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Biomedical subjects

Y Ugawa

Publications and source records attributed to Y Ugawa.

At least 73 records · Page 4Linked to original sources
PubMed1995

Electrical stimulation of the human descending motor tracts at several levels.

The descending motor tracts were activated using a high voltage electrical stimulation technique at four levels: the motor cortex, brainstem (around the pyramidal decussation), and the first and sixth thoracic vertebral levels (T1, T6). Electromyographic activity was recorded from the tibialis anterior or extensor digitorum brevis muscles. Consistent motor action potentials could be evoked in all normal subjects. The conduction velocity of the descending tracts was estimated to be 62 to 79 m/s. The sum of synaptic delay and utilization time at the motoneurons (spinal delay time) was estimated to be 0.5 +/- 0.3 ms indicating a mono- or oligosynaptic connection. In patients with diffusely affected descending tracts, the technique showed slowed conduction along the descending tracts and prolonged spinal delay time which may include the time required for temporal summation of excitatory postsynaptic potentials as well as synaptic delay and utilization time. In patients with a localized lesion, localized conduction delay was found at the appropriate segment.

Adult↗
PubMed1995

[Electromyographic analysis of cortical myoclonus and focal dystonia].

We have done a few physiological studies on six patients with cortical reflex myoclonus and three patients with unilateral focal dystonia caused by a discrete cerebrovascular lesion in the basal ganglia. The silent period after magnetic cortical stimulation was normal or slightly prolonged in all the patients with cortical myoclonus. In contrast, in patients with focal dystonia, it was shortened in the muscles on the contralateral side to the lesion, whereas normal in duration on the ipsilateral side. Excessive inputs from the disinhibited supplementary motor cortex to the primary motor cortex due to a lesion of the basal ganglia must cause this shortening in the dystonic hand muscles. Excitability recovery of the motor cortex after hypersynchronous activation by magnetic stimulation should be prolonged in the myoclonic patients. Cortico-cortical inhibition of the motor cortex studied with paired magnetic stimulation technique was disturbed in both the patients with myoclonus and those with dystonia. This result suggested that the disinhibition of the motor cortex is present in both disorders. Based on these results, we conclude that the motor cortex is similarly disinhibited in both disorders, but recovery function from hypersynchronous activation is different between these two groups.

Basal Ganglia↗
PubMed1994

Excitation of the motor cortex associated with the E2 phase of cutaneous reflexes in man.

We investigated excitability changes of the motor cortex associated with the E2 phase of cutaneous reflexes in the first dorsal interosseous muscle using transcranial electrical and magnetic stimulation of the motor cortex in humans. EMG responses to combined cutaneous and weak magnetic cortical stimulation, which were elicited during the E2 phase of cutaneous reflexes, were larger than those by the same magnetic cortical stimulation alone. This facilitatory effect was reduced or even inhibitory effect was seen when the intensity of cortical stimulation was increased. Responses to weak electrical cortical stimulation were less affected by the combined cutaneous stimulation. The same facilitatory effect on responses to weak magnetic cortical stimulation was also observed in single motor unit recordings, too. Dissociation between facilitatory effects on the responses evoked by weak magnetic and weak electrical cortical stimulations suggests that the motor cortical excitability is increased in association with the E2 phase. The present results are consistent with the hypothesis that the E2 phase is a kind of transcortical reflex.

Adult↗
PubMed1994

Suppression of motor cortical excitability by electrical stimulation over the cerebellum in ataxia.

We studied the effect of electrical stimulation over the cerebellum on electromyographic responses evoked by magnetic stimulation over the cerebral motor cortex in 41 normal volunteers and 32 patients with ataxia due to various disorders. In all the normal subjects, stimulation over the cerebellum significantly reduced the size of electromyographic response in the first dorsal interosseous muscle evoked by magnetic cortical stimulation, when the cerebellar stimulus preceded the cortical stimulus by 5, 6, and 7 msec. This suppression was absent or reduced in ataxic patients who had atrophy of the cerebellar hemispheres as demonstrated by magnetic resonance imaging and in patients with dysfunction of the cerebellothalamocortical pathway who had lesions in the superior cerebellar peduncle or in the motor thalamus. In contrast, suppression was normal in ataxic patients who had pontine lesions that affected the pontocerebellar afferent pathway to the cerebellum. Results were also normal in patients without cerebellar ataxia, such as those with Parkinson's disease, sensory ataxia, and cerebrovascular disease without ataxia. We conclude that electrical stimulation activates cerebellar structures that suppress motor cortical excitability through a cerebellothalamocortical pathway and that the afferent systems to the cerebellum make no or little contribution to the effect. The technique described here would be useful for distinguishing ataxia due to lesions of cerebellar afferent pathway from other types of cerebellar ataxia.

