White Matter Integrity in Genetic High-Risk Individuals and First-Episode Schizophrenia Patients: Similarities and Disassociations

Distinct white matter abnormalities and cognitive impairments in deficit schizophrenia: A cross-sectional diffusion tensor imaging study

Deficit schizophrenia (DS), characterized by persistent and primary negative symptoms, is considered a promising homogeneous subtype of schizophrenia. According to the disconnection hypothesis, abnormalities in white matter fibers are common in schizophrenia. However, comprehensive measurement of white matter metrics and exploration of the relationships between neuroanatomical changes and cognitive functions in DS patients are still unknown. A cross-sectional study was conducted, including 35 DS patients, 37 non-deficit schizophrenia (NDS) patients, and 39 healthy controls (HC), all male and matched for age and education level. The tract-based spatial statistics method was performed to detect differences in fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD) and radial diffusivity (RD) among these three groups. Cognitive function in DS and NDS patients was assessed using the Mini-Mental State Examination (MMSE) and Mattis Dementia Rating Scale. Correlation analyses were performed between diffusion metrics in regions showing differences and clinical scales. The results showed significant differences in diffusion metrics (FA, RD, AD, MD) across DS, NDS, and HC groups, particularly in the corpus callosum, corona radiata, and thalamic radiations. Compare to NDS, DS patients exhibited more reductions in FA and increases in RD, especially in the right posterior thalamic radiation and right superior longitudinal fasciculus. Correlation analysis revealed that lower FA in specific regions was linked to worse cognitive and clinical symptoms. These findings reinforce the dysconnectivity hypothesis of schizophrenia and highlight the distinct pathological mechanisms of white matter impairments in DS. Correlations in crucial white matter regions suggest disruptions in thalamo-cortical feedback loops, potentially contributing to the cognitive impairments observed. This provides a deeper understanding of how structural brain changes relate to clinical symptoms.

Microstructural changes along the cingulum in young adolescents with psychotic experiences: An along-tract analysis

Psychotic experiences (PEs) such as hallucinations and delusions are common among young people without psychiatric diagnoses and are associated with connectivity and white matter abnormalities, particularly in the limbic system. Using diffusion magnetic resonance imaging (MRI) in adolescents with reported PEs and matched controls, we examined the cingulum white matter tract along its length rather than as the usually reported single indivisible structure. Complex regional differences in diffusion metrics were found along the bundle at key loci following Bonferroni significance adjustment (p < .00013) with moderate to large effect sizes (.11-.76) throughout all significant subsegments. In this prospective community-based cohort of school-age children, these findings suggest that white matter alterations in the limbic system may be more common in the general non-clinical adolescent population than previously thought. Such white matter alternations may only be uncovered using a similar more granular along-tract analysis of white matter tracts.

Tract-specific white matter microstructural alterations in subjects with schizophrenia and unaffected first-degree relatives

White matter tracts alterations have been reported in schizophrenia (SZ), but whether such abnormalities are associated with the effects of the disorder itself and/or genetic vulnerability remains unclear. Moreover, the specific patterns of different parts of these altered tracts have been less well studied. Thus, diffusion-weighted images were acquired from 38 healthy controls (HCs), 48 schizophrenia patients, and 33 unaffected first-degree relatives of SZs (FDRs). Diffusion properties of the 25 major tracts automatically extracted with probabilistic tractography were calculated and compared among groups. Regarding the peripheral regions of the tracts, significantly higher diffusivity values in the left superior longitudinal fasciculus (SLF) and the left anterior thalamic radiation (ATR) were observed in SZs than in HCs and unaffected FDRs. However, there were no significant differences between HCs and FDRs in these two tracts. While no main effects of group with respect to the core regions of the 25 tracts survived multiple comparisons correction, FDRs had significantly higher diffusivity values in the left medial lemniscus and lower diffusivity values in the middle cerebellar peduncle than HCs and SZs. These findings enhance the understanding of the abnormal patterns in the peripheral and core regions of the tracts in SZs and those at high genetic risk for schizophrenia. Our results suggest that alterations in the peripheral regions of the left SLF and ATR are features of established illness rather than genetic predisposition, which may serve as critical neural substrates for the psychopathology of schizophrenia.

