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Results for “Transcranial Magnetic Stimulation”

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PubMed2001

Elevated motor threshold in drug-free, cocaine-dependent patients assessed with transcranial magnetic stimulation.

BACKGROUND: Transcranial magnetic stimulation (TMS) provides a noninvasive method of examining cortical inhibitory and excitatory processes and cortical excitability in awake subjects. There is evidence from clinical and electroencephalographic (EEG) data that cortical excitability may be abnormal in some psychiatric populations. Chronic cocaine abuse influences a number of neurotransmitters that are involved in the excitatory/inhibitory balance of the cerebral cortex. This pilot study was conducted to ascertain the possible utility of TMS in examining cortical excitability in a population of chronic cocaine abusers. METHODS: The right and left motor thresholds of ten cocaine-dependent subjects, according to DSM-IV, and ten normal control subjects were examined using single pulse TMS. RESULTS: The resting motor thresholds resulting from stimulation of the right or the left motor cortical regions were significantly elevated in cocaine-dependent subjects compared with matched control subjects. CONCLUSIONS: These pilot data suggest that chronic cocaine use significantly alters cortical excitability in the direction of increased inhibition or decreased excitability. We hypothesize that this observation reflects adaptation to those effects of cocaine intoxication that promote cortical excitability and seizures.

Adult↗

PubMed2006

Reducing pain and unpleasantness during repetitive transcranial magnetic stimulation.

Repetitive transcranial magnetic stimulation (rTMS) is associated with significant scalp discomfort under the coil for a high percentage of participants, especially with high stimulation intensities (100% of motor threshold or higher) or frequencies (1 Hz or greater). Some patients in rTMS clinical trials have been unable to tolerate the pain and have dropped out. There seem to be no published studies of strategies to reduce the localized pain and discomfort associated with rTMS. Thus, the authors conducted preliminary pilot trials of 4 different strategies for managing discomfort associated with left prefrontal rTMS. Healthy adults rated the painfulness and unpleasantness of left prefrontal rTMS (10 Hz; 5 seconds, on; 30 seconds, off; at 100% and 120% of resting motor threshold) before and after (1) topical application of a eutectic mixture of local anesthetics cream, (2) scalp injection of lidocaine, (3) scalp injection of lidocaine and epinephrine, and (4) with or without 3 x 3-in thin foam sheets between the coil and scalp. The discomfort produced by rTMS under these experimental conditions was compared with the discomfort produced by stimulation with the same parameters without the interventions. Localized anesthetic injections were associated with a significant decrease in pain intensity and unpleasantness, whereas the eutectic mixture of local anesthetics cream had no effect on rTMS-related discomfort. The use of foam sheets was associated with a slight but noticeable decrease in pain intensity and unpleasantness. More systematic research is needed on the effectiveness of different strategies for reducing rTMS-related pain and discomfort.

Administration, Topical↗

PubMed2000

Cortical motor reorganization following early brain damage and hemispherectomy demonstrated by transcranial magnetic stimulation.

BACKGROUND: Transcranial magnetic stimulation (TMS) was utilized to study 7 patients who had undergone hemispherectomy for control of longstanding intractable epilepsy to assess cortical motor reorganization and MEP (motor evoked potentials) ipsilateral to the remaining hemisphere. Five patients were seizure-free post-operatively. All patients displayed a spastic hemiparesis, were able to walk, raise and bend the paretic arm and use the paretic hand to different degrees. METHODS: We examined MEP threshold, site of maximal response to TMS, and latency to the biceps brachii, abductor pollicis brevis and the anterior tibial muscles using a 7 and 12 cm diameter round coil. RESULTS: The following results were obtained: (1) No MEP could be induced to either side by use of the small coil. (2) When using the large coil MEP-threshold was elevated also when stimulating the non-affected hemisphere in comparison to normal controls. (3) Ipsilateral MEP were found to: be non-inducible in two patients, demonstrate largely increased latencies in 3 and be identical to contralateral MEP in two patients. (4) Ipsilateral MEP could be evoked more often in distal than proximal muscles. (5) The site of maximal ipsilateral MEP response was found approximately 2 cm anteriorly to that of the contralateral MEP to the non-affected side of the body (6) No correlation was found between the degree of hemiparesis and inducability of MEP. CONCLUSIONS: The pattern of reorganization of ipsilateral motor control following early brain damage and hemispherectomy appears to be extremely diverse and does not correlate with the degree of neurological impairment.

