Biomedical subjects

Claus Tempelmann

Publications and source records attributed to Claus Tempelmann.

10 recordsLinked to original sources

PubMed2006

Age-related water diffusion changes in human brain: a voxel-based approach.

The aim of the present study is to investigate age-related changes in water self-diffusion in cerebral white matter by analysing diffusion-weighted MRI from a sample of 54 healthy volunteers. A voxel-based analysis of the relative anisotropy and the apparent diffusion coefficients was performed by applying an optimized normalization protocol. Linear regression analysis revealed significant correlations with age in the corpus callosum, prefrontal regions, the internal capsule, the hippocampal complex, and the putamen. However, in other regions, such as those surrounding the ventricles, the insula, or the inferior frontal plane, significant correlations between age and ADC were observed, presumably as a result of morphological age-related variations. A mask procedure was carried out in order to distinguish between morphological involvement and real age-related white matter changes. Our results indicate that in interpreting the changes in each significant region it is necessary to proceed with precaution because the voxel-based statistical analysis might yield a mixture of two effects: (i) morphological changes that remain after the normalization procedure and (ii) actual diffusivity parameter changes. Anatomically defined regions of interest may help us to minimize morphologic involvement and draw comparisons with findings previously published.

Adult↗

PubMed2006

Determining language laterality by fMRI and dichotic listening.

For imaging studies on hemispheric specialization of the human brain, data about known functional asymmetries other than handedness would be valuable for a reliable interpretation of lateralized activation in individuals or groups of subjects. As certain aspects of language processing are observed to be a function of primarily the left, it can be used as a reference for other asymmetric processes such as sensory or cognitive skills. For analyzing language laterality, there are a variety of methods, but these differ in application or accuracy. In this study, we tested the reliability of two widely used methods - dichotic listening and fMRI - to determine language dominance in 30 individual subjects. The German adaptation of a dichotic listening test (Hättig, H., Beier, M., 2000. FRWT: a dichotic listening test for clinical and scientific contexts, Zeitschr f Neuropsychologie 11. 233-245.) classified 54% of the 26 right-handed subjects as left hemispheric dominant. The results of the fMRI paradigm (Fernández, G., de Greiff, A., von Oertzen, J., et al., 2001. Language mapping in less than 15 min: real-time functional MRI during routine clinical investigation. Neuroimage 14, 585-594.) tested on the same subjects, however, classified 92% of the right-handed subjects as left dominant. The main reason for this discrepancy was that the ear dominance score of many subjects in the dichotic listening test was too low to determine a reliable ear advantage. As a consequence, this specific dichotic listening test cannot be used to determine language laterality in individual subjects. On the other hand, the fMRI results are consistent with numerous studies showing left dominant language processing in more than 90% of right-handers. In some subjects, however, language laterality critically depends on the areas used to determine the laterality index.

Acoustic Stimulation↗

PubMed2006

Endoscopic eye tracking system for fMRI.

Here we introduce a new video-based real-time eye tracking system suitable for functional magnetic resonance imaging (fMRI) application. The described system monitors the subject's eye, which is illuminated with infrared light, directly at the headcoil using an endoscopic fibre optical system. This endoscopic technique assures reliable, easy-to-use and fast adjustment. It requires only a minimal amount of equipment at the headcoil and inside the examination room. Moreover, the short distance between the image acquisition optics and the eye provides high spatial tracking resolution. Interference from physiological head movement is effectively reduced by simultaneous tracking of both eye and head movements.

Computer Systems↗

PubMed2004

Eddy current correction in diffusion-weighted imaging using pairs of images acquired with opposite diffusion gradient polarity.

