Biomedical subjects

C Weiller

Publications and source records attributed to C Weiller.

At least 55 records · Page 3Linked to original sources

PubMed2001

Motor cortex plasticity during forced-use therapy in stroke patients: a preliminary study.

Treatment-induced plastic changes were investigated in the brains of stroke patients in the subacute stage of illness. Nine patients participated in 1 week of conventional physiotherapy. In the subsequent week conventional physiotherapy was combined with forced-use therapy. Focal transcranial magnetic stimulation was used to determine the motor output areas of the abductor pollicis brevis muscles prior to the treatment and after the first and after the second week. Motor performance was evaluated using the Nine Hole Peg Test, the Frenchay Arm Test and vigorometry to measure the grip strength. Before treatment the cortical representation area of the paretic hand muscle was significantly smaller than the contralateral side. This difference persisted after the first week of physiotherapy. In contrast, the motor output map in the affected hemisphere was significantly enlarged after forced-use therapy. This increase in motor cortex excitability was accompanied by a significant improvement in dexterity. Across the two treatment weeks the centres of the motor output maps shifted significantly stronger in the affected hemisphere than in unaffected hemisphere, suggesting the recruitment of adjacent brain areas. We conclude that the combination of forced-use therapy and conventional physiotherapy enhances motor cortex excitability and improves motor performance compared to a preceding conventional physiotherapy alone. Due to the small number of patients and the lack of a control group, these results are preliminary observations and require replication in a larger sample.

Aged↗

PubMed2001

Inhibition of ipsilateral motor cortex during phasic generation of low force.

OBJECTIVE: To study the effect of different types of unilateral pinch grips on excitability of the ipsilateral motor cortex. METHODS: In 9 healthy volunteers, transcranial magnetic stimuli (TMS) were applied over one motor cortex while the subjects performed either phasic or tonic ipsilateral pinch grips with different force levels (range 1-40% maximum voluntary contraction, MVC). Motor evoked potentials (MEP) were recorded from the relaxed contralateral first dorsal interosseous muscle (FDI) and were compared to MEPs obtained during muscle relaxation of both hands. In additional experiments, transcranial electrical stimuli (TES) were administered and F waves were recorded after electrical stimulation of the ulnar nerve. RESULTS: Phasic pinch grips with low force (1 and 2% MVC) induced a significant decrease of TMS-induced MEP amplitudes. The effect lasted for about 100 ms after reaching the force level and was similar for both right and left-handed pinch grips. TES-induced MEPs and F waves remained unchanged. In contrast, tonic contractions (20 and 40% MVC) enhanced MEPs in the homologous FDI. CONCLUSIONS: Phasic pinch grips with low force inhibit the motor cortex responsible for the contralateral homologous hand muscle. This effect, which is probably mediated transcallosally, might act at the level of the motor cortex.

Adult↗

PubMed2001

Disinhibition of somatosensory and motor cortex in mitochondriopathy without myoclonus.

OBJECTIVE: To test electrophysiologically, if patients with mitochondriopathy but without evidence of myocloni have subclinical signs of disinhibition in motor and somatosensory cortices. METHODS: Two patients were studied and compared with age-matched control groups. RESULTS: In both patients, giant somatosensory evoked potentials after median nerve stimulation and a reduced intracortical inhibition tested by transcranial magnetic stimulation in a paired pulse paradigm indicated a dysfunction of inhibitory circuits in the motor as well as the somatosensory cortex. In addition, the somatosensory evoked 600 Hz activity recorded by magnetoencephalography was abolished. CONCLUSIONS: Patients with mitochondriopathy may suffer from a subclinical disturbance of inhibition in the sensorimotor cortex. The loss of 600 Hz activity indicates that these high-frequency oscillations could reflect the activity of inhibitory neurons in the somatosensory cortex.

Adult↗

PubMed2001

Motor cortex disinhibition in Alzheimer's disease.

OBJECTIVES: To explore subclinical disturbances in the motor cortex of patients with Alzheimer's disease (AD). METHODS: We used transcranial magnetic stimulation in a paired pulse technique to test intracortical inhibition (ICI) and intracortical facilitation in mildly to moderately demented AD patients with a normal neurological examination. Patients were studied before and during treatment with the cholinesterase inhibitor donepezil. RESULTS: AD patients had a reduced ICI compared to an age-matched control group. The amount of disinhibition correlated with the severity of dementia. Treatment with 10 mg donepezil daily was associated with an increase of ICI. CONCLUSIONS: The subclinical motor cortex disinhibition in AD patients indicates a functional disturbance, and is probably associated with a cholinergic deficit.

