Biomedical subjects

V Glauche

Publications and source records attributed to V Glauche.

7 recordsLinked to original sources

PubMed2005

Time course of wallerian degeneration after ischaemic stroke revealed by diffusion tensor imaging.

Wallerian degeneration (WD) after ischaemic stroke is a well known phenomenon following a stereotypical time course. Whereas conventional magnetic resonance imaging fails to detect signal intensity changes until four weeks after stroke, diffusion tensor imaging (DTI) reveals changes related to WD only after days. DTI was used to monitor the time course of Wallerian degeneration of the pyramidal tract from the early subacute to the late chronic stage of ischaemic stroke in two patients. A progressive decrease of fractional anisotropy was found along the pyramidal tract in the cerebral peduncle below the primary lesion resulting from progressive changes in the principal diffusivities, as well as a slight increase in the orientationally averaged diffusivity in the chronic phase. These signal changes reflect the progressive disintegration of fibre structures resulting from WD.

Anisotropy↗

PubMed2004

Somatotopic organization of human somatosensory cortices for pain: a single trial fMRI study.

The ability to locate pain plays a pivotal role in immediate defense and withdrawal behavior. However, how the brain localizes nociceptive information without additional information from somatotopically organized mechano-receptive pathways is not well understood. To investigate the somatotopic organization of the nociceptive system, we applied Thulium-YAG-laser evoked pain stimuli, which have no concomitant tactile component, to the dorsum of the left hand and foot in randomized order. We used single-trial functional magnetic resonance imaging (fMRI) to assess differential hemodynamic responses to hand and foot stimulation for the group and in a single subject approach. The primary somatosensory cortex (SI) shows a clear somatotopic organization ipsi- and contralaterally to painful stimulation. Furthermore, a differential representation of hand and foot stimulation appeared within the contralateral opercular--insular region of the secondary somatosensory cortex (SII). This result provides evidence that both SI and SII encode spatial information of nociceptive stimuli without additional information from the tactile system and highlights the concept of a redundant representation of basic discriminative stimulus features in human somatosensory cortices, which seems adequate in view of the evolutionary importance of pain perception.

Adult↗

PubMed2003

Pharmacologically modulated fMRI--cortical responsiveness to levodopa in drug-naive hemiparkinsonian patients.

According to the basal ganglia-thalamocortical circuit model, dopamine depletion in the nigrostriatal system leads to hypoactivation in the supplementary motor area (SMA) and the primary motor cortex (M1) in Parkinson's disease. This functional cortical deafferentation and its reversibility by levodopa (L-dopa) treatment has been established in previous studies for SMA but remains controversial for M1. We used functional MRI (fMRI) and a simple finger opposition task to correlate blood oxygenation level-dependent (BOLD) signal changes with motor performance, assessed separately for each hand between fMRI scanning sessions. Eight drug-naive patients with an akinetic idiopathic hemiparkinsonian syndrome (Hoehn and Yahr stage 1-1.5) and 10 healthy controls were studied. Patients performed a simple, auditory-paced random finger- opposition task every 3 s before and repeatedly every 20 min after intake of 300 mg of fast-release L-dopa. M1 contralateral to the affected hand and SMA, predominantly of the contralateral side, showed a BOLD signal increase after L-dopa intake. Furthermore, comparing BOLD responses of M1 and SMA between the patients and controls revealed that these areas were hypoactive before L-dopa treatment. Signal changes in M1 and SMA were highly correlated with motor performance, which increased after L-dopa intake. This result is not confounded by a performance effect because the motor task employed during scanning was identical throughout all sessions. In contrast to previous imaging studies in which cortical reorganization in Parkinson's disease was thought to have caused M1 hyperactivation, our data are in accordance with the hypothesis that, in de novo idiopathic hemiparkinsonian syndrome, motor cortex hypoactivation in contralateral M1 and bilateral SMA is caused by a decreased input from the subcortical motor loop, which is reversible by L-dopa.

Adult↗

PubMed2002

Distortion-free diffusion tensor imaging of cranial nerves and of inferior temporal and orbitofrontal white matter.

