Biomedical subjects

Ralf Schlösser

Publications and source records attributed to Ralf Schlösser.

7 recordsLinked to original sources

PubMed2006

Neural correlates of working memory dysfunction in first-episode schizophrenia patients: an fMRI multi-center study.

Working memory dysfunction is a prominent impairment in patients with schizophrenia. Our aim was to determine cerebral dysfunctions by means of functional magnetic resonance imaging (fMRI) in a large sample of first-episode schizophrenia patients during a working memory task. 75 first-episode schizophrenia patients and 81 control subjects, recruited within a multi-center study, performed 2- and 0-back tasks while brain activation was measured with fMRI. In order to guarantee comparability between data quality from different scanners, we developed and adopted a standardized, fully automated quality assurance of scanner hard- and software as well as a measure for in vivo data quality. After these quality-control measures had been implemented, 48 patients and 57 controls were included in the final analysis. During attention-related processes, even when the performance between patients and controls was comparable, there was a recognizable emergence of cerebral dysfunctions with hypoactivations in the ventrolateral prefrontal cortex (VLPFC), in the superior temporal cortex and in the thalamus. During working memory performance, parietal hypoactivations, especially in the precuneus, were prominent and were accompanied by poorer performance in patients. A hyperfrontality emerged in the ventrolateral prefrontal cortex. Hence, results point to a dysfunctional ventrolateral prefrontal-parietal network during working memory in patients, suggesting impairments in basic functions such as retrieval, storage and maintenance. The brain activation pattern of this large and significant sample of first-episode schizophrenia patients indicates an imbalanced system failing to adjust the amount of brain activity required in the cerebral network involved in attention and working memory.

Adolescent↗

PubMed2006

Temporal changes in neural activation during practice of information retrieval from short-term memory: an fMRI study.

Several findings indicate that practice in working memory tasks leads to signal decreases in task-relevant regions. However, the precise dynamics underlying these signal decreases and how they are correlated with improvements in behavioral performance are still matters of debate. We used functional magnetic resonance imaging (fMRI) to assess the cerebral correlates of the practice-related transition from controlled to automatic processing for the retrieval of information maintained in working memory storage. Exponential signal decreases and increases were modeled as covariates of interest. In addition, a bivariate regression analysis on the change in BOLD signal for two a priori hypothesized prefrontal regions (VLPFC, DLPFC) and the change in behavioral performance was conducted to examine the relationship between practice-related changes in cerebral activation and performance. We found exponential practice-related signal decreases mainly in the right superior frontal gyrus/DLPFC (BA 8/9/46), the middle frontal gyrus bilaterally (BA 10/11), the left precentral gyrus (BA 4/6) and the dorsal part of the right anterior cingulate cortex (BA 32). An exponential signal increase was detectable in the posterior cingulate cortex adjacent to the corpus callosum. In addition, there was a correlation between the practice-related change in BOLD signal in the DLPFC (BA 8/9) and the practice-related change in behavioral performance. These results suggest that the transition from controlled to automatic working memory processing is associated with exponential signal decreases in task-relevant regions. The temporal changes in brain activation patterns could be attributed to enhanced efficiency of information processing as a result of cognitive practice.

Adult↗

PubMed2003

Altered effective connectivity in drug free schizophrenic patients.

The present fMRI study aimed to investigate effective connectivity within a cortical-subcortical-cerebellar information processing network in drug free schizophrenic patients while performing a 2-back working memory task. The finding of enhanced thalamo-cortical and cortico-cortical intrahemispheric connectivity could be interpreted as a compensatory increase of neuronal connection strength consistent with a model of cortical inefficiency in schizophrenic patients. Additionally, the result could be integrated into a model of deficient thalamo-cortical filter functions. Conversely, lower interhemispheric connectivity of the frontal and parietal association cortex appears to be the functional correlate of reduced cognitive performance in schizophrenic patients. The study demonstrated the feasibility to model information processing within cognitive networks and provided additional evidence for the concept of cognitive dysmetria in schizophrenia.

Adult↗

PubMed2003

Altered effective connectivity during working memory performance in schizophrenia: a study with fMRI and structural equation modeling.