Aged↗

PubMed2001

A novel locus for autosomal dominant, non-syndromic hearing impairment (DFNA18) maps to chromosome 3q22 immediately adjacent to the DM2 locus.

Investigating a large German pedigree with non-syndromic hearing impairment of early onset and autosomal dominant mode of inheritance, linkage to known DFNA loci was excluded and in a subsequent genomic scan the phenotype was mapped to a 10-cM interval on chromosome 3q22; a maximum two-point lod score of 3.77 was obtained for the marker D3S1292. The new locus, DFNA18, is excluded from neighbouring deafness loci, DFNB15 and USH3, and it overlaps with the recently described DM2/PROMM locus. As hearing loss has been described as one feature of the PROMM phenotype, the DFNA18 gene might also be responsible for hearing loss in DM2/PROMM.

Chromosome Mapping↗

PubMed2001

Apparent diffusion coefficient decreases and magnetic resonance imaging perfusion parameters are associated in ischemic tissue of acute stroke patients.

Perfusion-and diffusion-weighted magnetic resonance imaging scans are thought to allow the characterization of tissue at risk of infarction. The authors tested the hypothesis that the apparent diffusion coefficient (ADC) decrease should be associated with the severity of the perfusion deficit in ischemic tissue of acute stroke patients. Perfusion-and diffusion-weighted scans were performed in 11 patients with sudden onset of neurologic deficits within the last 6 hours and T2-weighted magnetic resonance imaging scans were obtained after 6 days. Parameter images of the maximum of the contrast agent concentration, time to peak, relative cerebral blood volume, relative cerebral blood flow, and relative mean transit time were computed from the perfusion-weighted data. A threshold function was used to identify tissue volumes with stepwise ADC decreases. An onionlike distribution of successively decreasing ADC values was found, with the lowest ADC in the center of the ischemic region. Correspondingly, tissue perfusion decreased progressively from the periphery toward the ischemic core. This effect was most pronounced in the time-to-peak maps, with a linear association between ADC decrease and time-to-peak increase. Apparent diffusion coefficient values decreased from the periphery toward the ischemic core, and this distribution of ADC values was strongly associated with the severity of the perfusion deficit.

Adult↗

PubMed2001

Surface orientation discrimination activates caudal and anterior intraparietal sulcus in humans: an event-related fMRI study.

Perception of surface orientation is an essential step for the reconstruction of the three-dimensional (3D) structure of an object. Human lesion and functional neuroimaging studies have demonstrated the importance of the parietal lobe in this task. In primate single-unit studies, neurons in the caudal part of the intraparietal sulcus (CIP) were found to be active during the extraction of surface orientation through monocular (two-dimensional) cues such as texture gradients and linear perspective as well as binocular (3D) cues such as disparity gradient and orientation disparity. We used event-related fMRI to study the functional neuroanatomy of surface orientation discrimination using stimuli with monocular depth cues in six volunteers. Both posterior (CIP) and anterior (AIP) areas within the intraparietal sulcus showed a stronger activation during surface orientation as compared with a control (color discrimination) task using identical stimuli. Furthermore, the signal changes in CIP showed a greater performance effect than those in AIP, suggesting that CIP is tightly linked to the discrimination task.

Adult↗

PubMed2001

Spontaneous oscillations in cerebral blood flow velocity give evidence of different autonomic dysfunctions in various types of headache.

