Functional and structural brain asymmetries in patients with schizophrenia and bipolar disorders

Altered Hemispheric Asymmetry of Functional Hierarchy in Schizophrenia

BACKGROUND/OBJECTIVES

Schizophrenia is a severe psychiatric disorder characterized by deficits in perception and advanced cognitive functions. Prior studies have reported abnormal lateralization in cortical morphology and functional connectivity in schizophrenia. However, it remains unclear whether schizophrenia affects hemispheric asymmetry in the hierarchical organization of functional connectome.

METHODS

Here, we apply a gradient mapping framework to the hemispheric functional connectome to estimate the first three gradients, which characterize unimodal-to-transmodal, visual-to-somatomotor, and somatomotor/default mode-to-multiple demand hierarchy axes. We then assess between-group differences in intra- and inter-hemispheric asymmetries of these three functional gradients.

RESULTS

We find that, compared to healthy controls, patients with schizophrenia exhibit significantly altered hemispheric asymmetry in functional gradient across multiple networks, including the dorsal attention, ventral attention, visual, and control networks. Region-level analyses further reveal that patients with schizophrenia show significantly abnormal hemispheric gradient asymmetries in several cortical regions in the dorsal prefrontal gyrus, medial superior frontal gyrus, and somatomotor areas. Lastly, we find that hemispheric asymmetries in functional gradients can differentiate between patients and healthy controls and predict the severity of positive symptoms in schizophrenia.

CONCLUSIONS

Collectively, these findings suggest that schizophrenia is associated with altered hemispheric asymmetry in functional hierarchy, providing novel perspectives for understanding the atypical brain lateralization in schizophrenia.

Aberrant brain language network in schizophrenia spectrum disorder: a systematic review of its relation to language signs beyond symptoms

Background

Language disturbances are a core feature of schizophrenia, often studied as a formal thought disorder. The neurobiology of language in schizophrenia has been addressed within the same framework, that language and thought are equivalents considering symptoms and not signs. This review aims to systematically examine published peer-reviewed studies that employed neuroimaging techniques to investigate aberrant brain-language networks in individuals with schizophrenia in relation to linguistic signs.

Methods

We employed a language model for automatic data extraction. We selected our studies according to the PRISMA recommendations, and we conducted the quality assessment of the selected studies according to the STROBE guidance.

Results

We analyzed the findings from 37 studies, categorizing them based on patient characteristics, brain measures, and language task types. The inferior frontal gyrus (IFG) and superior temporal gyrus (STG) exhibited the most significant differences among these studies and paradigms.

Conclusions

We propose guidelines for future research in this field based on our analysis. It is crucial to investigate larger networks involved in language processing, and language models with brain metrics must be integrated to enhance our understanding of the relationship between language and brain abnormalities in schizophrenia.

Epigenome Defines Aberrant Brain Laterality in Major Mental Illnesses

Brain-hemisphere asymmetry/laterality is a well-conserved biological feature of normal brain development. Several lines of evidence, confirmed by the meta-analysis of different studies, support the disruption of brain laterality in mental illnesses such as schizophrenia (SCZ), bipolar disorder (BD), attention-deficit/hyperactivity disorder (ADHD), obsessive compulsive disorder (OCD), and autism. Furthermore, as abnormal brain lateralization in the planum temporale (a critical structure in auditory language processing) has been reported in patients with SCZ, it has been considered a major cause for the onset of auditory verbal hallucinations. Interestingly, the peripheral counterparts of abnormal brain laterality in mental illness, particularly in SCZ, have also been shown in several structures of the human body. For instance, the fingerprints of patients with SCZ exhibit aberrant asymmetry, and while their hair whorl rotation is random, 95% of the general population exhibit a clockwise rotation. In this work, we present a comprehensive literature review of brain laterality disturbances in mental illnesses such as SCZ, BD, ADHD, and OCD, followed by a systematic review of the epigenetic factors that may be involved in the disruption of brain lateralization in mental health disorders. We will conclude with a discussion on whether existing non-pharmacological therapies such as rTMS and ECT may be used to influence the altered functional asymmetry of the right and left hemispheres of the brain, along with their epigenetic and corresponding gene-expression patterns.

A multiscale characterization of cortical shape asymmetries in early psychosis

Psychosis has often been linked to abnormal cortical asymmetry, but prior results have been inconsistent. Here, we applied a novel spectral shape analysis to characterize cortical shape asymmetries in patients with early psychosis across different spatial scales. We used the Human Connectome Project for Early Psychosis dataset (aged 16-35), comprising 56 healthy controls (37 males, 19 females) and 112 patients with early psychosis (68 males, 44 females). We quantified shape variations of each hemisphere over different spatial frequencies and applied a general linear model to compare differences between healthy controls and patients with early psychosis. We further used canonical correlation analysis to examine associations between shape asymmetries and clinical symptoms. Cortical shape asymmetries, spanning wavelengths from about 22 to 75 mm, were significantly different between healthy controls and patients with early psychosis (Cohen's d = 0.28-0.51), with patients showing greater asymmetry in cortical shape than controls. A single canonical mode linked the asymmetry measures to symptoms (canonical correlation analysis r = 0.45), such that higher cortical asymmetry was correlated with more severe excitement symptoms and less severe emotional distress. Significant group differences in the asymmetries of traditional morphological measures of cortical thickness, surface area, and gyrification, at either global or regional levels, were not identified. Cortical shape asymmetries are more sensitive than other morphological asymmetries in capturing abnormalities in patients with early psychosis. These abnormalities are expressed at coarse spatial scales and are correlated with specific symptom domains.