Structural connectivity associated with familial risk for mental illness: A meta‐analysis of diffusion tensor imaging studies in relatives of patients with severe mental disorders

Schizophrenia (SCZ), bipolar disorder (BD), and major depressive disorder (MDD) are heritable conditions with overlapping genetic liability. Transdiagnostic and disorder‐specific brain changes associated with familial risk for developing these disorders remain poorly understood. We carried out a meta‐analysis of diffusion tensor imaging (DTI) studies to investigate white matter microstructure abnormalities in relatives that might correspond to shared and discrete biomarkers of familial risk for psychotic or mood disorders. A systematic search of PubMed and Embase was performed to identify DTI studies in relatives of SCZ, BD, and MDD patients. Seed‐based d Mapping software was used to investigate global differences in fractional anisotropy (FA) between overall and disorder‐specific relatives and healthy controls (HC). Our search identified 25 studies that met full inclusion criteria. A total of 1,144 relatives and 1,238 HC were included in the meta‐analysis. The overall relatives exhibited decreased FA in the genu and splenium of corpus callosum (CC) compared with HC. This finding was found highly replicable in jack‐knife analysis and subgroup analyses. In disorder‐specific analysis, compared to HC, relatives of SCZ patients exhibited the same changes while those of BD showed reduced FA in the left inferior longitudinal fasciculus (ILF). The present study showed decreased FA in the genu and splenium of CC in relatives of SCZ, BD, and MDD patients, which might represent a shared familial vulnerability marker of severe mental illness. The white matter abnormalities in the left ILF might represent a specific familial risk for bipolar disorder.

The role of white matter abnormality in the left anterior corona radiata: In relation to formal thought disorder in patients with schizophrenia

White matter abnormality has been widely reported in patients with schizophrenia (Sz). However, few studies have focused on the relationship between the white matter deficit and formal thought disorder (FTD). Moreover, the role of genetic high risk in FTD-related white matter deficit remains unclear. The present study recruited 46 Sz patients, 18 unaffected first-degree relatives of Sz patients, and 29 healthy controls. There was a widespread fractional anisotropy (FA) reduction in Sz. In addition, reduced FA in the left anterior corona radiata was related to more severe FTD symptoms in Sz. However, the genetic high-risk group only showed lower mean FA in the left anterior limb of the internal capsule than healthy controls. Our findings suggest that abnormality in the left anterior corona radiata may only occur in Sz but not in the genetic high-risk group. Such an abnormality might be associated with the severity of FTD symptoms. Meanwhile, genetic vulnerability may contribute to the abnormality in the left anterior limb of the internal capsule. Better analytical methods are needed to validate our results.

Relationship of Corpus Callosum Integrity with Working Memory, Planning, and Speed of Processing in Patients with First-Episode and Chronic Schizophrenia

There is a paucity of reports examining the relationship between the integrity of the corpus callosum (CC) and different aspects of cognitive functioning in patients with first-episode (FES) and chronic schizophrenia (CS) simultaneously; furthermore, what results exist are inconclusive. We used diffusion tensor imaging tractography to investigate differences in integrity in five regions of the CC between FES, CS, and healthy controls (HC). Additionally, we analyzed correlations between these regions' integrity and working memory, planning, and speed of processing. Eighteen patients with FES, 55 patients with CS, and 30 HC took part in the study. We assessed cognitive functions with four tasks from Measurement and Treatment Research to Improve Cognition in Schizophrenia. Patients with CS showed lower fractional anisotropy (FA) in Region 5 (statistical trend) and higher mean diffusivity (MD) in Regions 4 and 5 than HC, and patients with FES had higher MD in Region 3 (statistical trend) than HC. Both clinical groups performed worse on working memory and speed of processing tasks than HC, and patients with CS scored worse than HC on independent planning, and worse than FES and HC on dependent planning. Moreover, in patients with CS, MD in Region 3 was correlated with verbal working memory. Our results suggest that patients with FES and CS are characterized by impaired integrity of the middle and posterior CC, respectively. We confirmed that both clinical groups have cognitive impairments. Moreover, the integrity of the middle CC may influence planning in patients with CS.