OBJECTIVES: Our objectives were to determine if: (1) patients with migraine have B wave abnormalities in comparison to normal controls and patients with chronic tension headache and (2) patients with chronic tension headache have an imbalance in autonomic activity that is reflected in differences in Mayer wave activity in comparison to normal controls. BACKGROUND: B waves and Mayer waves are spontaneous oscillations in cerebral blood flow velocity with a frequency of 0.5 to 3 or 4 to 7 cycles per minute, respectively, and can be measured by transcranial Doppler sonography. There is experimental evidence that B waves are generated by certain brain stem nuclei which modulate the lumen of the small intracerebral vessels via monoaminergic nerve endings. In contrast, Mayer waves in cerebral blood flow velocity have no central generator but mirror the Mayer waves in arterial blood pressure which represent peripheral autonomic activity. Migraine may be attributed to a neurotransmitter imbalance in brain stem nuclei. Dysfunctions of the peripheral autonomic nervous system are known in patients with chronic tension headache. METHODS: Using bilateral transcranial Doppler monitoring of the middle cerebral artery B waves and Mayer waves were studied in 30 patients with migraine without aura, 28 subjects with tension-type headache, and 30 normal controls. Coefficient of variation as a quantitative parameter for amplitude of waves and the mean frequency were calculated from the envelope curves of the Doppler spectra. RESULTS: The coefficient of variation of B waves was higher in migrainous patients compared with patients with tension-type headache and normal controls (P<.05), indicating an increase in activity of brain stem nuclei in migraine only. Patients with chronic tension headaches had lower values for Mayer wave activity in comparison with normal controls (P<.05), a sign of an impairment of sympathetic activity. CONCLUSIONS: Our data support the dysfunction of the brain stem monoaminergic/serotonergic system in migraine. In contrast, patients with chronic tension headache have an autonomic dysfunction of peripheral origin presenting as a decrease of sympathetic activity.

Adult↗

PubMed2000

The influence of lorazepam on somatosensory-evoked fast frequency (600 Hz) activity in MEG.

The generators of high frequency bursts (600-Hz activity) detected at the parietal scalp over the primary somatosensory cortex after electrical stimulation of peripheral nerves are not yet known. We investigated the influence of benzodiazepine on the somatosensory-evoked 600-Hz activity by means of neuromagnetic measurements and source analysis. After oral administration of lorazepam, the latency of the 600-Hz burst activity was increased; specifically later peaks were delayed more than earlier peaks. In contrast, the latency of the concurrent primary cortical low frequency response (N20m) was not significantly changed. The source strengths of both N20m and 600-Hz bursts were significantly increased. Our results provide evidence for two components of the 600-Hz activity with a different generator structure.

Adult↗

PubMed2000

Effects of passive tactile co-activation on median ulnar nerve representation in human SI.

In animals simple passive co-activation causes a fusion and expansion of the involved cortical representations. We used passive tactile finger co-activation for 40 min to investigate cortical representational changes in the human somatosensory cortex. Magnetic source imaging revealed that the euclidean distance between median and ulnar nerve somatosensory evoked fields (SEF) was significantly reduced after application of 600 synchronous airpuff stimuli to the fingertips of four fingers. In the control experiment without co-activation no significant change in distance was observed. Perception threshold and spatial two-point discrimination were not affected by the synchronous stimulation. This is in contrast to blind three-finger Braille readers who frequently mislocalize stimuli applied to the reading fingers. This points to a lack of behavioural relevance or the short duration of co-activation.

Adult↗

PubMed2000

Hemodynamic assessment of acute stroke using dynamic single-slice computed tomographic perfusion imaging.

BACKGROUND: Stroke management would benefit from a broadly available imaging tool that detects perfusion deficits in patients with acute stroke. OBJECTIVE: To determine the role of dynamic, single-slice computed tomographic (CT) perfusion imaging (CTP) in the assessment of acute middle cerebral artery stroke. DESIGN AND PATIENTS: Imaging with CTP and CT within the first 6 hours of symptom onset and before the start of treatment in a consecutive clinical series of 22 patients (mean age, 68.3 years; 14 women; studied within 143 +/- 96 minutes of stroke onset). SETTING: A stroke unit in a university hospital. MAIN OUTCOME MEASURES: Area of the perfusion deficit (nAP(0)) from time-to-peak maps, hemispheric lesion area from follow-up CT (HLA(F)), final infarct volume, and stroke recovery (National Institutes of Health Stroke Scale scores). RESULTS: Eighteen patients had perfusion deficits in the middle cerebral artery territory and corresponding hypoattenuation in follow-up CT. Three patients with normal CTP findings showed lacunar infarctions or normal findings on follow-up CT. In 1 patient, CTP did not reveal a territorial deficit above the imaging slice. The overall sensitivity and specificity of CTP for the detection of perfusion deficits in patients with proven territorial infarction (n = 18) on follow-up CT were 95% and 100%, respectively. The nAP(0) was significantly correlated with the National Institutes of Health Stroke Scale score at admission (P<.003) and the HLA(F) (P<.001). Different stroke patterns were identified in patients with follow-up CTP (n = 10): (1) initial perfusion deficit and partial nutritional reperfusion (nAP(0)>HLA(F); n = 6), (2) initial perfusion deficit and nonnutritional reperfusion (nAP( 0)>/=HLA(F); n = 2), and (3) initial perfusion deficit without reperfusion (nAP(0)>/=HLA(F); n = 2). CONCLUSIONS: Computed tomographic perfusion imaging detects major perfusion deficits in the middle cerebral artery territory. Because CTP is broadly available, it may play a role in acute stroke management. Arch Neurol. 2000;57:1161-1166

