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Biomedical subjects

C Weiller

Publications and source records attributed to C Weiller.

At least 73 records · Page 4Linked to original sources
PubMed2000

[Clinical applications of single photon emission tomography in neurology. 2. Dementia, psychoses, inflammation, skull and brain injuries].

This article gives in his second part a critical review of the clinical applications of SPECT with perfusion markers and receptor ligands in dementing disorders and psychosis. In addition this review discusses clinical applications of SPECT investigations with perfusion markers in inflammatory diseases of the central nervous system and in brain trauma.

Brain↗
PubMed1999

Multiple somatotopic representations in the human cerebellum.

The classic view of representation in the cerebellum assumes two homunculi, one in the anterior lobe and one in the posterior lobe. Functional imaging has confirmed this somatotopy in the human anterior lobe but not, so far, in the posterior lobe. Using fMRI, we found separate peaks of activation for finger and toe in three ipsilateral cerebellar regions. In both the anterior and posterior lobe, the toe representation was semicircular around the finger area, with peaks of activation aligned in accord with the classic homunculi. Also, segregated peaks of activation were found in the pyramis vermis. These results confirm the existence of a second homunculus in the posterior lobe of the human cerebellum and suggest a third one.

Adult↗
PubMed1999

A blueprint for movement: functional and anatomical representations in the human motor system.

Despite a clear somatotopic organization of the motor cortex, a movement can be learned with one extremity and performed with another. This suggests that there exists a limb-independent coding for movements. To dissociate brain regions coding for movement parameters from those relevant to the chosen effector, subjects wrote their signature with their dominant index finger and ipsilateral big toe, and we determined those areas activated by both conditions using functional magnetic resonance imaging. The results show that movement parameters for this highly trained movement are stored in secondary sensorimotor cortices of the extremity with which it is usually performed, i.e., the dominant hand, including dorsal and ventral lateral premotor cortices. These areas can be accessed by the foot and are therefore functionally independent from the primary representation of the effector. Thus, somatotopy in secondary structures in the human motor system seems to be defined functionally, and not on the basis of anatomical representations.

Adult↗
PubMed1999

Abnormal motor cortex organization contralateral to early upper limb amputation in humans.

We performed both a functional magnetic resonance imaging (fMRI) study using single slice FLASH technique and an investigation with transcranial magnetic stimulation (TMS) in a 21-year-old patient. He had suffered a left upper extremity amputation at age 7. Anteflexion of the amputation stump produced an unusual, broad activation contralateral to the movement. TMS revealed an enlarged cortical motor output area of the deltoid muscle at the amputation stump. Application of paired magnetic stimulation demonstrated decreased intracortical inhibition (ICI). A T1-weighted image indicated a lack of the characteristic shape of the central sulcus contralateral to the amputation. In addition to previous functional studies, these new structural data suggest that maturation of the central sulcus develops in response to daily practice of the contralateral hand, possibly until adolescence.

Adult↗
PubMed1999

Motor plasticity induced by synchronized thumb and foot movements.

We used focal transcranial magnetic stimulation to examine the effects of 120 synchronized thumb and foot movements on the motor output map of the right abductor pollicis brevis muscle (APB) (experiment 1). To evaluate the performance, the latencies between the onset of the electromyographic activity (EMG) of the two muscles were measured. As control, 120 asynchronous thumb and foot movements were performed (experiment 2). Exclusively in experiment 1, the center of gravity (CoG) of the output map moved medially in the direction of the foot representation area (mean 7 mm, P<0.05) and returned into its original location within 1 h. In experiment 2, the CoG remained unchanged (mean displacement, 0.68 mm into a lateral direction; not significant). The effect in experiment 1 was independent of an improvement in performance. We conclude that a short-lasting training of synchronous movements induces modulations of motor output maps which probably occur due to interactions between hand and foot representation areas in the motor cortex.

Adult↗
PubMed1999

Learning, plasticity, and recovery in the central nervous system.

Cerebral functions can be described by the interaction of different brain regions as parts of distributed networks. Learning is seen as a refinement of the connection between the various parts of these networks. Plastic changes, as illustrated in brain charting techniques, are the result of learning (or use) in normal brains or found as adaptation (active or passive) after peripheral or central lesions. The relation between brain reorganization and recovery of function is investigated by two recent studies relating the training-induced improvement of lost function to changes in the brain. Others search for the effects of passive stimulation and drug influences. Independently of the approach, however, the general idea is that recovery can be seen as a reconnection between the remaining parts of the disturbed network.

Adaptation, Physiological↗
PubMed1999

Training-induced brain plasticity in aphasia.