Adult↗

PubMed1992

Silent period measurement revives as a valuable diagnostic tool with transcranial magnetic stimulation.

Following magnetic transcranial stimulation (TCS) a post-excitatory pause can be observed in surface electromyographic (EMG) recordings from pre-innervated muscles. We studied the duration of this silent period (SP) in the abductor pollicis brevis muscle while varying the stimulus intensity (SI) and the amount of the voluntary tonic contraction in 23 normal adults aged 20-78 years. A multivariate linear regression analysis revealed a positive correlation of SP with SI and a slight negative correlation with age. In 11 hemiparetic patients a relative increase of the SP was found on the affected side despite normal central motor conduction time. A marked shortening of the SP in relation to controls was observed in 6 parkinsonian patients.

Adult↗

PubMed2000

The cerebral hemodynamics of repetitive transcranial magnetic stimulation.

Repetitive transcranial magnetic stimulation (rTMS) has been shown to be effective in the treatment of affective disorders. However, only little is known about hemodynamic physiological and safety aspects of this method. We studied the cerebral hemodynamics as measured by transcranial Doppler sonography in 20 healthy subjects during different rTMS procedures. Mean cerebral blood flow velocity (CBFV), pulsatility index (PI), and oxygen consumption were recorded continuously and averaged directly after the rTMS procedure. RTMS did not influence blood pressure, pulse rate, or blood oxygenation. There was a maximal increase of CBFV in the middle cererbal artery (MCA) of 3.6% and 5.6% during 10 Hz and 20 Hz stimulation, respectively. This increase was only seen on the stimulated left hemisphere. The PI remained unchanged during the whole procedure. It is likely that the increase of CBFV is due to dilatation of the small resistance vessels rather than due to vasoconstriction of the MCA. In terms of cerebral hemodynamics, rTMS is a safe and well-tolerated technique with a lower increase of CBFV than that seen in electroconvulsive therapy.

Adult↗

PubMed2000

Assessment of facial nerve function in acoustic tumor disease by nasal muscle F waves and transcranial magnetic stimulation.

Standard transcranial magnetic stimulation and nasal muscle F-wave recordings were used to assess proximal facial nerve function in 27 patients with unilateral acoustic tumors (mean diameter, 29 mm) and clinically intact facial nerve function. Latency measurements for F waves and cortical magnetic stimulation were abnormal. Moreover, F ratios, central motor conduction time, and the ratio of response latency to cortical and cisternal magnetic stimulation were significantly increased. Amplitudes were unchanged. Correlation analysis with tumor diameter as dependent variable yielded maximum r values for F-wave latencies (0.57) and F ratios (0.41), whereas for magnetic stimulation, a significant correlation could be found (0.4) only for cortical stimulation. Nasal muscle F-wave recording can reveal clinically inapparent facial nerve dysfunction. Its efficacy in predicting tumor diameter seems to be superior to that of standard magnetic stimulation.

Adult↗

PubMed2004

Short-term modulation of regional excitability and blood flow in human motor cortex following rapid-rate transcranial magnetic stimulation.

