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P Schwenkreis

Publications and source records attributed to P Schwenkreis.

16 recordsLinked to original sources
PubMed2005

Transcallosal inhibition across the menstrual cycle: a TMS study.

OBJECTIVE: To determine if there are steroid-dependent changes in transcallosal transfer during the menstrual cycle in normal women. METHODS: We tested 13 normally cycling women during the menstrual, follicular and midluteal phases. Blood levels of estradiol (E) and progesterone (P) were determined by radioimmunoassay. Ipsilateral tonic voluntary muscle activity suppression, called ipsilateral silent period (iSP), was evoked by applying transcranial magnetic stimulation (TMS) over the left motor cortex and by measuring the EMG of the ipsilateral first dorsal interosseus (FDI) muscle. Both iSP-duration and transcallosal conduction times were measured and related to cycle phase and steroid levels. RESULTS: Duration of iSPs varied over the cycle with largest differences between follicular and midluteal phases. During the midluteal phase high levels of P were significantly related to short iSPs. This relation also applied to E levels and iSPs during the follicular phase. CONCLUSIONS: Our study shows for the first time that the transcallosal transfer is modulated by E and P and changes over the menstrual cycle. SIGNIFICANCE: It is suggested that gonadal steroid hormones affect the interhemispheric interaction and change the functional cerebral organization sex dependently via its neuromodulatory properties on GABAergic and glutamatergic neurons.

Adult↗
PubMed2004

[Visual cortex in the Tolosa-Hunt syndrome. Functional imaging for the detection of a psychogenic disorder--a case report].

Besides painful ophthalmoplegia, patients suffering from Tolosa-Hunt syndrome often present increasing loss of visual perception. The impairment of the optic nerve leads to a delay of the VEP (visual evoked potentials) responses. Using the method of magnetic resonance imaging (MRI), some patients present unspecific alterations in the vicinity of the optic nerve. However, both methods (VEP and MRI) are unsuitable to assess the effect of an impaired optic nerve function on neuronal processing in the visual cortex. We report one patient suffering from Tolosa-Hunt syndrome affecting the optic nerve. We used fMRI (functional magnetic resonance imaging) to show how this impairment of the optic nerve alters cortical processing of visual information. The activity of the unaffected visual cortex was bilaterally reduced when compared to healthy volunteers but greater that obtained from patients suffering from bilateral occipital infarction. Our results offer new opportunities to assess the efficiency of therapy in patients with increasing loss of visual perception due to the Tolosa-Hunt syndrome. Further studies are necessary to investigate, whether fMRI also provides the possibility to assess the efficiency of drug therapy on optic nerve function.

Humans↗
PubMed2004

Amphetamine enhances training-induced motor cortex plasticity.

OBJECTIVES: Repetitive synchronized movements lead to short-term plastic changes in the primary motor cortex, which can be assessed by transcranial magnetic stimulation (TMS). Drugs which enhance such plastic changes could be of therapeutical interest, e.g. in patients with cerebral lesions. MATERIAL AND METHODS: We studied the effect of amphetamine on motor performance and plastic changes in the motor cortex as revealed by TMS mapping in healthy humans, who had to train a repetitive synchronized movement over 1 h. RESULTS: Cortical plastic changes observed after 1 h of training were more pronounced with amphetamine, whereas motor performance did not differ between training sessions with and without amphetamine. CONCLUSION: We conclude that amphetamine is able to enhance training-induced motor cortex plasticity. This effect could be due to its known influence on the GABAergic and glutamatergic system, but might also result from its role as an indirect catecholaminergic agonist.

Adult↗
PubMed2003

Bilateral motor cortex disinhibition in complex regional pain syndrome (CRPS) type I of the hand.

BACKGROUND: Complex regional pain syndrome type I (CRPS I) develops as a consequence of trauma affecting the limbs, without obvious nerve lesion. Its features include pain, edema, autonomic dysfunction, movement disorder, and trophic changes. CNS involvement is suggested by the symptoms, but the pathophysiology of CRPS I is unknown. OBJECTIVE: To assess excitability changes in the motor cortex in patients with CRPS I. METHODS: The authors studied 25 patients with unilateral CRPS I involving the hand by means of transcranial magnetic stimulation using a paired-pulse paradigm. Motor threshold (MT) and intracortical inhibition and facilitation were determined on the affected and the clinically unaffected side. A control group of 20 healthy subjects was studied. RESULTS: The authors found a significant reduction of intracortical inhibition on both sides of patients with CRPS compared with control subjects, whereas intracortical facilitation and MT did not differ significantly. However, in the patients' group, the presence of allodynia significantly decreased MT. CONCLUSIONS: The authors showed a bilateral disinhibition of the motor cortex in patients with complex regional pain syndrome.

Adult↗
PubMed2003

[Therapeutic use of cannabinoids in neurology].