Acute Disease↗

PubMed2000

Motor cortex disinhibition of the unaffected hemisphere after acute stroke.

We studied motor cortex excitability in the nonlesioned hemisphere of patients with a large cortical infarction. Patients with a severe hemiparesis due to a stroke were compared with age-matched, healthy controls. Paired transcranial magnetic stimuli were applied over the unaffected hemisphere to investigate intracortical inhibition and facilitation. In the patient group, intracortical inhibition was reduced. We suggest that this disinhibition is due to an impairment of transcallosal fibers and may affect recovery.

Acute Disease↗

PubMed2000

Riluzole suppresses motor cortex facilitation in correlation to its plasma level. A study using transcranial magnetic stimulation.

The aim of our study was to measure the effects of the glutamate antagonist riluzole on different parameters of motor excitability, using transcranial magnetic stimulation (TMS) during 7 days of riluzole administration, and to correlate these effects with riluzole plasma levels. Nine healthy volunteers received a dose of 100 mg riluzole from day 1 to 7 of the study period. Electrophysiological examinations were performed on day 1 before and 2 h, 5 h and 8 h after riluzole administration, on day 2, day 3 and day 5 before riluzole administration, and on day 8. Plasma samples were taken simultaneously. The excitability of the motor cortex, supraspinal and spinal motor pathways was tested by studying intracortical facilitation and inhibition, the cortical silent period and motor threshold after TMS, as well as the peripheral silent period and F-wave amplitudes after electrical peripheral nerve stimulation. We found a significant reduction of intracortical facilitation, which correlated significantly with riluzole plasma levels. To a lesser extent, intracortical inhibition was enhanced on day 1, motor threshold was increased on day 8 and F-wave amplitudes were reduced. These changes did not correlate with riluzole plasma levels. We conclude that the main effect of riluzole in vivo is a reduction of intracortical facilitation, which is closely related to the drug's level in the plasma. The most probable mechanism involves an effect on glutamatergic synaptic transmission.

Adult↗

PubMed2000

Motor cortex disinhibition in acute stroke.

OBJECTIVES: To test whether a disinhibition occurs in the human motor cortex after stroke. METHODS: Patients with a mild to moderate hemiparesis after an acute unilateral ischemic stroke were compared with age-matched healthy controls. We used paired transcranial magnetic stimuli (TMS) to investigate intracortical inhibition and facilitation. Single TMS were applied to obtain a cortical silent period. RESULTS: Intracortical inhibition was significantly reduced in the affected hemisphere at interstimulus intervals of 2, 3 and 4 ms. The cortical silent period was significantly prolonged when compared to the unaffected hemisphere of the patients and to the control group. Motor cortex disinhibition observed in stroke patients was associated either with minimal impairment at the onset of symptoms or with rapidly improving motor functions. CONCLUSIONS: Motor cortex disinhibition occurs in humans after stroke. We suggest that this disinhibition is indicative of compensatory mechanisms, which are involved in recovery-related reorganization.

Acute Disease↗

PubMed2000

Training-induced changes of motor cortex representations in stroke patients.

OBJECTIVE: To study changes in motor cortex representations after a single session of physiotherapy in stroke patients. METHODS: TMS mapping was used to evaluate the motor output map of the abductor pollicis brevis (APB) in both hemispheres. Stroke patients (4-8 weeks after the infarction) were studied prior to a training session aimed at improving dexterity and 1 h and 1 day after the training. RESULTS: Prior to the training, the APB representation area in the affected hemisphere was significantly smaller than on the non-affected side. After therapy, the cortical motor output to the paretic APB was significantly enlarged, and motor function was improved. One day later, these effects were partially reversed. Motor thresholds remained significantly increased in the affected hemisphere before and after the therapy. CONCLUSION: A single session of physiotherapy produces a use-dependent enlargement of motor cortex representations paralleled by an improvement of motor function in stroke patients.

