Life-threatening respiratory failure due to cranial dystonia after dental procedure in a patient with multiple system atrophy.

We report on a woman with a an 8-year history of multiple system atrophy with predominance of parkinsonism who developed jaw-locking oromandibular dystonia within hours after insertion of ill-fitting dentures. Dystonia spread rapidly to involve other facial muscles and the larynx causing stridor with respiratory failure necessitating crush intubation.     

Visuomotor control within a distributed parieto-frontal network

The aim of this functional magnetic resonance imaging study was to investigate differences in visuomotor control with increasing task complexity. Twelve right-handed volunteers were asked to perform their signature under different degrees of visual control: internally generated movement with closed eyes, signing with open eyes, tracking the line of the projected signature forwards, and tracking the line of the projected signature backwards. There was a gradual onset and disappearance of activation within a distributed network. Parietal, lateral and medial frontal brain areas were activated during all conditions, confirming the involvement of a parieto-frontal system. The weight of activation shifted with increasing task complexity. Internally generated movements activated predominantly the inferior parietal lobule and the ventral premotor cortex, as well as the rostral cingulate area, pre-supplementary motor area (pre-SMA) and SMA proper. Opening the eyes reduced SMA and cingulate activation and activated increasingly the occipito-parietal areas with higher task complexity. Visually guided movements produced an activation predominantly in the superior parietal lobule and dorsal premotor cortex. This study bridges human activation studies with the results of neurophysiological studies with monkeys. It confirms a gradual transition of visuomotor control with increasing task complexity within a distributed parieto-frontal network.     

Reversible changes in echo planar perfusion- and diffusion-weighted MRI in status epilepticus

Perfusion imaging (PI) demonstrated increased perfusion and diffusion-weighted imaging (DWI) showed high signal limited to the left temporoparietal cortex in a 68-year-old man with nonconvulsive status epilepticus. The EEG showed a slow delta-wave focus. The patient recovered and PI, DWI and EEG changes completely resolved. Received: 2 July 1999/Accepted: 13 July 1999     

The influence of extra- and intracranial artery disease on the BOLD signal in FMRI

Functional MRI is based on the vascular response due to neuronal activation. The underlying mechanism of fMRI is the blood oxygenation level-dependent (BOLD) effect-a complex interplay between changes in the cerebral metabolisation rate of oxygen (CMRO2), neurovascular coupling, and the resulting hemodynamic response. An intact neurovascular coupling is essential for the detection of the BOLD signal and it seems likely that a disturbed cerebrovascular reserve capacity (CVRC) alters the BOLD response. We tested the hypothesis that extra- or intracranial artery disease influences the BOLD signal. Twenty-one patients with extra- or intracranial stenosis were studied with BOLD sensitive T2*-weighted MRI. All patients presented with transient or prolonged reversible ischemic symptoms ipsilateral to the artery disease but were asymptomatic at the time point of the MRI study. fMRI was performed employing a simple motor task (fist closure right and left). Additionally, the CVRC was assessed applying carbogen gas during serial T2*-weighted MRI for the calculation of CO(2) reactivity maps of the relative signal change. Signal differences between both hemispheres were compared in individual subjects and with healthy subjects. Patients with disturbed CVRC in the CO(2) reactivity maps showed either a significantly reduced (n = 5) or a negative (n = 1) BOLD signal in the affected compared to the unaffected primary sensorimotor cortex during fist closure. Patients with intact CVRC showed no significant BOLD signal differences between affected and unaffected hemisphere. Extra- or intracranial artery disease influences CVRC and consequently the BOLD signal. This observation is important for the clinical application of fMRI paradigms.     

Reduction of excitability ("inhibition") in the ipsilateral primary motor cortex is mirrored by fMRI signal decreases

Functional magnetic resonance imaging (fMRI) was used to investigate how focal cortical inhibition affects the blood oxygen level-dependent (BOLD) signal. Phasic low force pinch grip reduces excitability of the ipsilateral primary motor cortex. This task was used to study BOLD signal changes during inhibition. Six right-handed normal volunteers participated in the study. They were asked to perform a right-handed pinch grip repetitively at 1 Hz and 5% of their individual maximal voluntary contraction (MVC). Data were acquired with a 1.5 Tesla Magnetom and continuous multislice T2*-weighted images. The contralateral primary motor cortex (M1) revealed an activation in the knob-shaped hand representation of the central sulcus area. More importantly, a decreased (often referred to as "negative") BOLD signal in the ipsilateral M1 was observed. We suggest phasic low force pinch grip as a reproducible, easy model of focal inhibition. Decreased cortical excitability presents as decreased BOLD signal using fMRI.     