The individuality of shape asymmetries of the human cerebral cortex

Asymmetries of the cerebral cortex are found across diverse phyla and are particularly pronounced in humans, with important implications for brain function and disease. However, many prior studies have confounded asymmetries due to size with those due to shape. Here, we introduce a novel approach to characterize asymmetries of the whole cortical shape, independent of size, across different spatial frequencies using magnetic resonance imaging data in three independent datasets. We find that cortical shape asymmetry is highly individualized and robust, akin to a cortical fingerprint, and identifies individuals more accurately than size-based descriptors, such as cortical thickness and surface area, or measures of inter-regional functional coupling of brain activity. Individual identifiability is optimal at coarse spatial scales (~37 mm wavelength), and shape asymmetries show scale-specific associations with sex and cognition, but not handedness. While unihemispheric cortical shape shows significant heritability at coarse scales (~65 mm wavelength), shape asymmetries are determined primarily by subject-specific environmental effects. Thus, coarse-scale shape asymmetries are highly personalized, sexually dimorphic, linked to individual differences in cognition, and are primarily driven by stochastic environmental influences.

Intermittent theta burst stimulation over the parietal cortex has a significant neural effect on working memory

The crucial role of the parietal cortex in working memory (WM) storage has been identified by fMRI studies. However, it remains unknown whether repeated parietal intermittent theta‐burst stimulation (iTBS) can improve WM. In this within‐subject randomized controlled study, under the guidance of fMRI‐identified parietal activation in the left hemisphere, 22 healthy adults received real and sham iTBS sessions (five consecutive days, 600 pulses per day for each session) with an interval of 9 months between the two sessions. Electroencephalography signals of each subject before and after both iTBS sessions were collected during a change detection task. Changes in contralateral delay activity (CDA) and K‐score were then calculated to reflect neural and behavioral WM improvement. Repeated‐measures ANOVA suggested that real iTBS increased CDA more than the sham one (p = .011 for iTBS effect). Further analysis showed that this effect was more significant in the left hemisphere than in the right hemisphere (p = .029 for the hemisphere‐by‐iTBS interaction effect). Pearson correlation analyses showed significant correlations for two conditions between CDA changes in the left hemisphere and K score changes (ps <.05). In terms of the behavioral results, significant K score changes after real iTBS were observed for two conditions, but a repeated‐measures ANOVA showed a nonsignificant main effect of iTBS (p = .826). These results indicate that the current iTBS protocol is a promising way to improve WM capability based on the neural indicator (CDA) but further optimization is needed to produce a behavioral effect.

Reduced Microstructural Lateralization in Males with Chronic Schizophrenia: A Diffusional Kurtosis Imaging Study

Decreased brain lateralization is considered a trait marker of schizophrenia. Whereas reductions in both functional and macrostructural gray matter laterality in schizophrenia are well established, the investigation of gray matter microstructural lateralization has so far been limited to a small number of ex vivo studies, which limits the understanding of neurobiological substrates involved and development of adequate treatments. The aim of the current study was to assess in vivo gray matter microstructure lateralization patterns in schizophrenia by employing the diffusion kurtosis imaging (DKI)-derived mean kurtosis (MK) metric. MK was calculated for 18 right-handed males with chronic schizophrenia and 19 age-matched healthy control participants in 46 bilateral gray matter regions of interest (ROI). Microstructural laterality indexes (μLIs) were calculated for each subject and ROI, and group comparisons were conducted across regions. The relationship between μLI values and performance on the Wisconsin Card Sorting Test (WCST) was also evaluated. We found that compared with healthy controls, males with chronic schizophrenia had significantly decreased μLI across cortical and subcortical gray matter regions, which was correlated with poorer performance on the WCST. Our results suggest the ability of DKI-derived MK to capture gray matter microstructural lateralization pathology in vivo.

Pretreatment abnormalities in white matter integrity predict one-year clinical outcome in first episode schizophrenia

Schizophrenia is a serious mental illness for which the mainstay of treatment is antipsychotics. Up to 30% of schizophrenia patients show limited response to antipsychotics. Identifying these patients before treatment could guide individualized treatment for improving outcomes in those not likely to show robust benefit from antipsychotics. Diffusion tensor imaging was performed with 56 drug-naïve first-episode schizophrenia patients and 69 matched healthy controls. Patients were followed clinically after one-year of antipsychotic treatment and classified at that point into groups of 17 poor outcome and 39 good outcome patients based on whether they showed at least a 50% reduction of Positive and Negative Syndrome Scale (PANSS) scores from baseline. Tract-based spatial statistics were applied to assess white matter microstructure in the two patient subgroups and healthy controls. Poor outcome patients showed reduced pretreatment fractional anisotropy (FA) in left cingulum and anterior thalamic radiation and increased FA in right superior and inferior longitudinal fasciculus compared with good outcome patients. FA in each of these four tracts was decreased in both patient subgroups relative to healthy controls. Considered together, the four altered tracts showed promising ability to differentiate poor from good outcome patients (sensitivity = 74.4%, specificity = 95.2%, AUC = 0.90, p < 0.001), and superior prediction of clinical outcome to baseline PANSS scores (p < 0.015). Prediction of outcomes using DTI features was not related to duration of untreated psychosis. Baseline alterations in white matter integrity may identify schizophrenia patients less likely to respond to treatment, which could be useful information for stratification in clinical trials and for individualized treatment planning.