Executive Dysfunctions in Schizophrenia: A Critical Review of Traditional, Ecological, and Virtual Reality Assessments

In recent years, interest has grown in measuring executive function in schizophrenia with ecological and virtual reality (VR) tools. However, there is a lack of critical analysis comparing those tools with traditional ones. This paper aims to characterize executive dysfunction in schizophrenia by comparing ecological and virtual reality assessments with traditional tools, and to describe the neurobiological and psychopathological correlates. The analysis revealed that ecological and VR tests have higher levels of verisimilitude and similar levels of veridicality compared to traditional tools. Both negative symptoms and disorganization correlate significantly with executive dysfunction as measured by traditional tools, but their relationships with measures based on ecological and VR methods are still unclear. Although there is much research on brain correlates of executive impairments in schizophrenia with traditional tools, it is uncertain if these results will be confirmed with the use of ecological and VR tools. In the diagnosis of executive dysfunction, it is important to use a variety of neuropsychological methods—especially those with confirmed ecological validity—to properly recognize the underlying characteristics of the observed deficits and to implement effective forms of therapy.

Multimodal MRI assessment for first episode psychosis: A major change in the thalamus and an efficient stratification of a subgroup

Multi‐institutional brain imaging studies have emerged to resolve conflicting results among individual studies. However, adjusting multiple variables at the technical and cohort levels is challenging. Therefore, it is important to explore approaches that provide meaningful results from relatively small samples at institutional levels. We studied 87 first episode psychosis (FEP) patients and 62 healthy subjects by combining supervised integrated factor analysis (SIFA) with a novel pipeline for automated structure‐based analysis, an efficient and comprehensive method for dimensional data reduction that our group recently established. We integrated multiple MRI features (volume, DTI indices, resting state fMRI—rsfMRI) in the whole brain of each participant in an unbiased manner. The automated structure‐based analysis showed widespread DTI abnormalities in FEP and rs‐fMRI differences between FEP and healthy subjects mostly centered in thalamus. The combination of multiple modalities with SIFA was more efficient than the use of single modalities to stratify a subgroup of FEP (individuals with schizophrenia or schizoaffective disorder) that had more robust deficits from the overall FEP group. The information from multiple MRI modalities and analytical methods highlighted the thalamus as significantly abnormal in FEP. This study serves as a proof‐of‐concept for the potential of this methodology to reveal disease underpins and to stratify populations into more homogeneous sub‐groups.

White Matter Microstructure across the Psychosis Spectrum

Diffusion-weighted imaging (DWI) is a neuroimaging technique that has allowed us an unprecedented look at the role that white matter microstructure may play in mental illnesses, such as psychosis. Psychosis-related illnesses, including schizophrenia, are increasingly viewed as existing along a spectrum; spectrums may be defined based on factors such as stage of illness, symptom severity, or genetic liability. This review first focuses on an overview of some of the recent findings from DWI studies. Then, it examines the ways in which DWI analyses have been extended across the broader psychosis spectrum, or spectrums, and what we have learned from such approaches.

Cingulum bundle abnormalities and risk for schizophrenia

BACKGROUND

The cingulum bundle (CB) is a major white matter fiber tract of the limbic system that underlies cingulate cortex, passing longitudinally over the corpus callosum. The connectivity of this white matter fiber tract plays a major role in emotional expression, attention, motivation, and working memory, all of which are affected in schizophrenia. Myelin related CB abnormalities have also been implicated in schizophrenia. The purpose of this study is to determine whether or not CB abnormalities are evident in individuals at clinical high risk (CHR) for psychosis, and whether or not cognitive deficits in the domains subserved by CB are related to its structural abnormalities.

