Visual context processing in bipolar disorder: a comparison with schizophrenia

Irregularity of visual motion perception and negative symptoms in schizophrenia

Schizophrenia (SZ) is a severe psychiatric disorder characterized by perceptual, emotional, and behavioral abnormalities, with cognitive impairment being a prominent feature of the disorder. Recent studies demonstrate irregularity in SZ with increased variability on the neural level. Is there also irregularity on the psychophysics level like in visual perception? Here, we introduce a methodology to analyze the irregularity in a trial-by-trial way to compare the SZ and healthy control (HC) subjects. In addition, we use an unsupervised clustering algorithm K-means + + to identify SZ subgroups in the sample, followed by validation of the subgroups based on intraindividual visual perception variability and clinical symptomatology. The K-means + + method divided SZ patients into two subgroups by measuring durations across trials in the motion discrimination task, i.e., high, and low irregularity of SZ patients (HSZ, LSZ). We found that HSZ and LSZ subgroups are associated with more negative and positive symptoms respectively. Applying a mediation model in the HSZ subgroup, the enhanced irregularity mediates the relationship between visual perception and negative symptoms. Together, we demonstrate increased irregularity in visual perception of a HSZ subgroup, including its association with negative symptoms. This may serve as a promising marker for identifying and distinguishing SZ subgroups.

Altered Use of Context During Visual Perception in Psychotic Psychopathology: A Neurophysiological Investigation of Tuned and Untuned Suppression During Contrast Perception

BACKGROUND AND HYPOTHESIS

The human visual system streamlines visual processing by suppressing responses to textures that are similar to their surrounding context. Surround suppression is weaker in individuals with schizophrenia (ISZ); this altered use of visuospatial context may relate to the characteristic visual distortions they experience.

STUDY DESIGN

To understand atypical surround suppression in psychotic psychopathology, we investigated neurophysiological responses in ISZ, healthy controls (HC), individuals with bipolar disorder (IBP), and first-degree relatives (ISZR/IBPR). Participants performed a contrast judgment task on a circular target with annular surrounds, with concurrent electroencephalography. Orientation-independent (untuned) suppression was estimated from responses to central targets with orthogonal surrounds; the orientation-dependence of suppression was estimated by fitting an exponential function to the increase in suppression as surrounds became more aligned with the center.

RESULTS

ISZ exhibited weakened untuned suppression coupled with enhanced orientation-dependence of suppression. The N1 visual evoked potential was associated with the orientation-dependence of suppression, with ISZ and ISZR (but not IBP or IBPR) showing enhanced orientation-dependence of the N1. Collapsed across orientation conditions, the N1 for ISZ lacked asymmetry toward the right hemisphere; this reduction in N1 asymmetry was associated with reduced untuned suppression, real-world perceptual anomalies, and psychotic psychopathology. The overall amplitude of the N1 was reduced in ISZ and IBP.

CONCLUSIONS

Key measures of symptomatology for ISZ are associated with reductions in untuned suppression. Increased sensitivity for ISZ to the relative orientation of suppressive surrounds is reflected in the N1 VEP, which is commonly associated with higher-level visual functions such as allocation of spatial attention or scene segmentation.

Visual surround suppression at the neural and perceptual levels

Surround suppression was initially identified as a phenomenon at the neural level in which stimuli outside the neuron's receptive field alone cannot activate responses but can modulate neural responses to stimuli covered inside the receptive field. Subsequent studies showed that surround suppression is not only a critical property of neurons across species and brain areas but also has been found in visual perceptions. More importantly, surround suppression varies across individuals and shows significant differences between normal controls and patients with certain mental disorders. Here, we combined results from related literature and summarized the findings derived from physiological and psychophysical evidence. We first outline the basic properties of surround suppression in the visual system and perceptions. Then, we mainly summarize the differences in perceptual surround suppression among different human subjects. Our review suggests that there is no consensus regarding whether the strength of perceptual surround suppression could be used as an effective index to distinguish particular populations. Then, we summarized the similar mechanisms for surround suppression and cognitive impairments to further explore the potential clinical applications of surround suppression. A clearer understanding of the mechanisms of surround suppression in neural responses and perceptions is necessary for facilitating its clinical applications.

