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S Tobimatsu

Publications and source records attributed to S Tobimatsu.

At least 37 records · Page 2Linked to original sources
PubMed2000

[A case of chronic toluene intoxication presenting stimulus-sensitive segmental spinal myoclonus].

We reported a 48-year-old male who showed stimulus-sensitive spinal myoclonus due to chronic toluene intoxication. He has been exposed to thinner for more than 30 years as a painter, and occasionally experienced an episode of headache, nausea and dizziness because of acute thinner intoxication. He noted tremor of his hands 10 years ago. He also noticed memory disturbance since the end of 1997. Neurological examination revealed postural tremor of his fingers on the bilateral sides and the left arm. In addition, rhythmic myoclonic jerks were induced in the right upper limb muscles by a tendon tap given on the right brachioradialis muscles. Surface EMG revealed repetitive grouping discharges in those two muscles approximately 100 msec after the tendon tap which continued for about 30-50 msec. A long loop reflex (C-reflex) and giant SEPs were not observed in his right upper limb, and EEG showed no spike. Urinary excretion of N-benzoylglycine, which was a metabolite of toluene was increased (1.17 g/l). Therefore, he was diagnosed as a case of chronic toluene intoxication. His myoclonic jerks were considered to be stimulus-sensitive spinal myoclonus, because they were induced segmentally and because cortical hyperexcitability was not seen. This is the first report to describe the occurrence of stimulus-sensitive spinal myoclonus in the case of chronic toluene intoxication.

Chronic Disease↗
PubMed1999

Motor and somatosensory evoked potential findings in HTLV-I associated myelopathy.

The central motor and sensory conduction times were measured using the motor and somatosensory evoked potentials in 21 patients with HTLV-I associated myelopathy/tropical spastic paraparesis (HAM/TSP) to evaluate the functions of the corticospinal tract and posterior column. The control subjects were closely matched for gender, age and height with the patients in the central sensory conduction time (CSCT) and central motor conduction time (CMCT) studies. An abnormal upper limb (UL) CMCT was present in six of 34 limbs (17.6%) while the lower limb (LL) CMCT was abnormal in 31 of 42 limbs (73.8%). No patients had an abnormal UL CSCT while the LL CSCT was abnormal in 10 of 32 limbs (31.3%). The frequency of abnormal LL CMCT was significantly higher than that for an abnormal LL CSCT. The duration of the disease and the disability score did not significantly influence the evoked potential findings. These results indicate that major lesions of the spinal cord in HAM/TSP patients tend to be localized more in the descending corticospinal pathways than in the ascending posterior columns at the thoracic spinal cord level. This finding also closely agrees with the clinico-pathological findings of HAM/TSP.

Adult↗
PubMed1999

Idiopathic cortical myoclonus restricted to the lower limbs: correlation between MEPs and 99mTc-ECD single photon emission computed tomography activation study.

We report a 63-year-old woman with cortical reflex myoclonus restricted to the bilateral lower limbs. Somatosensory evoked cortical potentials to posterior tibial nerve stimulation were enlarged with C-responses. Jerk-locked back averaging of the EEG identified a cortical spike related to myoclonic jerks. Motor evoked potentials recorded from the abductor hallucis muscle showed an exaggerated late response. These findings suggest hyperexcitability of the sensorimotor cortex. 99mTc-ECD single photon emission computed tomography (SPECT) after stimulation of the posterior tibial nerve showed increased perfusion in the contralateral peri-Rolandic area which corresponded to the hyperexcitable region. A SPECT activation study as well as MEPs therefore can be employed to determine the hyperexcitable region in cortical myoclonus.

Brain↗
PubMed1999

Chromatic sensitive epilepsy: a variant of photosensitive epilepsy.

We herein report 4 Japanese children who suffered epileptic seizures while watching a popular animated TV program. They showed a photoparoxysmal response that is more frequently observed in response to rapid color (blue/red) frame changes than monochromatic ones. These patients were all considered to have photosensitive epilepsy; however, chromatic sensitivity also plays an important role in the generation of such seizures.

Adolescent↗
PubMed1999

Visual evoked potentials in school children: a comparative study of transient and steady-state methods with pattern reversal and flash stimulation.