Repetitive transcranial magnetic stimulation (rTMS) of the human primary motor cortex (M1) provides a means of inducing lasting changes in cortical excitability and synaptic activity. Here we combined rTMS with positron emission tomography of regional cerebral blood flow (rCBF) to examine how an rTMS-induced change in intracortical excitability of inhibitory circuits affects regional synaptic activity. In a first set of experiments, we gave 150 biphasic pulses of 5 Hz rTMS at 90% of active motor threshold to left M1 and used single- and paired-pulse TMS to assess the conditioning effects of rTMS on motor cortical excitability at rest. rTMS conditioning led to a selective decrease in short-latency intracortical inhibition (SICI) without affecting short-latency intracortical facilitation or corticospinal excitability. The decrease in SICI lasted for approximately 8 min. In a second experiment, we used the same rTMS protocol and measured changes in regional synaptic activity (as indexed by rCBF) during and for up to 14 min after the end of rTMS. Subthreshold 5 Hz rTMS induced a region-specific increase in resting rCBF in the stimulated M1 lasting approximately 8 min. These results suggest that in the stimulated M1, temporary attenuation of SICI is paralleled by an increase in synaptic activity, consistent with reduced efficacy of intracortical GABA(A)-ergic synapses. The present findings demonstrate that short trains of low-intensity 5 Hz rTMS can be used to induce a transient change in function within a distinct cortical area. This opens up new possibilities for studying acute reorganization at the systems level in the intact human brain.

Adult↗

PubMed1999

Cerebral function revealed by transcranial magnetic stimulation.

Although transcranial magnetic stimulation (TMS) has been introduced only recently, it is safe and provides a painless, inexpensive noninvasive method for the evaluation of brain function. Determining central motor conduction time (CMCT) permits assessment of the corticospinal pathways. Mapping the central representation of muscles provides a method for investigating the cortical reorganization that follows training, amputation and injury to the central nervous system. Such studies of human plasticity may have important implications for neurorehabilitation. TMS also provides a method whereby cortical excitability can be noninvasively evaluated, which is likely to have important implications in the study of epilepsy, movement disorders and related conditions. TMS is useful in tracking the flow of information from one brain region to another and in investigations of cognition and functional localization, thereby complementing information obtained using functional imaging techniques, which have superior spatial but inferior temporal resolution. Finally, TMS is currently being investigated as a method for establishing cerebral dominance and as a therapeutic tool in the treatment of depression. Investigations for treatment of other neurologic and psychiatric conditions are likely to be undertaken.

Animals↗

PubMed2003

Measurement of voluntary activation of fresh and fatigued human muscles using transcranial magnetic stimulation.

Recently, transcranial magnetic stimulation of the motor cortex (TMS) revealed impaired voluntary activation of muscles during maximal efforts. Hence, we evaluated its use as a measure of voluntary activation over a range of contraction strengths in both fresh and fatigued muscles, and compared it with standard twitch interpolation using nerve stimulation. Subjects contracted the elbow flexors isometrically while force and EMG from biceps and triceps were recorded. In one study, eight subjects made submaximal and maximal test contractions with rests to minimise fatigue. In the second study, eight subjects made sustained maximal contractions to reduce force to 60 % of the initial value, followed by brief test contractions. Force responses were recorded following TMS or electrical stimulation of the biceps motor nerve. In other contractions, EMG responses to TMS (motor evoked potentials, MEPs) or to stimulation at the brachial plexus (maximal M waves, Mmax) were recorded. During contractions of 50 % maximum, TMS elicited large MEPs in biceps (> 90 % Mmax) which decreased in size (to approximately 70 % Mmax) with maximal efforts. This suggests that faster firing rates made some motor units effectively refractory. With fatigue, MEPs were also smaller but remained > 70 % Mmax for contractions of 50-100 % maximum. For fresh and fatigued muscle, the superimposed twitch evoked by motor nerve and motor cortex stimulation decreased with increasing contraction strength. For nerve stimulation the relation was curvilinear, and for TMS it was linear for contractions of 50-100 % maximum (r2 = 1.00). Voluntary activation was derived using the expression: (1 - superimposed twitch/resting twitch) x 100. The resting twitch was measured directly for nerve stimulation and for TMS, it was estimated by extrapolation of the linear regression between the twitch and voluntary force. For cortical stimulation, this resulted in a highly linear relation between voluntary activation and force. Furthermore, the estimated activation corresponded well with contraction strength. Using TMS or nerve stimulation, voluntary activation was high during maximal efforts of fresh muscle. With fatigue, both measures revealed reduced voluntary activation (i.e. central fatigue) during maximal efforts. Measured with TMS, this central fatigue accounted for one-quarter of the fall in maximal voluntary force. We conclude that TMS can quantify voluntary activation for fresh or fatigued muscles at forces of 50-100 % maximum. Unlike standard twitch interpolation of the elbow flexors, voluntary activation measured with TMS varies in proportion to voluntary force, it reveals when extra output is available from the motor cortex to increase force, and it elicits force from all relevant synergist muscles.

