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R J Seitz

Publications and source records attributed to R J Seitz.

At least 19 recordsLinked to original sources
PubMed2006

Visual cortex activation in kinesthetic guidance of reaching.

The purpose of this research was to determine the cortical circuit involved in encoding and controlling kinesthetically guided reaching movements. We used (15)O-butanol positron emission tomography in ten blindfolded able-bodied volunteers in a factorial experiment in which arm (left/right) used to encode target location and to reach back to the remembered location and hemispace of target location (left/right side of midsagittal plane) varied systematically. During encoding of a target the experimenter guided the hand to touch the index fingertip to an external target and then returned the hand to the start location. After a short delay the subject voluntarily moved the same hand back to the remembered target location. SPM99 analysis of the PET data contrasting left versus right hand reaching showed increased (P < 0.05, corrected) neural activity in the sensorimotor cortex, premotor cortex and posterior parietal lobule (PPL) contralateral to the moving hand. Additional neural activation was observed in prefrontal cortex and visual association areas of occipital and parietal lobes contralateral and ipsilateral to the reaching hand. There was no statistically significant effect of target location in left versus right hemispace nor was there an interaction of hand and hemispace effects. Structural equation modeling showed that parietal lobe visual association areas contributed to kinesthetic processing by both hands but occipital lobe visual areas contributed only during dominant hand kinesthetic processing. This visual processing may also involve visualization of kinesthetically guided target location and use of the same network employed to guide reaches to visual targets when reaching to kinesthetic targets. The present work clearly demonstrates a network for kinesthetic processing that includes higher visual processing areas in the PPL for both upper limbs and processing in occipital lobe visual areas for the dominant limb.

Adult↗
PubMed2006

Quantitative assessment of recovery from motor hemineglect in acute stroke patients.

BACKGROUND AND PURPOSE: Motor hemineglect is characterized by an underutilization of one side of the body. It is a higher-order motor disorder that resembles hemiplegia although being substantially different from it due to a preserved motor output system. Its role for poststroke recovery is still unclear. METHODS: We studied 52 patients presenting with acute hemiparetic stroke over the first 7 days after symptom onset. Nineteen patients had unilateral motor hemineglect. Impairment was clinically assessed with the European Stroke Scale and a multifactorial motor score. It was further assessed quantitatively, as overall arm activity was measured continuously by Actiwatches. Lesion volumes were measured morphometrically within 24 h on perfusion- and diffusion-weighted magnetic resonance images and on average on day 9 by T2-weighted magnetic resonance imaging. RESULTS: Patients with motor hemineglect were characterized by significantly reduced initial arm activity in comparison to patients without motor hemineglect. This was paralleled by larger brain lesions in the patients with motor hemineglect. Patients with motor neglect either recovered virtually completely (5 cases; 2/5 left hemisphere; 3/5 treated with recombinant tissue plasminogen activator, rt-PA) within 7 days or did not improve at all (14 cases; 3/14 left hemisphere; 3/14 rt-PA treated). CONCLUSION: Our data reveal a high incidence of motor hemineglect in patients with acute stroke. They further show that these patients are more severely compromised than those without motor hemineglect. A rapid and near complete recovery was observed in about one fourth of the motor hemineglect patients and may be related to involvement of the left hemisphere or to therapy with thrombolysis.

Aged↗
PubMed2006

EFNS guideline on neuroimaging in acute stroke. Report of an EFNS task force.

Neuroimaging techniques are necessary for the evaluation of stroke, one of the leading causes of death and neurological impairment in developed countries. The multiplicity of techniques available has increased the complexity of decision making for physicians. We performed a comprehensive review of the literature in English for the period 1965-2005 and critically assessed the relevant publications. The members of the panel reviewed and corrected an initial draft, until a consensus was reached on recommendations stratified according to the European Federation of Neurological Societies (EFNS) criteria. Non-contrast computed tomography (CT) scan is the established imaging procedure for the initial evaluation of stroke patients. However, magnetic resonance imaging (MRI) has a higher sensitivity than CT for the demonstration of infarcted or ischemic areas and depicts well acute and chronic intracerebral hemorrhage. Perfusion and diffusion MRI together with MR angiography (MRA) are very helpful for the acute evaluation of patients with ischemic stroke. MRI and MRA are the recommended techniques for screening cerebral aneurysms and for the diagnosis of cerebral venous thrombosis and arterial dissection. For the non-invasive study of extracranial vessels, MRA is less portable and more expensive than ultrasonography but it has higher sensitivity and specificity for carotid stenosis. Transcranial Doppler is very useful for monitoring arterial reperfusion after thrombolysis, for the diagnosis of intracranial stenosis and of right-to-left shunts, and for monitoring vasospasm after subarachnoid hemorrhage. Currently, single photon emission computed tomography and positron emission tomography have a more limited role in the evaluation of the acute stroke patient.