Adult↗
PubMed1994

Magnetic stimulation of corticospinal pathways at the foramen magnum level in humans.

Magnetic stimulation done with a double cone coil placed over the back of the head activated descending motor pathways and produced electromyographic responses in muscles of the arms and legs. The latencies of these responses were the same as those of responses to electrical brainstem stimulation. The threshold was lowest when the coil was placed over the inion or below it on the median line. Placement of the coil on the side ipsilateral to the muscle was more effective than placement on the contralateral side. These results indicate that activation occurs at the foramen magnum level (just below the pyramidal decussation). Collision experiments that used cortical and magnetic brainstem stimulation indicated that the major part of the responses to the latter stimulation were conducted via the large diameter component of the corticospinal tract. Collision experiments done with the peripheral nerve and magnetic brainstem stimulation showed that this stimulation produced a single descending volley in the descending tract. We conclude that magnetic brainstem stimulation produces a single descending volley in the corticospinal tract at the foramen magnum level with less discomfort.

Adult↗
PubMed1994

Motor cortex inhibition in patients with ataxia.

We studied the effects of a subthreshold magnetic stimulus over the motor cortex and an electrical stimulus over the cerebellum on EMG responses produced by a suprathreshold magnetic stimulus over the motor cortex. In normal subjects, both subthreshold conditioning stimuli and cerebellar stimuli could suppress responses to suprathreshold magnetic test stimuli when given at appropriate timings: "cortico-cortical" and "cerebellar" inhibition, respectively. In all patients with degenerative ataxias and patients with a lesion in the cerebellar thalamus, the "cortico-cortical" inhibition was normal and the "cerebellar" inhibition was absent. We conclude that cerebellar systems make no or little contribution to the above-mentioned "cortico-cortical" inhibition.

Adult↗
PubMed1994

Transcranial stimulation of the leg area of the motor cortex in humans.

We used transcranial magnetic stimulation on nine normal volunteers to establish an effective way to stimulate the leg area of the motor cortex. Three types of coils: a large figure-eight coil, small figure-eight coil, and a round coil were used. Surface electromyographic activities were recorded from the left tibialis anterior muscle, and the latencies and amplitudes compared with those obtained by anodal electrical stimulation. The most stable responses were obtained when the large figure-eight coil was centered over the vertex and backward current was run through it or when the round coil was centered two to three centimeters anterior to the vertex with left-flowing current in it at the posterior widening. The latencies obtained under these stimulation conditions were the same as those obtained by electrical stimulation. We conclude that direct activation of the pyramidal cells occurs in the leg area of the motor cortex in all forms of magnetic and electrical stimulation.

Electric Stimulation↗
PubMed1994

Axial myoclonus mediated by the propriospinal tract: a case report.

We describe a patient with axial myoclonus. Myoclonus first occurred in the upper abdominal muscle and spread up to the neck muscle and down to the lower abdominal muscle. Physiological studies of the jerks revealed that the myoclonus arose in the thoracic spinal cord and spread slowly up and down the spinal cord at about 3 m/s. We conclude that the myoclonus is mediated by the propriospinal tract.

Adult↗
PubMed1994

Negative myoclonus.

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Electromyography↗
PubMed1993

Interhemispheric facilitation of the hand area of the human motor cortex.

We investigated interaction of the human bilateral hand motor area using two magnetic stimulators. A conditioning shock over the motor cortex facilitated the response evoked in the ipsilateral first dorsal interosseous muscle by a test shock over the contralateral motor cortex given under the limiting conditions of a small conditioning shock over a very small area and a small test shock. This effect was so weak that it was not elicited under slightly different conditions. We conclude that an excitatory, but weak, connection between strictly homotopic areas of the bilateral hand motor cortices exists in humans.

Adult↗
PubMed1993

Giant somatosensory evoked magnetic field in patients with myoclonus epilepsy.

We investigated somatosensory evoked magnetic fields (SEFs) and somatosensory evoked potentials (SEPs) in patients with myoclonus epilepsy. The median nerve was stimulated at the wrist, and responses were recorded over the contralateral hemisphere. The source of the enlarged cortical component of the giant SEF was localized on the post-central sensory cortex. The P1 component of the giant cortical response was composed mainly of a tangentially oriented dipole at area 3b. This is the first magnetoencephalographic analysis of an abnormally enlarged somatosensory cortical response.

Aged↗
PubMed1993

The interval between the positive peak of premyoclonus spike and the onset of myoclonus is shorter than the cortical latency in cortical myoclonus.

