PubMed Health⌕ Search

Biomedical subjects

C Weiller

Publications and source records attributed to C Weiller.

At least 37 records · Page 2Linked to original sources
PubMed2003

Motor excitability in a patient with a somatosensory cortex lesion.

OBJECTIVE: We report a patient with an ischemic lesion in right somatosensory cortex who developed dystonic posturing and pseudo-athetotic involuntary left-sided finger movements during voluntary muscle contractions. METHODS: Motor excitability was assessed using transcranial magnetic stimulation techniques and electrical peripheral nerve stimulation. Results obtained from abductor digiti minimi muscles of both hands were compared. RESULTS: On the affected side, silent period duration and intracortical inhibition were reduced, indicating a loss of inhibitory properties. Intracortical facilitation was enhanced. Stimulus-response curves showed a smaller increase of motor evoked potential amplitudes when recorded during muscle relaxation, but not during voluntary muscle activation. CONCLUSIONS: The results suggest that, under normal conditions, somatosensory cortex modifies inhibitory as well as excitatory properties in the motor system.

Dystonic Disorders↗
PubMed2003

Interhemispheric effects of high and low frequency rTMS in healthy humans.

OBJECTIVE: We investigated whether repetitive transcranial magnetic stimulation (rTMS) applied to the right motor cortex modified the excitability of the unstimulated left motor cortex. METHODS: Interhemispheric effects of 0.5 and 5 Hz subthreshold rTMS over the right motor cortex were examined by single pulse and paired pulse TMS and by transcranial electrical stimulation (TES) applied to the unstimulated left motor cortex. The effects of (a) 1800 pulses real and sham rTMS with 5 Hz, (b) 180 pulses real and sham rTMS with 0.5 Hz and (c) 1800 pulses real rTMS with 0.5 Hz were studied. RESULTS: Following 5 Hz right motor rTMS motor evoked potential (MEP) amplitudes induced by single pulse TMS over the left motor cortex increased significantly. Intracortical inhibition (ICI) and facilitation (ICF) and MEP amplitudes evoked by TES were unchanged. Sham stimulation had no influence on motor cortex excitability. After 180 pulses right motor cortex rTMS with 0.5 Hz a significant decrease of left motor ICF, but no change in single pulse MEP amplitudes was found. A similar trend was observed with 1800 pulses rTMS with 0.5 Hz. CONCLUSIONS: High frequency right motor rTMS can increase left motor cortex excitability whereas low frequency right motor rTMS can decrease it. These effects outlast the rTMS by several minutes. The underlying mechanisms mediating interhemispheric excitability changes are likely to be frequency dependent.

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↗
PubMed2003

Contralateral coding of imagined body parts in the superior parietal lobe.

In monkeys, neurons in the superior parietal lobe (area 5) code for spatial position of contralateral body parts by combining visual and somatosensory signals. Using a modified version of the classical mental rotation task, we were able to demonstrate that in humans activation in the contralateral superior parietal lobe could be evoked when mental rotation was combined with motor imagery of hands. These findings show that even in the absence of visual and somatosensory input, information provided by motor imagery suffices to induce contralateral superior parietal lobe monitoring of the imagined limb configuration. This constitutes an important prerequisite for effective imagined motor practice that can be used to improve actual motor performance.

Analysis of Variance↗
PubMed2003

Motor system abnormalities in hereditary spastic paraparesis type 4 (SPG4) depend on the type of mutation in the spastin gene.

BACKGROUND: Hereditary spastic paraparesis (HSP) denotes a group of inherited neurological disorders with progressive lower limb spasticity as their clinical hallmark; a large proportion of autosomal dominant HSP belongs to HSP type 4, which has been linked to the SPG4 locus on chromosome 2. A variety of mutations have been identified within the SPG4 gene product, spastin. OBJECTIVE: Correlation of genotype and electrophysiological phenotype. MATERIAL: Two large families with HSP linked to the SPG4 locus with a very similar disease with respect to age of onset, progression, and severity of symptoms. METHODS: Mutation analysis was performed by PCR from genomic DNA and cDNA, and direct sequencing. The motor system was evaluated using transcranial magnetic stimulation. RESULTS: Patients differ in several categories depending on the type of mutation present. CONCLUSIONS: For the first time in hereditary spastic paraparesis, a phenotypic correlate of a given genetic change in the spastin gene has been shown.

Adenosine Triphosphatases↗
PubMed2002

Fatigue suppresses ipsilateral intracortical facilitation.