Are cerebral and behavioural lateralization related to anxiety-like traits in the animal model zebrafish (Danio rerio)?

Brain lateralization refers to hemispheric asymmetries in functions and/or neuroanatomical structures. Functional specialization in non-human animals has been mainly inferred through observation of lateralized motor responses and sensory perception. Only in a few cases has the influence of brain asymmetries on behaviour been described. Zebrafish has rapidly become a valuable model to investigate this issue as it displays epithalamic asymmetries that have been correlated to some lateralized behaviours. Here we investigated the relation between neuroanatomical or behavioural lateralization and anxiety using a light-dark preference test in adult zebrafish. In Experiment 1, we observed how scototaxis response varied as a function of behavioural lateralization measured in the detour task as turning preference in front of a dummy predator. In Experiment 2, foxD3:GFP transgenic adult zebrafish with left or right parapineal position, were tested in the same light-dark test as fish in Experiment 1. No correlation was found between the behaviour observed in the detour test and in the scototaxis test nor between the left- and right-parapineal fish and the scototaxis response. The consistency of results obtained in both experiments indicates that neither behavioural nor neuroanatomical asymmetries are related to anxiety-related behaviours measured in the light-dark test.

Covarying structural alterations in laterality of the temporal lobe in schizophrenia: A case for source-based laterality

The human brain is asymmetrically lateralized for certain functions (such as language processing) to regions in one hemisphere relative to the other. Asymmetries are measured with a laterality index (LI). However, traditional LI measures are limited by a lack of consensus on metrics used for its calculation. To address this limitation, source-based laterality (SBL) leverages an independent component analysis for the identification of laterality-specific alterations, identifying covarying components between hemispheres across subjects. SBL is successfully implemented with simulated data with inherent differences in laterality. SBL is then compared with a voxel-wise analysis utilizing structural data from a sample of patients with schizophrenia and controls without schizophrenia. SBL group comparisons identified three distinct temporal regions and one cerebellar region with significantly altered laterality in patients with schizophrenia relative to controls. Previous work highlights reductions in laterality (ie, reduced left gray matter volume) in patients with schizophrenia compared with controls without schizophrenia. Results from this pilot SBL project are the first, to our knowledge, to identify covarying laterality differences within discrete temporal brain regions. The authors argue SBL provides a unique focus to detect covarying laterality differences in patients with schizophrenia, facilitating the discovery of laterality aspects undetected in previous work.

A Prospective Longitudinal Investigation of Cortical Thickness and Gyrification in Schizophrenia

BACKGROUND

Cortical thickness (CT) and gyrification are complementary indices that assess different aspects of gray matter structural integrity. Both neurodevelopment insults and acute tissue response to antipsychotic medication could underlie the known heterogeneity of treatment response and are well-suited for interrogation into the relationship between gray matter morphometry and clinical outcomes in schizophrenia (SZ).

METHODS

Using a prospective design, we enrolled 34 unmedicated patients with SZ and 23 healthy controls. Patients were scanned at baseline and after a 6-week trial with risperidone. CT and local gyrification index (LGI) values were quantified from structural MRI scans using FreeSurfer 5.3.

RESULTS

We found reduced CT and LGI in patients compared to controls. Vertex-wise analyses demonstrated that hypogyrification was most prominent in the inferior frontal cortex, temporal cortex, insula, pre/postcentral gyri, temporoparietal junction, and the supramarginal gyrus. Baseline CT was predictive of subsequent response to antipsychotic treatment, and increase in CT after 6 weeks was correlated with greater symptom reductions.

CONCLUSIONS

In summary, we report evidence of reduced CT and LGI in unmedicated patients compared to controls, suggesting involvement of different aspects of gray matter morphometry in the pathophysiology of SZ. Importantly, we found that lower CT at baseline and greater increase of CT following 6 weeks of treatment with risperidone were associated with better clinical response. Our results suggest that cortical thinning may normalize as a result of a good response to antipsychotic medication, possibly by alleviating potential neurotoxic processes underlying gray matter deterioration.

Genetic Intersections of Language and Neuropsychiatric Conditions

PURPOSE OF REVIEW

To better understand the shared basis of language and mental health, this review examines the behavioral and neurobiological features of aberrant language in five major neuropsychiatric conditions. Special attention is paid to genes implicated in both language and neuropsychiatric disorders, as they reveal biological domains likely to underpin the processes controlling both.

RECENT FINDINGS

Abnormal language and communication are common manifestations of neuropsychiatric conditions, and children with impaired language are more likely to develop psychiatric disorders than their peers. Major themes in the genetics of both language and psychiatry include master transcriptional regulators, like FOXP2; key developmental regulators, like AUTS2; and mediators of neurotransmission, like GRIN2A and CACNA1C.