Adult↗

PubMed2000

Reduced vasomotor reactivity in cerebral microangiopathy : a study with near-infrared spectroscopy and transcranial Doppler sonography.

BACKGROUND AND PURPOSE: Reduction of cerebral blood flow and vasomotor reactivity (VMR) are thought to play an important role in the pathogenesis of cerebral microangiopathy. The aim of our study was to determine whether near-infrared spectroscopy (NIRS) can detect a reduced VMR in patients with microangiopathy, whether NIRS reactivities correlate with VMR assessed by transcranial Doppler sonography (TCD), and whether the differing extents of patients' microangiopathy demonstrated on MRI or CT can be distinguished by both noninvasive techniques. METHODS: We compared the VMR of 46 patients with cerebral microangiopathy with 13 age-matched control subjects. Patients were classified with the Erkinjuntti scale. We monitored cerebral blood flow velocity (CBFV) in both middle cerebral arteries by TCD, changes in concentration of oxyhemoglobin (HbO(2)), deoxyhemoglobin (Hb) and blood volume (HbT) by NIRS, mean arterial blood pressure, and end-tidal CO(2) (EtCO(2)) during normocapnia and hypercapnia. VMRs were calculated as percent change of CBFV (NCR) and as absolute change in concentration of HbO(2), Hb, and HbT per 1% increase in EtCO(2) (CR-HbO(2), CR-Hb, CR-HbT). RESULTS: NCR and NIRS reactivities were significantly reduced in patients with cerebral microangiopathy. CR-HbO(2) and CR-Hb showed a close correlation with NCR, and NCR and NIRS reactivities were related to the severity of cerebral microangiopathy according to the Erkinjuntti scale. Validity of NCR and NIRS reactivities were similar. CONCLUSIONS: VMR is reduced in patients with cerebral microangiopathy and can be noninvasively assessed in basal arteries (with TCD) and brain parenchyma (with NIRS). Reduction of CO(2)-induced VMR, as measured by NIRS and TCD, may indicate the severity of microangiopathy.

Aged↗

PubMed2000

Treatment-induced cortical reorganization after stroke in humans.

BACKGROUND AND PURPOSE: Injury-induced cortical reorganization is a widely recognized phenomenon. In contrast, there is almost no information on treatment-induced plastic changes in the human brain. The aim of the present study was to evaluate reorganization in the motor cortex of stroke patients that was induced with an efficacious rehabilitation treatment. METHODS: We used focal transcranial magnetic stimulation to map the cortical motor output area of a hand muscle on both sides in 13 stroke patients in the chronic stage of their illness before and after a 12-day-period of constraint-induced movement therapy. RESULTS: Before treatment, the cortical representation area of the affected hand muscle was significantly smaller than the contralateral side. After treatment, the muscle output area size in the affected hemisphere was significantly enlarged, corresponding to a greatly improved motor performance of the paretic limb. Shifts of the center of the output map in the affected hemisphere suggested the recruitment of adjacent brain areas. In follow-up examinations up to 6 months after treatment, motor performance remained at a high level, whereas the cortical area sizes in the 2 hemispheres became almost identical, representing a return of the balance of excitability between the 2 hemispheres toward a normal condition. CONCLUSIONS: This is the first demonstration in humans of a long-term alteration in brain function associated with a therapy-induced improvement in the rehabilitation of movement after neurological injury.

Adult↗

PubMed2000

[Clinical applications of single photon emission tomography in neuromedicine. 1. Neuro-oncology, epilepsy, movement disorders, cerebrovascular disease].

Single photon emission tomography is, because of its availability and the relatively low costs, the functional imaging modality currently most widely used for clinical applications in the brain. Beside the application of radiopharmaceuticals for the assessment of regional cerebral blood flow there is an increasing clinical use of more selective SPECT-radiopharmaceuticals, like amino acid analogs or receptor ligands. This article gives in his first part a critical review of the clinical applications of SPECT in neuro-oncology, epilepsy, basal ganglia disorders and cerebrovascular disease.

Cerebrovascular Disorders↗