It has long been a matter of debate whether recovery from aphasia after left perisylvian lesions is mediated by the preserved left hemispheric language zones or by the homologous right hemisphere regions. Using PET, we investigated the short-term changes in the cortical network involved in language comprehension during recovery from aphasia. In 12 consecutive measurements of regional cerebral blood flow (rCBF), four patients with Wernicke's aphasia, caused by a posterior left middle cerebral artery infarction, were tested with a language comprehension task. Comprehension was estimated directly after each scan with a modified version of the Token Test. In the interval between the scans, the patients participated in brief, intense language comprehension training. A significant improvement in performance was observed in all patients. We correlated changes in blood flow measured during the language comprehension task with the scores achieved in the Token Test. The regions which best correlated with the training-induced improvement in verbal comprehension were the posterior part of the right superior temporal gyrus and the left precuneus. This study supports the role of the right hemisphere in recovery from aphasia and demonstrates that the improvement in auditory comprehension induced by specific training is associated with functional brain reorganization.

Adult↗
PubMed1999

Mapping plastic brain changes after acute lesions.

The combination of different mapping techniques has yielded new insights in reorganization processes after acute lesions in humans. Recent research focused not only on lesion-induced plasticity, but also on therapy-induced reorganization of the brain. Data from animal experiments has expanded our knowledge of mechanisms that underlie plastic changes.

Acute Disease↗
PubMed1999

The influence of conductivity changes in boundary element compartments on the forward and inverse problem in electroencephalography and magnetoencephalography.

Source localization based on magnetoencephalographic and electroencephalographic data requires knowledge of the conductivity values of the head. The aim of this paper is to examine the influence of compartment conductivity changes on the neuromagnetic field and the electric scalp potential for the widely used three compartment boundary element models. Both the analysis of measurement data and the simulations with dipoles distributed in the brain produced two significant results. First, we found the electric potentials to be approximately one order of magnitude more sensitive to conductivity changes than the magnetic fields. This was valid for the field and potential topology (and hence dipole localization), and for the amplitude (and hence dipole strength). Second, changes in brain compartment conductivity yield the lowest change in the electric potentials topology (and hence dipole localization), but a very strong change in the amplitude (and hence in the dipole strength). We conclude that for the magnetic fields the influence of compartment conductivity changes is not important in terms of dipole localization and strength estimation. For the electric potentials however, both dipole localization and strength estimation are significantly influenced by the compartment conductivity.

Electric Conductivity↗
PubMed1999

[Role of positron emission tomography (PET) and single photon emission tomography (SPECT) in so-called "multiple chemical sensitivity"].

Functional imaging with SPECT and PET is increasingly used to prove evidence for the existence of a syndrome "Multiple Chemical Sensitivity" (MCS) and plays a major role in legal trials to justify compensation for the exposure to solvents. This paper critically reviews the literature on the use of SPECT and PET for the determination of MCS. The authors come to the conclusion that the current data are not sufficient to justify the claim of the existence of such a syndrome. The low specificity of the observed PET and especially SPECT-findings makes it very difficult to establish a cause-result relationship and therefore makes the use of these methods in legal trials on this issue doubtful.

Humans↗
PubMed1998

Motor cortex plasticity during constraint-induced movement therapy in stroke patients.

Stroke patients in the chronic phase received constraint-induced (CI) movement therapy. The motor cortex was spatially mapped using focal transcranial magnetic stimulation (TMS) before and after 2 weeks of treatment. Motor-output areas of the abductor pollicis brevis muscle, motor evoked potential (MEP) amplitudes and location of centre of gravity (CoG) of motor cortex output were studied. After CI therapy, motor performance improved substantially in all patients. There was also an increase of motor output area size and MEP amplitudes, indicating enhanced neuronal excitability in the damaged hemisphere for the target muscles. The mean centre of gravity of the motor output maps was shifted considerably after the rehabilitation, indicating the recruitment of motor areas adjacent to the original location. Thus, even in chronic stroke patients, reduced motor cortex representations of an affected body part can be enlarged and increased in level of excitability by an effective rehabilitation procedure. The data therefore demonstrate a CNS correlate of therapy-induced recovery of function after nervous system damage in humans.

Brain Mapping↗
PubMed1998

Imaging recovery from stroke.

Brain imaging techniques illustrate the plastic potential even of the adult human brain in healthy subjects as in patients with peripheral or central lesions. Recovery of lost function through a persistent structural lesion in the central nervous system is accompanied by a complex and individually variable pattern of reorganisation of the brain. Changes depend on the site of the lesion and are found in both hemispheres, the damaged and the sound one within a pre-existing, widespread and bilateral organised and parallel processing network without the formation of new centres. This implies changes at rest with increased or decreased activity and altered activation patterns during performance of the restituted function. Within the primary motor system an activation at the rim of the infarct, extension into neighbouring representations, which outflow is not disturbed, altered recruitment pattern of motor cortex neurons, and recruitment of ipsilateral direct descending corticospinal tract pathways originating in the sound hemisphere are found. Disruption of the primary system leads to re-weighting of activity between the various representational levels with increased activity in secondary of higher order areas. Early sensory reorganisation indicates the potential for recovery of lost motor function. Behavioural language training in aphasics results in improvement of altered comprehension function, which is related to right hemisphere activation. Thus, reorganisation can be beneficial and training or rehabilitation influence the pattern of reorganisation.

