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Rüdiger J Seitz

Publications and source records attributed to Rüdiger J Seitz.

32 records · Page 2Linked to original sources
PubMed2004

Bimanual recoupling by visual cueing in callosal disconnection.

The cerebral control of bimanual movements is not completely understood. We investigated a 59-year-old, right-handed man who presented with an acute bimanual coordination deficit. Magnetic resonance imaging showed a lesion involving the entire corpus callosum, which was found on stereotactic biopsy to be an ischemic infarct. Paired-pulse transcranial magnetic stimulation indicated that the patient had a lack of interhemispheric inhibition, while intracortical inhibition in motor cortex of either side was normal. Functional magnetic resonance imaging showed activation of the left SMA, the bilateral motor cortex and anterior cerebellum during spontaneous bimanual thumb-index oppositions, which were uncoupled as evident from simultaneous electromyographic recordings. In contrast, when the bimanual thumb-index oppositions were cued by a visual stimulus, the movements of both hands were tightly correlated. This synchronized activity was accompanied by additional activations bilateral in lateral occipital cortex, dorsal premotor cortex and cerebellum. The data suggest that the visually cued movements of both hands were recoupled by action of a bihemispheric motor network.

Aged↗
PubMed2004

Delayed shrinkage of the brain after ischemic stroke: preliminary observations with voxel-guided morphometry.

BACKGROUND AND PURPOSE: The most important effect of cerebral ischemia is brain infarction. In this magnetic resonance imaging (MRI) study, the authors aimed at assessing postischemic brain atrophy. METHODS: Ten patients suffering from their first acute cerebral ischemia in the territory of the middle cerebral artery were studied retrospectively. Three-dimensional MRI volume scans were recorded in the acute and chronic stage after infarction and analyzed voxel by voxel intraindividually with the newly developed voxel-guided morphometry. RESULTS: Shrinkage of brain tissue was detected in all patients, not only in the perilesional cortical structures but also in contralateral homolog cortex areas and subcortically in the striatum and thalamus. This secondary shrinkage was not related to the size of the infarcts or to the clinical outcome of patients. CONCLUSIONS: Our study suggests that delayed brain atrophy after acute ischemic stroke involved areas anatomically connected with the ischemic brain lesion but nevertheless was accompanied by a simultaneous improvement of the neurological deficit.

Atrophy↗
PubMed2004

Reorganisation of cerebral circuits in human ischemic brain disease.

Animal experiments suggest that reorganisation of cerebral representations is the neurobiological basis of post-lesional recovery. In human ischemic brain disease recovery is a dynamic and sustained process beginning after stroke manifestation. The mechanisms underlying recovery can be investigated non-invasively in the human brain using functional neuroimaging and transcranial magnetic stimulation (TMS). In the acute stage, the mismatch area of the perfusion deficit and the impaired water diffusion as assessed by magnetic resonance imaging (MRI) shows the brain tissue that potentially can be rescued by thrombolysis or emergency carotid endarterectomy. Since spontaneous motor recovery is a function of the corticospinal tract integrity, early reperfusion of ischemic tissue is critical. In the subacute and chronic stage after stroke, recovery of motor function was shown to take place irrespective of a concomitant affection of the somatosensory system. Functional MRI with simultaneous recordings of the electromyogram provides evidence that the abnormal activation of motor and premotor cortical areas in both hemispheres related to finger movements has a large interindividual variability. As evident from TMS, recovery results from regression of perilesional inhibition and from remote intracortical disinhibition. Repetitive training, constraint induced training and motor imagery can augment recovery promoting a re-emerging activation in the affected hemisphere. Evolution of altered local perilesional and large-scale bihemispheric circuits appears to allow for post-lesional deficit compensation.

Brain Ischemia↗
PubMed2003

Body scheme gates visual processing.

We used functional magnetic resonance imaging (fMRI) to explore how guidance of motor acts is influenced by the visually perceived body scheme. We found that when subjects view their hand as their opposite hand, i.e., the right hand is seen as the left hand and vice versa, activation in the visual cortex was lateralized opposite to the seen hand. This demonstrates for the first time that our body scheme to which vision relates our environment is already represented at the level of visual cortex.