Stronger tilt aftereffects in individuals diagnosed with schizophrenia spectrum disorders but not bipolar disorder

An altered use of context and experience to interpret incoming information has been posited to explain schizophrenia symptoms. The visual system can serve as a model system for examining how context and experience guide perception and the neural mechanisms underlying putative alterations. The influence of prior experience on current perception is evident in visual aftereffects, the perception of the "opposite" of a previously viewed stimulus. Aftereffects are associated with neural adaptation and concomitant change in strength of lateral inhibitory connections in visually responsive neurons. In a previous study, we observed stronger aftereffects related to orientation (tilt aftereffects) but not luminance (negative afterimages) in individuals diagnosed with schizophrenia, which we interpreted as potentially suggesting altered cortical (but not subcortical) adaptability and local changes in excitatory-inhibitory interactions. Here, we tested whether stronger tilt aftereffects were specific to individuals with schizophrenia or extended to individuals with bipolar disorder. We measured tilt aftereffects and negative afterimages in 32 individuals with bipolar disorder, and compared aftereffect strength to a previously reported group of 36 individuals with schizophrenia and 22 healthy controls. We observed stronger tilt aftereffects, but not negative afterimages, in individuals with schizophrenia as compared to both controls and individuals with bipolar disorder, who did not differ from each other. These results mitigate concerns that stronger tilt aftereffects in schizophrenia are a consequence of medication or of the psychosocial consequences of a severe mental illness.

The Psychosis Human Connectome Project: Design and rationale for studies of visual neurophysiology

Visual perception is abnormal in psychotic disorders such as schizophrenia. In addition to hallucinations, laboratory tests show differences in fundamental visual processes including contrast sensitivity, center-surround interactions, and perceptual organization. A number of hypotheses have been proposed to explain visual dysfunction in psychotic disorders, including an imbalance between excitation and inhibition. However, the precise neural basis of abnormal visual perception in people with psychotic psychopathology (PwPP) remains unknown. Here, we describe the behavioral and 7 tesla MRI methods we used to interrogate visual neurophysiology in PwPP as part of the Psychosis Human Connectome Project (HCP). In addition to PwPP (n = 66) and healthy controls (n = 43), we also recruited first-degree biological relatives (n = 44) in order to examine the role of genetic liability for psychosis in visual perception. Our visual tasks were designed to assess fundamental visual processes in PwPP, whereas MR spectroscopy enabled us to examine neurochemistry, including excitatory and inhibitory markers. We show that it is feasible to collect high-quality data across multiple psychophysical, functional MRI, and MR spectroscopy experiments with a sizable number of participants at a single research site. These data, in addition to those from our previously described 3 tesla experiments, will be made publicly available in order to facilitate further investigations by other research groups. By combining visual neuroscience techniques and HCP brain imaging methods, our experiments offer new opportunities to investigate the neural basis of abnormal visual perception in PwPP.

Weakened untuned gain control is associated with schizophrenia while atypical orientation-tuned suppression depends on visual acuity

Perceptual distortions are core features of psychosis. Weakened contrast surround suppression has been proposed as a neural mechanism underlying atypical perceptual experiences. Although previous work has measured suppression by asking participants to report the perceived contrast of a low-contrast target surrounded by a high-contrast surround, it is possible to modulate perceived contrast solely by manipulating the orientation of a matched-contrast center and surround. Removing the bottom-up segmentation cue of contrast difference and isolating orientation-dependent suppression may clarify the neural processes responsible for atypical surround suppression in psychosis. We examined surround suppression across a spectrum of psychotic psychopathology including people with schizophrenia (PSZ; N = 31) and people with bipolar disorder (PBD; N = 29), first-degree biological relatives of these patient groups (PBDrel, PSZrel; N = 28, N = 21, respectively), and healthy controls (N = 29). PSZ exhibited reduced surround suppression across orientations; although group differences were minimal at the condition that produced the strongest suppression. PBD and PSZrel exhibited intermediate suppression, whereas PBDrel performed most similarly to controls. Intriguingly, group differences in orientation-dependent surround suppression magnitude were moderated by visual acuity. A simulation in which visual acuity and/or focal attention interact with untuned gain control reproduces the observed pattern of results, including the lack of group differences when orientation of center and surround are the same. Our findings further elucidate perceptual mechanisms of impaired center-surround processing in psychosis and provide insights into the effects of visual acuity on orientation-dependent suppression in PSZ.