Experimental data in animals and humans have demonstrated connections between right and left motor cortices. Interactions between these cortical areas can be explored with electrical or magnetic stimulation. In the present study we examined the interhemispheric effect of fatigue on intracortical facilitation (ICF) and inhibition (ICI) using a paired-pulse transcranial magnetic stimulation (TMS) paradigm. Ten healthy subjects performed pinch grips with their left hand with 50% maximum voluntary contraction (MVC) until fatigue occurred. In the control experiment, the same number of pinch grips was performed with 5% MVC without inducing fatigue. Motor evoked potentials (MEP) produced by single and paired pulse TMS over the left motor cortex were recorded from right first dorsal interosseous muscle (FDI) and right abductor digiti minimi muscle (ADM) before and after the tasks. ICF of the right FDI was significantly reduced after fatigue ( P=0.0008). Fifteen minutes after finishing the task ICF had returned to baseline values. There was no change of ICF of right FDI in the control experiment without inducing fatigue. In both experiments the right ADM did not show significant MEP changes. Additional control experiments showed that M-responses and F-waves were unchanged in right FDI after performing the fatigue task with left FDI, and TMS test pulse amplitudes were significantly reduced in left FDI after fatigue. Fatigue caused by pinch grips induces a short-lasting and task-specific suppression of intracortical facilitation in the motor cortex of an homologous contralateral hand muscle. These results indicate interhemispheric interactions between the two motor cortices that are still effective after cessation of movements.

Adult↗
PubMed2002

Event-related fMRI reveals cortical sites involved in contextual sentence integration.

We examined the effects of difficulty of sentential integration on blood oxygenation level-dependent contrast changes. Difficulty of integration was operationalized as the degree to which sentence-final nouns matched the expectations generated by preceding context. Nine young adults read short sentence fragments (e.g., "The pilot flies.") which were completed by highly expected nouns (e.g., "the plane"), unexpected yet semantically legal nouns (e.g., "the kite"), nouns that violated the verbs' selection restriction rules (e.g., "the book"), and pseudowords (e.g., "the foop") and made quick lexical decisions on the sentence-final item. Overall, word completions resulted in higher changes in activation than pseudoword completions. The largest of those changes were observed in left angular and posterior middle temporal gyri, suggesting that despite the lexical nature of the task, word stimuli embedded in sentence contexts triggered integrative-semantic processes beyond a lexical level. A region-of-interest analysis in left inferior frontal and left posterior middle temporal areas revealed activation for both unexpected and anomalous completions when compared to expected completions. Thus, while the underlying processing mechanisms may differ, sentential integration appears similarly effortful for these two types of completions. Our findings are consistent with previous reports of local increases in activation as a function of (syntactic) complexity, while extending the findings to processing demands of semantic integration. Because of its sensitivity to changes in semantic congruence and the implicit nature of the task involved, we argue that the present paradigm is well suited to study patients with potential semantic deficits after brain damage.

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

Subcortical structures involved in pain processing: evidence from single-trial fMRI.

Pain is processed in multiple cortical and subcortical brain areas. Subcortical structures are substantially involved in different processes that are closely linked to pain processing, e.g. motor preparation, autonomic responses, affective components and learning. However, it is unclear to which extent nociceptive information is relayed to and processed in subcortical structures. We used single-trial functional magnetic resonance imaging (fMRI) to identify subcortical regions displaying hemodynamic responses to painful stimulation. Thulium-YAG (yttrium-aluminum-granate) laser evoked pain stimuli, which have no concomitant tactile component, were applied to either hand of healthy volunteers in a randomized order. This procedure allowed identification of areas displaying differential fMRI responses to right- and left-sided stimuli. Hippocampal complex, amygdala, red nucleus, brainstem and cerebellum were activated in response to painful stimuli. Structures related to the affective processing of pain showed bilateral activation, whereas structures involved in the generation of withdrawal behavior, namely red nucleus, putamen and cerebellum displayed differential (i.e. asymmetric) responses according to the side of stimulation. This suggests that spatial information about the nociceptive stimulus is made available in these structures for the guidance of defensive and withdrawal behavior.

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↗
PubMed2002

Experience with 123I-iomazenil SPECT in acute cerebral infarction.