METHODS

Diffusion Tensor Imaging (DTI) was performed on a 3 T magnet. DT tractography was used to evaluate CB in 20 individuals meeting CHR criteria (13 males/7 females) and 23 healthy controls (12 males/11 females) group matched on age, gender, parental socioeconomic status, education, and handedness. Fractional anisotropy (FA), a measure of white matter coherence and integrity, radial diffusivity (RD), thought to reflect myelin integrity, trace, a possible marker of atrophy, and axial diffusivity (AD), thought to reflect axonal integrity, were averaged over the entire tract and used to investigate CB abnormalities in individuals at CHR for psychosis compared with healthy controls.

RESULTS

Significant group differences were found between individuals at CHR for psychosis and controls for FA (p = 0.028), RD (p = 0.03) and trace (p = 0.031), but not for AD (p = 0.09). We did not find any significant correlations between DTI measures and clinical symptoms.

CONCLUSION

These findings suggest abnormalities (possibly myelin related) in the CB in individuals at CHR for psychosis.

White matter integrity in schizophrenia and bipolar disorder: Tract- and voxel-based analyses of diffusion data from the Connectom scanner

Background

Diffusion imaging abnormalities have been associated with schizophrenia (SZ) and bipolar disorder (BD), indicating impaired structural connectivity. Newer methods permit the automated reconstruction of major white matter tracts from diffusion-weighted MR images in each individual's native space. Using high-definition diffusion data from SZ and BP subjects, we investigated brain white matter integrity using both an automated tract-based and voxel-based methods.

Methods

Using a protocol matched to the NIH (Young-Adult) Human Connectome Project (and collected on the same customized ‘Connectom’ scanner), diffusion scans were acquired from 87 total participants (aged 18–30), grouped as SZ (n = 24), BD (n = 33) and healthy controls (n = 30). Fractional anisotropy (FA) of eighteen white matter tracks were analyzed using the TRACULA software. Voxel-wise statistical analyses of diffusion data was carried out using the tract-based spatial statistics (TBSS) software. TRACULA group effects and clinical correlations were investigated using analyses of variance and multiple regression.

Results

TRACULA analysis identified a trend towards lower tract FA in SZ patients, most significantly in the left anterior thalamic radiation (ATR; p = .04). TBSS results showed significantly lower FA voxels bilaterally within the cerebellum and unilaterally within the left ATR, posterior thalamic radiation, corticospinal tract, and superior longitudinal fasciculus in SZ patients compared to controls (FDR corrected p < .05). FA in BD patients did not significantly differ from controls using either TRACULA or TBSS. Multiple regression showed FA of the ATR as predicting chronic mania (p = .0005) and the cingulum-angular bundle as predicting recent mania (p = .02) in patients. TBSS showed chronic mania correlating with FA voxels within the left ATR and corpus callosum.

Conclusions

White matter abnormality in SZ varies in severity across different white matter tract regions. Our results indicate that voxel-based analysis of diffusion data is more sensitive than tract-based analysis in identifying such abnormalities. Absence of white matter abnormality in BD may be related to medication effects and age.

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Our study investigated white matter integrity in 87 young schizophrenia, bipolar disorder and control subjects with a tract-based (TRACULA) and a voxel-based (TBSS) approach, using high-definition diffusion imaging data obtained from the Human Connectome Project ‘Connectom’ scanner.

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TRACULA evaluated fractional anisotropy (FA) from 18 white matter tracts. TBSS evaluated regional white matter FA.

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TRACULA identified a trend towards lower tract FA in schizophrenia subjects across multiple tracts. TBSS results showed mainly unilaterally decreased FA voxels in schizophrenia subjects. FA in bipolar patients did not significantly differ from controls with either method.