Humans↗
PubMed2005

Cingulate cortex activation and competing responses: the role of preparedness for competition.

Regional cerebral blood flow (rCBF) was studied in a task, where a preparatory stimulus (S1) cued for an imperative second stimulus (S2) which was associated with a response. Two preparatory stimuli cued unequivocally each for one response. In contrast, a third preparatory stimulus cued for two response alternatives which appeared for the same ratio (each in 50% of all trials) introducing response competition. In a first experimental condition, non-arbitrary, unambiguous stimuli were used as S1 to enable the subjects to prepare their responses. In a second and third scan, arbitrary preparatory stimuli were used during different stages of awareness for the S1-S2 association. Subjects performed this task "naive" without knowledge about the S1-S2 association and also in an experimental condition being aware of the S1-S2 association. Button presses after unambiguous, non-arbitrary preparatory stimuli activated the right middle frontal gyrus and inferior parietal lobe if S1 was associated with a definite response. When the subjects did not know the S1-S2 relation, left prefrontal cortex activation was associated with trials including definite responses. Performing the same S1-S2 response condition after subjects knew their relation right prefrontal and left parietal areas became additionally engaged. However, in the first experimental condition using unambiguous, non-arbitrary stimuli and in the third, "aware" experimental condition when S1 was coupled with two response alternatives, the anterior cingulate cortex was activated. As these experimental conditions have in common, that the preparatory stimulus shares information about the upcoming competing response alternatives they highlight the evaluative role of the anterior cingulate cortex for competing actions.

Adult↗
PubMed2005

Recruitment of contralesional motor cortex in stroke patients with recovery of hand function.

In neuroimaging studies of stroke patients, coactivation may account for increased recruitment of bilateral motor areas when moving the affected limb. Here we studied eight patients after stroke with fMRI and simultaneous EMG. Bilateral recruitment of premotor and primary motor cortices was evident in five patients with strictly unilateral performance per EMG. Because patients had excellent motor recovery, this increased recruitment suggests an adaptive response to the infarct.

Adaptation, Physiological↗
PubMed2005

Functional activation within the PI-DWI mismatch region in recovery from ischemic stroke: preliminary observations.

In this study, we sought to investigate if brain tissue affected by ischemia can accommodate areas of activation related to restoration of brain function following ischemic stroke. In two patients perfusion imaging (PI) and diffusion weighted imaging (DWI) obtained in the acute phase after stroke was coregistered with BOLD imaging of brain functions acquired when profound recovery had occurred. Both patients suffered from thrombembolic brain infarction due to dissection of the internal carotid artery (ICA) characterized by a severe PI-DWI mismatch in the acute stage of stroke. Following ICA recanalization and clinical recovery BOLD imaging showed task-specific activation adjacent to the infarct lesion within the former PI-DWI mismatch area. The data in these two stroke patients provide evidence that brain tissue at risk of infarction as shown by the PI-DWI mismatch can survive and, thereby, constitute the major site underlying post-ischemic recovery.

Adult↗
PubMed2005

Reorganization of cerebral circuits in human brain lesion.

Recovery after focal brain lesions is supposed to be mediated by cerebral reorganization. Stroke is a powerful model to study these processes in the human brain, since middle cerebral artery infarction is a common neurological disease with a clearly defined onset of a lateralized sensorimotor deficit syndrome. Brain tumours constitute a further model differing from stroke by their slow lesion dynamics. Evidence from functional neuroimaging and transcranial magnetic stimulation will be presented showing that recovery of hand function is related to reorganization of local perilesional and large-scale circuits involving the contralesional hemisphere.

Adaptation, Physiological↗
PubMed2004

The effect of combined thrombolysis with rtPA and tirofiban on ischemic brain lesions.

To determine the effect of systemic thrombolysis with low-dose recombinant tissue plasminogen activator (rtPA) and the body-weight adjusted platelet GPIIb/IIIa receptor antagonist tirofiban, the authors performed lesion volumetry on magnetic resonance perfusion and diffusion images recorded before thrombolysis and on T2-weighted magnetic resonance images on day 8. Treatment with rtPA and tirofiban (n = 13) resulted in a 50% lesion reduction (p < 0.03), while lesion reduction was less in rtPA treatment (n = 16) and absent in nontreated patients (n = 18).

