-
[show abstract]
[hide abstract]
ABSTRACT: We aimed at detecting neurophysiological changes, in the primary motor tongue representation in adults with persistent stuttering.
Using transcranial magnetic stimulation in 12 patients and 14 controls, we examined motor threshold, motor-evoked potential (MEP) input-output curve, short-term intracortical inhibition (SICI) and intracortical facilitation (ICF), based on eight trials per conditioning-test interval.
In controls inhibition of the MEP-amplitude at short inter-stimulus intervals (ISI) and facilitation of the MEP-amplitude at long ISIs was evident. Patients showed an inhibition at ISI 3 ms and weaker non-significant inhibition at ISI 2 ms; this delay of inhibitory activity was especially prominent in the right hemisphere. Facilitation was reduced at ISI 10 and 15 ms in patients. Furthermore, MEP input-output curve was steeper in patients. Motor thresholds did not differ between groups.
In persistent stuttering intracortical excitability of the primary motor tongue representation is altered with a deviant time course for inhibitory activity in the right hemisphere and reduced paired-pulse facilitation.
These results specify changes in intracortical networks possibly mediated by altered GABAergic regulations in persistent stuttering. Thus, a better understanding of pathomechanisms and a potential role in understanding pharmacological treatment responses emerge by using transcranial magnetic stimulation.
Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology 03/2011; 122(9):1802-11. · 3.12 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The intensity of transcranial magnetic stimulation (TMS) is typically adjusted by changing the amplitude of the induced electrical field, while its duration is fixed. Here we examined the influence of two different pulse durations on several physiological parameters of primary motor cortex excitability obtained using single pulse TMS.
A Magstim Bistim(2) stimulator was used to produce TMS pulses of two distinct durations. For either pulse duration we measured, in healthy volunteers, resting and active motor thresholds, recruitment curves of motor evoked potentials in relaxed and contracting hand muscles as well as contralateral (cSP) and ipsilateral (iSP) cortical silent periods.
Motor thresholds decreased by 20% using a 1.4 times longer TMS pulse compared to the standard pulse, while there was no significant effect on threshold adjusted measurements of cortical excitability. The longer pulse duration reduced pulse-to-pulse variability in cSP.
The strength of a TMS pulse can be adjusted both by amplitude or pulse duration. TMS pulse duration does not affect threshold-adjusted single pulse measures of motor cortex excitability.
Using longer TMS pulses might be an alternative in subjects with very high motor threshold. Pulse duration might not be relevant as long as TMS intensity is threshold-adapted. This is important when comparing studies performed with different stimulator types.
Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology 05/2010; 121(11):1915-21. · 3.12 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Stimulation frequency has been considered the most important factor in conventional repetitive transcranial magnetic stimulation (rTMS) for determining the direction of after effects on corticospinal excitability. Here, we examined the functional relevance of breaks during high-frequency subthreshold rTMS for the induction of facilitatory after effects.
The after effects on corticospinal excitability of a standard 5Hz rTMS protocol in a block design were compared to a continuous rTMS protocol using the same number of pulses. In addition the effect of current direction both for rTMS and single pulse TMS was included in the study design.
While 5Hz rTMS in a standard block design induces facilitatory after effects on corticospinal excitability, the continuous protocol does not induce facilitation but rather inhibition. In our study only rTMS using an initially posterior-anterior current direction in the brain leads to significant neuroplastic effects at all.
Breaks during conventional high-frequency rTMS are a crucial factor determining the direction of induced neuroplastic changes.
These results contribute to the understanding of rTMS-induced neuroplasticity and are important for the design of rTMS protocols both for experimental and clinical studies.
Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology 12/2009; 121(3):426-30. · 3.12 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Restless legs syndrome (RLS) is a common neurological disorder complicated in many patients by augmentation to dopaminergic therapy or comorbidities such as neuropathic pain.
To explore the effectiveness of pregabalin in RLS in a pragmatic clinical setting.
After observing improvement of restless legs symptoms in seven patients treated with pregabalin for neuropathic pain, we extended the clinical observation to a total of 16 patients with secondary RLS, in most of them due to neuropathy, and to three patients with idiopathic RLS.
Three patients discontinued pregabalin because of side effects (rash, fatigue, loss of efficacy). The other 16 patients self-rated a satisfactory or good alleviation of RLS symptoms and maintained pregabalin, five with add-on medication, on a mean daily dose of 305 mg (standard deviation, 185 mg), and with a mean duration of 217 (standard deviation, 183) days.
These data propose pregabalin as a new option in the treatment of secondary RLS for patients with neuropathic pain, which should be further investigated with randomized, placebo-controlled trials.
Acta Neurologica Scandinavica 06/2007; 115(5):347-50. · 2.47 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Repetitive transcranial magnetic stimulation (rTMS) can modify cortical excitability and is widely used for clinical and research purposes. We sought to determine the intra- and interindividual variability of its effects on motor cortex excitability, and whether repeated paired-pulses yield less variability than repeated single-pulses.
We investigated rTMS over the left motor cortex of 6 healthy subjects and recorded motor evoked potentials (MEPs) from the right abductor digiti minimi muscle. Eighty single suprathreshold stimuli or conditioning-test pairs of stimuli were delivered at 2Hz frequency. The pairs consisted of a subthreshold pulse followed by a suprathreshold pulse after 2, 5 or 10ms. In each subject we studied all types of rTMS 5 times on separate days. Single suprathreshold pulses at 0.17Hz preceded rTMS for baseline determination.