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With TRACULA, multiple regression showed that anterior thalamic radiation FA predicted chronic affectivity and cingulum-angular bundle FA predicted recent mania in patients. With TBSS, chronic mania correlated with FA voxels within the left anterior thalamic radiation and corpus callosum.

Disruptions in White Matter Maturation and Mediation of Cognitive Development in Youths on the Psychosis Spectrum

BACKGROUND

Psychosis onset typically occurs in adolescence, and subclinical psychotic experiences peak in adolescence. Adolescence is also a time of critical neural and cognitive maturation. Using cross-sectional data from the Philadelphia Neurodevelopmental Cohort, we examined whether regional white matter (WM) development is disrupted in youths with psychosis spectrum (PS) features and whether WM maturation mediates the relationship between age and cognition in typically developing (TD) youths and youths with PS features.

METHODS

We examined WM microstructure, as assessed via diffusion tensor imaging, in 670 individuals (age 10-22 years; 499 TD group, 171 PS group) by using tract-based spatial statistics. Multiple regressions were used to evaluate age × group interactions on regional WM indices. Mediation analyses were conducted on four cognitive domains-executive control, complex cognition, episodic memory, and social cognition-using a bootstrapping approach.

RESULTS

There were age × group interactions on fractional anisotropy (FA) in the superior longitudinal fasciculus (SLF) and retrolenticular internal capsule. Follow-up analyses revealed these effects were significant in both hemispheres. Bilateral SLF FA mediated the relationship between age and complex cognition in the TD group, but not the PS group. Regional FA did not mediate the age-associated increase in any of the other cognitive domains.

CONCLUSIONS

Our results showed aberrant age-related effects in SLF and retrolenticular internal capsule FA in youths with PS features. SLF development supports emergence of specific higher-order cognitive functions in TD youths, but not in youths with PS features. Future mechanistic explanations for these relationships could facilitate development of earlier and refined targets for therapeutic interventions.

The development of brain white matter microstructure

Throughout infancy, childhood, and adolescence, our brains undergo remarkable changes. Processes including myelination and synaptogenesis occur rapidly across the first 2-3 years of life, and ongoing brain remodeling continues into young adulthood. Studies have sought to characterize the patterns of structural brain development, and early studies predominately relied upon gross anatomical measures of brain structure, morphology, and organization. MRI offers the ability to characterize and quantify a range of microstructural aspects of brain tissue that may be more closely related to fundamental neurodevelopmental processes. Techniques such as diffusion, magnetization transfer, relaxometry, and myelin water imaging provide insight into changing cyto- and myeloarchitecture, neuronal density, and structural connectivity. In this review, we focus on the growing body of literature exploiting these MRI techniques to better understand the microstructural changes that occur in brain white matter during maturation. Our review focuses on studies of normative brain development from birth to early adulthood (∼25 years), and places particular emphasis on longitudinal studies and newer techniques that are being used to study microstructural white matter development. All imaging methods demonstrate consistent, rapid microstructural white matter development over the first 3 years of life, suggesting increased myelination and axonal packing. Diffusion studies clearly demonstrate continued white matter maturation during later childhood and adolescence, though the lack of consistent findings in other modalities suggests changes may be mainly due to axonal packing. An emerging literature details differential microstructural development in boys and girls, and connects developmental trajectories to cognitive abilities, behaviour, and/or environmental factors, though the nature of these relationships remains unclear. Future research will need to focus on newer imaging techniques and longitudinal studies to provide more detailed information about microstructural white matter development, particularly in the childhood years.

