Identification of Motor Area by Transcranial Magnetic Stimulation Using an “Eight-Figure”Coil in Patients with Motor Paralysis Daisuke NAKA 1,3 , Kazuyoshi FUNAHASHI 1 , Mitsuhiro OGURA 1 , Toshikazu KUWATA 1 , Mitsukazu NAKAI 1 , Kunio NAKAI 1 , Toru ITAKURA 1 , Norihiko KOMAI 1 , Shoogo UENO 2 1Department of Neurological Surgery, Wakayama Medical College 2Department of Computer Science and Communication Engineering, Kyushu University Keyword: Motor evoked potential , Magnetic stimulation , Eight-figure coil , Motor area , Motor Paralysis pp.27-34
Published Date 1995/1/10
DOI https://doi.org/10.11477/mf.1436900961
  • Abstract
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In patients with motor paralysis, we tried to indentify the functional motor area by transcranial magnetic sti-mulation using an “eight-figure” coil designed by Ueno.

Motor evoked potentials (MEPs) were recorded in 7 patients from 50 to 64 years old, and in 5 normal volun-teers 26 to 45 years old. They were stimulated at 49 points over an unilateral hand motor area, and at 21 points over a foot motor area, and surface MEPs were recorded on their contralateral thenar muscle and abductor hallucis brevis muscle. In normal volunteers, the optimal eddy current for stimulating the hand motor area was directed anteriorly parallel to the mid-line, and for stimulating the foot motor area, it was postero-laterally directed with an angle of 45 degrees towards the midline. MEPs could be induced at their muscle contractions during which their thumbs and middle fingers softly touched each other, and their hal-luxes slightly flexed. In five patients two kinds of am-plitude mappings reconstructed from MEPs were obtained at rest or at muscle contraction. A line con-necting these two peaks on an amplitude mapping was regarded as an “MEP-motor area”. A geographical dif-ference between the MEP-motor area and MRI-motor area (identified by an MRI surface image) was studied at muscle contraction and at rest.

In normal subjects the sites of the MEP-motor area and of the MRI-motor area coincided, whereas, in pa-tients with space-occupying lesions near the central sul-cus, the MEP-motor areas were located 1 to 2 cm pos-terior to MRI-motor areas. Motor area was detected in 2 MEP mappings recorded at rest and in 3 mappings at voluntary muscle contraction. Another 3 mappings failed to show any MEP peaks either at rest or at mus-cle contraction.

Two of 3 cases whose mappings did not show any MEPs even during the muscle contraction had muscle weakness (2/5 and 0/5 in MMT). In all but one with milder motor paresis (stronger than 3/5 in MMT). MEP mappings showed prominent peaks at hand and foot areas.

Transcranial magnetic stimulation for detecting the motor area is easy to perform and painless for the pa-tients. It can present the precise location of the motor area in normal subjects and is regarded to be a useful method to detect the motor area from over the scalp. But in patients with lesions near central sulcus, it should be kept in mind that the MEP-motor area is slightly different from the MRI-motor area, probably clue to the dislocation or distortion of the pyramidal ax-ons. The activation of muscle contraction by transcra-nial magnetic stimulation is thought to be a useful man-euver to evoke MEPs and to detect the cortical motor area from over the scalp in patients with motor para-lysis.

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