The day-to-day variability of MEPs during either type of rTMS was small compared to the subject-to-subject variability. MEPs increased during all types of rTMS except for interstimulus interval (ISI) 2ms. Paired-pulses yielded less variability than single-pulse rTMS.
Motor responses to rTMS show a high interindividual, but a low intraindividual variability. Repeated paired-pulses yield less variability than repeated single-pulses.
Clinical Neurophysiology 03/2002; 113(2):265-9. · 3.41 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The excitability of human brainstem interneurons is measured by the blink reflex recovery cycle and is abnormal in blepharospasm. We wondered whether the results of this paradigm depend on the stimulus intensity.
We investigated the blink reflex recovery cycle in 13 healthy control subjects and in 13 patients with blepharospasm (7 of them treated with botulinum toxin) using 4 levels of stimulus intensity (5, 12, 19 and 26 mA) and two interstimulus intervals (ISIs, 150 or 250 ms).
In all groups the inhibition of the second R2 response was reduced with strong stimulus intensities: In controls, the inhibition of the second R2 decreased significantly (e.g. young controls, ISI 150 ms, from 89.6+/-15.6% at 5 mA to 21.9+/-49.7% at 26 mA, mean+/-standard deviation). In patients the R2 inhibition found at 5 mA was converted in an R2 facilitation at 26 mA, irrespective of the status of treatment. In addition, the patients' results at 5 mA did not differ significantly from the controls' results at 26 mA.
The R2 inhibition and its sensitivity to detect abnormal interneuronal excitability depend on the stimulus intensity, which may act by modifying the excitability of the R2 interneurons.
Clinical Neurophysiology 01/2002; 112(12):2293-9. · 3.41 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: To investigate by means of transcranial magnetic stimulation (TMS) the effect of a single oral dose of the GABA derivate piracetam on intracortical facilitatory I-wave interaction.
The study was performed in 8 healthy volunteers. Before, 1, 3, 6, and 24 h after intake of 4000 mg piracetam, MEPs in the relaxed abductor digiti minimi muscle were elicited by a recently introduced double pulse TMS technique with a suprathreshold first and a subthreshold second stimulus. From interstimulus intervals of 0.5-5.1 ms 3 periods were observed in which MEP facilitation showed maxima - so-called peaks of I-wave interaction - and which were separated by two troughs with no facilitation. We studied the changes in timing and size of the peaks over time.
With piracetam, I-wave peaks showed a reduction in size as well as a shortening of the latencies at which the peaks occurred. Both changes were significant at 6 h after drug intake compared to baseline. The effects were partially reversible after 24 h.
The mode of action of piracetam within the nervous system is almost unknown. The peak size reduction was similar to effects that were seen under GABAergic drugs, although GABAergic properties of piracetam have not been observed so far. Shortening of the I-wave peak latencies is a new phenomenon. The results are discussed on the basis of the known therapeutic effects of piracetam in cortical myoclonus and as nootropic agent.
Clinical Neurophysiology 03/2001; 112(2):275-9. · 3.41 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: To study the time course of the changes of the inhibitory network of the human motor system, we investigated the silent period (SP) in 7 healthy subjects by double suprathreshold transcranial magnetic stimulation (TMS).
SPs and motor evoked potentials (MEPs) were recorded from the voluntarily activated right abductor digiti minimi muscle. Conditioning and test stimuli were delivered with equal intensity, which was set to yield a baseline SP duration of 130 ms by a single pulse, and with various interstimulus intervals (ISIs). In addition, a control experiment with adjustment of the intensity of single stimuli was performed.
At ISIs of 20 and 30 ms the test pulse SP duration was prolonged, without increasing the MEP amplitude. The SP duration shortened at longer ISIs and showed a significant depression between ISIs of 60-110 ms. The shortened SP was accompanied by a diminished MEP. The control experiment revealed that the SPs evoked by the adjusted pulses were significantly shorter than the test pulse SPs.
A conditioning stimulus can prolong and shorten the test pulse SP duration at different ISIs. The prolongation is probably cortically generated, whereas the shortening is likely to occur at a cortical and spinal level.
Clinical Neurophysiology 11/2000; 111(10):1868-72. · 3.41 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In order to determine the extent to which the recovery cycle of the blink reflex is modified by voluntary contraction of the eyelids we investigated the electrically elicited blink reflex with paired stimuli of identical intensity in 9 healthy subjects. We pseudorandomly administered two interstimulus intervals (150 ms and 250 ms) in three different conditions of voluntary contraction of the orbicularis oculi muscle (relaxed, mild lid closure and strong lid closure). Our results show that inhibition of the R2 response following the second stimulus is significantly reduced with voluntary contraction. In addition, we found significantly larger amplitudes and shorter latencies of R1 and R2 with voluntary contraction. We conclude that in healthy subjects, voluntary eyelid contraction causes facilitation or disinhibition not only in the nuclei of the seventh cranial nerve, but also in the polysynaptic pathway of the R2. The possible implications on the interpretation of clinical data are discussed.
Acta Neurologica Scandinavica 08/1998; 98(1):29-35. · 2.47 Impact Factor
