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One hypothesis proposed to underlie formal thought disorder (FTD), the incoherent speech is seen in some patients with schizophrenia, is that it reflects impairment in frontal/executive function. While this proposal has received support in neuropsychological studies, it has been relatively little tested using functional imaging. This study aimed to examine brain activations associated with FTD, and its two main factor-analytically derived subsyndromes, during the performance of a working memory task.
Seventy patients with schizophrenia showing a full range of FTD scores and 70 matched healthy controls underwent fMRI during the performance of the 2-back version of the n-back task. Whole-brain corrected, voxel-based correlations with FTD scores were examined in the patient group.
During 2-back performance the patients showed clusters of significant inverse correlation with FTD scores in the inferior frontal cortex and dorsolateral prefrontal cortex bilaterally, the left temporal cortex and subcortically in the basal ganglia and thalamus. Further analysis revealed that these correlations reflected an association only with ‘alogia’ (poverty of speech, poverty of content of speech and perseveration) and not with the ‘fluent disorganization’ component of FTD.
This study provides functional imaging support for the view that FTD in schizophrenia may involve impaired executive/frontal function. However, the relationship appears to be exclusively with alogia and not with the variables contributing to fluent disorganization.
Functional brain activity has been only studied marginally in schizoaffective disorder (SAD), a disorder whose nosological status is controversial. The present study investigated the prefrontal cortex (PFC) activity of schizomanic patients during performance of a working memory task.
13 schizoaffective patients, with current schizomanic episode (Young> 18); and 26 sex- and age-matched healthy controls underwent functional magnetic resonance imaging (fMRI) while performing baseline, 1-back and 2-back versions of the n-back task. Linear models were used to obtain maps of activations and deactivations in the groups.
During performance of the n-back task, controls showed activation in a cluster of frontal areas and de-activation in the medial orbitofrontal and anterior cingulate cortex. The SAD patients showed significantly less activation in prefrontal areas than the controls. They also showed a marked failure to de-activate in medial frontal cortex. The SAD patients’ impaired task performance was associated with both reduced activation of the dorsolateral PFC and reduced de-activation of the medial frontal areas.
Schizomanic patients show failure of activation in a network of cortical regions, and also a failure to de-activate the ventromedial PFC and anterior cingulate cortex. This latter area corresponds to the one of the components of the 'default mode network´. This pattern of abnormality is similar to that found by our group to characterise schizophrenia (failure to activate and failure to de-activate), but different from that which characterises manic patients (failure to de-activate only).
Social cognition has been associated with functional outcome in patients with first episode psychosis (FEP). Social cognition has also been associated with neurocognition and cognitive reserve. Although cognitive reserve, neurocognitive functioning, social cognition, and functional outcome are related, the direction of their associations is not clear. Therefore, the main aim of this study was to analyze the influence of social cognition as a mediator between cognitive reserve and cognitive domains on functioning in FEP both at baseline and at 2 years.
The sample of the study was composed of 282 FEP patients followed up for 2 years. To analyze whether social cognition mediates the influence of cognitive reserve and cognitive domains on functioning, a path analysis was performed. The statistical significance of any mediation effects was evaluated by bootstrap analysis.
At baseline, as neither cognitive reserve nor the cognitive domains studied were related to functioning, the conditions for mediation were not satisfied. Nevertheless, at 2 years of follow-up, social cognition acted as a mediator between cognitive reserve and functioning. Likewise, social cognition was a mediator between verbal memory and functional outcome. The results of the bootstrap analysis confirmed these significant mediations (95% bootstrapped CI (−10.215 to −0.337) and (−4.731 to −0.605) respectively).
Cognitive reserve and neurocognition are related to functioning, and social cognition mediates in this relationship.
Positive symptoms are a useful predictor of aggression in schizophrenia. Although a similar pattern of abnormal brain structures related to both positive symptoms and aggression has been reported, this observation has not yet been confirmed in a single sample.
To study the association between positive symptoms and aggression in schizophrenia on a neurobiological level, a prospective meta-analytic approach was employed to analyze harmonized structural neuroimaging data from 10 research centers worldwide. We analyzed brain MRI scans from 902 individuals with a primary diagnosis of schizophrenia and 952 healthy controls.
The result identified a widespread cortical thickness reduction in schizophrenia compared to their controls. Two separate meta-regression analyses revealed that a common pattern of reduced cortical gray matter thickness within the left lateral temporal lobe and right midcingulate cortex was significantly associated with both positive symptoms and aggression.
These findings suggested that positive symptoms such as formal thought disorder and auditory misperception, combined with cognitive impairments reflecting difficulties in deploying an adaptive control toward perceived threats, could escalate the likelihood of aggression in schizophrenia.