Cerebrovascular Disorders↗
PubMed1998

Experimental cranial pain elicited by capsaicin: a PET study.

Using a positron emission tomography (PET) study it was shown recently that in migraine without aura certain areas in the brain stem were activated during the headache state, but not in the headache free interval. It was suggested that this brain stem activation is inherent to the migraine attack itself and represents the so called 'migraine generator'. To test this hypothesis we performed an experimental pain study in seven healthy volunteers, using the same positioning in the PET scanner as in the migraine patients. A small amount of capsaicin was administered subcutaneously in the right forehead to evoke a burning painful sensation in the first division of the trigeminal nerve. Increases of regional cerebral blood flow (rCBF) were found bilaterally in the insula, in the anterior cingulate cortex, the cavernous sinus and the cerebellum. Using the same stereotactic space limits as in the above mentioned migraine study no brain stem activation was found in the acute pain state compared to the pain free state. The increase of activation in the region of the cavernous sinus however, suggests that this structure is more likely to be involved in trigeminal transmitted pain as such, rather than in a specific type of headache as was suggested for cluster headache.

Acute Disease↗
PubMed1998

A review of differences between basal ganglia and cerebellar control of movements as revealed by functional imaging studies.

The role of the basal ganglia and cerebellum in the control of movements is unclear. We summarize results from three groups of PET studies of regional CBF. The results show a double dissociation between (i) selection of movements, which induces differential effects in the basal ganglia but not the cerebellum, and (ii) sensory information processing, which involves the cerebellum but not the basal ganglia. The first set of studies concerned motor learning of a sequence of finger movements; there was a shift of activation in the anterior-posterior direction of the basal ganglia which paralleled changes in the motor areas of the frontal cortex. During new learning, the dorsolateral prefrontal cortex and striatum (caudate nucleus and anterior putamen) were activated. When subjects had to select movements, the premotor cortex and mid-putamen were activated. With automatic (overlearned) movements, the sensorimotor cortex and posterior putamen were activated. When subjects paid attention to overlearned actions, activation shifted back to the dorsolateral prefrontal cortex and striatum. The cerebellum was not activated when subjects made new decisions, attended to their actions or selected movements. These results demonstrate components of basal ganglia-(thalamo)-cortical loops in humans. According to earlier studies in animals we propose that the basal ganglia may be concerned with selecting movements or the selection of appropriate muscles to perform a movement selected by cortical areas (e.g. premotor cortex). Secondly, a visuomotor co-ordination task was examined. In the absence of visual control over arm movements, subjects were required to use a computer mouse to either generate new lines or to re-trace lines on a computer screen. The neocerebellum (hemispheres of the posterior lobe, cerebellar nuclei and cerebellar vermis), not the basal ganglia, was more engaged when lines were re-traced (compared with new line generation). Animal experiments have shown that error detection (deviation from given lines) and correction occurs during line re-tracing but not line generation. Our data suggest that the neocerebellum (not the basal ganglia) is involved in monitoring and optimizing movements using sensory (proprioceptive) feedback. Thirdly, the relative contribution of sensory information processing to the signal during active/passive execution of a motor task (flexion and extension of the elbow) was examined; it was found that 80-90% of the neocerebellar signal could be attributed to sensory information processing. The basal ganglia were not involved in sensory information processing. They may be concerned with movement/ muscle selection (efferent motor component); the neocerebellum may be concerned with monitoring the outcome (afferent sensory component) and optimizing movements using sensory (feedback) information.

Basal Ganglia↗
PubMed1998

Involvement of the human cerebellum during habituation of the acoustic startle response: a PET study.

The present study investigated the involvement of the human cerebellum in the habituation of the acoustic startle response using PET. The startle response was elicited in seven young, healthy subjects by a tone presented via headphones. Startle responses were recorded from the right sternocleidomastoid muscle. Regional cerebral blood flow (rCBF) was assessed in nine scans and one startle stimulus was applied during each scan. The reduction of size of the sternocleidomastoid muscle response was correlated with changes in rCBF during the ongoing process of startle response habituation. A significant decrease of rCBF was found in the medial cerebellum. These data are consistent with an involvement of the medial parts of the human cerebellum in non-associative learning as proposed by previous animal studies.

Acoustic Stimulation↗