Combined influence of medication and symptom severity on visual processing in bipolar disorder

Previous studies have reported visual impairments in patients with bipolar disorder (BPD), but unclear were whether clinical variables would be associated with those disturbances. Here, we investigate the relationship between visual functioning, in terms of color discrimination, and the impact of BPD duration, mood state, and the patients' medication. Forty-five participants (25-45 years old) were recruited for this study. Color discrimination was performed using the Cambridge Colour Test. Serial multiple mediations were run to investigate the assumption of association between color discrimination and the clinical variables. Our findings showed that, compared with healthy controls, BPD patients' performance was worse for the Protan, Deutan, and Tritan vectors, revealing deterioration of color discrimination. In addition, the mediation analyses revealed a strong direct (p < .001) and moderate-to-high indirect effects (p < .01) of medication and symptom severity on color discrimination. Overall, both longer the duration of the disease and greater the symptom severity of BPD patients resulted in worse performance. It highlights the importance of examining the wider clinical context of an affective disorder to understand how it affects visual processing in this population.

Spatial suppression of chromatic motion

Center-surround antagonism, as a ubiquitous feature in visual processing, usually leads to inferior perception for a large stimulus compared to a small one. For example, it is more difficult to judge the motion direction of a large high-contrast pattern than that of a small one. However, this spatial suppression in the motion dimension was only reported for luminance motion, and was not found for chromatic motion. Given that center-surround suppression only occurs for strong visual inputs, we hypothesized that previous failure in finding spatial suppression of chromatic motion might be due to weak chromatic motion being induced with stimuli of limited parameters. In this study, we used phase-shift discrimination and motion-direction discrimination tasks to measure motion spatial suppression induced by stimuli of two spatial frequencies (0.5 and 2 cpd) and two contrasts (low and high). We found that spatial suppression of the chromatic motion was stably observed for stimuli of high spatial frequency (2 cpd) and high contrast and spatial summation occurred for stimuli of low spatial frequency (0.5 cpd). Intriguingly, there was no correlations between the motion spatial suppressions of luminance motion and chromatic motion, implying that the two types of spatial suppression are not originated from the same neural processing. Our findings indicate that spatial suppression also exists for chromatic motion, and the mechanisms underlying the spatial suppression of chromatic motion is different from that of luminance motion.

Structural and Functional Connectivity of Visual Cortex in Schizophrenia and Bipolar Disorder: A Graph-Theoretic Analysis

Visual processing abnormalities in schizophrenia (SZ) are poorly understood, yet predict functional outcomes in the disorder. Bipolar disorder (BD) may involve similar visual processing deficits. Converging evidence suggests that visual processing may be relatively normal at early stages of visual processing such as early visual cortex (EVC), but that processing abnormalities may become more pronounced by mid-level visual areas such as lateral occipital cortex (LO). However, little is known about the connectivity of the visual system in SZ and BD. If the flow of information to, from, or within the visual system is disrupted by reduced connectivity, this could help to explain perceptual deficits. In the present study, we performed a targeted analysis of the structural and functional connectivity of the visual system using graph-theoretic metrics in a sample of 48 SZ, 46 BD, and 47 control participants. Specifically, we calculated parallel measures of local efficiency for EVC and LO from both diffusion weighted imaging data (structural) and resting-state (functional) imaging data. We found no structural connectivity differences between the groups. However, there was a significant group difference in functional connectivity and a significant group-by-region interaction driven by reduced LO connectivity in SZ relative to HC, whereas BD was approximately intermediate to the other 2 groups. We replicated this pattern of results using a different brain atlas. These findings support and extend theoretical models of perceptual dysfunction in SZ, providing a framework for further investigation of visual deficits linked to functional outcomes in SZ and related disorders.

