficits in psychotic disorders, studies are needed on the integration of visual and non-visual components of eye movement control to improve the understanding of sensorimotor information processing in these disorders. Non-visual inputs to eye movement control include prediction of future target velocity from extrapolation of past visual target movement and anticipation of future target movements. It is unclear whether non-visual input is impaired in patients with schizophrenia. We recorded smooth pursuit eye movements in 21 patients with schizophrenia spectrum disorder, 22 patients with bipolar disorder, and 24 controls. In a foveo-fugal ramp task, the target was either continuously visible or was blanked during movement. We determined peak gain (measuring overall performance), initial eye acceleration (measuring visually driven pursuit), deceleration after target extinction (measuring prediction), eye velocity drifts before onset of target visibility (measuring anticipation), and residual gain during blanking intervals (measuring anticipation and prediction). In both patient groups, initial eye acceleration was decreased and the ability to adjust eye acceleration to increasing target acceleration was impaired. In contrast, neither deceleration nor eye drift velocity was reduced in patients, implying unimpaired non-visual contributions to pursuit drive. Disturbances of eye movement control in psychotic disorders appear to be a consequence of deficits in sensorimotor transformation rather than a pure failure in adding cognitive contributions to pursuit drive in higher-order cortical circuits. More generally, this deficit might reflect a fundamental imbalance between processing external input and acting according to internal preferences.

Perspective-taking abilities in the balance between autism tendencies and psychosis proneness

Difficulties with the ability to appreciate the perspective of others (mentalizing) is central to both autism and schizophrenia spectrum disorders. While the disorders are diagnostically independent, they can co-occur in the same individual. The effect of such co-morbidity is hypothesized to worsen mentalizing abilities. The recent influential 'diametric brain theory', however, suggests that the disorders are etiologically and phenotypically diametrical, predicting opposing effects on one's mentalizing abilities. To test these contrasting hypotheses, we evaluated the effect of psychosis and autism tendencies on the perspective-taking (PT) abilities of 201 neurotypical adults, on the assumption that autism tendencies and psychosis proneness are heritable dimensions of normal variation. We show that while both autism tendencies and psychosis proneness induce PT errors, their interaction reduced these errors. Our study is, to our knowledge, the first to observe that co-occurring autistic and psychotic traits can exert opposing influences on performance, producing a normalizing effect possibly by way of their diametrical effects on socio-cognitive abilities. This advances the notion that some individuals may, to some extent, be buffered against developing either illness or present fewer symptoms owing to a balanced expression of autistic and psychosis liability.

Vision, language and a protective mechanism towards psychosis

The absence of co-occurrence of schizophrenia with congenital/early blindness (CB) has led to the claim that CB confers protection against schizophrenia. It has recently been shown that the protective effects are particularly reinforced in cases of CB of cortical origin, since cases of CB of peripheral origin and schizophrenia in fact exist. The present work shows that the protection extends to psychosis more broadly and describes the brain basis of the protective mechanism and its relation to the language faculty and the language areas of the brain.

Diametrical diseases reflect evolutionary-genetic tradeoffs: Evidence from psychiatry, neurology, rheumatology, oncology and immunology

Tradeoffs centrally mediate the expression of human adaptations. We propose that tradeoffs also influence the prevalence and forms of human maladaptation manifest in disease. By this logic, increased risk for one set of diseases commonly engenders decreased risk for another, diametric, set of diseases. We describe evidence for such diametric sets of diseases from epidemiological, genetic and molecular studies in four clinical domains: (i) psychiatry (autism vs psychotic-affective conditions), (ii) rheumatology (osteoarthritis vs osteoporosis), (iii) oncology and neurology (cancer vs neurodegenerative disorders) and (iv) immunology (autoimmunity vs infectious disease). Diametric disorders are important to recognize because genotypes or environmental factors that increase risk for one set of disorders protect from opposite disorders, thereby providing novel and direct insights into disease causes, prevention and therapy. Ascertaining the mechanisms that underlie disease-related tradeoffs should also indicate means of circumventing or alleviating them, and thus reducing the incidence and impacts of human disease in a more general way.

Cognitive trade-offs and the costs of resilience

Genetic, endocrinological, and psychological evidence demonstrates that resilience commonly trades off with sensitivity. The existence of such trade-offs indicates that resilience bears costs as well as benefits, and that some disorders can best be conceptualized in terms of extremes of trade-offs rather than expression of deficits. Testing for cognitive trade-offs should be a priority for psychiatry, psychology, neuroscience, and genetics.

