ping conditions. Our results suggest that the soleus H-reflexduring the passive stepping was modulated by the peripheralinputs in similar pattern seen in normal walking and thatthe load-related inputs have no significant effect on the soleusH-reflex size.

doi:10.1016/j.clinph.2008.01.093

69. Effect of motor imagery on the excitability of the anterior

horn cells as tested by antidromic invasion, which induces F-

waves by backfiring—Motohiko Hara, Jun Kimura, D.

David Walker, Shinichirou Taniguchi, Hiroo Ichikawa,

Reiko Fujisawa, Hiroshi Shimizu, Tatsuya Abe, Toshio

Soma, Thoru Yamada University of Iowa, Iowa City, IA,

USA)

To test the effect of motor imagery as compared to voluntarymuscle contraction on the excitability of the anterior horn cells,we studied F-wave persistence and amplitude, monitoring theforce by a transducer. F-waves were recorded from the first dorsalinterosseus muscle at rest and under a battery of motor taskswhich comprised mental imagery and mild to moderate abductionof the index finger in 10 increments up to 30% of the maximalforce. During each step lasting for 20 s, 20 stimuli were appliedto the ulnar nerve at the wrist at the rate of one per second. In12 healthy subjects, F-wave persistence (mean ± SD) significantly(p < 0.05) increased from 32.5 ± 11.9% at rest to 58.3 ± 15.2%during motor imagery and to 87–91% during voluntary contrac-tion. Similarly, F-wave amplitude significantly (p < 0.05)increased from 41.3 ± 77.1 lV at rest to 91.2 ± 142.7 lV duringmotor imagery and to 183–274 lV during voluntary contraction.In contrast, F-wave latency changed little regardless of motortasks. Motor imagery, though to a lesser degree than muscle con-traction, effectively enhances the excitability of the anterior horncells, thereby increasing F-wave persistence and amplitude abovethe baseline.

doi:10.1016/j.clinph.2008.01.094

70. Mexiletine suppresses excessive axonal persistent sodiumcurrents in painful neuropathy—Sagiri Isose, Sonoko Mis-

awa, Setsu Sawai, Kazuaki Kanai, Takamichi Hattori,

Satoshi Kuwabara Chiba University Hospital, Chiba, Japan)

One of the mechanisms for neuropathic pain is an increasedsodium channel expression associated with axonal regeneration,and resulting axonal hyperexcitability. We investigated whetheraxonal sodium currents increase in patients with painful neurop-athy, and whether mexiletine administration suppresses the exces-sive sodium currents in vivo. The technique of latent addition withcomputerized threshold-tracking was used to estimate nodal per-sistent sodium currents in superficial radial sensory axons of eightpatients with painful neuropathy caused by diabetes or neurotoxicdrugs. Excitability testing was performed before and after treat-ment with mexiletine. Before treatment, persistent sodium cur-rents estimated by latent addition were significantly greater inpatients, compared with normal control (p = 0.001). After treat-

ment, there was pain relief in seven of the patients, associated witha substantial decrease in persistent sodium currents (p = 0.02) Inpatients with neuropathic pain, persistent sodium currents in sen-sory axons are increased, resulting in axonal hyperexcitability.Mexiletine suppresses the excessive nodal sodium currents, andthereby neuropathic pain.

doi:10.1016/j.clinph.2008.01.095

71. Intraoperative monitoring of visual-evoked potential fortemporal lesions – Correlation between VEP findings and

postoperative visual field—Takeshi Itakura, Tatsuya

Sasaki, Hiromichi Kasuya, Ryoji Munakata, Hiroyuki

Muramatsu, Jun Sakuma, Masato Matsumoto, Kyouichi

Suzuki Fukushima Medical University, Fukushima, Japan)

Object: To evaluate the usefulness of visual-evoked potential(VEP) monitoring during surgery in or near the temporal lobe,the authors analyzed the correlation between intraoperativeVEP findings and postoperative visual field.

Methods: Intraoperative VEP monitoring was performed in17 patients whose lesions located in or near the temporal lobe.The electroretinogram (ERG) was also recorded to confirmwhether the light stimulus reached the retina or not. Allpatients underwent surgery under total venous anesthesia withpropofol.

Result: Both ERG and VEP were recorded in all 17 patients.In 15 of 17 patients without VEP changes, postoperative visualfields did not change in 14 and one patient developed partialdefect of homonymous quadrant visual field. In two patientswhose VEPs were significantly aggravated at the end of surgery,postoperative visual field test revealed complete homonymoushemianopsia.

Conclusions: Intraoperative VEP monitoring enabled us todetect injury which caused complete hemianopsia postoperatively,but not partial visual field defect. Our monitoring method hassome limitation in the sensitivity.

doi:10.1016/j.clinph.2008.01.096

72. Neuronal activity of the globus pallidus in dystonia—

Kazutaka Kobayashi, Koichiro Sumi, Toshiharu Otaka,

Toshiki Obuchi, Toshikazu Kano, Takafumi Nagaoka,

Hideki Oshima, Chikashi Fukaya, Takamitsu Yamamoto,

Yoichi Katayama Nihon University School of Medicine,

Tokyo, Japan)