Dynamic monitoring of transmembrane potential changes: a study of ion channels using an electrical double layer-gated FET biosensor

In this research, we have designed, fabricated and characterized an electrical double layer (EDL)-gated AlGaN/GaN high electron mobility transistor (HEMT) biosensor array to study the transmembrane potential changes of cells. The sensor array platform is designed to detect and count circulating tumor cells (CTCs) of colorectal cancer (CRC) and investigate cellular bioelectric signals. Using the EDL FET biosensor platform, cellular responses can be studied in physiological salt concentrations, thereby eliminating complex automation. Upon investigation, we discovered that our sensor response follows the transmembrane potential changes of captured cells. Our whole cell sensor platform can be used to monitor the dynamic changes in the membrane potential of cells. The effects of continuously changing electrolyte ion concentrations and ion channel blocking using cadmium are investigated. This methodology has the potential to be used as an electrophysiological probe for studying ion channel gating and the interaction of biomolecules in cells. The sensor can also be a point-of-care diagnostic tool for rapid screening of diseases.

Cortical Thickness of Functionally Defined Visual Areas in Schizophrenia and Bipolar Disorder

Patients with schizophrenia show specific abnormalities in visual perception, and patients with bipolar disorder may have related perceptual deficits. During tasks that highlight perceptual dysfunction, patients with schizophrenia show abnormal activity in visual brain areas, including the lateral occipital complex (LOC) and early retinotopic cortex. It is unclear whether the anatomical structure of those visual areas is atypical in schizophrenia and bipolar disorder. In members of those two patient groups and healthy controls, we localized LOC and early retinotopic cortex individually for each participant using functional magnetic resonance imaging (MRI), then measured the thickness of those regions of interest using structural MRI scans. In both regions, patients with schizophrenia had the thinnest cortex, controls had the thickest cortex, and bipolar patients had intermediate cortical thickness. A control region, motor cortex, did not show this pattern of group differences. The thickness of each visual region of interest was significantly correlated with performance on a visual object masking task, but only in schizophrenia patients. These findings suggest an anatomical substrate for visual processing abnormalities that have been found with both neural and behavioral measures in schizophrenia and other severe mental illnesses.

Social neuroscience: undoing the schism between neurology and psychiatry

Multiple disorders once jointly conceived as "nervous diseases" became segregated by the distinct institutional traditions forged in neurology and psychiatry. As a result, each field specialized in the study and treatment of a subset of such conditions. Here we propose new avenues for interdisciplinary interaction through a triangulation of both fields with social neuroscience. To this end, we review evidence from five relevant domains (facial emotion recognition, empathy, theory of mind, moral cognition, and social context assessment), highlighting their common disturbances across neurological and psychiatric conditions and discussing their multiple pathophysiological mechanisms. Our proposal is anchored in multidimensional evidence, including behavioral, neurocognitive, and genetic findings. From a clinical perspective, this work paves the way for dimensional and transdiagnostic approaches, new pharmacological treatments, and educational innovations rooted in a combined neuropsychiatric training. Research-wise, it fosters new models of the social brain and a novel platform to explore the interplay of cognitive and social functions. Finally, we identify new challenges for this synergistic framework.

The polygenic risk for bipolar disorder influences brain regional function relating to visual and default state processing of emotional information

Genome-wise association studies have identified a number of common single-nucleotide polymorphisms (SNPs), each of small effect, associated with risk to bipolar disorder (BD). Several risk-conferring SNPs have been individually shown to influence regional brain activation thus linking genetic risk for BD to altered brain function. The current study examined whether the polygenic risk score method, which models the cumulative load of all known risk-conferring SNPs, may be useful in the identification of brain regions whose function may be related to the polygenic architecture of BD. We calculated the individual polygenic risk score for BD (PGR-BD) in forty-one patients with the disorder, twenty-five unaffected first-degree relatives and forty-six unrelated healthy controls using the most recent Psychiatric Genomics Consortium data. Functional magnetic resonance imaging was used to define task-related brain activation patterns in response to facial affect and working memory processing. We found significant effects of the PGR-BD score on task-related activation irrespective of diagnostic group. There was a negative association between the PGR-BD score and activation in the visual association cortex during facial affect processing. In contrast, the PGR-BD score was associated with failure to deactivate the ventromedial prefrontal region of the default mode network during working memory processing. These results are consistent with the threshold-liability model of BD, and demonstrate the usefulness of the PGR-BD score in identifying brain functional alternations associated with vulnerability to BD. Additionally, our findings suggest that the polygenic architecture of BD is not regionally confined but impacts on the task-dependent recruitment of multiple brain regions.