Adult↗
PubMed2003

Mirror apraxia affects the peripersonal mirror space. A combined lesion and cerebral activation study.

Mirror apraxia is a condition in which patients with lesions of the posterior parietal cortex have deficits in reaching to objects presented through a mirror. The aim of the present study was to investigate possible mechanisms underlying this disorder. First, we addressed the question of whether mirror apraxia is exhibited to the same extent in peripersonal and in body space. Four patients with lesions of the posterior parietal lobe on either side and with marked mirror apraxia were required to reach for objects that were presented to them through a mirror and located either in body space (i.e. on the body surface) or in peripersonal space (i.e. in the reaching distance). Whereas reaching for objects located in body space was flawless in all patients, the performance deteriorated when the same objects were transferred to the peripersonal space. Although the objects were located only a few centimetres above the body surface, the patients reached towards the virtual object in the mirror. Based on these results we suggest that mirror apraxia may originate from a dissociation between the representations of body schema and peripersonal space and that objects located on the body surface become integrated into the body schema. In the second part of the study, using positron emission tomography study (PET), we studied the cerebral activation pattern during reaching to objects presented through a mirror in the peripersonal space in healthy subjects. The results show that increased neural activity in the anterior part of the intraparietal sulcus and in the dorsal premotor cortex was bound to the transformation of the target position from the mirror space to the real space. In contrast, the activity related to object localization in the mirror occurred at the parieto-occipital junction. Both mirror and arm transformation involved the medial posterior part of the superior parietal lobule, putatively area V6a. The results demonstrate that acting through a mirror is processed in a number of cortical areas of the dorsal stream.

Aged↗
PubMed2003

Thrombolysis with recombinant tissue plasminogen activator and tirofiban in stroke: preliminary observations.

BACKGROUND AND PURPOSE: We sought to investigate the feasibility of the combined use of low-dose recombinant tissue plasminogen activator (rtPA) and tirofiban, a glycoprotein IIb/IIIa (GPIIb/IIIa) receptor antagonist, for systemic thrombolysis in acute stroke. METHODS: Consecutive patients who were treated with systemic application of low-dose rtPA and body weight-adjusted tirofiban (rtPA+T group; n=37) were evaluated retrospectively during 1999-2001. Patients in the rtPA+T group were compared with a group of patients treated with a dose of 0.9 mg/kg body weight in a different center (rtPA group; n=119). The 41 patients with infarctions of the middle cerebral artery territory who were not eligible for thrombolytic treatment because of medical contraindications or arrival in the hospital >3 hours after stroke onset served as controls. For matched comparisons, the National Institutes of Health Stroke Scale on admission and the Rankin Scale on discharge 5 days after stroke were used. RESULTS: The patients treated with rtPA+T or rtPA improved (P<0.05) compared with the controls at discharge; patients in the rtPA+T and rtPA groups reached a Rankin Scale score of 0 to 2 in 63% and 55%, respectively, while only 16% of the controls achieved this score. Death rates (8% in rtPA+T group and 5% in rtPA group) were similar among the 2 treatment groups. They included 1 fatal hemorrhage in the rtPA+T group and 4 fatal hemorrhages in the rtPA group. Five percent of the untreated patients developed symptomatic, nonfatal cerebral hemorrhage. CONCLUSIONS: Systemic combined thrombolysis with rtPA+T seems to be a feasible treatment in acute stroke.

Acute Disease↗
PubMed2003

Secondary progressive chronic manganism associated with markedly decreased striatal D2 receptor density.

We describe a patient with chronic manganism due to intoxication 40 years ago. Whereas previous reports on acute or subacute intoxication have shown no or only small reductions in striatal D2 receptor density, we found markedly decreased D2 receptor density using (18)F-methylspiperone PET in this very late stage of chronic manganism, supporting the hypothesis that manganese intoxication may trigger a neurodegenerative disease process.

Aged↗
PubMed2003

A fronto-parietal circuit for tactile object discrimination: an event-related fMRI study.

