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S Tobimatsu

Publications and source records attributed to S Tobimatsu.

At least 55 records · Page 3Linked to original sources
PubMed1997

Visual evoked potentials in the vicinity of the optic tract during stereotactic pallidotomy.

We recorded visual evoked responses in eight patients with Parkinson's disease, using a depth electrode either at or below the stereotactic target in the ventral part of the globus pallidus internus (GPi), which is located immediately dorsal to the optic tract. Simultaneously, scalp visual evoked potentials (VEPs) were also recorded from a mid-occipital electrode with a mid-frontal reference electrode. A black-and-white checkerboard pattern was phase reversed at 1 Hz; check size was 50 min of arc . Pallidal VEPs to full field stimulation showed an initial positive deflection, with a latency of about 50 ms (P50), followed by a negatively with a mean latency of 80 ms (N80). The mean onset latency of P50 was about 30 ms. P50 and N80 were limited to the ventralmost of the GPi and the ansa lenticularis. Left half field stimulation evoked responses in the right ansa lenticularis region while right half field stimulation did not, and vice versa. These potentials thus seemed to originate posterior to the optic chiasm. The scalp VEPs showed typical triphasic wave forms consisting of N75, P100 and N145. The location of the recording electrode in the ansa lenticularis region did not modify the scalp VEP. These results suggest that P50 and N80 are near-field potentials reflecting the compound action potentials from the optic tract. Therefore, N75 of the scalp VEPs may represent an initial response of the striate cortex but not of the lateral geniculate nucleus.

Aged↗
PubMed1997

Different effects of cholinergic agents on responses recorded from the cat visual cortex and lateral geniculate nucleus dorsalis.

We investigated the effect of cholinergic agents on the cat visual evoked potentials (VEPs) recorded from the primary visual cortex (V1) and lateral geniculate nucleus dorsalis (LGNd) to determine on which level of the visual pathway the cholinergic system acts. VEPs to the alternation of 0.1 cycles per degree sinusoidal gratings at 1 and 4 Hz were recorded from N2O-anesthetized cats directly from the surface of V1 and LGNd. The depth of recording in LGNd was determined by the site where the maximal response was obtained by 1 Hz stimulation. VEPs to 4 Hz stimulation, which showed sinusoidal waveforms and were analyzed by fast Fourier transforms, were used as indicators for modulation by cholinergic agents. Physostigmine, an acetylcholinesterase inhibitor, 0.7 mg/kg i.v., suppressed the amplitude of the responses more at V1 (suppression ratio: mean +/- SD, 85.4 +/- 9.3%) than at LGNd (32.4 +/- 30.7%) (P < 0.05). Conversely, scopolamine, a muscarinic receptor blocker, 0.7 mg/kg i.v., increased the amplitude of the responses more at V1 (enhancement ratio: mean +/- SD, 60.3 +/- 22.3%) than at LGNd (-22.2 +/- 22.5%) (P < 0.05). These results indicate that the V1 changes reflect a direct cortical cholinergic effect, probably by modulating the cholinergic projection from the nucleus basalis of Meynert to V1.

Animals↗
PubMed1997

Bilateral striate cortex contusion presenting with cerebral asthenopia rather than cortical blindness.

We report a 22-year-old female with a history of contusion of bilateral occipital lobes at the age of 1 year. Magnetic resonance imaging confirmed severe lesion in bilateral striate cortices which should have resulted in cortical blindness. However, she displayed a fairly good visual function presenting only cerebral asthenopia and the restriction of the visual field. A positron emission tomography revealed that no areas other than the primary visual cortices responded to visual stimuli. Thus, her residual vision may be attributable to plasticity of the visual cortex in humans.

Adult↗
PubMed1996

Western versus Asian types of multiple sclerosis: immunogenetically and clinically distinct disorders.

The polymorphism of HLA-DRB1, -DRB3, and -DRB5 genes as well as magnetic resonance images of the brain and spinal cord were studied in 57 Japanese patients with multiple sclerosis (MS). Twenty-three patients clinically displayed selective involvement of the optic nerve and spinal cord and were classified as having Asian-type MS. The other 34 patients had disseminated central nervous system involvement and were classified as having Western-type MS. Patients with Asian-type MS had fewer brain lesions shown by magnetic resonance imaging, but more gadolinium-enhanced spinal cord lesions than did patients with Western-type MS (47% vs 17%). Furthermore, the DR2-associated DRB1*1501 allele and DRB5*0101 allele were associated with Western-type MS (41.2%), but not with either Asian-type MS (0%) or healthy control subjects (14.2%). Heterogeneity in the immunogenetic background and in the magnetic resonance imaging features between the two subtypes of MS thus suggests the presence of two etiologically distinct diseases in Asians.