Atypical lateralization in neurodevelopmental and psychiatric disorders: What is the role of stress?

Hemispheric asymmetries are a major organizational principle of the human brain. In different neurodevelopmental and psychiatric disorders, like schizophrenia, autism spectrum disorders, depression, dyslexia and posttraumatic stress disorder, functional and/or structural hemispheric asymmetries are altered compared to healthy controls. The question, why these disorders all share the common characteristic of altered hemispheric asymmetries despite vastly different etiologies and symptoms remains one of the unsolved mysteries of laterality research. This review is aimed at reviewing potential reasons for why atypical lateralization is so common in many neurodevelopmental and psychiatric disorders. To this end, we review the evidence for overlaps in the genetic and non-genetic factors involved in the ontogenesis of different disorders and hemispheric asymmetries. While there is evidence for genetic overlap between different disorders, only few asymmetry-related loci have also been linked to disorders and importantly, those effects are mostly specific to single disorders. However, there is evidence for shared non-genetic influences between disorders and hemispheric asymmetries. Most neurodevelopmental and psychiatric disorders show alterations in the hypothalamic-pituitary adrenocortical (HPA) axis and maternal as well as early life stress have been implicated in their etiology. Stress has also been suggested to affect hemispheric asymmetries. We propose a model in which early life stress as well as chronic stress not only increases the risk for psychiatric and neurodevelopmental disorders but also changes structural and functional hemispheric asymmetries leading to the aberrant lateralization patterns seen in these disorders. Thus, pathology-related changes in hemispheric asymmetries are not a factor causing disorders, but rather a different phenotype that is affected by partly overlapping ontogenetic factors, primarily stress.

Altered syntactic abilities in first episode patients: An inner phenomenon characterizing psychosis

BACKGROUND

Research has consistently shown that language abilities represent a core dimension of psychosis; however, to date, very little is known about syntactic comprehension performance in the early stages of psychosis. This study aims to compare the linguistic abilities involved in syntactic comprehension in a large group of First Episode Psychosis (FEP) patients and healthy controls (HCs).

METHODS

A multiple choice test of comprehension of syntax was administered to 218 FEP patients (166 non-affective FEP patients [FEP-NA] and 52 affective FEP patients [FEP-A]) and 106 HCs. All participants were asked to match a sentence they listen with one out of four vignettes on a pc screen. Only one vignette represents the stimulus target, while the others are grammatical or non-grammatical (visual) distractors. Both grammatical and non-grammatical errors and performance in different syntactic constructions were considered.

RESULTS

FEP committed greater number of errors in the majority of TCGB language domains compared to HCs. Moreover, FEP-NA patients committed significantly more non-grammatical (z = -3.2, p = 0.007), locative (z = -4.7, p < 0.001), passive-negative (z = -3.2, p = 0.02), and relative (z = -4.6, p < 0.001) errors compared to HCs as well as more passive-affirmative errors compared to both HCs (z = -4.3, p < 0.001) and FEP-A (z = 3.1, p = 0.04). Finally, we also found that both FEP-NA and FEP-A committed more grammatical (FEP-NA: z = -9.2, p < 0.001 and FEP-A: z = -4.4, p < 0.001), total (FEP-NA: z = -8.2, p < 0.001 and FEP-A: z = 3.9, p =  0.002), and active-negative (FEP-NA: z = -5.8, p < 0.001 and FEP-A: z = -3.5, p = 0.01) errors compared to HCs.

CONCLUSIONS

This study shows that the access to syntactic structures is already impaired in FEP patients, especially in those with FEP-NA, ultimately suggesting that language impairments represent a core and inner feature of psychosis even at early stages.

Discordant attributes of structural and functional brain connectivity in a two-layer multiplex network

Several studies have suggested that functional connectivity (FC) is constrained by the underlying structural connectivity (SC) and mutually correlated. However, not many studies have focused on differences in the network organization of SC and FC, and on how these differences may inform us about their mutual interaction. To explore this issue, we adopt a multi-layer framework, with SC and FC, constructed using Magnetic Resonance Imaging (MRI) data from the Human Connectome Project, forming a two-layer multiplex network. In particular, we examine node strength assortativity within and between the SC and FC layer. We find that, in general, SC is organized assortatively, indicating brain regions are on average connected to other brain regions with similar node strengths. On the other hand, FC shows disassortative mixing. This discrepancy is apparent also among individual resting-state networks within SC and FC. In addition, these patterns show lateralization, with disassortative mixing within FC subnetworks mainly driven from the left hemisphere. We discuss our findings in the context of robustness to structural failure, and we suggest that discordant and lateralized patterns of associativity in SC and FC may provide clues to understand laterality of some neurological dysfunctions and recovery.

Functional Hemispheric (A)symmetries in the Aged Brain-Relevance for Working Memory

Functional hemispheric asymmetries have been described in different cognitive processes, such as decision-making and motivation. Variations in the pattern of left/right activity have been associated with normal brain functioning, and with neuropsychiatric diseases. Such asymmetries in brain activity evolve throughout life and are thought to decrease with aging, but clear associations with cognitive function have never been established. Herein, we assessed functional laterality during a working memory task (N-Back) in a healthy aging cohort (over 50 years old) and associated these asymmetries with performance in the test. Activity of lobule VI of the cerebellar hemisphere and angular gyrus was found to be lateralized to the right hemisphere, while the precentral gyrus presented left > right activation during this task. Interestingly, 1-Back accuracy was positively correlated with left > right superior parietal lobule activation, which was mostly due to the influence of the left hemisphere. In conclusion, although regions were mostly symmetrically activated during the N-Back task, performance in working memory in aged individuals seems to benefit from lateralized involvement of the superior parietal lobule.