Previous studies of somatosensory object discrimination have been focused on the primary and secondary sensorimotor cortices. However, we expected the prefrontal cortex to also become involved in sequential tactile discrimination on the basis of its role in working memory and stimulus discrimination as established in other domains. To investigate the contributions of the different cerebral structures to tactile discrimination of sequentially presented objects, we obtained event-related functional magnetic resonance images from seven healthy volunteers. Our results show that right hand object exploration involved left sensorimotor cortices, bilateral premotor, parietal and temporal cortex, putamen, thalamus, and cerebellum. Tactile exploration of parallelepipeds for subsequent object discrimination activated further areas in the dorsal and ventral portions of the premotor cortex, as well as parietal, midtemporal, and occipital areas of both cerebral hemispheres. Discriminating a parallelepiped from the preceding one involved a bilateral prefrontal-anterior cingulate-superior temporal-posterior parietal circuit. While the prefrontal cortex was active with right hemisphere dominance during discrimination, there was left hemispheric prefrontal activation during the delay period between object presentations. Delay related activity was further seen in the anterior intraparietal area and the fusiform gyrus. The results reveal a prominent role of the human prefrontal cortex for somatosensory object discrimination in correspondence with recent models on stimulus discrimination and working memory.

Adult↗
PubMed2003

Remote changes in cortical excitability after stroke.

Changes in the cerebral metabolism and the excitability of brain areas remote from an ischaemic brain lesion have been reported in animals and humans and implicated as a mechanism relevant to functional recovery. The aim of the present study was to determine whether changes in the inhibitory and excitatory activity in motor cortex of the non-affected hemisphere are present in stroke patients, and whether these changes are related to the extent of the patients' recovery of function. Transcranial magnetic stimulation (TMS) was used to study the first dorsal interosseus muscle (FDI) of the non-affected hand in 13 patients with good recovery of hand function after stroke, and was compared with left hemispheric stimulation in 13 healthy age-matched volunteers. In the first experiment, paired-pulse TMS with the conditioning stimulus (CS) set at 80% of the subject's motor threshold (MT) and interstimulus intervals (ISIs) of 2, 3, 10 and 15 ms was used. In the second experiment, different intensities of CS were used to study its inhibitory effect on a succeeding suprathreshold test stimulus at an ISI that was kept constant at 2 ms. In a third experiment, the rise in motor evoked potential (MEP) amplitudes with increasing stimulus intensities was measured. In two additional control experiments, the effect of left versus right hemispheric stimulation in normal volunteers and good versus poor recovery of hand function in patients after stroke on the excitability of inhibitory and excitatory activity was studied. MT, mean test MEP and recruitment curves were similar in patients and healthy volunteers. In those patients with good recovery, paired-pulse excitability was increased at ISIs of 2 and 3 ms, similar to healthy volunteers at ISIs of 10 and 15 ms. When tested with different CS intensities at an ISI of 2 ms, inhibitory activity was similar in patients and healthy subjects at small CS intensities, but faded rapidly at higher CS intensities in patients. In contrast, in patients with poor recovery, this increase in cortical excitability at higher CS intensities was not seen. The similarity of MT, mean test MEP and recruitment curves in patients and healthy volunteers indicates that the overall corticomotoneuronal excitability has not changed in patients. The similarity of the inhibitory effect at low CS intensities in the patients with good recovery and healthy subjects, and the steeper increase of conditioned MEP amplitude at higher CS intensities in the recovering patients suggest that in the patients' contralesional motor cortex the balance of excitatory and inhibitory activity was shifted towards an increase of excitatory activity in the neuronal circuits tested at ISIs of 2 and 3 ms. This shares similarities to mechanisms implicated as relevant for reorganizational processes after experimental brain injury and may be relevant for functional recovery after stroke. The absence of changes in cortical excitability in patients with poor recovery supports the relevance of our findings for recovery.

Adult↗
PubMed2003

Gender-specific differences of hypometabolism in mTLE: implication for cognitive impairments.