This review gives insight into the potential therapeutical role of cannabinoids in neurology. Preclinical data are presented which could give a rationale for the clinical use of cannabinoids in the fields of multiple sclerosis, spasticity, epilepsy, movement disorders, and neuroprotection after traumatic head injury or ischemic stroke. Besides, clinical data (case reports, open-label and randomised controlled studies) dealing with the therapeutical use of cannabinoids in these fields are reported and discussed. At present, clinical data are insufficient to recommend the use of cannabinoids in any neurological disease as standard therapy. Several questions still have to be answered (which cannabinoid? which way of administration? stimulation of endogenous cannabinoids? separation between desired and undesired effects?), and controlled studies are still needed to clarify the potential therapeutical role of cannabinoids in neurology.

Analgesics↗
PubMed2003

NMDA-mediated mechanisms in cortical excitability changes after limb amputation.

OBJECTIVES: The aim of our study was to determine the role of N-methyl-d-aspartate (NMDA)-mediated mechanisms in cortical excitability changes after limb amputation, and their possible relationship to phantom pain. MATERIALS AND METHODS: Sixteen upper limb amputees who were suffering from chronic phantom pain received the NMDA-antagonist memantine or placebo for 3 weeks. Intracortical inhibition (ICI) and intracortical facilitation (ICF) were determined at baseline and on day 21 using transcranial magnetic stimulation. Simultaneously, phantom pain intensity was assessed. RESULTS: Memantine reduced ICF and enhanced ICI to roughly the same extent as seen in healthy subjects in a previous study. These changes were not correlated to the reduction of phantom pain. CONCLUSION: We therefore conclude that NMDA-mediated mechanisms influence changes of ICI and ICF occurring after limb amputation. However, our results suggest that these cortical excitability changes and phantom pain are independent of each other.

Adult↗
PubMed2001

Repetitive training of a synchronised movement induces short-term plastic changes in the human primary somatosensory cortex.

The aim of our study was to assess possible short-term plastic changes in the human primary somatosensory cortex (S1) induced by a repetitive synchronised movement of the right thumb and shoulder. We therefore performed a source localisation of somatosensory evoked potentials after median nerve stimulation in twelve healthy subjects before and after 1 h of motor training. We found a significant medial shift of the N20 dipole on the left hemisphere after training, whereas the dipole location on the right hemisphere remained unchanged. However, no significant correlation was seen between the dipole shift and the improvement in motor performance. We conclude that repetitive synchronised movements are able to induce plastic changes in the contralateral S1, which might be mainly due to the synchronised proprioceptive input.

Adult↗
PubMed2001

Shifts in cortical representations predict human discrimination improvement.

We report experiments combining assessment of spatial tactile discrimination behavior and measurements of somatosensory-evoked potentials in human subjects before and after short-term plastic changes to demonstrate a causal link between the degree of altered performance and reorganization. Plastic changes were induced by a Hebbian coactivation protocol of simultaneous pairing of tactile stimuli. As a result of coactivation, spatial discrimination thresholds were lowered; however, the amount of discrimination improvement was variable across subjects. Analysis of somatosensory-evoked potentials revealed a significant, but also variable shift in the localization of the N20-dipole of the index finger that was coactivated. The Euclidean distance between the dipole pre- and post-coactivation was significantly larger on the coactivated side (mean 9.13 +/- 3.4 mm) than on the control side (mean 4.90 +/- 2.7 mm, P = 0.008). Changes of polar angles indicated a lateral and inferior shift on the postcentral gyrus of the left hemisphere representing the coactivated index finger. To explore how far the variability of improvement was reflected in the degree of reorganization, we correlated the perceptual changes with the N20-dipole shifts. We found that the changes in discrimination abilities could be predicted from the changes in dipole localization. Little gain in spatial discrimination was associated with small changes in dipole shifts. In contrast, subjects who showed a large cortical reorganization also had lowest thresholds. All changes were highly selective as no transfer to the index finger of the opposite, non-coactivated hand was found. Our results indicate that human spatial discrimination performance is subject to improvement on a short time scale by a Hebbian stimulation protocol without invoking training, attention, or reinforcement. Plastic processes related to the improvement were localized in primary somatosensory cortex and were scaled with the degree of the individual perceptual improvement.

Adult↗
PubMed2001

Assessment of reorganization in the sensorimotor cortex after upper limb amputation.