The main impact of functional neuroimaging has been its ability to locate neuronal activity either directly (EEG, MEG) or through the hemodynamic response caused by neuronal activity (PET, fMRI). In the past decade functional neuroimaging has been extended to investigate how brain regions interact, using the concepts of functional and effective connectivity. These concepts are further strengthened by estimates of anatomical connectivity of the same subject. A tool to determine anatomical connectivity in vivo may be provided by diffusion tensor imaging (DTI) methods. These can be used to determine the orientation of fiber bundles in white matter on the basis of the diffusion characteristics of water. Commonly, DTI data are acquired using echo planar imaging which suffers from susceptibility artifacts in orbitofrontal and inferior temporal cortex. Here we demonstrate the use of an alternative pulse sequence, diffusion-weighted single-shot STEAM, for assessing fiber orientation in orbitofrontal cortex and the cranial nerves. The scope of DTI needs to be extended to these structures to investigate psychiatric disorders in which orbitofrontal pathology or temporo-frontal disconnection have been postulated.

Adult↗

PubMed2002

Painful stimuli evoke different stimulus-response functions in the amygdala, prefrontal, insula and somatosensory cortex: a single-trial fMRI study.

Only recently have neuroimaging studies moved away from describing regions activated by noxious stimuli and started to disentangle subprocesses within the nociceptive system. One approach to characterizing the role of individual regions is to record brain responses evoked by different stimulus intensities. We used such a parametric single-trial functional MRI design in combination with a thulium:yttrium-aluminium-granate infrared laser and investigated pain, stimulus intensity and stimulus awareness (i.e. pain-unrelated) responses in nine healthy volunteers. Four stimulus intensities, ranging from warm to painful (300-600 mJ), were applied in a randomized order and rated by the subjects on a five-point scale (P0-4). Regions in the dorsolateral prefrontal cortex and the intraparietal sulcus differentiated between P0 (not perceived) and P1 but exhibited no further signal increase with P2, and were related to stimulus perception and subsequent cognitive processing. Signal changes in the primary somatosensory cortex discriminated between non-painful trials (P0 and P1), linking this region to basic sensory processing. Pain-related regions in the secondary somatosensory cortex and insular cortex showed a response that did not distinguish between innocuous trials (P0 and P1) but showed a positive linear relationship with signal changes for painful trials (P2-4). This was also true for the amygdala, with the exception that, in P0 trials in which the stimulus was not perceived (i.e. 'uncertain' trials), the evoked signal changes were as great as in P3 trials, indicating that the amygdala is involved in coding 'uncertainty', as has been suggested previously in relation to classical conditioning.

Adult↗

PubMed2001

Surface orientation discrimination activates caudal and anterior intraparietal sulcus in humans: an event-related fMRI study.

Perception of surface orientation is an essential step for the reconstruction of the three-dimensional (3D) structure of an object. Human lesion and functional neuroimaging studies have demonstrated the importance of the parietal lobe in this task. In primate single-unit studies, neurons in the caudal part of the intraparietal sulcus (CIP) were found to be active during the extraction of surface orientation through monocular (two-dimensional) cues such as texture gradients and linear perspective as well as binocular (3D) cues such as disparity gradient and orientation disparity. We used event-related fMRI to study the functional neuroanatomy of surface orientation discrimination using stimuli with monocular depth cues in six volunteers. Both posterior (CIP) and anterior (AIP) areas within the intraparietal sulcus showed a stronger activation during surface orientation as compared with a control (color discrimination) task using identical stimuli. Furthermore, the signal changes in CIP showed a greater performance effect than those in AIP, suggesting that CIP is tightly linked to the discrimination task.

Adult↗

PubMed1999

fMRI during word processing in dyslexic and normal reading children.

The present study addresses phonological processing in children with developmental dyslexia. Following the hypothesis of a core deficit of assembled phonology in dyslexia a set of hierarchically structured tasks was applied that specifically control for different kinds of phonological coding (assembled versus addressed phonological strategies). Seventeen developmental dyslexics and 17 normal reading children were scanned during four different tasks: (1) passive viewing of letter strings (control condition), (2) passive reading of non-words, (3) passive reading of legal words, and (4) a task requiring phonological transformation. Statistical analysis of the data was performed using statistical parametric mapping (SPM96). Comparison of patterns of activation in dyslexic and normal reading children revealed significant differences in Broca's area and the left inferior temporal region for both, non-word reading and the phonological transformation task. The present data provide new evidence for alteration of the phonological system in dyslexic children, and in particular, the system that mediates assembled phonological coding.

Adolescent↗