PURPOSE: To determine gender differences of hypometabolism and their implications for cognitive impairment in patients with medically refractory mesial temporal lobe epilepsy (mTLE). METHODS: Regional cerebral glucose metabolism (rCMRGlu) was studied in 42 patients (21 male, 21 female) with either left- or right-sided mTLE (22 left, 20 right) and in 12 gender- and age-matched healthy controls during resting wakefulness and in 12 sex- and age-matched healthy controls. Clinical characteristics were balanced across the patient subgroups. All patients were subjected to neuropsychological assessment: 41 patients had histologic changes of definite or probable hippocampal sclerosis. RESULTS: Data analysis based on pixel-by-pixel comparisons and on a laterality index of regions of interest (ROIs) showed significant depressions of the mean rCMRGlu extending beyond the mesiotemporal region and temporolateral cortex to extratemporal regions including the frontoorbital and insular cortex in mTLE patients. Extramesiotemporal hypometabolism prevailed in the male patients. Metabolic asymmetry in temporal and frontal regions was related to performance in the Trail-Making Test and WAIS-R subitems. CONCLUSIONS: Our data showed a gender-specific predominance of extramesiotemporal hypometabolism in male patients with mTLE related to abnormalities of temporal and frontal lobe functions.

Adult↗
PubMed2002

Hemispheric dissociation of visual-pattern processing and visual rotation.

We aimed at investigating whether on-line and delayed visual pattern processing activated different areas in human prefrontal and parietal cortex. For this purpose we measured the regional cerebral blood flow (rCBF) during simultaneous and successive visual matrix processing in 10 right-handed subjects. Delayed matching to sample activated predominantly left hemispheric ventrolateral prefrontal cortex, Broca's area and parts of the parietal cortex. In contrast, visuospatial matrix rotation showed activation of the right dorsolateral prefrontal cortex and parietal lobe. The present results suggest a hemispheric dissociation of fronto-parietal circuits with a left dominance for visual pattern processing like storage and a right dominance for visuospatial processing.

Adult↗
PubMed2002

Neural correlates of visuospatial imagery.

We studied changes in regional cerebral blood flow (rCBF) in 10 healthy right-handed subjects during a visuospatial imagery task. The subject's task consisted of drawing imagined lines connecting encircled numbers in ascending order and estimating the number of lines crossing. Compared with a control task in which there were no crossed lines, there were significant rCBF increases in the cingulate gyrus, the adjacent superior frontal gyrus and in the left inferior parietal cortex. The rCBF changes of the latter area correlated with task performance time. Since these activation areas are close to those in imagery of movement trajectories, we concluded that they appear to be a subsystem for processing mental visuospatial images.

Adult↗
PubMed2002

MR imaging in acute stroke: diffusion-weighted and perfusion imaging parameters for predicting infarct size.

PURPOSE: To investigate the predictive value of the ischemic lesion size, as depicted in the acute stroke phase on diffusion-weighted magnetic resonance (MR) images and time-to-peak (TTP) maps of tissue perfusion imaging, for infarct size, as derived from T2-weighted imaging in the postacute phase. MATERIALS AND METHODS: Fifty patients who underwent diffusion-weighted and perfusion imaging within 1-24 hours after stroke onset and a follow-up T2-weighted investigation after about 8 days were included. Lesion volumes were evaluated by using a semiautomatic thresholding technique. Volumetric results of acute diffusion-weighted and perfusion imaging were analyzed in comparison with follow-up T2-weighted images and in terms of the time difference between symptom onset and initial MR imaging. RESULTS: At diffusion-weighted imaging, the acute lesion defined by a signal intensity increase of more than 20%, compared with the contralateral side, showed the best correlation with the infarct size after 1 week. At perfusion imaging, the best predictor relative to the contralateral side was a delay of more than 6 seconds on TTP maps. Temporal analysis of volumetric results, which depended on the time difference between symptom onset and examination, revealed two patient subgroups. CONCLUSION: Diffusion-weighted imaging helped to predict the size of the lesion on T2-weighted images obtained after about 8 days in patients with a symptom onset of more than 4 hours (r = 0.96), while in patients with a symptom onset of less than 4 hours, perfusion imaging provided important additional information about brain tissue with impaired perfusion.

Acute Disease↗