Investigation of superior longitudinal fasciculus fiber complexity in recent onset psychosis

BACKGROUND

Standard diffusion tensor imaging measures (e.g., fractional anisotropy; FA) are difficult to interpret in brain regions with crossing white-matter (WM) fibers. Diffusion spectrum imaging (DSI) can be used to resolve fiber crossing, but has been difficult to implement in studies of patients with psychosis given long scan times.

METHODS

We used four fold accelerated compressed sensing to accelerate DSI acquisition to investigate the superior longitudinal fasciculus (SLF) in 27 (20M/7F) patients with recent onset psychosis and 23 (11M/12F) healthy volunteers. Dependent measures included the number of crossing fiber directions, multi directional anisotropy (MDA), which is a measure sensitive to the anisotropy of the underlying water diffusion in regions of crossing fibers, generalized FA (GFA) computed from the orientation distribution function, FA and tract volume.

RESULTS

Patients demonstrated a greater number of crossing WM fibers, lower MDA, GFA and FA in the left SLF compared to healthy volunteers. Patients also demonstrated a reversal in the normal (R>L) asymmetry of crossing fiber directions in the SLF and a lack of normal (L>R) asymmetry in MDA, GFA and FA compared to healthy volunteers. Lower GFA correlated significantly (p<0.05) with worse overall neuropsychological functioning; posthoc tests revealed significant effects with verbal functioning and processing speed.

CONCLUSIONS

Our findings provide the first in vivo evidence for abnormal crossing fibers within the SLF among individuals with psychosis and their functional correlates. A reversal in the normal pattern of WM asymmetry of crossing fibers in patients may be consistent with an aberrant neurodevelopmental process.

Gyrification Connectomes in Unmedicated Patients With Schizophrenia and Following a Short Course of Antipsychotic Drug Treatment

Schizophrenia (SZ) is a d isease characterized by brain dysconnectivity and abnormal brain development. The study of cortical gyrification in schizophrenia may capture underlying alterations reflective of neurodevelopmental abnormalities more accurately than other imaging modalities. Graph-based connectomic approaches have been previously used in schizophrenia to study structural and functional brain covariance using a diversity of techniques. The goal of the present study was to evaluate morphological covariance using a measure of local gyrification index in patients with schizophrenia. The aims of this study were two-fold: (1) Evaluate the structural covariance of local gyrification index using graph theory measures of integration and segregation in unmedicated patients with schizophrenia compared to healthy controls and (2) investigate changes in these measures following a short antipsychotic drug (APD) treatment. Using a longitudinal prospective design, structural scans were obtained prior to treatment in 34 unmedicated patients with SZ and after 6 weeks of treatment with risperidone. To control for the effect of time, 23 matched healthy controls (HC) were also scanned twice, 6 weeks apart. The cortical surface of each structural image was reconstructed and local gyrification index values were computed using FreeSurfer. Local gyrification index values where then parcellated into atlas based regions and entered into a 68 × 68 correlation matrix to construct local gyrification index connectomes for each group at each time point. Longitudinal comparisons showed significant group by time interactions for measures of segregation (clustering, local efficiency) and modularity, but not for measures of integration (path length, global efficiency). Post-hoc tests showed increased clustering, local efficiency, and modularity connectomes in unmedicated patients with SZ at baseline compared to HC. Post-hoc tests did not show significant within group differences for HCs or patients with SZ. After 6 weeks of treatment, there were no significant differences between the groups on these measures. Abnormal cortical topography is detected in schizophrenia and is modified by short term APD treatment reflective of decreases in hyper-specialization in network connectivity. We speculate that changes in the structural organization of the brain is achieved through the neuroplastic effects that APDs have on brain tissue, thus promoting more efficient brain connections and, possibly, a therapeutic effect.

40 Hz Auditory Steady-State Response: The Impact of Handedness and Gender

The 40 Hz auditory steady-state response (ASSR) is a periodic response to a periodic stimulation. Its sources are located in the primary auditory cortex and the asymmetry of the planum temporale has previously been associated with hand preference and gender-related differences; thus subject's handedness and gender could potentially influence ASSRs. Nevertheless, electrophysiological studies of ASSRs are mainly dominated by right-handed participants and the observed findings can only be generalized to the right-handed populations. However, for a potential use of 40 Hz ASSR as a translational biomarker of neuropsychiatric disorders, it is important to investigate the response in association to handedness and gender. We included an equal number of left-handed and right-handed males and females and recorded EEG responses during left-ear, right-ear and both ears stimulation. The results of the study suggest that the processing of 40 Hz auditory stimulation depends on the subjects' gender and handedness: significantly lower phase-locking and strength of 40 Hz ASSRs were observed in left-handed females as compared to left-handed males, but right-handers did not differ in 40 Hz ASSRs. Our observation of the opposite impact of gender in the examined handedness groups stresses the importance of careful consideration of handedness and gender factors when evaluating the determinants of inter individual variability of 40 Hz ASSRs. This finding is of particular importance for clinical studies in psychiatry and neurology.

