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Biomedical subjects

R Kakigi

Publications and source records attributed to R Kakigi.

At least 163 records · Page 9Linked to original sources
PubMed1987

The effect of aging on somatosensory evoked potentials following stimulation of the posterior tibial nerve in man.

Spinal- and scalp-recorded somatosensory evoked potentials following stimulation of the posterior tibial nerve were obtained in 20 normal young subjects, and 45 aged subjects who were classified into group A (61-74 years) and group B (75-88 years). The results may be summarized as follows: (1) Spinal potentials, N19 at the twelfth thoracic vertebra and N28 at the second cervical vertebra, were significantly prolonged in latency in aged subjects. The interpeak latency, N19-N28, which represents the conduction time through the spinal cord, was also prolonged in aged subjects. (2) The interpeak latencies, P28-N31 and P28-P35, which represent the conduction time from the medial lemniscus to the thalamus and to the sensory cortex, respectively, were prolonged in aged subjects, particularly in group B. (3) The interpeak latencies of cortical potentials following P35, which represent the intracortical transit times, did not show any significant difference between young and aged subjects. (4) Amplitudes of the spinal, and short- and middle-latency cortical potentials were smaller in the aged subjects than those of young subjects, particularly the far-field N31 potential at Cz' electrode. In contrast, the long-latency cortical potentials were larger in aged subjects, although not significantly so.

Adult↗
PubMed1987

Generator mechanisms of giant somatosensory evoked potentials in cortical reflex myoclonus.

In order to clarify the generator mechanisms for giant cortical evoked potentials, scalp topographies of somatosensory evoked potentials (SEPs) following various types of stimulation, including electrical nerve trunk and finger stimulation and mechanical stimulation, were investigated in 5 patients with cortical reflex myoclonus. For SEPs evoked by median nerve stimulation, not only the P25 and N34 components in central and parietal regions but also N25 in the frontal region were markedly enlarged in each patient. Their scalp distributions were not significantly different from those of normal subjects. P25 and N25, but not N34, were considerably attenuated by interfering tactile stimulation applied to the hand. The components corresponding to P25, N25 and N34 following electrical stimulation of the digital nerves as well as mechanical stimulation of the finger were also remarkably large and showed scalp distributions similar to those for median nerve SEPs. It is therefore concluded that the giant cortical SEPs of cortical reflex myoclonus are generated in those areas of the primary sensory cortex which generate normal SEPs, in response to an input, at least in part, from cutaneous afferents on the basis of an extremely enhanced cortical excitability.

Biomechanical Phenomena↗
PubMed1987

Somatosensory evoked potentials following stimulation of the lower limb in cortical reflex myoclonus.

Generating mechanisms of giant somatosensory evoked potentials (SEPs) following stimulation of the posterior tibial nerve as well as the big toe were investigated in three patients with cortical reflex myoclonus. Scalp distributions of recognisable components were very similar to those in normal subjects, except that their amplitude was much larger. The tibial nerve SEPs were remarkably attenuated by interfering tactile stimulation. Therefore, the giant SEPs observed in the present cases seem to be, at least partially, due to input from cutaneous nerve fibres on the background of extremely enhanced excitability in area 3b of the primary sensory cortex where normal SEPs are generated.

Adolescent↗
PubMed1986

Ipsilateral and contralateral SEP components following median nerve stimulation: effects of interfering stimuli applied to the contralateral hand.

Somatosensory evoked potentials (SEPs) recorded over the hemisphere ipsilateral and contralateral to the electrically stimulated median nerve were analysed in the presence or absence of interfering movement, tactile and vibratory activity in the contralateral hand. In the control wave forms the early potentials recorded over the ipsilateral frontal region, P19 and N25, showed apparent phase reversal with N19 and P25 respectively in the contralateral parietal region and were therefore considered to be produced by the same generator in the primary sensory cortex. All other potentials recorded over the ipsilateral hemisphere were of the same polarity and similar latency to potentials present contralaterally, and their amplitude diminished progressively with distance from the contralateral hemisphere. They were therefore believed to be volume-conducted from the contralateral hemisphere, rather than originating in the ipsilateral hemisphere through uncrossed ascending pathways or interhemispheric connections. The distribution of effects produced by interfering activity in the contralateral hand was demonstrated by subtracting the 'interference' from the 'control' response to derive a 'difference' wave form. Difference potentials present over the contralateral scalp were consistent with influence on generators in the contralateral hemisphere. In particular, voluntary movement of the contralateral hand resulted in difference potentials distributed in accordance with a proposed generator in area 3a or 4. No consistent difference potentials were found in the ipsilateral parietal region. In the ipsilateral frontal region, however, an upward potential whose latency was around 55 msec was proposed to be due to a generator in the supplementary motor area of the contralateral hemisphere.

Adult↗
PubMed1986

Influence of concurrent tactile stimulation on somatosensory evoked potentials following posterior tibial nerve stimulation in man.

