Basic visual dysfunction allows classification of patients with schizophrenia with exceptional accuracy

Early visual processing and adaptation as markers of disease, not vulnerability: EEG evidence from 22q11.2 deletion syndrome, a population at high risk for schizophrenia

We investigated visual processing and adaptation in 22q11.2 deletion syndrome (22q11.2DS), a condition characterized by an increased risk for schizophrenia. Visual processing differences have been described in schizophrenia but remain understudied early in the disease course. Electrophysiology was recorded during a visual adaptation task with different interstimulus intervals to investigate visual processing and adaptation in 22q11.2DS (with (22q+) and without (22q−) psychotic symptoms), compared to control and idiopathic schizophrenia groups. Analyses focused on early windows of visual processing. While increased amplitudes were observed in 22q11.2DS in an earlier time window (90–140 ms), decreased responses were seen later (165–205 ms) in schizophrenia and 22q+. 22q11.2DS, and particularly 22q−, presented increased adaptation effects. We argue that while amplitude and adaptation in the earlier time window may reflect specific neurogenetic aspects associated with a deletion in chromosome 22, amplitude in the later window may be a marker of the presence of psychosis and/or of its chronicity/severity.

D-Serine: A Cross Species Review of Safety

Background:D-Serine, a direct, full agonist at the D-serine/glycine modulatory site of the N-methyl-D-aspartate-type glutamate receptors (NMDAR), has been assessed as a treatment for multiple psychiatric and neurological conditions. Based on studies in rats, concerns of nephrotoxicity have limited D-serine research in humans, particularly using high doses. A review of D-serine's safety is timely and pertinent, as D-serine remains under active study for schizophrenia, both directly (R61 MH116093) and indirectly through D-amino acid oxidase (DAAO) inhibitors. The principal focus is on nephrotoxicity, but safety in other physiologic and pathophysiologic systems are also reviewed. Methods: Using the search terms "D-serine," "D-serine and schizophrenia," "D-serine and safety," "D-serine and nephrotoxicity" in PubMed, we conducted a systematic review on D-serine safety. D-serine physiology, dose-response and efficacy in clinical studies and dAAO inhibitor safety is also discussed. Results: When D-serine doses >500 mg/kg are used in rats, nephrotoxicity, manifesting as an acute tubular necrosis syndrome, seen within hours of administration is highly common, if not universal. In other species, however, D-serine induced nephrotoxicity has not been reported, even in other rodent species such as mice and rabbits. Even in rats, D--serine related toxicity is dose dependent and reversible; and does not appear to be present in rats at doses producing an acute Cmax of <2,000 nmol/mL. For comparison, the Cmax of D-serine 120 mg/kg, the highest dose tested in humans, is ~500 nmol/mL in acute dosing. Across all published human studies, only one subject has been reported to have abnormal renal values related to D-serine treatment. This abnormality did not clearly map on to the acute tubular necrosis syndrome seen in rats, and fully resolved within a few days of stopping treatment. DAAO inhibitors may be nephroprotective. D-Serine may have a physiologic role in metabolic, extra-pyramidal, cardiac and other systems, but no other clinically significant safety concerns are revealed in the literature. Conclusions: Even before considering human to rat differences in renal physiology, using current FDA guided monitoring paradigms, D-serine appears safe at currently studied maximal doses, with potential safety in combination with DAAO inhibitors.

Visual N80 latency as a marker of neuropsychological performance in schizophrenia: Evidence for bottom-up cognitive models

OBJECTIVE

Cognitive deficits and visual impairment in the magnocellular (M) pathway, have been independently reported in schizophrenia. The current study examined the association between neuropsychological (NPS) performance and visual evoked potentials (VEPs: N80/P1 to M- and P(parvocellular)-biased visual stimuli) in schizophrenia and healthy controls.

METHODS

NPS performance and VEPs were measured in n = 44 patients and n = 34 matched controls. Standardized NPS-scores were combined into Domains and a PCA (Principal Component Analysis) generated Composite. Group differences were assessed via (M)ANOVAs, association between NPS and VEP parameters via PCA, Pearson's coefficient and bootstrapping. Logistic regression was employed to assess classification power.

