The present study examined the integrity of the P300 component of the event-related potential (ERP) in patients at high imminent risk for schizophrenia in relation to healthy comparison subjects and ...patients in the recent-onset and chronic stages of schizophrenia.
The P300 was recorded by using an auditory oddball task in 10 patients clinically considered at risk of being prodromally symptomatic for schizophrenia, 10 patients with recent-onset schizophrenia, 14 patients with chronic schizophrenia, 14 young healthy comparison subjects, who were age-matched to the high-risk and recent-onset schizophrenia groups, and 14 older healthy comparison subjects, who were age-matched to the chronic schizophrenia group.
High-risk subjects displayed smaller than normal P300 amplitudes at the parietal, centroparietal and central scalp locations. The observed P300 amplitude abnormalities in high-risk subjects were severe, being comparable in magnitude to the abnormalities seen in recent-onset and chronic schizophrenia subjects. However, whereas high-risk subjects showed P300 amplitude abnormalities that were bilaterally symmetrical, subjects with recent-onset schizophrenia and, particularly, subjects with chronic schizophrenia exhibited abnormalities that were markedly larger over the left temporal scalp sites.
Patients at high imminent risk for developing a first florid psychotic episode seem to manifest auditory P300 amplitude abnormalities that are similar, but not identical, to those observed in patients in the recent-onset and chronic stages of schizophrenia. These results support the idea that auditory P300 abnormalities in schizophrenia reflect a primary cognitive and pathophysiological feature of the illness.
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.
By subtracting of gray matter maps from opposing hemispheres of the brain, independent component analysis of structural imaging data may identify covarying components across hemispheres, designated as source‐based laterality. The loading coefficients from components can then be utilized to assess hemispheric differences between brain regions. Comparing laterality‐based components between participants with and without schizophrenia revealed three temporal and one cerebellar region where brain volume is altered across hemispheres.
: An analysis of all pediatric cadaveric renal transplant recipients in the UK and Eire was undertaken to review the outcomes of pediatric cadaveric renal transplantation and to consider the ...implications for organ allocation procedures for pediatric recipients. Factors influencing the outcome of 1,252 pediatric cadaveric renal transplants in the UK and Eire in the 10‐yr period from 1 January 1986 to 31 December 1995 were analyzed by Cox proportional hazards regression, including analysis of four distinct post‐transplant epochs (0–3 months, 3–12 months, 12–36 months, and beyond 36 months). At the time of analysis (December 2000), 113 (11%) recipients had died and 47% of grafts had failed. In the multi‐factorial modelling, the factors significantly affecting transplant outcome were cold ischaemia time, donor and recipient age and human leucocyte antigen (HLA) matching. Epoch analysis demonstrated that these factors operated at different times post‐transplant. Cold ischaemia time had a strong influence on outcome at 3 months. A highly significant increased risk of graft failure was associated with donors under 5 yr of age. Young recipients had an increased risk of failure in the short term, but beyond 1 yr post‐transplant there were few failures in young recipients while a steady rate of graft loss persisted in the older children. In terms of HLA matching, the worst outcome was observed for two HLA‐DR mismatched grafts, while 000 and favorably matched kidneys (100, 010, 110 HLA‐A, ‐B, ‐DR mismatches) survived longest. Hence, a policy of exchanging organs on the basis of HLA matching is justified for 000 mismatched and favorably matched kidneys. The poor outcome associated with very young donors should discourage pediatric units from transplanting kidneys from such young donors. The reasons for late losses in older recipients need investigation.
A broad definition of sensory gating refers to the ability of the brain to modulate its sensitivity to incoming sensory stimuli. This definition allows the concept of gating to include both the ...capacities to minimize or stop responding to incoming irrelevant stimuli (gating out) and to re-respond when a novel stimulus is presented or a change occurs in ongoing stimuli (gating in). In order to further characterize the function of sensory gating, we examined the attenuation (decreased responding) and augmentation (increased responding) of the P50 EP amplitudes in 22 normal volunteers. Three EP paradigms, each including a number of conditions, designed to examine both EP habituation (inhibition) and dishabituation (excitation) were administered to each subject. In conditions designed to examine habituation (identical pairs of clicks or trains of repetitive identical clicks), the P50 behaved, as expected, with decrease of the amplitude with repetition. In conditions designed to examine dishabituation the amplitude of the P50, EP did not decrease as much (and frequently increased) with stimulus change. The results suggest that the P50 EP is sensitive to the effects of stimulus repetition and stimulus change and can be used to study the different aspects of sensory gating.
