Study findings suggest that (1) processing speed contributes to the association between white matter microstructure and working memory in schizophrenia and (2) white matter impairment in schizophrenia is regional tract-specific, particularly in tracts normally supporting processing speed performance.

Although schizophrenia is a brain disorder, increasing evidence suggests that there may be body-wide involvement in this illness. However, direct evidence of brain structures involved in the presumed peripheral-central interaction in schizophrenia is still unclear. Seventy-nine previously treatment-naïve first-episode schizophrenia patients who were within 2-week antipsychotics initial stabilization, and 41 age- and sex-matched healthy controls were enrolled in the study. Group differences in subcortical brain regional structures measured by MRI and the subclinical cardiovascular, metabolic, immune, and neuroendocrine biomarkers as indexed by allostatic load, and their associations were explored. Compared with controls, patients with schizophrenia had significantly higher allostatic load (P = .001). Lateral ventricle (P < .001), choroid plexus (P < .001), and thalamus volumes (P < .001) were significantly larger, whereas amygdala volume (P = .001) was significantly smaller in patients. The choroid plexus alone was significantly correlated with higher allostatic load after age, sex, education level, and the total intracranial volume were taken into account (t = 3.60, P < .001). Allostatic load was also significantly correlated with PANSS positive (r = 0.28, P = .016) and negative (r = −0.31, P = .008) symptoms, but in opposite directions. The peripheral multisystemic and central nervous system abnormalities in schizophrenia may interact through the choroid plexus during the early stage of the illness. The choroid plexus might provide a sensitive structural biomarker to study the treatment and prevention of brain-periphery interaction abnormalities in schizophrenia.

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Schizophrenia, a devastating psychiatric illness with onset in the late teens to early 20s, is thought to involve disrupted brain connectivity. Functional and structural disconnections of cortical networks may underlie various cognitive deficits, including a substantial reduction in the speed of information processing in schizophrenia patients compared with controls. Myelinated white matter supports the speed of electrical signal transmission in the brain. To examine possible neuroanatomical sources of cognitive deficits, we used a comprehensive diffusion-weighted imaging (DWI) protocol and characterized the white matter diffusion signals using diffusion kurtosis imaging (DKI) and permeability-diffusivity imaging (PDI) in patients (n = 74), their nonill siblings (n = 41), and healthy controls (n = 113). Diffusion parameters that showed significant patient-control differences also explained the patient-control differences in processing speed. This association was also found for the nonill siblings of the patients. The association was specific to processing-speed abnormality but not specific to working memory abnormality or psychiatric symptoms. Our findings show that advanced diffusion MRI in white matter may capture microstructural connectivity patterns and mechanisms that govern the association between a core neurocognitive measureprocessing speed-and neurobiological deficits in schizophrenia that are detectable with in vivo brain scans. These non-Gaussian diffusion white matter metrics are promising surrogate imaging markers for modeling cognitive deficits and perhaps, guiding treatment development in schizophrenia.diffusion-weighted imaging | schizophrenia | processing speed | cognitive deficits | endophenotypes A lthough pharmaceutical interventions alleviate clinical symptoms, such as delusions and hallucinations, for some patients, schizophrenia remains a debilitating illness, often times leading to long-term disabilities and severe cognitive deficits (1). Discovering the underlying neurobiology behind these core cognitive deficits in schizophrenia patients may present a viable strategy to identify biomarkers for supporting pathophysiology and comprehensive treatment research. Two decades of research have implicated impaired brain connectivity as a source of functional disability in schizophrenia (1, 2). Delayed information processing is one of the most robust cognitive deficits (3, 4) and may contribute to other cognitive impairments in working memory and executive function (4-6).Myelinated axons in the brain's white matter (WM) support its functionality by propagating electric signal transmissions through saltatory conductance (7,8). Reports of WM abnormalities in patients with schizophrenia are common and include reduced fractional anisotropy (FA) of water diffusion measured by diffusion tensor imaging (DTI) MRI (9-11) as well as reduced axonal myelin levels and glial cell density in postmortem brain studies (12)(13)(14). Identifying the key WM microstructural properties that explain the patient-control...

Schizophrenia is associated with abnormalities in the structure and functioning of white matter, but the underlying neuropathology is unclear. We hypothesized that increased tryptophan degradation in the kynurenine pathway could be associated with white matter microstructure and biochemistry, potentially contributing to white matter abnormalities in schizophrenia. To test this, fasting plasma samples were obtained from 37 schizophrenia patients and 38 healthy controls and levels of total tryptophan and its metabolite kynurenine were assessed. The ratio of kynurenine to tryptophan was used as an index of tryptophan catabolic activity in this pathway. White matter structure and function were assessed by diffusion tensor imaging (DTI) and 1 H magnetic resonance spectroscopy (MRS). Tryptophan levels were significantly lower (po0.001), and kynurenine/tryptophan ratios were correspondingly higher (p = 0.018) in patients compared with controls. In patients, lower plasma tryptophan levels corresponded to lower structural integrity (DTI fractional anisotropy) (r = 0.347, p = 0.038). In both patients and controls, the kynurenine/tryptophan ratio was inversely correlated with frontal white matter glutamate level (r = − 0.391 and − 0.350 respectively, p = 0.024 and 0.036). These results provide initial evidence implicating abnormal tryptophan/ kynurenine pathway activity in changes to white matter integrity and white matter glutamate in schizophrenia.