Adult↗
PubMed2004

Unified inflectional processing of regular and irregular verbs: a PET study.

Psycholinguistic theories propose different models of inflectional processing of regular and irregular verbs: dual mechanism models assume separate modules with lexical frequency sensitivity for irregular verbs. In contradistinction, connectionist models propose a unified process in a single module. We conducted a PET study using a 2 x 2 design with verb regularity and frequency. We found significantly shorter voice onset times for regular verbs and high frequency verbs irrespective of regularity. The PET data showed activations in inferior frontal gyrus (BA 45), nucleus lentiformis, thalamus, and superior medial cerebellum for both regular and irregular verbs but no dissociation for verb regularity. Our results support common processing components for regular and irregular verb inflection.

Adult↗
PubMed2004

Use-dependent cortical plasticity in thalidomide-induced upper extremity dysplasia: evidence from somaesthesia and neuroimaging.

In this study cerebral reorganization was investigated in thalidomide-damaged subjects who use their feet to compensate for their malformed upper extremities. Tactile localization across toes was combined with fMRI to study use-dependent plasticity of the human somatosensory cortex. The manner of compensatory foot use was assessed by a questionnaire. In the behavioural experiment toes were stimulated with above threshold monofilaments and subjects had to report which toe was stimulated. When feet were employed for all everyday actions subjects made significantly fewer errors in the localization task. In subjects who use their feet only for specific actions such as grasping objects there were as many localization errors as in the control group of thalidomide-affected subjects with normal extremities. However, the patterns of mislocalizations were different with less errors occurring for the toe of the dominant foot involved in these actions. Functional MRI showed stronger haemodynamic responses to electrical stimulation of the toes in subjects using their feet for everyday actions as compared to controls. Our data show that long-term use of the feet for fine sensorimotor skills leads to better performance in tactile localization and changes in cerebral SI representation supporting the notion of use-dependent plasticity in the somatosensory cortex.

Activities of Daily Living↗
PubMed2004

Concepts on neurological disease evolution.

Degenerative neurological diseases evolve progressively with an insidious onset, while relapsing neurological diseases may remit completely or result in progressive deficits. Since the affected systems can be assessed by clinical evaluation and ascribed to disease-specific pathology--today already in vivo using neuroimaging, the mechanisms underlying neurological disease manifestation can also be studied. For the most frequent neurological diseases with a relapsing clinical course, such as multiple sclerosis, brain infarction and epilepsy, it is shown that disease-specific aetiopathogenesis, lesion-specific pathophysiology and unspecific bystanders determine disease manifestation. Nevertheless, prediction of progression or relapse of a neurological disease is poor due to ill-defined relations of molecular genetic markers and disease evolution. Recent research on aetiopathogenesis and pathophysiology providing new perspectives for selective therapeutic interventions and relapse prevention is discussed.

Biological Evolution↗
PubMed2004

Left and right superior parietal lobule in tactile object discrimination.

Tactile object discrimination is one of the major manual skills of humans. While the exploring finger movements are not perceived explicitly, attention to the movement-evoked kinaesthetic information gates the tactile perception of object form. Using event-related functional magnetic resonance imaging in seven healthy subjects we found one area in the right superior parietal cortex, which was specifically activated by kinaesthetic attention during tactile object discrimination. Another area with similar location in the left hemisphere was related to the maintenance of tactile information for subsequent object discrimination. We conclude that kinaesthetic information is processed in the anterior portion of the superior parietal cortex (aSPL) with a right hemispheric predominance for discrimination and a left hemispheric predominance for information maintenance.

Adult↗
PubMed2004

The role of V5 (hMT+) in visually guided hand movements: an fMRI study.

Electrophysiological studies in animals suggest that visuomotor control of forelimb and eye movements involves reciprocal connections between several areas (striate, extrastriate, parietal, motor and premotor) related to movement performance and visuospatial coding of movement direction. The extrastriate area MT [V5 (hMT+) in humans] located in the "dorsal pathway" of the primate brain is specialized in the processing of visual motion information. The aim of our study was to investigate the functional role of V5 (hMT+) in the control of visually guided hand movements and to identify the corresponding cortex activation implicated in the visuomotor tasks using functional magnetic resonance imaging. Eight human subjects performed visually guided hand movements, either continuously tracking a horizontally moving target or performing ballistic tracking movements of a cursor to an eccentric stationary target while fixating a central fixation cross. The tracking movements were back-projected onto the screen using a cursor which was moved by an MRI-compatible joystick. Both conditions activated area V5 (hMT+), right more than left, particularly during continuous tracking. In addition, a large-scale sensorimotor circuit which included sensorimotor cortex, premotor cortex, striatum, thalamus and cerebellum as well as a number of cortical areas along the intraparietal sulcus in both hemispheres were activated. Because activity was increased in V5 (hMT+) during continuous tracking but not during ballistic tracking as compared to motion perception, it has a pivotal role during the visual control of forelimb movements as well.