In 6 patients with cortical myoclonus, the intervals between the positive peak of the premyoclonus cortical spike and the onset of the myoclonic jerk [interval (Sp-Mcl)] were precisely measured by the computer-assisted jerk-locked averaging method. The intervals (Sp-Mcl) were 13.0-15.8 ms for the abductor pollicis brevis, 8.0-10.4 ms for the extensor digitorum communis and 5.5 ms for the biceps brachii, respectively. These were apparently shorter than the normal latencies of the responses elicited by transcranial cortical stimulation. The difference between the interval (Sp-Mcl) and the spinal latency was -0.8 to 3.5 ms, which was not long enough for the time required for the descending volleys going down from the cortex to the spinal cord. We have concluded that the motor cortex is activated before the positive peak of the premyoclonus spike in cortical myoclonus.

Adult↗
PubMed1993

[Propriospinal myoclonus--a case report].

Propriospinal myoclonus is one type of myoclonus that is proposed to originate in the spinal cord and spread up and down via propriospinal tract. There are a few reports describing the detailed electrophysiological findings of this myoclonus. In this communication, we present the results of electrophysiological analysis of a patient with propriospinal myoclonus. A 23-year-old woman suddenly noticed abdominal pain, which spontaneously faded in a few hours. Irregular involuntary flexion jerks of the trunk appeared spontaneously without pain or hiccups after this episode. It involved the bilateral axial muscles; sternocleidomastoid muscles (SCM), paravertebral muscles (PVM), abdominal muscles (ABD), and intercostal muscles (ICM), but not the limb muscles. It was worsened by the mental stress, but not by her posture or position. While she slept, the jerks were not observed. Routine laboratory examinations were all normal. Magnetic resonance imaging of the spinal cord revealed no abnormalities. The electrophysiological studies done on this patient are polymyography, back-averaging of the EEG activity preceding spontaneous jerks (jerk-locked averaging (JLA), and movement related cerebral potential (MRCP) preceding the involuntary jerks and voluntary abdominal movements. No EEG activities preceding the myoclonus were demonstrated by JLA or MRCP. No MRCP recorded preceding the myoclonus suggests that the jerk is not a self-initiated or externally triggered voluntary movement. Polymyography revealed that the jerks involved the bilateral axial muscles including SCM, PVM, ICM, and ABD, but not the limb muscles. Homologous muscles were activated synchronously. The duration of EMG bursts was variable ranging 50 to 250 ms in these muscles.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Results of endoscopic management of carpal-tunnel syndrome in long-term haemodialysis versus idiopathic patients.

The purpose of this paper is to compare the results of our endoscopic management of carpal-tunnel syndrome caused by long-term haemodialysis to that with no apparent cause (idiopathic). We have operated on 551 hands in 370 patients using the Universal Subcutaneous Endoscope system under local anaesthesia without a pneumatic tourniquet on an out-patient basis since 1986. Ninety-six hands in 64 patients who suffered from carpal-tunnel syndrome from long-term haemodialysis and 85 hands in 52 patients who suffered from carpal-tunnel syndrome for no apparent cause were statistically analysed using complete pre- and postoperative electrophysiological and clinical studies for periods of time ranging from over 6 months to 4.8 years (mean 16.9 months). Electrophysiological and clinical results showed that our endoscopic management in long-term haemodialysis patients is effective, safe and yields the same results as in patients who suffered from carpal-tunnel syndrome for no apparent cause.

Adult↗
PubMed1993

[Dyskinesia in metabolic encephalopathy].

We have described several kinds of involuntary movements occurring in metabolic encephalopathies. They are often associated with slowing of electroencephalographic basic activities and with loss of consciousness. Laboratory studies disclose the cause of the encephalopathies. Asterixis, first reported in hepatic encephalopathy, is produced by EMG silence during voluntary contraction. Myoclonus is associated with a short excessive EMG discharges. Tremor is caused by grouping EMG discharges. Some other kinds of involuntary movements are seen in metabolic encephalopathies. Clinical features of hepatic, uremic, hypoxic, and hypoglycemic encephalopathies are briefly described.

Brain Diseases, Metabolic↗
PubMed1993

Results of endoscopic management of carpal tunnel syndrome.

This paper is a retrospective study of 27 women with carpal tunnel syndrome (39 hands) who underwent a new endoscopic operative procedure utilizing the Universal Subcutaneous Endoscope system developed by the lead author. Operations on 199 hands were performed under local anesthesia on an outpatient basis. The etiology was considered idiopathic in all cases. Complete preoperative and postoperative clinical and electrophysiologic data were analyzed in 39 hands. The follow-up period ranged from 12 to 45.8 months (mean, 18.3 months). Symptoms of sensory disturbances disappeared in an average of 20 weeks in all patients. Electrophysiologic studies showed definite improvement when compared with preoperative studies. No complications were recorded. Clinical and electrophysiologic results showed that the less-invasive management of carpal tunnel syndrome by endoscopy is safe and effective.

Ambulatory Surgical Procedures↗