OBJECTIVE: Flash visual evoked potentials (VEPs) are commonly used in pediatrics, because children are sometimes uncooperative. We performed a comparative study of transient and steady-state VEPs with pattern reversal (PR) and flash (light-emitting diode, LED) stimulation. METHODS: We recorded VEPs in 15 boys and 17 girls (aged 6-12 years) using 4 different stimulus conditions. The latency and amplitude of transient VEPs (T-VEPs) were measured. Steady-state VEPs (S-VEPs) were Fourier analyzed, and both the phase and amplitude of the major components were obtained. RESULTS: The mean P100 latency of LED T-VEPs was longer and had a greater variability than that of PR T-VEPs. The LED T-VEPs had an amplitude of about double that of PR T-VEPs. The first harmonic response in the LED and second harmonic in PR were the major components of S-VEPs. The phases of PR and LED S-VEPs had narrow angular dispersions and amplitudes showed marked intersubject variability. Sex and age had no significant effect on both T-VEPs and S-VEPs. CONCLUSIONS: Reproducible VEPs with 4 stimulus conditions can be obtained in school children. T-VEPs and S-VEPs are clinically useful because these methods provide complementary information.

Brain↗
PubMed1999

Parvocellular and magnocellular visual processing in spinocerebellar degeneration and Parkinson's disease: an event-related potential study.

OBJECTIVE: We recorded event-related potentials (ERPs) using appropriate visual stimuli to establish a non-invasive method that separately investigates the parvocellular (P) and magnocellular (M) visual functions, and to evaluate the visual function in spinocerebellar degeneration (SCD) and Parkinson's disease (PD). METHODS: Eight SCD and 10 PD patients were compared with 11 age-matched control subjects. In the P-task, subjects were required to discriminate equiluminant red (frequent) and green (rare) random dots. In the M-task, moving random dots on a rotating cylinder (frequent) and those moving irregularly (rare) were discriminated. RESULTS: Control subjects showed an endogenous positive component at 400 ms (P400(p)) with an early exogenous negative potential (N160(p)) in the P-task. In the M-task, N160(m) and P400(m) were recorded. A deuteranope lacked P400(p) with normal P400(m). In SCD, P400(p) latency and N160(p)-P400(p) interval were increased with normal N160(p) latency. N160(m) latency was also increased while N160(m)-P400(m) interval was normal. In PD, there were no significant changes in the P-task but P400(m) latency was increased with normal N160(m) latency. CONCLUSIONS: SCD patients may have not only abnormal higher processing in the P-pathway but abnormal fundamental processing in the M-pathway. PD may have impaired higher processing of the M-pathway with the preserved P-function.

Aged↗
PubMed1999

The effect of spatial frequency on chromatic and achromatic steady-state visual evoked potentials.

OBJECTIVE: Little is known about the physiological properties of the major components of steady-state visual evoked potentials (VEPs). Based on the hypothesis that isoluminant color and high contrast pattern differentially activate the parvo- and magnocellular pathways, we studied difference in spatial frequency function between chromatic and achromatic VEPs to sinusoidal gratings. METHODS: Steady-state VEPs to isoluminant chromatic (red-green) and high contrast (90%) achromatic (black-white) sinusoidal gratings with nine spatial frequencies (0.5 to 8.0 cycles/degrees (cpd)) at 4 Hz (8 reversals/s) were recorded in 13 normal subjects. VEPs were Fourier analyzed to obtain phase and amplitude of the second (2F) and fourth (4F) harmonic responses. RESULTS: The 2F amplitude of chromatic VEPs decreased above 4.0 cpd in a low-pass function while that of achromatic VEPs showed a band-pass function with a peak at 4.0 cpd. The 4F amplitude of chromatic VEPs was not affected significantly by spatial frequency whereas that of achromatic VEPs exhibited a high-pass function. The phases of 2F and 4F showed a non-monotonic function of spatial frequency in both chromatic and achromatic stimuli with peaks at middle spatial frequencies. CONCLUSION: Chromatic and achromatic visual stimuli differently affected 2F and 4F components, which thus suggests that 2F and 4F components are generated from different neuronal subgroups largely in the parvocellular pathway.

Adolescent↗
PubMed1999

Steady-state vibration somatosensory evoked potentials: physiological characteristics and tuning function.

OBJECTIVE: The steady-state somatosensory evoked potentials (S-SEPs) to vibratory stimulation were recorded to characterize their physiological properties. METHODS: Vibratory stimuli were applied to the right palmar surface in 10 normal subjects. A total of 200 responses were recorded from electrodes at 2 cm posterior to C3, Cz and C4 and 2 cm anterior to C3. All responses were Fourier analyzed and the amplitudes of the first (1F) and second (2F) harmonic components were thus obtained. The effects of modulation frequency (5-30 Hz) and stimulus intensity (0.001-0.1 Newton (N)) on S-SEPs were studied. RESULTS: The amplitudes of 1F and 2F were greatest at the electrode 2 cm posterior to C3, 1F being predominant. The mean 1F amplitudes as a function of modulation frequency showed a bimodal distribution with a trough at 14 Hz and a peak at 21 Hz. The mean 1F amplitudes showed a linear increase of up to 0.05 N and thereafter reached a plateau against the logarithmic stimulus intensity axis. CONCLUSION: Vibratory S-SEPs may originate from the primary somatosensory cortex and provide information on the fast-adapting mechanoreceptive afferents. The temporal resonance at 21 Hz places the somatosensory system between the visual and auditory systems.