Brachial Plexus↗

PubMed2000

How coil-cortex distance relates to age, motor threshold, and antidepressant response to repetitive transcranial magnetic stimulation.

Repetitive transcranial magnetic stimulation (rTMS) is a tool with antidepressant potential that uses a coil placed on the scalp to produce a powerful magnetic field that directly stimulates only the outermost cortex. MRI scans were obtained in 29 depressed adults involved in an rTMS antidepressant clinical treatment. These scans were analyzed to investigate the effect of distance from coil to cortex on clinical parameters. Longer motor cortex distance, but not prefrontal distance, strongly correlated with increased motor threshold (P<0.01). Clinical antidepressant response did not correlate with either distance. The rTMS antidepressant responders, however, were significantly younger (t=-2.430, P<0.05), and there appears to be a maximum threshold of age and distance to prefrontal cortex for response.

Adult↗

PubMed2005

Repetitive transcranial magnetic stimulation of the dorsolateral prefrontal cortex affects divided attention immediately after cessation of stimulation.

Transcranial magnetic stimulation has evolved into a powerful neuroscientific tool allowing to interfere transiently with specific brain functions. In addition, repetitive TMS (rTMS) has long-term effects (e.g. on mood), probably mediated by neurochemical alterations. While long-term safety of rTMS with regard to cognitive functioning is well established from trials exploring its therapeutic efficacy, little is known on whether rTMS can induce changes in cognitive functioning in a time window ranging from minutes to hours, a time in which neurochemical effects correlated with stimulation have been demonstrated. This study examined effects of rTMS on three measures of executive function in healthy subjects who received one single rTMS session (40 trains of 2 s duration 20 Hz stimuli) at the left dorsolateral prefrontal cortex (DLPFC). Compared to a sham condition one week apart, divided attention performance was significantly impaired about 30-60 min after rTMS, while Stroop-interference and performance in the Wisconsin Card Sorting Test was unaffected after rTMS. Repetitive TMS of the left DLPFC, at stimulation parameters used in therapeutic studies, does not lead to a clinically relevant impairment of executive function after stimulation. However, the significant effect on divided attention suggests that cognitive effects of rTMS are not limited to the of acute stimulation, and may possibly reflect known neurochemical alterations induced by rTMS. Sensitive cognitive measures may be useful to trace those short-term effects of rTMS non-invasively in humans.

Adult↗

PubMedDate not supplied

[Transcranial magnetic stimulation of the facial nerve: evaluation of a new method in neurophysiological study of Bell's palsy].

Transcranial magnetic stimulation is a new technique used to stimulate brain areas as well as peripheral nerves in healthy, waking persons. To date this technique has appeared safe. The aim of the present study was to assess the clinical application of this method in patients with Bell's palsy. Electromyographic responses were elicited by electrical and magnetic transcranial stimulation of the facial nerve in 26 patients affected by Bell's palsy. Electrical stimulation: stimuli of 0.1 ms duration, and up to 15 V, were delivered through surface electrodes set 2.5 cm apart over the facial nerve at the stylomastoid foramen. Magnetic stimulation: the coil was placed tangent to the parieto-occipital surface of the scalp. The stimulus intensity was then increased stepwise until a supramaximal response was obtained. Recording: the focal recording electrode was placed ipsilateral to the side stimulated over the superior orbicularis oculi; the reference electrode was placed over the nasal bone. The patients were tested with two neurophysiological determinations: the first 15-30 days from the onset of the palsy; the second 30-60 days after the first. A clinical follow-up was performed six months after the second determination. The results indicate that, contrary to traditional electroneurography, transcranial magnetic stimulation is not able to supply useful neurophysiological indications in patients with Bell's palsy. Although the absence of compound muscle action potential upon stimulation of the side with the lesion did demonstrate some impediment to conduction, it did not have any prognostic value since it was also present in patients who were clinically well at the time of the second check-up.

