Transcranial Magnetic Stimulation Responses Research Articles

Characterisation of paired-pulse transcranial magnetic stimulation conditions yielding intracortical inhibition or I-wave facilitation using a threshold-hunting paradigm.

Short-interval, paired-pulse transcranial magnetic stimulation (TMS) is usually used to demonstrate intracortical inhibition. It was shown recently that with short-interval, paired-pulse TMS a facilitation - called intracortical I-wave facilitation - can also be demonstrated. It was the aim of this study to investigate which stimulus conditions lead to intracortical inhibition and what conditions yield an intracortical I-wave facilitation in a hand muscle of normal subjects. Paired-pulse TMS responses with an interstimulus interval of 1.2 ms were obtained from the abductor digiti minimi muscle of four normal subjects. A threshold-hunting paradigm with hunting through first or second stimulus variation was used to obtain a curve of threshold-pair strengths. All subjects showed two branches of stimulus interaction on this diagram. If the first stimulus of a threshold pair was below approximately 65% of resting motor threshold it modified the response primarily due to the second stimulus through intracortical inhibition. However, if the first stimulus of a threshold pair exceeded approximately 65% of resting motor threshold it became responsible for the spinal action-potential initiation. The subsequent second stimulus served as a "booster" for the ongoing intracortical I-wave activity, making it impossible to observe the intracortical inhibition evoked by the first stimulus.

Perioperative lesions of the facial nerve: follow-up investigations using transcranial magnetic stimulation.

Peripheral facial palsy can occur after aural surgery and neurosurgery. Routine neurophysiological investigation (utilizing electrical stimulation and the blink reflex) does not allow the direct assessment of the site of a lesion. In the present study transcranial magnetic stimulation (TMS) was applied in order to evaluate the usefulness of this method for prognosis. Twenty-three patients with postoperative facial pareses (after removals of an acoustic neuroma in 12 patients and parotid tumors in 11) were investigated. Ipsilateral short-latency and contralateral long-latency responses (after cortex stimulation) were elicited. At the first examination (11.7 +/- 9 days after onset of the palsy) the components of the blink reflex were absent in all cases. Responses to electrical stimulation were abnormal in 80%. Ipsilateral short-latency responses after TMS could be obtained in 7 patients. Pathological long-latency TMS responses were elicited in 17 patients. Follow-up investigations up to 2 years revealed no prognostic aspects from peripheral electrical stimulation, the blink reflex and the short-latency TMS response. The absence or extent of delay in long-latency responses at first examination was strongly correlated with final clinical outcomes. As improvements of the responses preceded clinical regressions of the paresis, TMS proved to be an important neurophysiological method for an early prognosis of recovery after perioperative lesions of the facial nerve.

Prognostication of Bell's Palsy Using Transcranial Magnetic Stimulation

Transcranial magnetic stimulation (TMS) provides a method to noninvasive excitation of the facial nerve in its intracranial segment close to the internal acoustic meatus. Thus, the site of facial nerve activation with TMS is proximal to or within the site of the lesion in Bell's palsy. To evaluate the prognostic capability of TMS in unilateral Bell's palsy we examined 137 patients with this method, and compared the results with electroneuronography (ENoG). Within 0–4 days from the onset of palsy, the patients with elicitable TMS responses recovered better than those in whom TMS responses were not elicitable. If TMS was performed 5–9 days or 10–28 days after the onset of palsy, it did not provide any prognostic information. Based on amplitude side-to-side differences, ENoG did not contribute prognostic information during the first 9 days from the onset of palsy. Later on, 10–28 days after the onset of palsy, ENoG showed an increased capability to discriminate the patients with poor prognosis. Thus, elicitable facial motor response with TMS predicts good prognosis of Bell's palsy at an early stage whereas poor response with ENoG predicts less favorable prognosis at a later stage.

Magnetic facial nerve stimulation in Bell's palsy.

The transcranial magnetic stimulation (TMS) technique makes it possible to stimulate the intracranial part of the facial nerve. In a total of 51 patients with acute Bell's palsy, TMS was performed, and the responses were compared with those elicited by conventional extracranial electric stimulation (EES). Clinical recovery was evaluated at 258-539, mean 410, days from the beginning of the palsy. With both techniques the motor evoked potentials (MEPs) could always be elicited on the healthy side, the mean latency being 4.7 ms with TMS and 3.7 ms with EES. In the acute phase, TMS elicited MEPs on the paralyzed side in 47% of the patients, and EES in 98%. The patients with TMS elicitable MEPs during the first 4 days of the palsy had significantly better recovery than those without response (p less than 0.05). The difference in recovery between patients with or without elicitable TMS responses on days 5-8 and 9-14 was not significant. In EES, the amplitude difference between the two sides within the first 4 days was not significantly (p greater than 0.05) different. On days 9-14 the patients with a less than 80% difference between the two sides recovered significantly (p less than 0.05) better than those with a difference of greater than or equal to 80%, So, TMS may be of help in the early prognosis of Bell's palsy.