Neuronal cells are susceptible to cerebral ischaemia. As gamma-aminobutyric acid(A) (GABA(A)) receptors are specific for neurones, functional receptor imaging using I-iomazenil (IMZ), a ligand to the GABA benzodiazepine receptor, has been proposed as an imaging modality for the assessment of neuronal integrity. However, there is only limited experience with IMZ in patients with acute cerebral infarction. Therefore, the aim of this study was to evaluate IMZ single photon emission computed tomography (SPECT) in patients with acute cerebral ischaemia. IMZ SPECT was performed in 21 patients with acute cerebral infarction 7-10 days after stroke onset. Eleven patients underwent systemic thrombolysis within 6 h after symptom onset (group 1), whereas 10 patients were treated conservatively (group 2). IMZ (150-200 MBq) was injected intravenously and imaging was performed using a dedicated four-head SPECT camera at 5 min (perfusion) and 90 min (receptor distribution) post-injection, with an acquisition time of 50 min each. Images were analysed by visual inspection. Four patients showed normal IMZ distribution, and 17 patients showed abnormalities of IMZ uptake on both early and late images. In six patients with regional uptake deficits, a crossed cerebellar diaschisis was observed on early images. Cerebellar inhomogeneity of tracer uptake was absent at the time of late images in all six patients. In eight patients, areas of hypoperfusion corresponded exactly to the regions of receptor deficiency (match). In five patients, preserved neuronal integrity was present in hypoperfused areas (mismatch). In four patients, normally or even hyperperfused areas exhibited regional receptor deficiency (inverse mismatch). In conclusion, IMZ SPECT demonstrated differences between regional perfusion and receptor distribution in about one-half of patients 7-10 days after acute cerebral ischaemia. Interesting patterns between the early phase (perfusion) and the late phase (receptor distribution) were found. These patterns are indicative of the heterogeneous development of cerebral ischaemia where, even days after stroke onset, areas of hypoperfusion but preserved neuronal integrity may be present. However, the evaluation of the potential clinical and therapeutic impact of individual IMZ distribution patterns requires further investigation.

Adult↗
PubMed2002

Effect of intravenous thrombolysis on MRI parameters and functional outcome in acute stroke <6 hours.

BACKGROUND AND PURPOSE: The goals of this study were to examine MRI baseline characteristics of patients with acute ischemic stroke (AIS) and to study the influence of intravenous tissue plasminogen activator (tPA) on MR parameters and functional outcome using a multicenter approach. METHODS: In this open-label, nonrandomized study of AIS patients with suspected anterior circulation stroke, subjects received a multiparametric stroke MRI protocol (diffusion- and perfusion-weighted imaging and MR angiography) within 6 hours after symptom onset and on follow-up. Patients were treated either with tPA (thrombolysis group) or conservatively (no thrombolysis group). Functional outcome was assessed on day 90 (modified Rankin Score; mRS). RESULTS: We enrolled 139 AIS patients (no thrombolysis group, n=63; thrombolysis group, n=76). Patients treated with tPA were more severely affected (National Institutes of Health Stroke Scale score, 10 versus 13; P=0.002). Recanalization rates were higher in the thrombolysis group (Thrombolysis in Myocardial Infarction criteria 1 through 3 on day 1; 66.2% versus 32.7%; P<0.001). Proximal vessel occlusions resulted in larger infarct volumes and worse outcome (P=0.02). Thrombolysis was associated with a better outcome regardless of the time point of tPA treatment (< or =3 hours or 3 to 6 hours) (univariate analysis: mRS < or =2, P=0.017; mRS < or =1, P=0.023). Age (P=0.003), thrombolytic therapy at 0 to 6 hours (P=0.01), recanalization (P=0.016), lesion volume on day 7 (P=0.001), and initial National Institutes of Health Stroke Scale score (P=0.001) affected functional outcome (mRS on day 90) positively (multivariate analysis). The time point of tPA therapy affected the recanalization rate (P=0.024) but not final infarct volume. CONCLUSIONS: In this pilot study, tPA therapy had a beneficial effect on vessel recanalization and functional outcome. Multiparametric MRI delineates tissue at risk of infarction in AIS patients, which may be helpful for the selection of patients for tPA therapy. tPA therapy appeared safe and effective beyond a 3-hour time window. This study delivers the rationale for a randomized, MR-based tPA trial.

Acute Disease↗
PubMed2001

Increased excitability in the primary motor cortex and supplementary motor area in patients with phantom limb pain after upper limb amputation.

Using functional magnetic resonance imaging and single slice FLASH technique, we investigated reorganization of the hand representation of the primary sensorimotor cortex (SMC) in 16 patients with upper extremity amputation. Patients were asked to perform finger tapping with the intact hand, repetitive eye closing and anteflexion of the amputation stump or intact shoulder. Six normal volunteers served as control. In the normal volunteers activations during shoulder anteflexion, finger tapping and eye closure were located within the central sulcus in a medio-lateral fashion. Patients demonstrated invasion of the face or shoulder representation into the hand representation of the amputated limb. Eight phantom limb pain patients showed significantly greater activation in SMC and supplementary motor area (SMA) in contrast to eight patients without phantom limb pain. We conclude, that different parts of the motor system are affected in patients with phantom limb pain--possibly in the sense of an up-regulation of excitability.