The global spread of non-tuberculous mycobacteria (NTM) may be due to HIV/AIDS and other environmental factors. The symptoms of NTM and tuberculosis (TB) disease are indistinguishable, but their treatments are different. Lack of research on the epidemiology of NTM infections has led to underestimation of its prevalence within TB endemic countries. This study was designed to determine the prevalence and clinical characteristics of pulmonary NTM in Bamako. A cross-sectional study which include 439 suspected cases of pulmonary TB. From 2006 to 2013 a total of 332 (76%) were confirmed to have sputum culture positive for mycobacteria. The prevalence of NTM infection was 9.3% of our study population and 12.3% of culture positive patients. The seroprevalence of HIV in NTM group was 17.1%. Patients who weighed <55 kg and had TB symptoms other than cough were also significantly more likely to have disease due to NTM as compared to those with TB disease who were significantly more likely to have cough and weigh more than 55 kg (OR 0.05 (CI 0.02–0.13) and OR 0.32 (CI 0.11–0.93) respectively). NTM disease burden in Bamako was substantial and diagnostic algorithms for pulmonary disease in TB endemic countries should consider the impact of NTM.
Relatively few studies have investigated whether relatives of patients with bipolar disorder show brain functional changes, and these have focused on activation changes. Failure of de-activation during cognitive task performance is also seen in the disorder and may have trait-like characteristics since it has been found in euthymia.
A total of 20 euthymic patients with bipolar disorder, 20 of their unaffected siblings and 40 healthy controls underwent functional magnetic resonance imaging during performance of the n-back working memory task. An analysis of variance (ANOVA) was fitted to individual whole-brain maps from each set of patient–relative–matched pair of controls. Clusters of significant difference among the groups were used as regions of interest to compare mean activations/de-activations between them.
A single cluster of significant difference among the three groups was found in the whole-brain ANOVA. This was located in the medial prefrontal cortex, a region of task-related de-activation in the healthy controls. Both the patients and their siblings showed significantly reduced de-activation compared with the healthy controls in this region, but the failure was less marked in the relatives.
Failure to de-activate the medial prefrontal cortex in both euthymic bipolar patients and their unaffected siblings adds to evidence for default mode network dysfunction in the disorder, and suggests that it may act as a trait marker.
Functional imaging studies in relatives of schizophrenic patients have had inconsistent findings, particularly with respect to altered dorsolateral prefrontal cortex activation. Some recent studies have also suggested that failure of deactivation may be seen.
A total of 28 patients with schizophrenia, 28 of their siblings and 56 healthy controls underwent functional magnetic resonance imaging during performance of the n-back working memory task. An analysis of variance was fitted to individual whole-brain maps from each set of patient–relative–matched pair of controls. Clusters of significant difference among the groups were then used as regions of interest to compare mean activations and deactivations among the groups.
In all, five clusters of significant differences were found. The schizophrenic patients, but not the relatives, showed reduced activation compared with the controls in the lateral frontal cortex bilaterally, the left basal ganglia and the cerebellum. In contrast, both the patients and the relatives showed significant failure of deactivation compared with the healthy controls in the medial frontal cortex, with the relatives also showing less failure than the patients. Failure of deactivation was not associated with schizotypy scores or presence of psychotic-like experiences in the relatives.
Both schizophrenic patients and their relatives show altered task-related deactivation in the medial frontal cortex. This in turn suggests that default mode network dysfunction may function as a trait marker for schizophrenia.
The subgenual anterior cingulate cortex (sgACC) is considered to be an important site of abnormality in major depressive disorder. However, structural alterations in this region have not been a consistent finding and functional imaging studies have also implicated additional areas.
A total of 32 patients with major depressive disorder, currently depressed, and 64 controls underwent structural imaging with MRI. Also, 26 patients and 52 controls were examined using functional magnetic resonance imaging (fMRI) during performance of the n-back working memory task. Structural and functional changes were evaluated using whole-brain, voxel-based methods.
The depressed patients showed volume reductions in the sgACC and orbitofrontal cortex bilaterally, plus in both temporal poles and the hippocampus/parahippocampal gyrus on the left. Functional imaging revealed task-related hypoactivation in the left lateral prefrontal cortex and other regions, as well as failure of deactivation in a subcallosal medial frontal cortical area which included the sgACC.
Whole-brain, voxel-based analysis finds evidence of both structural and functional abnormality in the sgACC in major depressive disorder. The fact that the functional changes in this area took the form of failure of deactivation adds to previous findings of default mode network dysfunction in the disorder.
Schizo-affective disorder has not been studied to any significant extent using functional imaging. The aim of this study was to examine patterns of brain activation and deactivation in patients meeting strict diagnostic criteria for the disorder.
Thirty-two patients meeting Research Diagnostic Criteria (RDC) for schizo-affective disorder (16 schizomanic and 16 schizodepressive) and 32 matched healthy controls underwent functional magnetic resonance imaging (fMRI) during performance of the n-back task. Linear models were used to obtain maps of activations and deactivations in the groups.