Adult↗

PubMed1997

Responses of human single motor units to transcranial magnetic stimulation.

Transcranial electromagnetic brain stimuli elicit a complex response in the electromyogram of active human hand muscles. Relatively weak stimuli evoke a short-latency primary response via a presumably monosynaptic corticospinal path. This is followed by a silent period that is terminated by a second peak at a latency of 50-80 ms. The responses evoked in single motor units in flexor digitorum profundus (FDP) were recorded. Responses were elicited at the second-peak latency only in trials in which no primary response was elicited in that unit, and only when the stimulus was given during the first half of the interspike interval (ISI). When given during the second half of the ISI, the same stimulus evoked a primary response but no second peak response. Stronger stimuli suppressed the second peak by evoking a primary response in more trials. Having discharged at about 20 ms latency, the parent motoneurone was unable to discharge again at second-peak latency, 30-60 ms later. The response at second-peak latency was not modified by disengaging both FDP and the extensors of the distal interphalangeal joint. Hence, this response is not secondary to a stretch reflex provoked by activation of the finger extensors, nor is it the result of a cutaneous signal resulting from movement of the finger. The latencies suggest that the corticospinal volley evokes a beta-motoneurone-mediated twitch in FDP muscle spindles, which elicits an afferent volley that activates the motoneurone reflexly. The first 100 ms or so of the silent period is due to the realignment of the first post-stimulus spike in most trials to corticospinal latency; i.e. this is not necessarily the result of an inhibitory or disfacilitatory process. Still stronger stimuli increase the duration of the ISI in which the stimulus is given, indicating the presence of an inhibitory/disfacilitatory process.

Adult↗

PubMed2006

Transient tinnitus suppression induced by repetitive transcranial magnetic stimulation and transcranial direct current stimulation.

Modulation of activity in the left temporoparietal area (LTA) by 10 Hz repetitive transcranial magnetic stimulation (rTMS) results in a transient reduction of tinnitus. We aimed to replicate these results and test whether transcranial direct current stimulation (tDCS) of LTA could yield similar effect. Patients with tinnitus underwent six different types of stimulation in a random order: 10-Hz rTMS of LTA, 10-Hz rTMS of mesial parietal cortex, sham rTMS, anodal tDCS of LTA, cathodal tDCS of LTA and sham tDCS. A non-parametric analysis of variance showed a significant main effect of type of stimulation (P = 0.002) and post hoc tests showed that 10-Hz rTMS and anodal tDCS of LTA resulted in a significant reduction of tinnitus. These effects were short lasting. These results replicate the findings of the previous study and, in addition, show preliminary evidence that anodal tDCS of LTA induces a similar transient tinnitus reduction as high-frequency rTMS.

Acoustic Stimulation↗

PubMed1997

Post-stroke reorganization of brain motor output to the hand: a 2-4 month follow-up with focal magnetic transcranial stimulation.