Alleles↗
PubMed1996

Human VEPs to isoluminant chromatic and achromatic sinusoidal gratings: separation of parvocellular components.

To extract the responses specific to the parvocellular system (color vision and form perception) in humans, visual evoked potentials (VEPs) in response to the onset of isoluminant chromatic (red-green) and achromatic (black-white) sinusoidal gratings were recorded in 15 young adults. Chromatic stimulation evoked a characteristic negative wave (N1) with peak latencies around 120 msec. The amplitude resembled an inverse U-shaped function against the spatial frequency with a peak at 2 c/deg. In contrast, VEPs to achromatic gratings showed different spatial frequency characteristics with a peak at 5.3 c/deg. With variations in the luminous intensity ratio between the red and green gratings, N1 was seen to respond maximally to isoluminant stimulation. These results indicate that the combined use of isoluminant chromatic and achromatic patterns could stimulate the parvocellular system selectively in humans.

Adult↗
PubMed1996

The effect of binocular stimulation on each component of transient and steady-state VEPs.

We recorded the monocular and binocular VEPs to the alternation of sinusoidal gratings in order to evaluate the binocular interaction in each component of transient and steady-state VEPs in 13 normal subjects. Three spatial frequencies (1.3, 2.6 and 5.3 c/deg) with a 90% contrast were used as visual stimuli. The latencies and amplitudes of N70 and P100 of the transient VEPs were measured. The steady-state VEPs were Fourier analyzed, and both the phase and amplitude of the second (2F) and fourth (4F) harmonic responses were obtained. Binocular interaction was influenced by spatial frequency such that a binocular summation or even an inhibition occurred. For the transient VEPs, a binocular summation was more pronounced in the amplitude of N70 than in that of P100 at all spatial frequencies. There were no significant effects of binocular stimulation on latencies of N70 or P100. However, the latencies of N70 and P100 showed different spatial frequency characteristics. For the steady-state VEPs, the amplitude of 2F revealed a binocular summation that was more pronounced at 5.3 c/deg, whereas the 4F amplitude showed binocular inhibition at 2.6 and 5.3 c/deg. The 2F phase showed binocular inhibition at all spatial frequencies, whereas no such inhibition was observed in the 4F phase. These results suggest that individual components of transient and steady-state VEPs are physiologically distinct and may therefore be generated from different neuronal populations in striate cortex.

Adult↗
PubMed1996

Normal variability of the amplitude and phase of steady-state VEPs.

The present study quantifies the amplitude and phase variability of steady-state VEPs (S-VEPs) and compares this variability between subjects and between individual runs. The S-VEPs were recorded repeatedly in 14 normal subjects with varying spatial and temporal frequencies of sinusoidal gratings; 6 spatial frequencies (range 0.5-8.0 c/deg) with 3 temporal frequencies (4, 6 and 8 Hz) were used. A total of 75 responses were averaged and analyzed by the Fourier method. Four recordings were obtained in each spatio-temporal combination. In general, the phase data showed small inter- and intrasubject variability. As anticipated, the amplitude data showed a large degree of intersubject variability, although the intrasubject variability was very small. In addition, in some stimulus conditions the inter- and intrasubject variability increased, which thus suggested the existence of an optimal spatio-temporal combination. Therefore, these stimulus parameters should be taken into consideration when S-VEPs are applied in clinical practice.

Adult↗
PubMed1995

Functional mapping of the sensorimotor cortex: combined use of magnetoencephalography, functional MRI, and motor evoked potentials.

Combined use of magnetoencephalography (MEG), functional magnetic resonance imaging (f-MRI), and motor evoked potentials (MEPs) was carried out on one patient in an attempt to localise precisely a structural lesion to the central sulcus. A small cyst in the right frontoparietal region was thought to be the cause of generalised seizures in an otherwise asymptomatic woman. First the primary sensory cortex was identified with magnetic source imaging (MSI) of somatosensory evoked magnetic fields using MEG and MRI. Second, the motor area of the hand was identified using f-MRI during hand-squeezing. Then transcranial magnetic stimulation localised the hand motor area on the scalp, which was mapped onto the MRI. There was a good agreement between MSI, f-MRI and MEP as to the location of the sensorimotor cortex and its relationship to the lesion. Multimodality mapping techniques may thus prove useful in the precise localisation of cortical lesions, and in the preoperative determination of the best treatment for peri-rolandic lesions.