Seeing more clearly through psychosis: Depth inversion illusions are normal in bipolar disorder but reduced in schizophrenia

Schizophrenia patients with more positive symptoms are less susceptible to depth inversion illusions (DIIs) in which concave objects appear as convex. It remains unclear, however, the extent to which this perceptual advantage uniquely characterizes the schizophrenia phenotype. To address the foregoing, we compared 30 bipolar disorder patients to a previously published sample of healthy controls (N=25) and schizophrenia patients (N=30). The task in all cases was to judge the apparent convexity of physically concave faces and scenes. Half of the concave objects were painted with realistic texture to enhance the convexity illusion and the remaining objects were untextured to reduce the illusion. Subjects viewed objects stereoscopically or via monocular motion parallax depth cues. For each group, DIIs were stronger with texture than without, and weaker with stereoscopic information than without, indicating a uniformly normal response to stimulus alterations across groups. Bipolar patients experienced DIIs more frequently than schizophrenia patients but as commonly as controls, irrespective of the face/scene category, texture, or viewing condition (motion/stereo). More severe positive and disorganized symptoms predicted reduced DIIs for schizophrenia patients and across all patients. These results suggest that people with schizophrenia, but not bipolar disorder, more accurately perceive object depth structure. Psychotic symptoms-or their accompanying neural dysfunction-may primarily drive the effect presumably through eroding the visual system's generalized tendency to construe unusual or ambiguous surfaces as convex. Because such symptoms are by definition more common in schizophrenia, DIIs are at once state-sensitive and diagnostically specific, offering a potential biomarker for the presence of acute psychosis.

Visual Contextual Effects of Orientation, Contrast, Flicker, and Luminance: All Are Affected by Normal Aging

The perception of a visual stimulus can be markedly altered by spatial interactions between the stimulus and its surround. For example, a grating stimulus appears lower in contrast when surrounded by a similar pattern of higher contrast: a phenomenon known as surround suppression of perceived contrast. Such center–surround interactions in visual perception are numerous and arise from both cortical and pre-cortical neural circuitry. For example, perceptual surround suppression of luminance and flicker are predominantly mediated pre-cortically, whereas contrast and orientation suppression have strong cortical contributions. Here, we compare the perception of older and younger observers on a battery of tasks designed to assess such visual contextual effects. For all visual dimensions tested (luminance, flicker, contrast, and orientation), on average the older adults showed greater suppression of central targets than the younger adult group. The increase in suppression was consistent in magnitude across all tasks, suggesting that normal aging produces a generalized, non-specific alteration to contextual processing in vision.

FT-IR spectroscopy and multivariate analysis as an auxiliary tool for diagnosis of mental disorders: Bipolar and schizophrenia cases

In this study, a methodology based on Fourier-transform infrared spectroscopy and principal component analysis and partial least square methods is proposed for the analysis of blood plasma samples in order to identify spectral changes correlated with some biomarkers associated with schizophrenia and bipolarity. Our main goal was to use the spectral information for the calibration of statistical models to discriminate and classify blood plasma samples belonging to bipolar and schizophrenic patients. IR spectra of 30 samples of blood plasma obtained from each, bipolar and schizophrenic patients and healthy control group were collected. The results obtained from principal component analysis (PCA) show a clear discrimination between the bipolar (BP), schizophrenic (SZ) and control group' (CG) blood samples that also give possibility to identify three main regions that show the major differences correlated with both mental disorders (biomarkers). Furthermore, a model for the classification of the blood samples was calibrated using partial least square discriminant analysis (PLS-DA), allowing the correct classification of BP, SZ and CG samples. The results obtained applying this methodology suggest that it can be used as a complimentary diagnostic tool for the detection and discrimination of these mental diseases.

Reduced contextual effects on visual contrast perception in schizophrenia and bipolar affective disorder

BACKGROUND

The salience of a visual stimulus is often reduced by nearby stimuli, an effect known as surround suppression of perceived contrast, which may help in locating the borders of an object. Weaker surround suppression has been observed in schizophrenia but it is unclear whether this abnormality is present in other mental disorders with similar symptomatology, or is evident in people with genetic liability for schizophrenia.