Graph-based analysis of brain connectivity in schizophrenia

The present study evaluated brain connectivity using electroencephalography (EEG) data from 14 patients with schizophrenia and 14 healthy controls. Phase-Locking Value (PLV), Phase-Lag Index (PLI) and Directed Transfer Function (DTF) were calculated for the original EEG data and following current source density (CSD) transformation, re-referencing using the average reference electrode (AVERAGE) and reference electrode standardization techniques (REST). The statistical analysis of adjacency matrices was carried out using indices based on graph theory. Both CSD and REST reduced the influence of volume conducted currents. The largest group differences in connectivity were observed for the alpha band. Schizophrenic patients showed reduced connectivity strength, as well as a lower clustering coefficient and shorter characteristic path length for both measures of phase synchronization following CSD transformation or REST re-referencing. Reduced synchronization was accompanied by increased directional flow from the occipital region for the alpha band. Following the REST re-referencing, the sources of alpha activity were located at parietal rather than occipital derivations. The results of PLV and DTF demonstrated group differences in fronto-posterior asymmetry following CSD transformation, while for PLI the differences were significant only using REST. The only analysis that identified group differences in inter-hemispheric asymmetry was DTF calculated for REST. Our results suggest that a comparison of different connectivity measures using graph-based indices for each frequency band, separately, may be a useful tool in the study of disconnectivity disorders such as schizophrenia.

Graph-based analysis of brain connectivity in schizophrenia

The present study evaluated brain connectivity using electroencephalography (EEG) data from 14 patients with schizophrenia and 14 healthy controls. Phase-Locking Value (PLV), Phase-Lag Index (PLI) and Directed Transfer Function (DTF) were calculated for the original EEG data and following current source density (CSD) transformation, re-referencing using the average reference electrode (AVERAGE) and reference electrode standardization techniques (REST). The statistical analysis of adjacency matrices was carried out using indices based on graph theory. Both CSD and REST reduced the influence of volume conducted currents. The largest group differences in connectivity were observed for the alpha band. Schizophrenic patients showed reduced connectivity strength, as well as a lower clustering coefficient and shorter characteristic path length for both measures of phase synchronization following CSD transformation or REST re-referencing. Reduced synchronization was accompanied by increased directional flow from the occipital region for the alpha band. Following the REST re-referencing, the sources of alpha activity were located at parietal rather than occipital derivations. The results of PLV and DTF demonstrated group differences in fronto-posterior asymmetry following CSD transformation, while for PLI the differences were significant only using REST. The only analysis that identified group differences in inter-hemispheric asymmetry was DTF calculated for REST. Our results suggest that a comparison of different connectivity measures using graph-based indices for each frequency band, separately, may be a useful tool in the study of disconnectivity disorders such as schizophrenia.

Relationships between corpus callosum and language lateralization in patients with schizophrenia and bipolar disorders

OBJECTIVES

The question of whether there is a continuum or a dichotomy among patients with schizophrenia (SZ) and bipolar disorders (BD) has not been clearly resolved and remains a challenge. Thus, the identification of specific biomarkers of these disorders might be helpful. The present study investigated the volume of the corpus callosum (CC) and functional lateralization for language as potential biomarkers and their relationships in SZ and BD.

METHODS

The study included 20 patients with SZ, 20 patients with BD and 40 healthy controls (HC). A functional lateralization index (FLI) was computed for each participant within the language comprehension network. For each participant, the volume of the total CC and those of three subregions were extracted. These variables and their anatomo-functional relationships were investigated.

RESULTS

In comparison to HC, SZ patients presented a decreased leftward lateralization for language, whereas this was not found in BD patients. However, as compared to SZ patients and HC, BD patients showed a reduction in CC volume associated with a lower leftward lateralization for language.

CONCLUSIONS

Our study revealed that SZ patients displayed a reduction of the leftward functional lateralization for language; however, no reduction of CC volume was observed, whereas BD patients presented a decreased volume of the CC associated with a lower leftward asymmetry for language. The results of our study detected distinct anomalies in both SZ and BD that may be considered as specific biomarkers of these disorders related to neurodevelopmental models.

Reduced language lateralization in first episode schizophrenia: A near infrared spectroscopy study

BACKGROUND

Diminished functional lateralization in language-related areas is found in chronic schizophrenia (SZ). However, whether this reduced lateralization exists at the early stage of SZ remains unclear. The present study aimed to investigate language lateralization in first episode schizophrenia (FES) using near infrared spectroscopy (NIRS) during a letter version of verbal fluency test (VFT).

METHODS

A total of 28 FES patients and 33 healthy controls (HCs) underwent NIRS while performing a VFT. Six regions of interests (ROIs) were defined: the bilateral frontal-, inferior frontal gyrus (IFG), and temporal regions. Laterality index (LI) was calculated and compared between the two groups in ROIs. In addition, we investigated whether language lateralization was correlated with severity of clinical symptoms.

RESULTS

Across all ROIs, LI was significantly reduced in FES patients (p=0.037) compared to controls in the IFG region. In addition, LI was not found to be correlated with VFT performance, the PANSS positive, negative or general psychopathology subscales.