Adolescent↗
PubMed1999

Properties of rat cone-mediated electroretinograms during light adaptation.

PURPOSE: Our aim was to better understand how to isolate the cone-mediated response in rats. Therefore, we studied the difference of ERGs in the course of light adaptation between 2 and 20 Hz stimulus frequencies. METHODS: A total of 90 rats divided into 18 different groups were used following overnight dark adaptation. ERGs were recorded against 3 different adapting field luminances (1.15, 1. 50 or 1.75 log cd/m(2)) with a combination of 3 stimulus flash intensities (0.86, 1.30 or 2.03 log cd sec/m( 2)). The responses were obtained at 2 minute intervals for 25 minutes of light adaptation. RESULTS: The response of the rat cone ERG was large despite the small number of cones. The mean amplitude increased systematically from the dark-adapted value requiring more than 15 minutes to reach an asymptote at 2 Hz stimulation, but only 10 minutes at 20 Hz stimulation. The 2 Hz adaptation curves had biphasic pattern compared to the monophasic 20 Hz curve. This second increase in the amplitude at 2 Hz appeared at around 7-8 minutes as a function of adaptation time. This tendency was most evident when using a low adapting field luminance with a high flash intensity. CONCLUSIONS: Our results suggest that the rods intrude much more during light adaptation at 2 Hz stimulation in rodents than in humans. Therefore, 20 Hz flicker stimulation can better isolate more the cone-mediated function than 2 Hz stimulation during the course of light adaptation in rats. Furthermore, the functional characteristics of the cone in rats may be different from that in humans.

Adaptation, Ocular↗
PubMed1998

Visual evoked cortical magnetic responses to checkerboard pattern reversal stimulation: a study on the neural generators of N75, P100 and N145.

In an attempt to elucidate the neural generators of pattern reversal visual evoked potentials (PR-VEPs), we measured the visual evoked magnetic fields (PR-VEFs) using a 37-channel magnetoencephalography in six healthy young adults. A half-field checkerboard pattern was phase-reversed at a rate of 1 Hz to stimulate the right or left visual half-field, thus yielding 12 PR-VEFs in total from the six subjects. The simultaneously recorded scalp PR-VEPs showed three distinct components of N75, P100 and N145. Three corresponding components were also identified in the PR-VEFs with similar peak latencies (N75m, P100m and N145m). P100m and N145m were clearly identified in all 12 PR-VEFs, whereas N75m was observed in only nine of 12 PR-VEFs. The equivalent current dipoles (ECDs) of N75m, P100m and N145m were located closely to each other in the occipital cortex around the calcarine fissure contralateral to the stimulated visual field, when they were overlaid on the MRI. The reliability of dipole estimation was highest in P100m, followed by N145m while N75m showed the least reliability. The direction of the current flow of ECDs of N75m and N145m was from the medial to the lateral in the occipital cortex when viewed in a coronal section, whereas that for P100m was toward the medial. The ECD location of P100m changed according to the retinotopic organization when the upper or lower quadrant of the visual field was stimulated, with the ECDs being located in the lower or upper part, respectively, of the visual cortex. Our results therefore indicate that the neural origins of N75m, P100m and N145m of PR-VEFs are in the primary visual cortex on the contralateral side of the stimulated visual half-field, while the three components are physiologically distinct.

Adult↗
PubMed1998

Effects of sex, height and age on motor evoked potentials with magnetic stimulation.

Magnetic stimulation of the brain and cervical and lumbar spinal roots was performed on 48 healthy subjects in order to investigate the effects of sex, height and age on motor evoked potentials (MEPs). The compound muscle action potentials were recorded from the abductor pollicis brevis and abductor hallucis muscles. The central motor conduction time (CMCT) was measured between the cerebral cortex and the cervical root and also between the cerebral cortex and the lumbar root. A multiple regression analysis was used to determine which of the physical variables, namely sex, height and age, were significant. A significant gender difference was observed in the MEP latencies and CMCT of the leg, but not in those of the hand. Both height and age had a significant effect on the leg MEP latencies with a lesser effect on the hand MEP latencies. The leg CMCT was also significantly influenced by height and age, while the hand CMCT was not. These results thus suggest that physical variables are very important in defining normal MEPs, especially in the lower limbs. Therefore, when we assess motor function in patients with neurological disorders, both the patients and control groups should be matched for sex, height and age distribution.

Adult↗
PubMed1998

The effect of magnetic coil orientation on the excitation of the median nerve.