Adult↗
PubMed1995

Parvocellular and magnocellular contributions to visual evoked potentials in humans: stimulation with chromatic and achromatic gratings and apparent motion.

Psychophysical evidence suggests that two major parallel pathways, the parvocellular (P) and the magnocellular (M) pathways, exist in humans. We herein report that responses specific to the P and M systems can be recorded in human visual evoked potentials (VEPs) by using the appropriate stimuli. The onset of isoluminant chromatic (red-green) and high contrast achromatic sinusoidal gratings were used for stimulating the P-system. A chromatic stimulation evoked a characteristic negative wave (N1) with peak latencies around 120 msec. The amplitude showed an inverse U-shaped function as a function of spatial frequency with a peak at 2 c/deg. In contrast, VEPs to achromatic (black-white) gratings showed different spatial frequency characteristics with a peak at 5.3 c/deg. By varying the luminous intensity ratio between the red and green gratings, N1 was found to reach a maximum during isoluminant stimulation. An apparent motion display was used for stimulating the M-system. The speed of alternation (i.e., the interstimulus interval (ISI)) was varied to record both the transient and steady-state VEPs. Transient VEPs showed triphasic waves with the major positive peak (P1) at around 120 ms. Steady-state VEPs were quasi-sinusoidal waveforms, depending on the ISI, and were quite stable across all subjects. There was a also high correlation between the motion threshold and the VEP amplitude. The above observations indicate that characteristic potentials may distinguish between these two parallel visual systems in humans. Thus, the combined use of isoluminant color and high contrast achromatic gratings and an apparent motion display is considered to be useful for evaluating both systems electrophysiologically.

Adolescent↗
PubMed1995

The interaction of the somatosensory evoked potentials to simultaneous finger stimuli in the human central nervous system. A study using direct recordings.

In order to investigate the interaction of sensory electrophysiologic fields arising from the adjacent second (II) and third (III) fingers and the distant second and fifth (V) fingers, direct recordings of somatosensory evoked potentials (SEPs) were performed from the sensory and motor cortices, the sensory thalamic nucleus (nucleus ventralis caudalis, VC) and the cuneate nucleus in humans during neurosurgical operations. Electrical stimulation was given to the II, III or V fingers individually, and also to pairs of either the II and III fingers or the II and V fingers simultaneously. The interaction ratio (IR) was devised as the ratio of amplitude attenuation caused by the simultaneous stimulation to two fingers compared with the amplitude of the arithmetically summed SEPs to the individual stimulation of two fingers. The IRs were calculated on N20 and P25 from the sensory cortex, P22 from the motor cortex, P17thal from the VC, and N16cune and P35cune from the cuneate nucleus. With both stimulations to the II and III fingers and the II and V fingers, P25 showed the greatest IR, followed by P22, then by P17thal, with N16cune exhibited the smallest IR. N20 and P35cune showed similar IRs and significantly greater IRs with II and III finger stimulation compared with II and V finger stimulation. These results thus indicate that the interaction of somatosensory impulses occurs in several structures along the sensory pathway in CNS, including the cuneate nucleus, the sensory thalamic nucleus, as well as sensory and motor cortices, with the greatest IRs in the cerebral cortices and the weakest ones in the brain-stem.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1995

Aging and pattern visual evoked potentials.

Visual abilities decline during senescence. Age-related declines cannot be attributed entirely to changes in optical factors (senile miosis and opacification of the ocular media) and must therefore be caused by changes in the visual pathways. Because pattern visual evoked potentials (VEPs) provide information regarding the sensory function and integrity of the visual system, recent research on age-related changes in VEPs is reviewed. The results of this review show that stimulus parameters of VEPs (luminance, contrast, spatial and temporal frequencies) modify the age-related changes in VEPs. The visual system consists of multiple, parallel channels which process different information. Therefore, it is hypothesized that aging may affect the specific functional subdivisions in the visual pathways differentially.

Adolescent↗
PubMed1995

[Segmental muscular atrophy of unilateral upper limb associated with cervical disc herniation in a juvenile male].