CONCLUSIONS

Our study demonstrated a diminution of leftward functional lateralization in the IFG during a VFT in FES patients. This is the first NIRS study to report reduced functional lateralization in patients at the early stage of schizophrenia.

Hemispheric lateralization abnormalities of the white matter microstructure in patients with schizophrenia and bipolar disorder

BACKGROUND

Hemispheric lateralization of the brain occurs during development and underpins specialized functions. It is posited that aberrant neurodevelopment leads to abnormal brain lateralization in individuals with psychotic illnesses. Here, we sought to examine whether white matter hemispheric lateralization is abnormal in individuals with the psychotic spectrum disorders of schizophrenia and bipolar disorder.

METHODS

We examined the white matter microstructure lateralization in patients with schizophrenia, bipolar disorder with psychotic features and healthy controls by measuring the laterality indices of fractional anisotropy (FA) and mean diffusivity (MD). We also correlated the laterality indices with clinical measures.

RESULTS

We included 150 patients with schizophrenia, 35 with bipolar disorder and 77 healthy controls in our analyses. Shared FA lateralization abnormalities in patients with schizophrenia and bipolar disorder were found in the cerebral peduncle and posterior limb of internal capsule, with more extensive abnormalities in patients with bipolar disorder than in those with schizophrenia. The shared MD lateralization abnormalities were more widespread, extending to the subcortical, frontal-occipital, limbic and callosal tracts, with patients with bipolar disorder showing greater abnormalities than patients with schizophrenia. While lateralization was decreased in patients with schizophrenia, the lateralization was reversed in those with bipolar disorder, underpinned by the more pronounced microstructural abnormalities in the right hemisphere. The loss of FA lateralization in patients with schizophrenia was associated with lower quality of life and psychosocial functioning.

LIMITATIONS

Owing to the cross-sectional study design, we cannot confirm whether the lateralization abnormalities are neurodevelopmental or a consequence of psychosis onset or chronicity.

CONCLUSION

Shared and distinct white matter lateralization abnormalities were found in patients with schizophrenia and bipolar disorder. In distinct regions of abnormalities, the lateralization was attenuated in patients with schizophrenia and reversed in those with bipolar disorder.

Brain structure, function, and neurochemistry in schizophrenia and bipolar disorder-a systematic review of the magnetic resonance neuroimaging literature

Since Emil Kraepelin's conceptualization of endogenous psychoses as dementia praecox and manic depression, the separation between primary psychotic disorders and primary affective disorders has been much debated. We conducted a systematic review of case-control studies contrasting magnetic resonance imaging studies in schizophrenia and bipolar disorder. A literature search in PubMed of studies published between January 2005 and December 2016 was conducted, and 50 structural, 29 functional, 7 magnetic resonance spectroscopy, and 8 combined imaging and genetic studies were deemed eligible for systematic review. Structural neuroimaging studies suggest white matter integrity deficits that are consistent across the illnesses, while gray matter reductions appear more widespread in schizophrenia compared to bipolar disorder. Spectroscopy studies in cortical gray matter report evidence of decreased neuronal integrity in both disorders. Functional neuroimaging studies typically report similar functional architecture of brain networks in healthy controls and patients across the psychosis spectrum, but find differential extent of alterations in task related activation and resting state connectivity between illnesses. The very limited imaging-genetic literature suggests a relationship between psychosis risk genes and brain structure, and possible gene by diagnosis interaction effects on functional imaging markers. While the existing literature suggests some shared and some distinct neural markers in schizophrenia and bipolar disorder, it will be imperative to conduct large, well designed, multi-modal neuroimaging studies in medication-naïve first episode patients that will be followed longitudinally over the course of their illness in an effort to advance our understanding of disease mechanisms.

Lateralization of intrinsic frontoparietal network connectivity and symptoms in schizophrenia

It has been frequently reported that schizophrenia patients have reduced functional lateralization in the areas related to language processing. Furthermore, there is evidence supporting that schizophrenia patients have disrupted functional connectivity in the bilateral frontoparietal networks (FPNs), of which the left is strongly associated with a cognition-language paradigm, using resting-state functional magnetic resonance imaging (rsfMRI). To examine the laterality of resting-state functional connectivity in schizophrenia, we investigated the bilateral FPNs. We investigated 41 schizophrenia and 35 healthy participants using independent component analysis for rsfMRI. We extracted mean connectivity values of both left and right FPNs and calculated their laterality index by (left - right)/(left + right). Subsequently, we investigated group differences of these values and the correlation between these values and symptoms. In schizophrenia, mean connectivity values of both left and right FPNs were significantly lower than in healthy controls, whereas their laterality indices were not significantly different. However, correlation analyses revealed that the laterality index was negatively correlated with positive symptoms, and that mean connectivity of left FPN was negatively correlated with depressive symptoms in schizophrenia. Our results suggest that language-related networks and their laterality might be one of the neural correlates of schizophrenia symptoms.