OBJECTIVE: We wanted to investigate plastic changes occurring in the motor and somatosensory cortex after upper limb amputation, and their possible relationship to phantom pain. METHOD: To assess these plastic changes, we used transcranial magnetic stimulation (TMS) and source localization of somatosensory evoked potentials (SEP). Eleven patients with upper limb amputation were investigated. The phantom pain intensity was assessed by visual analogue scaling (VAS). RESULTS: Using TMS mapping, we found a significant lateralization of the amplitude-weighted centre of gravity (P<0.01) and an enlargement of the excitable area (P<0.05) on the hemisphere contralateral to the amputation. SEP mapping showed a significant medialization of the N20 dipole (P<0.05) on this side. None of these changes correlated with the phantom pain intensity. CONCLUSIONS: We conclude that after limb amputation, the relationship between plastic changes occurring in the sensorimotor cortex and phantom pain seems to be more complex than previously believed.

Adult↗
PubMed2000

Changes of cortical excitability in patients with upper limb amputation.

In our study we wanted to assess motor excitability in patients with upper limb amputation by means of transcranial magnetic stimulation (TMS). In 12 patients, TMS was applied using a paired pulse paradigm in order to test cortico-cortical excitability. Additional parameters of motor excitability like motor threshold and cortical silent period were also measured. Recordings from the amputated side were compared to the contralateral side and to healthy controls. We found a significant reduction of intracortical inhibition in forearm amputees and an enhancement of intracortical facilitation in upper arm amputees on the affected side. We conclude that after upper limb amputation, changes in the activity of intracortical interneuronal circuits appear in the affected hemisphere. These changes may depend on the level of amputation, and be the base of cortical reorganization.

Adult↗
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↗
PubMed1999

Influence of the N-methyl-D-aspartate antagonist memantine on human motor cortex excitability.

The aim of our study was to investigate the effect of the N-methyl-D-aspartate (NMDA) antagonist memantine on motor excitability in humans. Seven healthy volunteers received memantine or placebo, respectively, over a period of 8 days. At day 8, transcranial magnetic stimulation (TMS) was performed using a paired pulses paradigm in order to assess intracortical inhibition and facilitation. Additionally, motor threshold and silent period duration after TMS were measured as well as M waves, F waves and peripheral silent period after electrical peripheral nerve stimulation. Intracortical inhibition was enhanced, and intracortical facilitation reduced after memantine ingestion in comparison to placebo, whereas no significant difference could be observed regarding the other neurophysiological parameters. We conclude that the NMDA receptor is involved in the regulation of excitability of intracortical interneuronal circuits.

Adult↗
PubMed1999

Assessment of postexcitatory inhibition in patients with focal dystonia.

The aim of our present study was to detect whether a generalized disturbance of intracortical inhibitory mechanisms as assessed by transcranial magnetic stimulation (TMS) can be observed in a movement disorder with localized clinical expression, that is, in focal cervical dystonia. We measured motor threshold intensity, central motor conduction time and the duration of postexcitatory inhibition evoked by single and paired stimuli TMS from a small hand muscle in 20 patients with idiopathic cervical dystonia, and 21 healthy volunteers. A significant difference could not be found in any of the neurophysiological parameters between patients and controls. These findings are unlike the observations made in Parkinson's disease and Huntington's disease, where significant changes of postexcitatory inhibition after TMS can be observed. This suggests a lack of widespread change in activity of underlying cortical inhibitory mechanisms, as seen in other diseases of the extrapyramidal system with more generalized clinical involvement.

Adult↗
PubMed1998

Reduced intracortical facilitation in patients with cerebellar degeneration.

OBJECTIVES: Transcranial magnetic stimulation (TMS) was used to study intracortical inhibitory and excitatory phenomena in patients with cerebellar ataxia. METHODS: Motor evoked potentials (MEP) following single and paired TMS were recorded from the first dorsal interosseus muscle (FDI) in 15 patients with autosomal-dominant or idiopathic cerebellar ataxia and 15 age matched normal controls. RESULTS: MEP amplitudes after paired TMS with short interstimulus intervals (1-4 ms) showing intracortical inhibition in the control group were not significantly different in the patient group. In contrast, with longer interstimulus intervals (8-20 ms) mean MEP amplitudes were significantly reduced in the patient group, indicating a decrease of intracortical facilitation. The mean postexcitatory inhibition after TMS was also significantly prolonged in the patient group. CONCLUSION: Our findings support the idea that the cerebellum physiologically exerts a facilitatory influence on the motor cortex which is decreased in patients with a cerebellar degeneration.

Action Potentials↗
PubMed1997

The glutamate antagonist riluzole suppresses intracortical facilitation.

The effect of the glutamate antagonist riluzole on excitatory and inhibitory phenomena in the human motor system was studied by transcranial magnetic stimulation (TMS) and peripheral electrical nerve stimulation. The motor threshold, the intracortical inhibition and intracortical facilitation as assessed by paired TMS, the cortical and peripheral silent periods, F wave amplitudes and F wave latencies were measured. Riluzole suppressed the intracortical facilitation whereas other parameters remained unchanged, indicating that the neurotransmitter glutamate is mainly involved in facilitatory mechanisms in the motor system.

Adult↗