RESULTS

Patients showed general cognitive impairment, whereas group differences for VEP-parameters were non-significant. In patients, N80 latency across conditions loaded onto one factor with cognitive composite, showed significant negative correlations of medium effect sizes with NPS performance for M/P mixed stimuli and classified low and high performance with 70% accuracy.

CONCLUSION

The study provides no evidence for early visual pathway impairment but suggests a heightened association between early visual processing and cognitive performance in schizophrenia.

SIGNIFICANCE

Our results lend support to bottom-up models of cognitive function in schizophrenia and implicate visual N80 latency as a potential biomarker of cognitive deficits in schizophrenia.

Retinal ganglion cells dysfunctions in schizophrenia patients with or without visual hallucinations

The electroretinogram has revealed photoreceptor, bipolar cell, and, in one prior study, retinal ganglion cell (RGC) dysfunction in schizophrenia. The structural abnormalities of the RGC are well documented in schizophrenia and such abnormalities have been associated with visual hallucinations (VH) in neurological disorders. The goals of this study were: 1) to examine the functional responses of photoreceptors and RGC in schizophrenia patients in comparison with healthy controls; and 2) to compare the extent of retinal dysfunction in schizophrenia patients with or without VH. We recorded the flash electroretinogram in scotopic and photopic conditions, and the pattern electroretinogram, in schizophrenia patients (n = 29) and healthy controls (n = 29). Schizophrenia patients were divided in two groups: schizophrenia patients with VH (VH group, n = 12) and schizophrenia patients with auditory hallucinations or no hallucinations (AHNH group, n = 17). Our results replicate previous findings regarding photoreceptor dysfunction in schizophrenia. PERG results showed a significant increase of the P50 implicit time in schizophrenia patients compared with controls (t(55) = 2.1, p < .05, d = 0.55) and a significant increase of the N95 implicit time in schizophrenia patients compared with controls (t(55) = 4.2; p < .001, d = 0.66). We found an increased rod b-wave implicit time (dark-adapted 0.01 ERG) in the VH group compared to the AHNH group and to the control group, which was associated with lifetime VH score. Our results demonstrate a slowing of RGC signaling in schizophrenia patients, which could affect the quality of visual information reaching the visual cortex. The implications of the data for understanding VH in schizophrenia are discussed.

Retinal Nerve Fiber Layer Thickness Alterations after Electroconvulsive Therapy in Patients with Mental Illness

BACKGROUND

We hypothesized that the ongoing neurotrophic effects of electroconvulsive therapy (ECT) might be detected in the retinal nerve fiber layer (RNFL) using optical coherence tomography (OCT).

METHODS

This study was conducted using a prospective design. The RNFL thickness alterations of 18 psychiatric patients undergoing ECT were assessed using OCT. The results were compared with the RNFL thicknesses of 18 age and gender-matched healthy controls.

RESULTS

In the left eye, the average RNFL (p = 0.025), superior quadrant (p = 0.029), and nasal quadrant (p = 0.021) thicknesses were significantly increased after the last ECT treatment. In contrast to the right eye, the basal left-eye superior RNFL thickness (p = 0.038) and inferior quadrant (p = 0.007) thicknesses were significantly lower in the patients than in the healthy controls.

CONCLUSION

Here, we have revealed a significant lateralized influence of ECT on the left-eye RNFL. However, larger case series should be conducted before interpreting our current findings.

The P1 visual-evoked potential, red light, and transdiagnostic psychiatric symptoms