In echo-planar-based diffusion-weighted imaging (DWI) and diffusion tensor imaging (DTI), the evaluation of diffusion parameters such as apparent diffusion coefficients and anisotropy indices is affected by image distortions that arise from residual eddy currents produced by the diffusion-sensitizing gradients. Correction methods that coregister diffusion-weighted and non-diffusion-weighted images suffer from the different contrast properties inherent in these image types. Here, a postprocessing correction scheme is introduced that makes use of the inverse characteristics of distortions generated by gradients with reversed polarity. In this approach, only diffusion-weighted images with identical contrast are included for correction. That is, non-diffusion-weighted images are not needed as a reference for registration. Furthermore, the acquisition of an additional dataset with moderate diffusion-weighting as suggested by Haselgrove and Moore (Magn Reson Med 1996;36:960-964) is not required. With phantom data it is shown that the theoretically expected symmetry of distortions is preserved in the images to a very high degree, demonstrating the practicality of the new method. Results from human brain images are also presented.

Algorithms↗

PubMed2004

Quantitation of simulated short echo time 1H human brain spectra by LCModel and AMARES.

LCModel and AMARES, two widely used quantitation tools for magnetic resonance spectroscopy (MRS) data, were employed to analyze simulated spectra similar to those typically obtained at short echo times (TEs) in the human brain at 1.5 T. The study focused mainly on the influence of signal-to-noise ratios (SNRs) and different linewidths on the accuracy and precision of the quantification results, and their effectiveness in accounting for the broad signal contribution of macromolecules and lipids (often called the baseline in in vivo MRS). When applied in their standard configuration (i.e., fitting a spline as a baseline for LCModel, and weighting the first data points for AMARES), both methods performed comparably but with their own characteristics. LCModel and AMARES quantitation benefited considerably from the incorporation of baseline information into the prior knowledge. However, the more accurate quantitation of the sum of glutamate and glutamine (Glx) favored the use of LCModel. Metabolite-to-creatine ratios estimated by LCModel with extended prior knowledge are more accurate than absolute concentrations, and are nearly independent of SNR and line broadening.

Brain Chemistry↗

PubMed2004

Popout modulates focal attention in the primary visual cortex.

The influence of context-dependent interactions on attention-related neural activity was studied in the human primary visual cortex (V1) with event-related fMRI. Retinotopic field-sign mapping was used to determine the localization of V1 with respect to adjacent retinotopic areas. Observers reported the orientation of a Gabor patch at pre-cued extrafoveal locations when it was salient among distractor Gabors and when it was not. Saliency was caused by local orientation contrast between Gabors-a mechanism that is thought to arise from context-dependent interactions in the V1 proper. A comparison of the attention-related BOLD response for salient and non-salient stimuli in V1 revealed that salient Gabors caused a significantly smaller BOLD response than non-salient Gabors. This differential effect was not observed in higher-order visual areas (V3/V3A, MT+/LO, IPS). When attention was not focused onto the target, the size of the BOLD response was generally reduced in all visual areas, and no difference was seen in V1 for salient and non-salient Gabors. These findings suggest that contextual interactions underlying saliency influence attentional modulations in V1 and support the view that perceptual and attentional mechanisms share neural circuits at this early stage of visual processing.

Adult↗

PubMed2003

Focal thinning of the cerebral cortex in multiple sclerosis.

Brain atrophy as determined by quantitative MRI can be used to characterize disease progression in multiple sclerosis. Many studies have addressed white matter (WM) alterations leading to atrophy, while changes of the cerebral cortex have been studied to a lesser extent. In vivo, the cerebral cortex has been difficult to study due to its complex structure and regional variability. Measurement of cerebral cortex thickness at different disease stages may provide new insights into grey matter (GM) pathology. In the present investigation, we evaluated in vivo cortical thickness and its relationship to disability, disease duration, WM T2 hyper-intense and T1 hypo-intense lesion volumes. High-resolution MRI brain scans were obtained in 20 patients with clinically definite multiple sclerosis and 15 age-matched normal subjects. A novel method of automated surface reconstruction yielded measurements of the cortical thickness for each subject's entire brain and computed cross-subject statistics based on the cortical anatomy. Statistical thickness difference maps were generated by performing t-tests between patient and control groups and individual thickness measures were submitted to analyses of variance to investigate the relationship between cortical thickness and clinical variables. The mean overall thickness of the cortical ribbon was reduced in multiple sclerosis patients compared with controls [2.30 mm (SD 0.14) versus 2.48 mm (SD 0.11)], showing a significant main effect of group (controls versus patients). In patients, we found significant main effects for disability, disease duration, T2 and T1 lesion volumes. The visualization of statistical difference maps of the cortical GM thickness on inflated brains across the cortical surface revealed a distinct distribution of significant focal thinning of the cerebral cortex in addition to the diffuse cortical atrophy. Focal cortical thinning in frontal [2.37 mm (SD 0.17) versus 2.73 mm (SD 0.25)] and in temporal [2.65 mm (SD 0.15) versus 2.95 mm (SD 0.11)] brain regions was observed, even early in the course of the disease or in patients with mild disability. Patients with longstanding disease or severe disability, however, presented additionally with focal thinning of the motor cortex area [2.35 mm (SD 0.19) versus 2.74 mm (SD 0.15)]. We conclude that in vivo measurement of cortical thickness is feasible in patients suffering from multiple sclerosis. The data provide new insight into the cortical pathology in multiple sclerosis patients, revealing focal cortical thinning beside an overall reduction of the cortical thickness with disease progression.