Adolescent↗
PubMed2001

Structural and functional cortical abnormalities after upper limb amputation during childhood.

Functional reorganization has been well documented in the human adult brain after amputation of the arm. To assess the effects of amputation on the developing brain, we investigated six patients with upper limb amputation in early childhood and one with right dysmelia. Transcranial magnetic stimulation indicated contralateral cortical disinhibition and enlargement of the excitable area of the stump. FMRI data corroborated these plastic changes and also showed an ipsilateral functional reorganization. In the T1-weighted MRI, we found structural deformities of the contralateral and ipsilateral central sulcus in three patients and a contralateral atrophic parietal lobule in two patients. Therefore, arm amputation in childhood affects functional organization as well as anatomical structure in both hemispheres.

Adolescent↗
PubMed2001

Orally administered atropine enhances motor cortex excitability: a transcranial magnetic stimulation study in human subjects.

Oral application of atropine was used to test if a modulation of cholinergic neurotransmission changed motor excitability. Healthy volunteers received either 1 or 2 mg atropine. Paired transcranial magnetic stimulation was used to study intracortical inhibition and intracortical facilitation before, 1 h and 24 h after ingestion of atropine. In addition, the silent period, motor threshold, F wave and motor response amplitudes were measured. The 1 mg dose of atropine induced a loss of intracortical inhibition, the 2 mg dose produced an intracortical disinhibition and enhanced intracortical facilitation. These changes returned to baseline after 24 h. Other electrophysiological parameters remained unchanged. Thus, an antagonist of pre- and postsynaptic muscarinic receptors increased excitability in the human motor cortex in a dose-dependent manner, indicating an influence of the cholinergic system on motor cortex excitation.

Administration, Oral↗
PubMed2001

Dysfunction of vasomotor reactivity in severe sepsis and septic shock.

OBJECTIVE: Perfusion abnormalities are an overall phenomenon in severe sepsis and septic shock, leading to organ dysfunction. We investigated whether carbon dioxide (CO2)-induced vasomotor reactivity (VMR) is impaired in septic patients, compared with values obtained outside sepsis. DESIGN: Prospective, clinical study. SETTING: Six-bed neurologic critical care unit of a university hospital. PATIENTS AND PARTICIPANTS: Eight consecutive patients with severe sepsis and septic shock. MEASUREMENTS AND RESULTS: CO2-reactivity was measured during and outside a period of severe sepsis or septic shock according to ACCP/SCCM criteria by means of transcranial Doppler sonography and near-infrared spectroscopy (NIRS). VMR was calculated as the percentage change of cerebral blood flow velocity (normalized CO2-reactivity, NCR) and absolute changes in concentration of oxygenated hemoglobin, deoxygenated hemoglobin, total hemoglobin (HbO2, Hb, HbT) and Hbdiff (difference between HbO2 and Hb) in micromol/l per 1% increase in end-tidal CO2 (CR-HbO2, CR-Hb, CR-HbT, CR-Hbdiff). NCR and NIRS-reactivities were significantly reduced during severe sepsis and septic shock compared with values outside sepsis (mean, SD, Wilcoxon): NCR 11.0 (7.1) versus 30.7 (13.0), p < 0.02; CR-HbO2 0.70 (0.61) versus 2.33 (1.11), p < 0.02; CR-Hb -0.17 (0.74) versus -1.42 (1.28), p < 0.04; CR-HbT 0.53 (0.48) versus 1.05 (0.40), p < 0.03; CR-Hbdiff 0.91 (1.33) versus 3.75 (2.33), p < 0.02. This indicates a severely disturbed VMR. CONCLUSIONS: In the advent of a disturbed cerebral autoregulation, critical drops in blood pressure during sepsis are transferred directly into the vascular bed, leading to cerebral hypoperfusion. This mechanism might contribute to the pathogenesis of septic encephalopathy.

Aged↗
PubMed2001

Passive finger movement evoked fields in magnetoencephalography.

We studied neuromagnetic fields during passive finger movements in 11 normal subjects. Activation started 27 ms after the onset of movement and remained for about 100 ms. Four activation maxima occurred within this time range, PM1 at 27 ms, PM2 at 46 ms, PM3 at 85 ms, and PM4 at 125 ms. Not all components were distinguishable in every subject partly due to overlapping effects, but PM3 was present in all subjects. Magnetic source imaging (MSI) revealed dipolar sources within 1 cm of the central sulcus for all four components. The results suggest that studying the integrity of the sensorimotor system in patients regardless of their degree of motor impairment is feasible.

Adult↗