A reduced P1 visual-evoked potential amplitude has been reported across several psychiatric disorders, including schizophrenia-spectrum, bipolar, and depressive disorders. In addition, a difference in P1 amplitude change to a red background compared to its opponent color, green, has been found in schizophrenia-spectrum samples. The current study examined whether specific psychiatric symptoms that related to these P1 abnormalities in earlier studies would be replicated when using a broad transdiagnostic sample. The final sample consisted of 135 participants: 26 with bipolar disorders, 25 with schizophrenia-spectrum disorders, 19 with unipolar depression, 62 with no current psychiatric disorder, and 3 with disorders in other categories. Low (8%) and high (64%) contrast check arrays were presented on gray, green, and red background conditions during electroencephalogram, while an eye tracker monitored visual fixation on the stimuli. Linear regressions across the entire sample (N = 135) found that greater severity of both clinician-rated and self-reported delusions/magical thinking correlated with a reduced P1 amplitude on the low contrast gray (neutral) background condition. In addition, across the entire sample, higher self-reported constricted affect was associated with a larger decrease in P1 amplitude (averaged across contrast conditions) to the red, compared to green, background. All relationships remained statistically significant after covarying for diagnostic class, suggesting that they are relatively transdiagnostic in nature. These findings indicate that early visual processing abnormalities may be more directly related to specific transdiagnostic symptoms such as delusions and constricted affect rather than specific psychiatric diagnoses or broad symptom factor scales.

Precuneus functioning differentiates first-episode psychosis patients during the fantasy movie Alice in Wonderland

BACKGROUND

While group-level functional alterations have been identified in many brain regions of psychotic patients, multivariate machine-learning methods provide a tool to test whether some of such alterations could be used to differentiate an individual patient. Earlier machine-learning studies have focused on data collected from chronic patients during rest or simple tasks. We set out to unravel brain activation patterns during naturalistic stimulation in first-episode psychosis (FEP).

METHOD

We recorded brain activity from 46 FEP patients and 32 control subjects viewing scenes from the fantasy film Alice in Wonderland. Scenes with varying degrees of fantasy were selected based on the distortion of the 'sense of reality' in psychosis. After cleaning the data with a novel maxCorr method, we used machine learning to classify patients and healthy control subjects on the basis of voxel- and time-point patterns.

RESULTS

Most (136/194) of the voxels that best classified the groups were clustered in a bilateral region of the precuneus. Classification accuracies were up to 79.5% (p = 5.69 × 10-8), and correct classification was more likely the higher the patient's positive-symptom score. Precuneus functioning was related to the fantasy content of the movie, and the relationship was stronger in control subjects than patients.

CONCLUSIONS

These findings are the first to show abnormalities in precuneus functioning during naturalistic information processing in FEP patients. Correlational findings suggest that these alterations are associated with positive psychotic symptoms and processing of fantasy. The results may provide new insights into the neuronal basis of reality distortion in psychosis.

Neural activity during object perception in schizophrenia patients is associated with illness duration and affective symptoms

BACKGROUND

Abnormalities in visual processes have been observed in schizophrenia patients and have been associated with alteration of the lateral occipital complex and visual cortex. However, the relationship of these abnormalities with clinical symptomatology is largely unknown.

METHODS

We investigated the brain activity associated with object perception in schizophrenia. Pictures of common objects were presented to 26 healthy participants (age=36.9; 11 females) and 20 schizophrenia patients (age=39.9; 8 females) in an fMRI study.

RESULTS

In the healthy sample the presentation of pictures yielded significant activation (pFWE (cluster)<0.001) of the bilateral fusiform gyrus, bilateral lingual gyrus, and bilateral middle occipital gyrus. In patients, the bilateral fusiform gyrus and bilateral lingual gyrus were significantly activated (pFWE (cluster)<0.001), but not so the middle occipital gyrus. However, significant bilateral activation of the middle occipital gyrus (pFWE (cluster)<0.05) was revealed when illness duration was controlled for. Depression was significantly associated with increased activation, and anxiety with decreased activation, of the right middle occipital gyrus and several other brain areas in the patient group. No association with positive or negative symptoms was revealed.

CONCLUSIONS

Illness duration accounts for the weak activation of the middle occipital gyrus in patients during picture presentation. Affective symptoms, but not positive or negative symptoms, influence the activation of the right middle occipital gyrus and other brain areas.