Controls showed activation in a network of frontal and other areas and also deactivation in the medial frontal cortex, the precuneus and the parietal cortex. Schizo-affective patients activated significantly less in prefrontal, parietal and temporal regions than the controls, and also showed failure of deactivation in the medial frontal cortex. When task performance was controlled for, the reduced activation in the dorsolateral prefrontal cortex (DLPFC) and the failure of deactivation of the medial frontal cortex remained significant.
Schizo-affective disorder shows a similar pattern of reduced frontal activation to schizophrenia. The disorder is also characterized by failure of deactivation suggestive of default mode network dysfunction.
Deficits in memory and executive performance are well-established features of bipolar disorder and schizophrenia. By contrast, data on cognitive impairment in schizoaffective disorder are scarce and the findings are conflicting.
We used the Wechsler Memory Scale (WMS-III) and the Behavioural Assessment of the Dysexecutive Syndrome (BADS) to test memory and executive function in 45 schizophrenic patients, 26 schizomanic patients and 51 manic bipolar patients in comparison to 65 healthy controls. The patients were tested when acutely ill.
All three patient groups performed significantly more poorly than the controls on global measures of memory and executive functioning, but there were no differences among the patient groups. There were few differences in memory and executive function subtest scores within the patient groups. There were no differences in any test scores between manic patients with and without psychotic symptoms.
Schizophrenic, schizomanic and manic patients show a broadly similar degree of executive and memory deficits in the acute phase of illness. Our results do not support a categorical differentiation across different psychotic categories with regard to neuropsychological deficits.
It is not known whether first-episode psychosis is characterized by the same prefrontal cortex functional imaging abnormalities as chronic schizophrenia.
Thirty patients with a first episode of non-affective functional psychosis and 28 healthy controls underwent functional magnetic resonance imaging (fMRI) during performance of the n-back working memory task. Voxel-based analyses of brain activations and deactivations were carried out and compared between groups. The connectivity of regions of significant difference between the patients and controls was also examined.
The first-episode patients did not show significant prefrontal hypo- or hyperactivation compared to controls. However, they showed failure of deactivation in the medial frontal cortex. This area showed high levels of connectivity with the posterior cingulate gyrus/precuneus and parts of the parietal cortex bilaterally. Failure of deactivation was significantly greater in first-episode patients who had or went on to acquire a DSM-IV diagnosis of schizophrenia than in those who did not, and in those who met RDC criteria for schizophrenia compared to those who did not.
First-episode psychosis is not characterized by hypo- or hyperfrontality but instead by a failure of deactivation in the medial frontal cortex. The location and connectivity of this area suggest that it is part of the default mode network. The failure of deactivation seems to be particularly marked in first-episode patients who have, or progress to, schizophrenia.
Functional imaging studies using working memory tasks have documented both prefrontal cortex (PFC) hypo- and hyperactivation in schizophrenia. However, these studies have often failed to consider the potential role of task-related deactivation.
Thirty-two patients with chronic schizophrenia and 32 age- and sex-matched normal controls underwent functional magnetic resonance imaging (fMRI) scanning while performing baseline, 1-back and 2-back versions of the n-back task. Linear models were used to obtain maps of activations and deactivations in the groups.
The controls showed activation in the expected frontal regions. There were also clusters of deactivation, particularly in the anterior cingulate/ventromedial PFC and the posterior cingulate cortex/precuneus. Compared to the controls, the schizophrenic patients showed reduced activation in the right dorsolateral prefrontal cortex (DLPFC) and other frontal areas. There was also an area in the anterior cingulate/ventromedial PFC where the patients showed apparently greater activation than the controls. This represented a failure of deactivation in the schizophrenic patients. Failure to activate was a function of the patients' impaired performance on the n-back task, whereas the failure to deactivate was less performance dependent.
Patients with schizophrenia show both failure to activate and failure to deactivate during performance of a working memory task. The area of failure of deactivation is in the anterior prefrontal/anterior cingulate cortex and corresponds to one of the two midline components of the ‘default mode network’ implicated in functions related to maintaining one's sense of self.
Microelectromechanical systems (MEMS) are being used in many critical applications that require very high stress levels. To properly design MEMS components, mechanical properties should be characterized testing relevant sized samples that are fabricated with the same procedures as the final structure. In this paper we use atomic force microscopy (AFM) experiments to study the fracture strength statistics of polycrystalline SiC and SiN nanobeams, and compare their mechanical performance with the performance of previously tested Si nanostructures. Using the same AFM method and similar sample shape and sizes, allows a direct comparison to be made, which will be useful in determining the best material for different mechanical applications and also to validate the theoretical limits.
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