Biomedical subjects

Lukas Scheef

Publications and source records attributed to Lukas Scheef.

6 recordsLinked to original sources

PubMed2005

Volume reduction of the entorhinal cortex in subjective memory impairment.

To examine the biological basis of subjective memory impairment (SMI), defined as the feeling of memory worsening with normal memory performance, we measured the volume of the entorhinal cortex (EC) and the hippocampus in SMI subjects, patients with mild cognitive impairment (MCI), patients with Alzheimer's disease (AD) and healthy controls (CO). Compared with controls, the EC was smaller in the SMI group (left: p=0.060; right: p=0.045) and in the other two groups in the following order: CO>SMI>MCI>AD. The same sequence was observed with regard to hippocampal volumes, but the volume reduction of the left hippocampus in the SMI group only reached a trend towards significance (p=0.072) and the right was not significantly smaller compared with controls (p=0.37). Compared with controls the average (left/right) volume reduction of the EC was 18% (SMI), 26% (MCI) and 44% (AD). The mean volume reduction of the hippocampus was 6% (SMI), 16% (MCI) and 19% (AD). Our results mirror the temporal sequence of neurodegeneration in AD and support the concept of SMI as the first clinical manifestation of dementia.

Aged↗

PubMed2005

Functional 3.0-T MR assessment of higher cognitive function: are there advantages over 1.5-T imaging?

PURPOSE: To compare cortical activation patterns associated with manual motor decision tasks at 1.5- and 3.0-T functional magnetic resonance (MR) imaging. MATERIALS AND METHODS: The local ethics committee approved this study, and informed written consent was obtained. Ten right-handed healthy volunteers (eight men and two women; mean age, 35 years +/- 7 [standard deviation]) underwent functional MR imaging twice, once at 1.5 T and once at 3.0 T, while performing cognitive tasks that demanded manual motor decisions (letter-finger matching and lexical and semantic decisions). While stimulus presentation was blocked, an event-related model was employed to analyze subjects' individual responses. A group analysis of functional data was performed with a t test of 1.5- and 3.0-T results in the 10 subjects. RESULTS: Manual motor decisions activated a widespread network of motor- (primary motor, posterior parietal) and decision-related areas (superior frontal cortex or anterior cingulate) at both field strengths (P <.05, corrected). Moreover, additional functional activation was detected in medial (supplementary motor area) and dorsal premotor regions (P <.05, corrected) at 3.0-T functional MR imaging, which was not detectable with corresponding 1.5-T imaging. The mean t value for peak voxels in activated areas detectable with both systems was 1.3 times larger at 3.0 T than that at 1.5 T. CONCLUSION: Functional 3.0-T MR imaging allows detection of additional activation in cortical areas involved in higher executive motor functions compared with functional 1.5-T MR imaging.

Adult↗

PubMed2005

Mediotemporal contributions to semantic processing: fMRI evidence from ambiguity processing during semantic context verification.

The medial temporal lobe (MTL) is well known to be crucial for various types of memory; however, controversy remains as to which of its substructures contribute to semantic processing and, if so, to what extent. The current study addresses the issue of MTL contributions to semantic processing during lexico-semantic ambiguity processing by using functional magnetic resonance imaging (fMRI) in combination with a context verification task (CVT). The CVT required decisions on the semantic fit of congruent and incongruent target words to the overall meaning of preceding sentential contexts with and without semantic ambiguity. In two of the four experimental conditions (congruent homographic, incongruent homographic), target decisions were critically dependent on the successful processing of prior sentence-final lexico-semantic ambiguity. Semantic context verification per se evidenced bilateral activations of the hippocampus that were part of a functional network including inferior prefrontal and superior parietal cortices. Commonalities in activation differences pertaining to the specific cognitive component of lexico-semantic ambiguity processing were found in a left temporal lobe network that comprised activation foci in the temporal pole, the parahippocampal and fusiform gyri. The present results suggest that the hippocampus may well contribute to semantic processing, namely by a mnemonic function that serves to link the target meaning representation with the meaning of a prior sentence context. Contrary to previous reports from human lesion studies, the present findings further suggest, that the specific cognitive component of lexico-semantic ambiguity processing is neither dependent on the hippocampus nor exclusively subserved by the temporal pole, but also recruits an associative semantic memory function from the parahippocampal gyrus as well as a more general (bottom-up) semantic function from the fusiform gyrus.