A 25-year-old man first noticed atrophy of right upper arm at the age of 15. This symptom progressed for the following 3 years and then became stable. As he noted difficulty in elevating his right arm above the shoulder level, at the age of 25 he was admitted to our hospital. On neurological examination, he had right scapula alata, moderate atrophy and weakness of right triceps muscle. Right triceps reflex was absent. Other neurological examinations were normal. Needle electromyography revealed neurogenic patterns in the muscles of the C5-T1 segments. Cervical MRI and CT myelography revealed mild cervical disc protrusion toward the right side at the C5/6 level and atrophy of the middle and lower cervical cord on the right side, but nothing suggestive of the fexion myelopathy. The clinical manifestations of the patient resembled those of Hirayama disease, except for the distribution of the involved muscles. Since the most severely involved level of the cervical cord (C7 segment) corresponded to the level of the protruded cervical disc, it was suggested that the cervical disc herniation played an important role in the development of the myelopathy in this patient.

Adult↗
PubMed1994

Periodic synchronous discharges and visual evoked potentials in Creutzfeldt-Jakob disease: PSD-triggered flash VEPs.

We have developed the technique of flash visual evoked potentials (VEPs) triggered by periodic synchronous discharges (PSDs) to investigate the interaction between PSDs and VEPs in 3 patients with Creutzfeldt-Jakob disease (CJD). This technique enables us to explore the cerebral pathophysiology underlying CJD. Unexpectedly, we found that PSDs and VEPs did not interact even when VEPs were evoked in close temporal proximity to PSDs. Thus, it appears that PSDs are generated by a different neuronal mechanism from that involved in VEP generation.

Adult↗
PubMed1994

Temporal frequency deficit in patients with senile dementia of the Alzheimer type: a visual evoked potential study.

To study the temporal aspect of visual processing of senile dementia of the Alzheimer type (SDAT), we recorded the steady-state visual evoked potentials (VEPs) to LED goggle stimulation at five different temporal frequencies in 14 patients with SDAT and 14 control subjects. For comparison, we also studied 14 patients with vascular dementia (VD). All subjects were women, and their ages were closely matched. Temporal frequencies were 5, 10, 15, 20, and 30 Hz. The steady-state VEPs were Fourier analyzed, and both the amplitude and phase of the first and second harmonic responses were obtained. There was a significant difference in the amplitude across the three groups for stimulation at 15, 20, and 30 Hz, but no difference at a stimulation of 5 and 10 Hz. Multiple comparison tests revealed that patients with SDAT had a significantly smaller amplitude than normal controls. Patients with VD had lower amplitudes than normal subjects, but this was not statistically significant. In the phase data, there were also no statistically significant differences across the three groups for any of the temporal frequencies. These results indicate that a temporal frequency deficit exists in SDAT. This phenomenon may be explained by the pathology that affects the early stage of visual signal processing.

Aged↗
PubMed1994

Vitamin B12 metabolism and massive-dose methyl vitamin B12 therapy in Japanese patients with multiple sclerosis.

Serum vitamin B12 levels and unsaturated vitamin B12 binding capacities were measured in 24 patients with multiple sclerosis (MS), 73 patients with other neurological disorders and 21 healthy subjects. There was no decrease in the vitamin B12 levels, however, a significant decrease in the unsaturated vitamin B12 binding capacities was observed in patients with MS when compared with other groups. A massive dose of methyl vitamin B12 (60 mg every day for 6 months) was administered to 6 patients with chronic progressive MS, a disease which usually had a morbid prognosis and widespread demyelination in the central nervous system. Although the motor disability did not improve clinically, the abnormalities in both the visual and brainstem auditory evoked potentials improved more frequently during the therapy than in the pre-treatment period. We therefore consider that a massive dose methyl vitamin B12 therapy may be useful as an adjunct to immunosuppressive treatment for chronic progressive MS.

Adult↗
PubMed1994

[Visual information processing in humans].

Recent advances in parallel information processing of primates and humans have been reviewed. First, I review what is known about physiology and anatomy of the primate visual pathways. Several lines of evidence suggest that the primate visual system consists of the parvocellular (P) and the magnocellular (M) pathways. M-system originates from the A retinal ganglion cells that project to the visual cortex (V1) via the magnocellular layers of the lateral geniculate nucleus (LGN). This system plays an important role for motion and stereopsis. P-system derives from the B retinal ganglion cells that project to V1 via the parvocellular layers of the LGN. This system shows selectivity for color vision and form perception. Second, I focus on the information processing of the human visual pathways. Psychophysical evidence suggests that there are also P and M systems in humans. However, there have been few electrophysiological studies which intend to separate the responses specific to P and M systems in human visual evoked potentials (VEPs). Based on the physiological distinctions between P and M systems, the use of isoluminant color patterns and apparent motion display allows us to evaluate P and M systems, respectively.

Animals↗