METHOD

By examining surround suppression among subjects with schizophrenia or bipolar affective disorder, their unaffected biological relatives and healthy controls we sought to determine whether diminished surround suppression was specific to schizophrenia, and if subjects with a genetic risk for either disorder would show similar deficits. Measuring perceived contrast in different surround conditions also allowed us to investigate how this suppression depends on the similarity of target and surrounding stimuli.

RESULTS

Surround suppression was weaker among schizophrenia patients regardless of surround configuration. Subjects with bipolar affective disorder showed an intermediate deficit, with stronger suppression than in schizophrenia but weaker than control subjects. Surround suppression was normal in relatives of both patient groups. Findings support a deficit in broadly tuned (rather than sharply orientation- or direction-selective) suppression mechanisms.

CONCLUSIONS

Weak broadly tuned suppression during visual perception is evident in schizophrenia and bipolar affective disorder, consistent with impaired gain control related to the clinical expression of these conditions.

Suppressive mechanisms in visual motion processing: From perception to intelligence

Perception operates on an immense amount of incoming information that greatly exceeds the brain's processing capacity. Because of this fundamental limitation, the ability to suppress irrelevant information is a key determinant of perceptual efficiency. Here, I will review a series of studies investigating suppressive mechanisms in visual motion processing, namely perceptual suppression of large, background-like motions. These spatial suppression mechanisms are adaptive, operating only when sensory inputs are sufficiently robust to guarantee visibility. Converging correlational and causal evidence links these behavioral results with inhibitory center-surround mechanisms, namely those in cortical area MT. Spatial suppression is abnormally weak in several special populations, including the elderly and individuals with schizophrenia-a deficit that is evidenced by better-than-normal direction discriminations of large moving stimuli. Theoretical work shows that this abnormal weakening of spatial suppression should result in motion segregation deficits, but direct behavioral support of this hypothesis is lacking. Finally, I will argue that the ability to suppress information is a fundamental neural process that applies not only to perception but also to cognition in general. Supporting this argument, I will discuss recent research that shows individual differences in spatial suppression of motion signals strongly predict individual variations in IQ scores.

What visual illusions teach us about schizophrenia

Illusion, namely a mismatch between the objective and perceived properties of an object present in the environment, is a common feature of visual perception, both in normal and pathological conditions. This makes illusion a valuable tool with which to explore normal perception and its impairments. Although still debated, the hypothesis of a modified, and typically diminished, susceptibility to illusions in schizophrenia patients is supported by a growing number of studies. The current paper aimed to review how illusions have been used to explore and reveal the core features of visual perception in schizophrenia from a psychophysical, neurophysiological and functional point of view. We propose an integration of these findings into a common hierarchical Bayesian inference framework. The Bayesian formalism considers perception as the optimal combination between sensory evidence and prior knowledge, thereby highlighting the interweaving of perceptions and beliefs. Notably, it offers a holistic and convincing explanation for the perceptual changes observed in schizophrenia that might be ideally tested using illusory paradigms, as well as potential paths to explore neural mechanisms. Implications for psychopathology (in terms of positive symptoms, subjective experience or behavior disruptions) are critically discussed.

The tilt illusion: phenomenology and functional implications

The perceived orientation of a line or grating is affected by the orientation structure of the surrounding image: the tilt illusion. Here, I offer a selective review of the literature on the tilt illusion, focusing on functional aspects. The review explores the merits of mechanistic accounts of the tilt illusion based upon sensory gain control in which neuronal responses are normalized by the pooled activity of other units. The role of inhibition between orientation-selective neurons is discussed, and it is argued that their associated disinhibition must also be taken into account in order to model the full angular dependence of the tilt illusion on surround orientation. Parallels are drawn with adaptation as modulation by the temporal rather than spatial context within which an image fragment is processed. The chromatic selectivity of the tilt illusion and the extent of its dependence on the visibility of the surround are used to infer characteristics of the neuronal normalization pools and the loci in the cortical processing hierarchy at which gain control operates. Finally, recent evidence is discussed as to the possible clinical relevance of the tilt illusion as a biomarker for schizophrenia.