Adult↗

PubMed2003

Reduced hippocampal activation during encoding and recognition of words in schizophrenia patients.

OBJECTIVE: In patients with schizophrenia, impaired hippocampal activation either during encoding or recognition tasks has been observed in a few functional imaging experiments. In this fMRI study, the authors report results of word encoding and recognition in schizophrenia patients and healthy comparison subjects, with a special focus on correcting for behavioral recognition success in order to prevent a bias related to lower task performance in the schizophrenia patients. METHOD: The verbal encoding and recognition tasks were both first analyzed irrespective of recognition success. In a second analysis, recognition success was included in the block-designed encoding task as a covariate of no interest, and incorrectly classified items were rejected from the analysis of the event-related recognition task. RESULTS: Patients performed poorer on the recognition task than the comparison subjects. Bilateral hippocampal activation during encoding and recognition was observed in both groups. Right hippocampal activation in patients during recognition became significant only after exclusion of wrongly classified items. Group comparison revealed greater activation in the healthy comparison subjects in the left anterior hippocampus during encoding and bilaterally during recognition. Greater bilateral hippocampal activation in the healthy subjects and greater activation in the right anterior hippocampus in the schizophrenic patients were revealed after presentation of novel words, which were intermixed with previously encoded words in the recognition task. After exclusion of incorrectly classified items, the differences in the right hippocampus remained significant. CONCLUSIONS: This study provides evidence for disturbed hippocampal function during verbal encoding and recognition in patients with schizophrenia. It extends previous studies by correcting for the possible confound of differences in behavioral task performance. This approach further supports the concept of hippocampal dysfunction in schizophrenia.

Adult↗

PubMed2002

Novelty detection and repetition suppression in a passive picture viewing task: a possible approach for the evaluation of neuropsychiatric disorders.

The applicability of functional magnetic resonance imaging (fMRI) in patients with Alzheimer's disease (AD) or schizophrenia is frequently limited by cognitive impairment, which prevents the adequate execution of complex tasks. An experimental design that puts only minor demands on the patients' cognitive ability but engages disease-relevant brain structures would be of benefit. Novelty detection and repetition suppression are two basic components of memory that might be used to investigate specific brain areas under these conditions. Novelty detection has been related to hippocampal activation increases. Stimulus repetition related activation decreases (suppression) have been observed in the extrastriate cortex and have been related to perceptual priming. Both processes have been examined primarily in neuroimaging studies with complex cognitive tasks. We used event-related fMRI to investigate novelty- and repetition-related effects in an attended but passive picture-viewing task in healthy subjects. The differential activation, detected in the novel vs. repeated contrast, was located in the bilateral anterior hippocampus and in bilateral occipital and inferior-temporal areas. The hippocampal activation is of interest because medial temporal lobe lesions are key features in AD and schizophrenia. The repetition-related activation decreases in the extrastriate areas are of potential value in investigating the conflicting results regarding perceptual priming impairment in both disorders. Our results indicate that activation of disease-relevant brain regions under passive task conditions is possible. This might increase the utility of functional imaging in cognitively impaired patients.

Adult↗

PubMedDate not supplied

Curved-surface projection: an alternative method for visualizing functional MR imaging results.

Curved-surface projection (CSP) is a new technique for visualizing functional MR imaging data. This technique helps in identifying anatomic structures by demonstrating the whole gyral and sulcal pattern of the brain at once. Compared with other techniques, CSP preserves the spatial relation of eloquent areas to lesions. Especially in neurosurgical patients with space-occupying lesions, CSP helps in assigning the anatomy to its function.

Astrocytoma↗