A topographical study was made of SEPs following stimulation of the right posterior tibial nerve at the ankle, with and without concurrent tactile stimulation of the soles of either foot or the palm of the right hand. Effects of the interfering stimulus were best demonstrated by subtracting the wave forms to derive "difference' potentials. The majority of SEP components were significantly attenuated by tactile stimulation of the ipsilateral foot, and the difference wave form was of similar morphology to the control response. Components of opposite polarity peaking at 39 msec were consistent with the field of a cortical generator with dipolar properties, situated in the contralateral hemisphere just posterior to the vertex with the positive poles oriented towards the ipsilateral side. By analogy with median SEP findings, these potentials were believed to originate in the foot region of area 3b where neurones are mainly concerned with cutaneous sensory processing. When the tactile stimulus was applied to the contralateral foot, difference potentials maximally recorded just posterior to the vertex were of smaller amplitude but similar morphology to ipsilateral foot difference components. This suggested the possibility that input from the two lower extremities may converge at cortical or subcortical level, the effect being manifested in the response of certain neurones in area 3b. With both contralateral foot and ipsilateral hand stimulation, other difference potentials were present which suggested that there may be cortical regions responding to combinations of sensory stimuli applied to various parts of the body surface.

Adult↗
PubMed1986

Disseminated lesions at presentation in patients with optic neuritis.

Thirty five adults and two children with clinically isolated optic neuritis were examined by magnetic resonance imaging (MRI) to determine the presence of disseminated lesions within the brain at presentation and to compare these findings with the results of evoked potential studies. Of the adult patients, 61% showed lesions on the scans whereas the evoked potentials suggested the presence of lesions outside the visual system in 30%. MRI is a sensitive method for the demonstration of clinically unsuspected lesions in patients with uncomplicated optic neuritis.

Adolescent↗
PubMed1985

Effects on median nerve SEPs of tactile stimulation applied to adjacent and remote areas of the body surface.

Study of the influence of continuous tactile stimulation on somatosensory evoked potentials (SEPs) following electrical stimulation of the median nerve revealed an effect due to interfering input from both adjacent and remote regions of the body surface. The distribution of the effect was demonstrated by subtracting the 'interference' from the 'control' response to derive a 'difference' wave form. Tactile stimulation of the thumb ipsilateral to the stimulated median nerve produced a difference wave form in which a marked phase reversal was apparent between pre- and post-central areas for 2 complexes, at latencies of approximately 20 and 30 msec. It is proposed that this may have been due to partial 'saturation' of a generator in the hand region of area 3b in the primary somatosensory cortex (SI), which was then unable to respond fully to the median nerve impulse. A similar effect was observed when the interfering stimulus was applied to the ipsilateral little finger, possibly reflecting a process of 'surround inhibition.' Tactile stimulation of more remote regions (principally the face and contralateral hand) resulted in consistent difference wave forms in which the early components (less than 30 msec latency) had scalp distributions differing from one another but consistent with influence on generators in the face or hand region of the second somatosensory cortex (SII). Later potentials consistently identifiable in the difference wave forms were similar for all locations of the interfering stimulus apart from the ipsilateral thumb and were distributed in accordance with a proposed generator in the parietal 'association' cortex.

Adult↗
PubMed1984

Scalp topography of mechanically and electrically evoked somatosensory potentials in man.

Scalp topography of somatosensory evoked potentials following mechanical (SEPs(M)) and electrical (SEPs(E)) stimulation of the left middle finger was investigated with linked ear reference in 21 normal young adults. A small plastic ball (touch) or needle (pain) was used for the mechanical stimulation. With mechanical stimulation, at least 3 positive and 3 negative potentials (P19(M), N24(M), P29(M), N36(M), P49(M) and N61(M] were found in the post-rolandic area contralateral to the stimulation. The wave form in SEPs(M) was similar to those in SEPs(E), but the peak latency of each component in SEPs(M) was 1-4 msec longer than that in SEPs(E). Earlier components such as P19(M), N24(M) and P29(M) were not as clearly recognized as corresponding components in SEPs(E). However, the wave form recorded on the hemisphere ipsilateral to the stimulation or in the frontal area contralateral to the stimulation showed a greater difference from subject to subject. P19(M), N24(M) and P29(M) correlated positively both with arm length and height of the subject. There was no significant difference of the wave form between the linked ear reference and the bipolar (C4-Fz) derivation. Wave form of SEPs(M) by needle stimulation did not significantly differ from that by plastic ball stimulation.

Adult↗
PubMed1983

Scalp topography of the short latency somatosensory evoked potentials following posterior tibial nerve stimulation in man.

The scalp topography of the short latency somatosensory evoked potentials (SEPs) to unilateral posterior tibial nerve stimulation at the ankle was studied by using a non-cephalic reference in 22 normal young adults. At least 3 components (P28, N31 and N32) were identified preceding the major positive peak (P36). The first 2 components had similar peak latency at all scalp electrodes, and were considered to be generated in deep structures. However, N32 was localized to the hemisphere contralateral to the side of stimulation. P36 was maximal at the midline foot sensory area, or at the contralateral parasagittal area, and its amplitude decreased more steeply anteriorly than posteriorly. The peak latency of P36 progressively increased from ipsilateral to the side of stimulation in the coronal plane. P36 occurred earlier in the somatosensory area, and increased in peak latency anteriorly. Generator source of scalp-recorded far-field potentials (P28 and N31) remains to be elucidated. N32 might reflect activities of the thalamo-cortical pathway or an initial cortical response. P36 appeared to be generated in the somatosensory foot area.

Adult↗