A linguistic comparison between auditory verbal hallucinations in patients with a psychotic disorder and in nonpsychotic individuals: Not just what the voices say, but how they say it

BACKGROUND

Auditory verbal hallucinations (AVH) in psychotic patients are associated with activation of right hemisphere language areas, although this hemisphere is non-dominant in most people. Language generated in the right hemisphere can be observed in aphasia patients with left hemisphere damage. It is called "automatic speech", characterized by low syntactic complexity and negative emotional valence. AVH in nonpsychotic individuals, by contrast, predominantly have a neutral or positive emotional content and may be less dependent on right hemisphere activity. We hypothesize that right hemisphere language characteristics can be observed in the language of AVH, differentiating psychotic from nonpsychotic individuals.

METHOD

17 patients with a psychotic disorder and 19 nonpsychotic individuals were instructed to repeat their AVH verbatim directly upon hearing them. Responses were recorded, transcribed and analyzed for total words, mean length of utterance, proportion of grammatical utterances, proportion of negations, literal and thematic perseverations, abuses, type-token ratio, embeddings, verb complexity, noun-verb ratio, and open-closed class ratio.

RESULTS

Linguistic features of AVH overall differed between groups F(13,24)=3.920, p=0.002; Pillai's Trace 0.680. AVH of psychotic patients compared with AVH of nonpsychotic individuals had a shorter mean length of utterance, lower verb complexity, and more verbal abuses and perseverations (all p<0.05). Other features were similar between groups.

CONCLUSION

AVH of psychotic patients showed lower syntactic complexity and higher levels of repetition and abuses than AVH of nonpsychotic individuals. These differences are in line with a stronger involvement of the right hemisphere in the origination of AVH in patients than in nonpsychotic voice hearers.

La relation entre le volume du corps calleux et la latéralisation fonctionnelle pour le langage dans le trouble bipolaire et la schizophrénie : un biomarqueur cérébral pertinent ?

Introduction

Le trouble bipolaire (TB) et la schizophrénie (SZ) sont deux entités distinctes mais qui partagent certaines similarités [1]. Il apparaît donc nécessaire de mettre en évidence des biomarqueurs spécifiques de l’une ou l’autre de ces pathologies. Il a été démontré dans ces deux troubles l’existence d’anomalies du corps calleux (CC) [2] ainsi que des anomalies fonctionnelles liées au langage [3]. Cependant, le lien entre la volumétrie du CC et la latéralisation fonctionnelle pour le langage reste à préciser chez ces deux populations. Nous émettons l’hypothèse que ces deux pathologies présenteraient des anomalies cérébrales différentes.

Matériels et méthodes

Vingt patients TB, 20 patients SZ et 40 témoins volontaires sains (TVS) ont été inclus. Un index de latéralisation fonctionnelle (ILF) a été extrait chez chaque participant au sein du réseau de la compréhension du langage. Les données de volumétrie ont été calculées dans la totalité du CC et dans ses différentes sous-régions. Les relations anatomo-fonctionnelles entre ces variables ont été testées.

Résultats

Les patients SZ présentaient une réduction de l’ILF gauche pour le langage comparativement aux TVS, non retrouvée chez les patients TB. Une réduction du volume du CC a été mise en évidence chez les TB comparativement aux SZ et aux TVS. De plus, les patients TB présentaient une réduction du volume callosal associée à une diminution de l’ILF gauche pour le langage.

Conclusion

Notre étude a révélé l’existence d’une réduction de la volumétrie callosale chez les patients TB, laquelle pourrait être considérée comme un biomarqueur spécifique de cette pathologie. Il semblerait que ces anomalies puissent être à l’origine d’une diminution de la latéralisation fonctionnelle gauche pour le langage. Ainsi, ces résultats nous permettent de conclure que les patients TB auraient une altération du CC plus marquée que les patients SZ, suggérant que le TB et la SZ présentent des mécanismes physiopathologiques distincts.

Left-hemisphere lateralization for language and interhemispheric fiber tracking in patients with schizophrenia

BACKGROUND

It has been suggested that the degree of hemispheric specialization (HS) depends on the structural connectivity between the two hemispheres, that is to say the corpus callosum (CC). Studies, performed only on healthy participants, investigated this anatomo-functional relationship. Nevertheless, it has never been studied in schizophrenia. We therefore propose to study the anatomo-functional relationships between the integrity of interhemispheric connectivity and leftward functional lateralization for language in patients with schizophrenia compared with healthy participants, driven by a multimodal approach combining fMRI and DTI-based fiber tractography. We hypothesized that reduced leftward functional lateralization for language in patients with schizophrenia could be related to a callosal hypoconnectivity.

MATERIALS AND METHODS

Seventeen patients based on the DSM-IV, and 17 controls were included. The functional laterality index and interhemispheric diffusion values between homologue temporal regions, belonging to the language network, were individually extracted in order to study the anatomo-functional relationships.

RESULTS

In the patients, higher mean and radial diffusivity (RD) values (thicker myelin sheaths) were associated with less leftward lateralization. In contrast, the controls presented higher RD values and lower fractional anisotropy values (axonal loss) with more leftward lateralization.

CONCLUSIONS

Our study revealed a relationship between the CC and the HS for language, but did not provide evidence clarifying the direction of the relationship between callosal connectivity and functional lateralization for language. In particular, the present findings showed that the loss of integrity in interhemispheric callosal fibers was associated with reduced leftward cerebral dominance for language in patients with schizophrenia.