Antigen presentation of hen egg-white lysozyme but not of ribonuclease A is augmented by the major histocompatibility complex class II-associated invariant chain

The influence of the class II-associated invariant chain (Ii) on the presentation of the protein antigens hen egg-white lysozyme (HEL) and ribonuclease A (RNase) was investigated. For this purpose the Ii- rat-2 fibroblasts were transfected with I-Ak genes with or without Ii. Transfectants expressing Ii were superior in the presentation of the complete HEL protein to a panel of I-Ak-restricted T hybridomas characterized by distinct specificities for different HEL peptides and by different sensitivities to antigen concentration. There appeared to be a correlation between the antigen-presenting capacity and the amount of Ii, in that transfectants expressing large amounts of Ii were the best antigen presentors. The presentation of synthetic HEL peptides was not influenced by Ii. In contrast to the findings with HEL, the presentation of RNase by the same set of transfectants was clearly independent of Ii. Both antigens, HEL and RNase, required processing in the chloroquine-sensitive compartment. However, only the presentation of HEL but not of RNase could be efficiently blocked by brefeldin A. These data confirm that presentation of HEL depends on de novo synthesized class II molecules, whereas the presentation of RNase seems to be predominantly mediated by a pool of pre-existing class II molecules whose interaction with endocytosed antigen does not depend on Ii. These results suggest different mechanisms for the presentation of HEL and RNase and they raise the possibility that different antigens intersect the class II pathway at distinct intracellular locations.     

Two different reorganization patterns after rehabilitative therapy: an exploratory study with fMRI and TMS

We used two complementary methods to investigate cortical reorganization in chronic stroke patients during treatment with a defined motor rehabilitation program. BOLD ("blood oxygenation level dependent") sensitive functional magnetic resonance imaging (fMRI) and intracortical inhibition (ICI) and facilitation (ICF) measured with transcranial magnetic stimulation (TMS) via paired pulse stimulation were used to investigate cortical reorganization before and after "constraint-induced movement therapy" (CI). The motor hand function improved in all subjects after CI. BOLD signal intensity changes within affected primary sensorimotor cortex (SMC) before and after CI showed a close correlation with ICI (r = 0.93) and ICF (r = 0.76) difference before and after therapy. Difference in number of voxels and ICI difference before and after CI also showed a close correlation (r = 0.92) in the affected SMC over the time period of training. A single subject analysis revealed that patients with intact hand area of M1 ("the hand knob") and its descending motor fibers (these patients revealed normal motor evoked potentials [MEP] from the affected hand) showed decreasing ipsilesional SMC activation which was paralleled by an increase in intracortical excitability. This pattern putatively reflects increasing synaptic efficiency. When M1 or its descending pyramidal tract was lesioned (MEP from the affected hand was pathologic) ipsilesional SMC activation increased, accompanied by decreased intracortical excitability. We suggest that an increase in synaptic efficiency is not possible here, which leads to reorganization with extension, shift and recruitment of additional cortical areas of the sensorimotor network. The inverse dynamic process between both complementary methods (activation in fMRI and intracortical excitability determined by TMS) over the time period of CI illustrates the value of combining methods for understanding brain reorganization.     

Negative dip in BOLD fMRI is caused by blood flow--oxygen consumption uncoupling in humans.

The sensitivity of MRI for local changes in the deoxyhemoglobin concentration is the basis of the blood oxygen level dependent (BOLD) effect. Time-resolved fMRI studies during visual activation show an early signal intensity (SI) decrease indicating a short lasting uncoupling of oxygen consumption and cerebral blood flow (CBF) before a SI increase due to the overcompensating hemodynamic response occurs. Normal neuronal activity may be preserved despite absent vascular responsiveness. Here we show that a negative BOLD effect occurs during motor activation in an asymptomatic patient with severely disturbed cerebral autoregulation due to extracranial artery disease. This is thought to be due to oxygen consumption in the absence of a hemodynamic response. This rare case of a persisting uncoupling of oxygen metabolism and CBF serves as a model that supports changes of the cerebral blood oxygen saturation as the major contributor of the BOLD effect.