Previous studies suggested that auditory change-specific neural responses are attention-independent and reflect central auditory processing. The automaticity of the brain's response to infrequent ...changes in pitch within a series of auditory tone pips was examined in parallel functional magnetic resonance imaging (fMRI) and event-related potential (ERP) studies. Subjects performed a continuous perceptual-motor visual tracking task at two levels of difficulty while simultaneously hearing a series of task-irrelevant standard tone pips and infrequent pitch-deviant tones. fMRI results revealed that the unattended pitch-deviant tones strongly activated superior temporal and frontal cortical regions. These activations were significantly modulated by the tracking difficulty of the primary task. ERP results revealed that the amplitude of the scalp-negative component evoked by deviant tones (MMN) was attenuated during the more difficult tracking task. Our results demonstrate that the brain's response to task-irrelevant sensory changes is strongly influenced by intermodal attentional demands.
Turner syndrome is a genetic disorder that results from an abnormal or missing X chromosome in females and is typically associated with impairments in visuospatial, but not verbal, information ...processing. These visuospatial processing impairments may be exacerbated with increased task demands, such as those engaged during working memory (WM). While previous studies have examined spatial WM function in Turner syndrome, none have directly compared the neural correlates of spatial and verbal WM processes across the encoding, maintenance and retrieval phases. We employed both neurocognitive assessments and functional MRI (fMRI) to examine the neural circuitry underlying both verbal and visuospatial WM functions in individuals with Turner syndrome and normal controls. We furthermore examined the vulnerability of task-related fMRI activation to distracters presented during WM maintenance. Fifteen healthy female volunteers and eight individuals with Turner syndrome performed a delayed-response WM task during fMRI scanning. Neurocognitive tests revealed impaired performance across both verbal and spatial domains in Turner syndrome, with greater impairment on tasks with WM demands. Frontoparietal regions in controls showed significantly sustained levels of activation during visuospatial WM. This sustained activation was significantly reduced in the group with Turner syndrome. Domain-specific activation of temporal regions, in contrast, did not differ between the two groups. Sensory distraction during the WM maintenance phase did not differentially alter frontoparietal activation between the two groups. The results reveal impaired frontoparietal circuitry recruitment during visuospatial executive processing in Turner syndrome, suggesting a significant role for the X chromosome in the development of these pathways.
The ability to generate appropriate behaviors in response to changing situations requires both the alteration of ongoing behavior and the understanding of the global rules governing stimulus ...categorization in a given context. Neuropsychological tests that have been developed to measure this form of cognitive flexibility, such as the Wisconsin Card Sorting Test, have reliably demonstrated that individuals with lesions in regions of the prefrontal cortex and basal ganglia have difficulty generating a cognitive set and altering rule-governed behavior. Recent neuroimaging studies have supported the role of these brain regions in the performance of response shifting and cognitive set shifting. However, the precise role of these regions in the individual components of these tasks remains a contentious issue. Here, we used event-related functional magnetic resonance imaging (fMRI) to dissociate the neural circuitry involved in the alteration of ongoing behavior and the shifting of cognitive set. Participants viewed geometric shapes as they appeared individually in rapid succession and responded with an appropriate button press based upon whether the individual shape was a predetermined target stimulus. Responses were required for each shape presented. The fMRI results indicated that response shifting specifically activated a dorsal neural circuit comprised of the dorsolateral prefrontal cortex, anterior cingulate, and intraparietal sulcus. Shifts in cognitive set were mediated by ventrolateral prefrontal cortex, anterior cingulate, and striatum. These findings suggest that the alteration of ongoing behavior and shifting of cognitive set are mediated by two distinct neural systems interconnected by the anterior cingulate.
Crystallisation and annealing behaviour of two caesium borosilicate glass samples with approximate boroleucite composition were characterised by means of differential scanning calorimetry ...measurements as well as X-ray powder diffraction investigations with subsequent profile fitting of the observed patterns according to the Rietveld and/or Pawley method. While one sample crystallised primarily in an orthorhombic phase (
= 6.592(3) Å,
= 11.825(5) Å,
= 12.620(6) Å; possible space groups:
((26), setting:
),
2 (28) and
((51), setting:
)) which has been unknown until now and transformed irreversibly into the well-known cubic boroleucite phase at
≈ 850 °C, cubic caesium boroleucite (space group:
3̅
(230)) was crystallised directly from the other sample. In this case, the orthorhombic phase was metastable. At the onset temperature of glass crystallisation
= 770 °C, it existed only for about 75 min. The change of the lattice parameter
of the cubic unit cell of caesium boroleucite in the course of the thermal treatments was explained by the alteration of the size of the TO
tetrahedra (T = Si, B).
PDF