Adult↗
PubMed2003

Representational cortical plasticity associated with brain tumours: evidence from laser-induced interstitial thermotherapy.

OBJECTIVES: To test the hypothesis that cortical plasticity related to destructive tumour growth is functionally relevant. This hypothesis predicts that function is dependent on the intactness of tissue surrounding the tumour. MATERIAL AND METHODS: Eight patients underwent laser-induced interstitial thermotherapy (LITT) for minimally invasive palliative treatment of brain tumours located in eloquent frontal motor regions including the primary motor cortex. A multimodal approach was used to assess the functional outcome of patients after LITT in detail. RESULTS: Following LITT, motor function deteriorated in four patients. In three of these four patients the LITT-induced lesion involved minimal parts of adjacent non-tumorous tissue. By contrast, the other four patients whose LITT-induced signal changes were confined to the tumour, showed no functional deficits. CONCLUSION: These findings support the idea that peri-tumorous neuronal circuitry in motor competent areas may permanently take over those functions that were formerly represented in the neuronal tissue destroyed by the tumour.

Adult↗
PubMed2003

Carotid surgery in acute symptomatic patients.

OBJECTIVES: evaluation of urgent carotid artery surgery with new diagnostic techniques and changing surgical considerations at a university hospital. DESIGN, MATERIAL AND METHODS: prospective monitoring and assessment of outcome in 67 patients who underwent urgent carotid surgery because of symptomatic extracranial carotid artery involvement. Patients were examined via the stroke unit: duplex sonography was mandatory for diagnosis of extracranial carotid artery disease, as was proof of an open middle cerebral artery (MCA). Assessment of intracerebral damage followed CT or MR imaging procedures. Perioperative and surgical management was standardized. Neurological impairment was assessed pre-, postoperatively and at follow-up using the Rankin scale. "Urgent" was defined as "immediate" after the final diagnostic step had been performed. RESULTS: within a period of 26 months 67 symptomatic patients (58% stroke, 42% TIA) underwent urgent carotid surgery. Median time from admission to surgery was 2 days. In all but five cases flow through the ICA could technically be restored (93%). Thirty-day mortality was 3% and disease-related morbidity 13%. The one and two year survival rates were 92 and 90%, respectively. No ipsilateral recurrent stroke occurred during follow-up. CONCLUSIONS: clinical decision-making based on stratified diagnostic workup by means of extra- and intracranial as well as intracerebral hemodynamics using new imaging techniques may select patients who will benefit more from urgent surgery than from conservative management.

Acute Disease↗
PubMed2002

Ischemic brain tissue salvaged from infarction by the GP IIb/IIIa platelet antagonist tirofiban.

In an open pilot study, the authors tested whether the nonpeptide glycoprotein (GP) IIb/IIIa antagonist tirofiban, a highly effective and selective blocker of platelet aggregation, prevents the transition of ischemic brain tissue into the infarct proper as defined by MRI (perfusion-weighted/T2-weighted) in patients with acute ischemic stroke. The infarct volume (T2 lesion after 1 week) was smaller in treated patients (n = 10) compared with matched control subjects (n = 10; p = 0.029) with similar initial perfusion deficit (TTP-maps). The authors conclude that GP IIb/IIIa antagonists have therapeutic potential in acute stroke therapy.

Adult↗
PubMed2002

Conscious and subconscious sensorimotor synchronization--prefrontal cortex and the influence of awareness.

One of the most compelling challenges for modern neuroscience is the influence of awareness on behavior. We studied prefrontal correlates of conscious and subconscious motor adjustments to changing auditory rhythms using regional cerebral blood flow measurements. At a subconscious level, movement adjustments were performed employing bilateral ventral mediofrontal cortex. Awareness of change without explicit knowledge of the nature of change led to additional ventral prefrontal and premotor but not dorsolateral prefrontal activations. Only fully conscious motor adaptations to a changing rhythmic pattern showed prominent involvement of anterior cingulate and dorsolateral prefrontal cortex. These results demonstrate that while ventral prefrontal areas may be engaged in motor adaptations performed subconsciously, only fully conscious motor control which includes motor planning will involve dorsolateral prefrontal cortex.

Acoustic Stimulation↗