Focal transcranial magnetic stimulation (TCS) was employed for the representation of the motor cortex in a population of 18 patients to investigate the functional properties of hand motor areas 2-4 months after a monohemispheric stroke. Eleven sites were stimulated to elicit motor evoked potentials (MEPs) in abductor digiti minimi muscle after TCS of affected (AH) and unaffected (UH) hemispheres; recording sessions were performed at the beginning (T1) and after 8-10 weeks (T2) of neurorehabilitation. Barthel index and Canadian neurological scale scores were evaluated. A group of 20 healthy control subjects was enrolled. In stroke patients the AH was less excitable than normal, combined with a decrease in motor cortical output area (P < 0.05) in T1. In T2, there was an enlargement of the hand motor area on the AH combined with an improvement of clinical scores (P < 0.001). In T1 and T2, the amplitude of MEPs in the AH was reduced (P < 0.001) with a prolongation of central conduction time (P < 0.001) and with a tendency towards improvement in T2; the amplitude of contracted MEPs was larger than normal in the UH in T1. Both in T1 and T2, anomalous 'hot spot' (most excitable) scalp sites, never seen in normals, were often encountered (T2 > T1) on the AH and UH. Interhemispheric differences for topography and latency of MEPs were remarkably affected. Our data are consistent with a rearrangement of the brain motor cortical output between 2 and 4 months following stroke. The amelioration of the neurophysiological parameters was correlated with clinical improvement in disability and neurological scores. This study confirms the existence in adults of brain 'plasticity' still operating between 2 and 4 months from an acute vascular monohemispheric insult.

Action Potentials↗

PubMed2005

[Vagus nerve stimulation, repetitive transcranial magnetic stimulation, and electroconvulsive therapy in the treatment of depressive disorders].

Affective disorders, especially major depression, are the most common psychiatric disorders. Although well treatable, a number of patients do not or do not sufficiently respond to antidepressant pharmacotherapy. Therefore there is a need for safe and efficient alternative therapeutic strategies. Neurostimulatory therapies such as electroconvulsive therapy, repetitive transcranial magnetic stimulation, and vagus nerve stimulation belong to these alternatives. In this article we review their mechanisms of action and summarize efficacy and adverse effects.

Animals↗

PubMed2002

Transcranial magnetic stimulation and epilepsy.

Transcranial magnetic stimulation has been used to study generalized and focal epilepsies for more than a decade. The technique appears safe and has yielded important information about the mechanisms underlying epilepsy. Transcranial magnetic stimulation findings differ depending on the epilepsy syndrome, lending support to the concept that there are distinct pathophysiologies underlying each condition. In most studies of generalized epilepsies, transcranial magnetic stimulation has indicated a state of relative hyperexcitability of excitatory cortical interneurons and possibly inhibitory interneurons as well, which can be reversed through the actions of anticonvulsant medications. Transcranial magnetic stimulation studies in patients with a seizure focus in the motor cortex indicate increased cortical excitability and reduced inhibition, but in patients with seizure foci located elsewhere the findings are similar to those in generalized epilepsies. Transcranial magnetic stimulation has also been used to study the mode of action of anticonvulsants and may prove to be a useful means of testing the potential for new drugs to act as anticonvulsants. Repetitive transcranial magnetic stimulation may prove to have a therapeutic role by producing long-lasting cortical inhibition after a train of impulses.

Anticonvulsants↗

PubMed1995

[Analysis of cortical excitation and inhibition using transcranial magnetic stimulation].

The method of magnetic transcranial stimulation of the motor cortex produces both excitatory and inhibitory effect. Definition of excitability and inhibitory threshold represents clinically useful indicator. In order to reduce variability of the thresholds, it is important to notice mental activity, posture, type of magnetic stimulator, involuntary movement, muscle tonus and age. Excitability threshold was elevated in patients with stroke and reduced in patients with epilepsy. Enhancement of motor excitability by subthreshold magnetic stimulation of the motor cortex prior to voluntary movement was observed during simple reaction time measurement. Reaction time can be divided into a period of resting condition and the premotion facilitatory effect in the 50 approximately 60 ms after the target stimuli. In patients with Parkinson's disease, the prolongation of reaction time is due to a prolongation of a period of premotion facilitatory effect. Jerk-locked MEP is a useful technique to evaluate a change of motor excitability after voluntary or involuntary movement. To record jerk-locked MEP, magnetic stimulation of the motor cortex is delivered at varying intervals after the onset of the EMG activity. We classified the cortical reflex myoclonus into three forms according to changes of motor excitability after C reflex.

Electric Stimulation↗