Adult↗

PubMed2002

Delayed striate cortical activation during spatial attention.

Recordings of event-related potentials (ERPs) and event-related magnetic fields (ERMFs) were combined with functional magnetic resonance imaging (fMRI) to study visual cortical activity in humans during spatial attention. While subjects attended selectively to stimulus arrays in one visual field, fMRI revealed stimulus-related activations in the contralateral primary visual cortex and in multiple extrastriate areas. ERP and ERMF recordings showed that attention did not affect the initial evoked response at 60-90 ms poststimulus that was localized to primary cortex, but a similarly localized late response at 140-250 ms was enhanced to attended stimuli. These findings provide evidence that the primary visual cortex participates in the selective processing of attended stimuli by means of delayed feedback from higher visual-cortical areas.

Adult↗

PubMed2002

GABA-ergic modulation of prefrontal spatio-temporal activation pattern during emotional processing: a combined fMRI/MEG study with placebo and lorazepam.

Various prefrontal cortical regions have been shown to be activated during emotional stimulation, whereas neurochemical mechanisms underlying emotional processing in the prefrontal cortex remain unclear. We therefore investigated the influence of the GABA-A potentiator lorazepam on prefrontal cortical emotional-motor spatio-temporal activation pattern in a combined functional magnetic resonance imaging/magnetoencephalography study. Lorazepam led to the reversal in orbito-frontal activation pattern, a shift of the early magnetic field dipole from the orbito-frontal to medial prefrontal cortex, and alterations in premotor/motor cortical function during negative and positive emotional stimulation. It is concluded that negative emotional processing in the orbito-frontal cortex may be modulated either directly or indirectly by GABA-A receptors. Such a modulation of orbito-frontal cortical emotional function by lorazepam has to be distinguished from its effects on cortical motor function as being independent from the kind of processing either emotional or nonemotional.

Adult↗

PubMed2002

Analysis of pathways mediating preserved vision after striate cortex lesions.

This study investigated the neural substrates of preserved visual functioning in a patient with homonymous hemianopsia and Riddoch syndrome after a posterior cerebral artery stroke affecting the primary visual cortex (area V1). The limited visual abilities of this patient included above-chance verbal reports of movement and color change as well as discrimination of movement direction in the hemianopic field. Functional magnetic resonance imaging showed that motion and color-change stimuli presented to the hemianopic field produced activation in several extrastriate areas of the lesioned hemisphere that were defined using retinotopic mapping. Magnetoencephalographic recordings indicated that evoked activity occurred earlier in the higher-tier visual areas V4/V8 and V5 than in the lower-tier areas V2/V3 adjacent to the lesion. In addition, the functional magnetic resonance imaging analysis showed an increased functional connectivity between areas V4/V8 and V5 of the lesioned hemisphere in comparison with the same areas in the intact hemisphere during the presentation of color changes. These results suggest that visual perception after the V1 lesion in Riddoch syndrome is mediated by subcortical pathways that bypass V1 and project first to higher-tier visual areas V5 and V4/V8 and subsequently to lower-tier areas V2/V3.

Adult↗