The present study aimed to explore altered effective connectivity in schizophrenic patients while performing a 2-back working memory task. Twelve right-handed, schizophrenic patients treated with typical or atypical antipsychotics and 6 healthy control subjects were studied with fMRI while performing a "2-back" working memory task. Effective connectivity within a cortical-subcortical-cerebellar network for mnemonic information processing was assessed and compared between both groups. The path model included cortico-cortical connections comprising the parietal association cortex, ventrolateral prefrontal cortex (VLPFC), and the dorsolateral prefrontal cortex (DLPFC) as well as a cortico-cerebellar feedback loop comprising prefrontal cortex, contralateral cerebellum, and thalamus. Group differences were analyzed with a stacked models approach. Relative to normal controls, both patient groups revealed a pattern of reduced connectivity within the prefrontal-cerebellar and the cerebellar-thalamic limbs but enhanced connectivity in the thalamo-cortical limb of the cortical-cerebellar circuit. Moreover, a direct comparison of both treatment groups revealed enhanced connectivity in the interhemispheric connections between the cortical association areas in patients treated with atypical antipsychotics. However, right prefrontal and left parieto-frontal path coefficients were lower in the patient group receiving atypical antispychotic drugs. The findings suggest that the relationship between pathology in cortical-subcortical cerebellar networks and associated functional connectivity is complex and may include aspects of increased and decreased levels of connectivity consistent with the notion of "cognitive dysmetria" in schizophrenia. The observed pronounced connectivity within thalamo-cortical projections could be attributed to a compensatory increase of thalamic input in the presence of disrupted effective connectivity within the preceding limb of the cortical-cerebellar circuitry. The study demonstrated the feasibility of structural equation modeling for the investigation of group and treatment-related differences in effective connectivity and provides a promising approach to further disentangle the relationship between altered functional capacity and associated fMRI signal changes.

Adult↗

PubMed2003

Association of an interleukin-1beta gene polymorphism at position -511 with Alzheimer's disease.

Inflammation is thought to promote neuronal cell death in Alzheimer's disease (AD). The proinflammatory interleukin-1 is a main component in inflammatory pathways and is overexpressed in the brain of AD patients. Investigation of different polymorphisms in the interleukin-1 genes (IL-1alpha -889, IL-1beta -511, IL-1beta +3953) revealed associations between specific alleles and AD in that they increased the risk or modified the age at onset of AD. However, there are controversial findings from other studies which revealed no significant associations between these polymorphisms and AD; thus further evaluation of the association of IL-1 gene polymorphisms with AD and their role in pathogenesis is needed. In this study we examined the distribution of the IL-1beta -511 alleles in AD patients and a control sample of healthy individuals. An additional control population of non-demented depressive inpatients was recruited to exclude a confounding bias. The cerebrospinal fluid (CSF) levels of Abeta42 in AD patients were investigated to assess the influence of IL-1beta -511 genotypes. We found no significant association of the IL-1beta -511 polymorphism with AD, suggesting that the IL-1beta -511 polymorphism is no risk factor for AD. However, we found the Abeta42 CSF levels to be lower in carriers of the IL-1beta CC-genotype compared to carriers of the T-allele. Even though IL-1beta -511 polymorphism did not influence the risk of AD it might have a pathophysiological influence on the disease process.

Aged↗

PubMed2002

Characterization of BOLD-fMRI signal during a verbal fluency paradigm in patients with intracerebral tumors affecting the frontal lobe.

Previous studies have indicated that the BOLD-fMRI signal can be modified by tumor processes in close vicinity to functional brain areas. This effect has been investigated primarily for the perirolandic area but there is only a limited number of studies concerning frontal cortical regions. Therefore, the aim of the current study was to characterize BOLD-fMRI signal and activation patterns in patients with frontal brain tumors while performing a verbal fluency task. Six patients (ages 31-56 years) suffering from frontal (5 left sided and 1 right sided) intracerebral tumors were examined with fMRI while performing a verbal fluency task in a blocked paradigm design. Eight healthy volunteers served as the control group. The patients (5 right and 1 left handed) demonstrated left frontal activation which could be clearly located outside the tumor area and adjacent edema with varying degrees of additional right frontal activation. In the predominant left frontal activation cluster, the mean voxel based z-score and cluster size were not statistically different between patients and controls. The present fMRI study is indicating that language related BOLD signal changes in the frontal cortex of patients with tumors close to functional areas were comparable to the signal in normal controls. Additionally, the temporal hemodynamic response characteristic was comparable in both groups. This is an important finding consistent with PET results and corroborates the feasibility of functional mapping approaches in patients with tumors affecting the frontal lobe. Additional studies investigating alterations of the hemodynamic response depending on tumor location and histology are required in order to further elucidate the association between pathophysiology and BOLD fMRI signal.

Adult↗

PubMed2002

Patients' satisfaction with psychiatric treatment: comparison between an open and a closed ward.

The study compared patients' satisfaction with psychiatric inpatient treatment between an open and a closed ward. During a six-month period, all voluntarily participating patients on two wards of a psychiatric University hospital were investigated anonymously at admission and/or before discharge. A self-rating questionnaire (SATQ-98) was used to assess satisfaction with several domains of psychiatric inpatient treatment. In total, 135 questionnaires were received (retrieval rate 49%). The general level of satisfaction with treatment was high. General satisfaction, satisfaction with medication, ward equipment, visiting opportunities, and regulations for going out were significantly lower at discharge on the closed ward. Dissatisfaction with medication was related to low actual mood, and to low satisfaction with the frequency of psychotherapeutic interventions, visiting opportunities, and with the treating doctor. The results thus far strongly support the need for patients' satisfaction with treatment to be taken into account in order to improve psychiatric inpatient services, particularly on closed wards.

Adult↗