Pallidal neuronal activities in patients with primary general-ized dystonia have been reported to show low firing rate andabnormal pattern in spontaneous activity. We have analyzedthe activity of 69 neurons sampled from the globus pallidusinterna (GPi) and globus pallidus externa (GPe) in 6 patientswith dystonia. The pallidal neuronal activities were recordedunder the local anesthesia. For the analysis of firing rateand firing pattern, the pause index (PI), burst index (BI)and pause ratio (PR) were analyzed. The mean firing rate ofGPe and GPi were 44.2 ± 23.4 Hz and 48.9 ± 27.1 Hz, respec-

e92 Japanese Society of Clinical Neurophysiology / Clinical Neurophysiology 119 (2008) e75–e93

tively. This finding coincides with previous reports that the fir-ing occurs less frequently in the pallidum in dystonia com-pared with Parkinson’s disease (PD). Regarding BI and PI,no difference was found between dystonia and PD. Otherwise,the PR was higher in dystonia compared with PD. The char-acteristic firing pattern recorded in GPi and GPe was pausingin dystonia.

doi:10.1016/j.clinph.2008.01.097

73. Visual-evoked magnetic fields for pattern-reversal stim-

ulus in patients with occipital lesions—Akitake Kanno,

Nobukazu Nakasato, Satoru Fujiwara, Toshihiro Kumabe,Teiji Tominaga Kohnan Hospital and Tohoku University,

Sendai, Japan)

Visual-evoked magnetic fields (VEFs) can detect early com-ponents for pattern-reversal stimuli which are generated fromthe primary visual cortex (V1). The present study applied VEFsfor the localization of the V1 and evaluation of visual functionin 16 patients (10 males) with occipital lesions (7 with vascularmalformation, 6 with neoplasm and 3 with cerebral hemor-rhage). Monocular pattern-reversal stimuli were independentlypresented to the left and right half visual fields of the leftand right eyes. VEFs were measured by a helmet shapedMEG system (VectoreView, Elekta-Neuromag, Helsinki). Thesource of the P100m was estimated by a single dipole modeland was superimposed on the three-dimensional magnetic reso-nance image. VEFs were not detected for the correspondingvisual stimuli or the latency of P100m response was delayedin the 5 patients with homologous hemianopsia. In contrast,the P100m source was estimated on the calcarine fissure inthe 11 patients with no visual deficit, even in patients withlesions adjacent to the V1. VEFs provide a noninvasive methodto objectively evaluate visual-field deficit in patients with occip-ital lesions. Localization of the P100m source is also useful forpresurgical mapping.

doi:10.1016/j.clinph.2008.01.098

74. Proposition of an MEG phantom as the evaluation

standard—Gen Uehara, Isao Hashimoto, Masato Yumoto,

Hiroaki Tanaka, Tomoya Kimura, Toshimichi Nariata,Masakazu Miyamoto, Yoshiaki Adachi Kanazawa Institute

of Technology, Tokyo, Japan)

For performance evaluation of an MEG system, a phantom,meaning the trial reproduction of a Sarvas model to serve as anevaluation standard, is required. The conventional Sarvas modelreproduction used is a saline-filled sphere mounting the equivalent

current dipole electrodes inside. We have identified the reliabilityproblem of this conventional phantom such as the electrical dou-ble-layer nonlinearity caused by electrolysis.

On the other hand, the phantom proposed by Ilmoniemi et al.,which is an isosceles triangle with infinitely small base, has a guar-anteed current drive linearity making it a promising candidate asan evaluation standard. We have noted this point, and shown thatthe magnetic field generated by this phantom matches that of aSarvas model by the error of 0.2%. Based on this result, we havemade a prototype and performed analysis on the position of theequivalent current dipole and the accuracy of the moment bymeasuring the generated magnetic field with an MEG system.The error was 2.8 mm at maximum and 0.9 mm by average. Inkeeping pace with the improvement in MEG-system accuracy, arealization of a reliable standard phantom is awaited.

doi:10.1016/j.clinph.2008.01.099

75. MEG activities during a memory task in patients with

early Alzheimer’s disease and mild cognitive impairment—

Ryu Kurimoto, Ryouhei Ishii, Leonides Canuet, Koji Ikez-

awa, Masao Iwase, Hiromitsu Kazui, Toshiki Yoshimine,

Masatoshi Takeda Osaka University Graduate School of

Medicine, Osaka, Japan)

There are relatively few magnetoencephalography (MEG)studies on Alzheimer’s disease (AD) and mild cognitive impair-ment (MCI). In the present study, we compared the event-related desynchronization (ERD) during a memory task inAD, MCI patients and controls. Thirteen patients with probableAD were selected according to NINCDS-ADRDA criteria (age;75.6 ± 5.0, Mini-Mental State; 22.1 ± 2.6). Thirteen patientswith MCI were selected according to Petersen’s diagnostic crite-ria (age; 73.9 ± 5.0, Mini-Mental State; 26.8 ± 2.0). We alsoselected fourteen normal control subjects (age; 71.2 ± 6.8,Mini-Mental State; 28.6 ± 1.5). MEG activities were recordedwith a 64-channel whole head magnetometer in a magneticallyshielded room. The ERD in beta band (15–30 Hz) during amemory task was calculated by using beamforming methodimplemented in Brain Electrical Source Analysis (BESA).Group comparison of 3-D data was performed by using Brain-Voyager QX. The ERD was decreased significantly in right mid-dle and inferior-frontal gyri in MCI patients compared tocontrols. The ERD was decreased significantly in left superiorand middle-frontal gyri in AD patients compared to MCIpatients. The ERD was decreased significantly in right-frontallobe and left superior-frontal gyrus in AD patients comparedto controls.

doi:10.1016/j.clinph.2008.01.100

Japanese Society of Clinical Neurophysiology / Clinical Neurophysiology 119 (2008) e75–e93 e93