OBJECTIVE: We investigated the effect of magnetic coil orientation on the excitation of the median nerve in healthy subjects. METHODS: An 8-shaped coil, 3.2 cm in outer diameter, was used. The median nerve was stimulated at the elbow while the compound muscle action potentials (CMAPs) of abductor pollicis brevis muscle were recorded at 4 different directions of the induced current: orthodromic, antidromic, medio-lateral and latero-medial. RESULTS: We found that the amplitude of the CMAP was the greatest in a medio-lateral (ML) direction. We also measured the induced electric field in the saline tank that mimicked the forearm. The induced electric field and its spatial gradient were the greatest in the ML direction among 4 directions. CONCLUSION: The fact that the forearm is a restrictive volume conductor may result in the different effects of coil orientation on the excitation of the median nerve at the elbow.

Action Potentials↗
PubMed1998

Acute myelitis with hyperIgEaemia and mite antigen specific IgE: atopic myelitis.

An occurrence of acute localised myelitis was recently seen in four adult patients with atopic dermatitis who had hyperIgEaemia and mite antigen specific IgE. The total and mite antigen specific IgE was therefore studied in serum samples from 19 consecutive patients with acute localised myelitis of unknown aetiology, 56 patients with clinically definite multiple sclerosis, and 40 healthy controls. The total IgE concentration was significantly higher in acute localised myelitis (median=360 U/ml) than in multiple sclerosis (median=52 U/ml, p<0.0001) and the controls (median=85 U/ml, p=0.0002). The specific IgE to Dermatophagoides pteronyssinus was found more often in patients with acute localised myelitis (95%) than in patients with multiple sclerosis (34%, p<0.0001) and the controls (35%, p<0.0001) and the specific IgE to Dermatophagoides farinae was similar (acute localised myelitis 79%, multiple sclerosis 29% (p<0.0001), controls 30%, (p=0.0003). Atopic dermatitis coexisted more commonly in patients with acute localised myelitis (37%) than in patients with multiple sclerosis (0%, p<0.0001) and the controls (7.5%, p=0.0089). Therefore, acute localised myelitis with hyperIgEaemia, in which atopy to mite antigens seems to exist, may be a distinct subtype of allergic myelitis-that is, atopic myelitis.

Adult↗
PubMed1998

20-Hz flicker stimulus can isolate the cone function in rat retina.

Cone electroretinograms (ERGs) are typically isolated in humans by flicker stimuli against rod-desensitizing adapting fields. To investigate the manner in which adapting-field luminance affects the cone ERGs, we recorded ERGs in normal albino Sprague-Dawley rats with flicker stimuli presented against adapting fields that ranged in luminance from to 1.75 log cd/m2. A flicker rate of 20 Hz was used to isolate the cone ERGs under all adaptation conditions. We found the amplitudes of cone ERGs to increase with increasing adapting-field luminance. These response characteristics are similar to human ERGs using 30-Hz flicker stimuli, which suggests that flicker stimuli are a useful technique to isolate the cone function in rats.

Adaptation, Ocular↗
PubMed1998

Multimodality visual evoked potentials in evaluating visual dysfunction in optic neuritis.

Visual information is processed via multiple, parallel channels. The present study examined the clinical feasibility of multimodality visual evoked potentials (VEPs) in optic neuritis. We recorded transient VEPs to 30' checkerboard patterns, chromatic and achromatic sinusoidal gratings and apparent motion, and steady-state VEPs to achromatic gratings in 15 normal controls and 14 patients. VEPs to 30' checks were abnormal in 10 eyes (7 patients); however, considering all five modalities, abnormal responses were seen in 20 eyes (12 patients). Abnormality rates were not equal among the visual stimuli, which thus suggested possible dysfunction of individual subdivisions in the visual pathways. We conclude that use of multimodality VEPs may increase both understanding of the pathophysiology of the visual pathways and diagnostic yield.

Adult↗
PubMed1997

Jerk-locked back averaging and dipole source localization of magnetoencephalographic transients in a patient with epilepsia partialis continua.

In order to localize the generator site of epileptiform discharges, we applied the techniques of jerk-locked back averaging (JBA) of magnetoencephalographic (MEG) activities and dipole source localization in a patient with epilepsia partialis continua (EPC), who showed continuous, focal myoclonic jerks in the right arm. The myoclonic discharges in the right thenar muscle were used as a trigger pulse. JBA revealed consistent EEG and MEG transients that coincided consistently and constantly preceded the myoclonic jerks. The estimated dipoles of MEG were localized in a restricted area in the left precentral area, which closely correlated with the area of epileptic discharges recorded in electrocorticography. Therefore, JBA of MEG is considered to be a useful non-invasive method for localizing the epileptogenic area in EPC.

Aged↗