Topographic deficits in alpha-range resting EEG activity and steady state visual evoked responses in schizophrenia

Deficits in both resting alpha-range (8-12Hz) electroencephalogram (EEG) activity and steady state evoked potential (SSVEP) responses have been reported in schizophrenia. However, the topographic specificity of these effects, the relationship between resting EEG and SSVEP, as well as the impact of antipsychotic medication on these effects, have not been clearly delineated. The present study sought to address these questions with 256 channel high-density EEG recordings in a group of 13 schizophrenia patients, 13 healthy controls, and 10 non-schizophrenia patients with psychiatric diagnoses currently taking antipsychotic medication. At rest, the schizophrenia group demonstrated decreased alpha EEG power in frontal and occipital areas relative to healthy controls. With SSVEP stimulation centered in the alpha band (10Hz), but not with stimulation above (15Hz) or below (7Hz) this range, the occipital deficit in alpha power was partially reverted. However, the frontal deficit persisted and contributed to a significantly reduced topographic relationship between occipital and frontal alpha activity for resting EEG and 10Hz SSVEP alpha power in schizophrenia patients. No significant differences were observed between healthy and medicated controls or between medicated controls and schizophrenia. These findings suggest a potential intrinsic deficit in frontal eyes-closed EEG alpha oscillations in schizophrenia, whereby potent visual stimulation centered in that frequency range results in an increase in the occipital alpha power of these patients, which however does not extend to frontal regions. Future research to evaluate the cortical and subcortical mechanisms of these effects is warranted.

Specificity and sensitivity of visual evoked potentials in the diagnosis of schizophrenia: rethinking VEPs

Alterations of the visual evoked potential (VEP) component P1 at the occipital region represent the most extended functional references of early visual dysfunctions in schizophrenia (SZ). However, P1 deficits are not reliable enough to be accepted as standard susceptibility markers for use in clinical psychiatry. We have previously reported a novel approach combining a standard checkerboard pattern-reversal stimulus, spectral resolution VEP, source detection techniques and statistical procedures which allowed the correct classification of all patients as SZ compared to controls. Here, we applied the same statistical approach but to a single surface VEP - in contrast to the complex EEG source analyses in our previous report. P1 and N1 amplitude differences among spectral resolution VEPs from a POz-F3 bipolar montage were computed for each component. The resulting F-values were then Z-transformed. Individual comparisons of each component of P1 and N1 showed that in 72% of patients, their individual Z-score deviated from the normal distribution of controls for at least one of the two components. Crossvalidation against the distribution in the SZ-group improved the detection rate to 93%. In all, six patients were misclassified. Clinical validation yielded striking positive (78.13%) and negative (92.69%) predictive values. The here presented procedure offers a potential clinical screening method for increased susceptibility to SZ which should then be followed by high density electrode array and source detection analyses. The most important aspect of this work is represented by the fact that this diagnostic technique is low-cost and involves equipment that is feasible to use in typical community clinics.

Neural oscillatory deficits in schizophrenia predict behavioral and neurocognitive impairments

Paying attention to visual stimuli is typically accompanied by event-related desynchronizations (ERD) of ongoing alpha (7-14 Hz) activity in visual cortex. The present study used time-frequency based analyses to investigate the role of impaired alpha ERD in visual processing deficits in schizophrenia (Sz). Subjects viewed sinusoidal gratings of high (HSF) and low (LSF) spatial frequency (SF) designed to test functioning of the parvo- vs. magnocellular pathways, respectively. Patients with Sz and healthy controls paid attention selectively to either the LSF or HSF gratings which were presented in random order. Event-related brain potentials (ERPs) were recorded to all stimuli. As in our previous study, it was found that Sz patients were selectively impaired at detecting LSF target stimuli and that ERP amplitudes to LSF stimuli were diminished, both for the early sensory-evoked components and for the attend minus unattend difference component (the Selection Negativity), which is generally regarded as a specific index of feature-selective attention. In the time-frequency domain, the differential ERP deficits to LSF stimuli were echoed in a virtually absent theta-band phase locked response to both unattended and attended LSF stimuli (along with relatively intact theta-band activity for HSF stimuli). In contrast to the theta-band evoked responses which were tightly stimulus locked, stimulus-induced desynchronizations of ongoing alpha activity were not tightly stimulus locked and were apparent only in induced power analyses. Sz patients were significantly impaired in the attention-related modulation of ongoing alpha activity for both HSF and LSF stimuli. These deficits correlated with patients' behavioral deficits in visual information processing as well as with visually based neurocognitive deficits. These findings suggest an additional, pathway-independent, mechanism by which deficits in early visual processing contribute to overall cognitive impairment in Sz.

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.