Possible functional links among brain- and skull-related genes selected in modern humans

The sequencing of the genomes from extinct hominins has revealed that changes in some brain-related genes have been selected after the split between anatomically-modern humans and Neanderthals/Denisovans. To date, no coherent view of these changes has been provided. Following a line of research we initiated in Boeckx and Benítez-Burraco (2014a), we hypothesize functional links among most of these genes and their products, based on the existing literature for each of the gene discussed. The genes we focus on are found mutated in different cognitive disorders affecting modern populations and their products are involved in skull and brain morphology, and neural connectivity. If our hypothesis turns out to be on the right track, it means that the changes affecting most of these proteins resulted in a more globular brain and ultimately brought about modern cognition, with its characteristic generativity and capacity to form and exploit cross-modular concepts, properties most clearly manifested in language.

Schizophrenia and the eye

Although visual processing impairments are common in schizophrenia, it is not clear to what extent these originate in the eye vs. the brain. This review highlights potential contributions, from the retina and other structures of the eye, to visual processing impairments in schizophrenia and high-risk states. A second goal is to evaluate the status of retinal abnormalities as biomarkers for schizophrenia. The review was motivated by known retinal changes in other disorders (e.g., Parkinson’s disease, multiple sclerosis), and their relationships to perceptual and cognitive impairments, and disease progression therein. The evidence reviewed suggests two major conclusions. One is that there are multiple structural and functional disturbances of the eye in schizophrenia, all of which could be factors in the visual disturbances of patients. These include retinal venule widening, retinal nerve fiber layer thinning, dopaminergic abnormalities, abnormal ouput of retinal cells as measured by electroretinography (ERG), maculopathies and retinopathies, cataracts, poor acuity, and strabismus. Some of these are likely to be illness-related, whereas others may be due to medication or comorbid conditions. The second conclusion is that certain retinal findings can serve as biomarkers of neural pathology, and disease progression, in schizophrenia. The strongest evidence for this to date involves findings of widened retinal venules, thinning of the retinal nerve fiber layer, and abnormal ERG amplitudes. These data suggest that a greater understanding of the contribution of retinal and other ocular pathology to the visual and cognitive disturbances of schizophrenia is warranted, and that retinal changes have untapped clinical utility.

Schizophrenia and cortical blindness: protective effects and implications for language

The repeatedly noted absence of case-reports of individuals with schizophrenia and congenital/early developed blindness has led several authors to argue that the latter can confer protective effects against the former. In this work, we present a number of relevant case-reports from different syndromes that show comorbidity of congenital and early blindness with schizophrenia. On the basis of these reports, we argue that a distinction between different types of blindness in terms of the origin of the visual deficit, cortical or peripheral, is crucial for understanding the observed patterns of comorbidity. We discuss the genetic underpinnings and the brain structures involved in schizophrenia and blindness, with insights from language processing, laying emphasis on the three structures that particularly stand out: the occipital cortex, the lateral geniculate nucleus (LGN), and the pulvinar. Last, we build on previous literature on the nature of the protective effects in order to offer novel insights into the nature of the protection mechanism from the perspective of the brain structures involved in each type of blindness.

"To see or not to see: that is the question." The "Protection-Against-Schizophrenia" (PaSZ) model: evidence from congenital blindness and visuo-cognitive aberrations

The causes of schizophrenia are still unknown. For the last 100 years, though, both “absent” and “perfect” vision have been associated with a lower risk for schizophrenia. Hence, vision itself and aberrations in visual functioning may be fundamental to the development and etiological explanations of the disorder. In this paper, we present the “Protection-Against-Schizophrenia” (PaSZ) model, which grades the risk for developing schizophrenia as a function of an individual's visual capacity. We review two vision perspectives: (1) “Absent” vision or how congenital blindness contributes to PaSZ and (2) “perfect” vision or how aberrations in visual functioning are associated with psychosis. First, we illustrate that, although congenitally blind and sighted individuals acquire similar world representations, blind individuals compensate for behavioral shortcomings through neurofunctional and multisensory reorganization. These reorganizations may indicate etiological explanations for their PaSZ. Second, we demonstrate that visuo-cognitive impairments are fundamental for the development of schizophrenia. Deteriorated visual information acquisition and processing contribute to higher-order cognitive dysfunctions and subsequently to schizophrenic symptoms. Finally, we provide different specific therapeutic recommendations for individuals who suffer from visual impairments (who never developed “normal” vision) and individuals who suffer from visual deterioration (who previously had “normal” visual skills). Rather than categorizing individuals as “normal” and “mentally disordered,” the PaSZ model uses a continuous scale to represent psychiatrically relevant human behavior. This not only provides a scientific basis for more fine-grained diagnostic assessments, earlier detection, and more appropriate therapeutic assignments, but it also outlines a trajectory for unraveling the causes of abnormal psychotic human self- and world-perception.