Formal thought disorder is related to aberrations in language-related white matter tracts in patients with schizophrenia

This study examined the hypothesis that a fronto-temporal disconnection in the language network underpins formal thought disorder (FTD) in schizophrenia. Forty-nine patients with a schizophrenia spectrum disorder (27 with mild FTD, 22 with severe FTD) and 26 healthy controls (HC) were included. Overall psychopathology and FTD were assessed by the Positive and Negative Syndrome Scale and the Thought, Language, and Communication scale, respectively. White matter (WM) microstructure was analysed using Tract-Based Spatial Statistics. In patients, severity of overall FTD (TLC Sum Score) was predicted by decreased fractional anisotropy (FA) in the right superior longitudinal fasciculus (SLF), and severity of negative FTD (TLC Emptiness subscale) was predicted by increased FA in the left SLF and arcuate fasciculus (AF). Notably, these results were no longer significant after correction for multiple comparisons. Compared with HC, patients showed lower FA in all the investigated language-related WM tracts as well as across the whole WM skeleton. No difference in FA was found between patients with severe and patients with mild FTD. Our results are compatible with earlier studies reporting impairments in widely spread WM tracts including those related to language processing in patients with schizophrenia.

Avolition-Apathy and White Matter Connectivity in Schizophrenia: Reduced Fractional Anisotropy Between Amygdala and Insular Cortex

The avolition/apathy domain of negative symptoms includes motivation- and pleasure-related impairments. In people with schizophrenia, structural and functional abnormalities were reported in key regions within the motivational reward system, including ventral-tegmental area (VTA), striatum (especially at the level of the nucleus accumbens, NAcc), orbitofrontal cortex (OFC), as well as amygdala (Amy) and insular cortex (IC). However, the association of the reported abnormalities with avoliton-apathy is still controversial. In the present study, we investigated white matter connectivity patterns within these regions, using a probabilistic analysis of diffusion tensor imaging (DTI) data, in male subjects with schizophrenia. Thirty-five male subjects with schizophrenia (SCZ) and 17 male healthy controls (HC) matched for age, underwent DTI. SCZ were evaluated using the Schedule for Deficit Syndrome (SDS), the Positive and Negative Syndrome Scale (PANSS), and the MATRICS Consensus Cognitive Battery (MCCB). Probabilistic tractography was applied to investigate pathways connecting the Amy and the NAcc with the OFC and IC. Reduced fractional anisotropy (FA) was observed in left Amy-ventral anterior IC connections, in SCZ compared with controls. This abnormality was negatively correlated with avolition/apathy but not with expressive deficit scores. SCZ showed also a reduced connectivity index between right NAcc and medial OFC, as compared with controls. Finally, the left NAcc-dorsal anterior IC connectivity index was negatively correlated with working memory scores. Our results indicate that only the avolition/apathy domain of negative symptoms is related to abnormal connectivity in the motivation-related circuits. The findings also demonstrate that distinct alterations underlie cognitive impairment and avolition/apathy.

Is Schizophrenia a Disorder of Consciousness? Experimental and Phenomenological Support for Anomalous Unconscious Processing

Decades ago, several authors have proposed that disorders in automatic processing lead to intrusive symptoms or abnormal contents in the consciousness of people with schizophrenia. However, since then, studies have mainly highlighted difficulties in patients' conscious experiencing and processing but rarely explored how unconscious and conscious mechanisms may interact in producing this experience. We report three lines of research, focusing on the processing of spatial frequencies, unpleasant information, and time-event structure that suggest that impairments occur at both the unconscious and conscious level. We argue that focusing on unconscious, physiological and automatic processing of information in patients, while contrasting that processing with conscious processing, is a first required step before understanding how distortions or other impairments emerge at the conscious level. We then indicate that the phenomenological tradition of psychiatry supports a similar claim and provides a theoretical framework helping to understand the relationship between the impairments and clinical symptoms. We base our argument on the presence of disorders in the minimal self in patients with schizophrenia. The minimal self is tacit and non-verbal and refers to the sense of bodily presence. We argue this sense is shaped by unconscious processes, whose alteration may thus affect the feeling of being a unique individual. This justifies a focus on unconscious mechanisms and a distinction from those associated with consciousness.