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Biomedical subjects

Y H Sohn

Publications and source records attributed to Y H Sohn.

At least 19 recordsLinked to original sources
PubMed2005

Corticospinal disinhibition in paroxysmal kinesigenic dyskinesia.

OBJECTIVE: To investigate the underlying mechanism responsible for paroxysmal kinesigenic dyskinesia (PKD). METHODS: We performed a transcranial magnetic stimulation (TMS) study in 12 drug-naïve patients with PKD and 10 healthy volunteers. TMS parameters included resting motor threshold, recruitment curve of motor evoked potential amplitudes, short intracortical inhibition and facilitation, long intracortical inhibition (LICI), and silent period. We also measured compound muscle action potential. RESULTS: LICI, representing GABA-mediated inhibition, was significantly reduced in the patients (P = 0.033), while results for all other TMS parameters tested were comparable between the two groups. CONCLUSIONS AND SIGNIFICANCE: These results suggest that a specific type of corticospinal inhibitory mechanism is impaired in patients with PKD.

Action Potentials↗
PubMed2004

Cortical control of voluntary blinking: a transcranial magnetic stimulation study.

OBJECTIVE: To investigate cortical regions related to voluntary blinking. METHODS: Transcranial magnetic stimulation (TMS) was applied to the facial motor cortex (M1) and the midline frontal region (Fz) in 10 healthy subjects with eyes opened and closed. Motor-evoked potentials were recorded from the orbicularis oculi (OOC), orbicularis oris (OOR), abductor digiti minimi and tibialis anterior using surface and needle electromyography electrodes. Facial M waves and blink reflex were measured using supramaximal electrical stimulation of the facial and supraorbital nerves. RESULTS: TMS at Fz elicited 3 waves in OOC with no response in other tested muscles except for the early wave in OOR. Facial M1 stimulation produced only early and late waves. Because of their latencies, shapes, and relationship to coil position and stimulation intensity, early and late waves appeared to be analogous to the facial M wave and R1 component of the blink reflex. The intermediate wave at 6-8 ms latency was elicited in OOC by Fz stimulation with eyes closed. CONCLUSIONS: Since its latency matches the central conduction time of other cranial muscles and it has characteristic of muscle activation-related facilitation, the intermediate wave is presumably related to cortical stimulation. This result provides evidence that the cortical center for the upper facial movements, including blinking, is not principally located in the facial M1, but rather in the mesial frontal region.

Adult↗
PubMed2004

Flumazenil does not affect intracortical motor excitability in humans: a transcranial magnetic stimulation study.

OBJECTIVE: The motor cortex may be subject to tonic inhibitory drive. One inhibitory mechanism is supported by activity at benzodiazepine (BZP) receptors. In this study we investigate whether or not the BZP antagonist, flumazenil, increases cortical motor excitability in humans. METHODS: Eight healthy subjects received a 1 mg intravenous (i.v.) loading dose of flumazenil followed by a 0.5 mg i.v. infusion over the next 30 min. Before, during, and 1 h after flumazenil infusion, we measured cortical motor excitability using transcranial magnetic stimulation (TMS). This included resting motor threshold (rMT), paired-pulse measurements of intracortical inhibition and facilitation (ICI and ICF), recruitment curve (RC), and silent period (SP). We also measured F response and compound muscle action potential (CMAP) with peripheral nerve stimulation. The study was carried out using a randomized, double-blind crossover design controlled with a saline infusion. RESULTS: None of the measures of cortical or peripheral excitability were significantly affected by drug administration. CONCLUSIONS: Our findings suggest that flumazenil has no effect on cortical motor excitability in normal humans. SIGNIFICANCE: There does not appear to be any tonic activity at benzodiazepine receptors in the normal resting human motor cortex.

Action Potentials↗
PubMed2003

The usefulness of endoscopic hemoclipping for bleeding Dieulafoy lesions.

BACKGROUND AND STUDY AIMS: Dieulafoy lesion is a rare cause of massive gastrointestinal hemorrhage, most commonly from the proximal stomach. Surgery was regarded as the treatment of choice in the past, but recently endoscopic management has become the standard approach. However, the effectiveness of various endoscopic modalities in treating bleeding Dieulafoy lesion has been little studied. This study was therefore done to compare the hemostatic efficacy of endoscopic hemoclipping and epinephrine injection therapy. PATIENTS AND METHODS: Between January 1998 and December 2001, a consecutive series of 32 patients with bleeding Dieulafoy lesion underwent endoscopic treatment. They were randomly treated either by endoscopic epinephrine injection therapy (n = 16) or by hemoclipping (n = 16). We compared mortality rate, primary hemostasis rate, and rebleeding rate between two groups. RESULTS: There was no bleeding-related death in either group. There was no significant difference in primary hemostasis rates between the hemoclipping group (93.8 %) and epinephrine injection group (87.5 %, P = 1.00). There was a trend toward a lower rate of need for multiple endoscopic sessions to achieve permanent hemostasis in the hemoclipping group compared with the epinephrine injection group (6.3 % vs. 31.3 %, P = 0.086). Hemoclipping was significantly more effective in preventing recurrent bleeding than epinephrine injection therapy (0 % vs. 35.7 %, P < 0.05). With regard to lesion site, hemoclipping was significantly more effective in preventing recurrent bleeding of gastric body Dieulafoy lesion than epinephrine injection therapy (0 % vs. 50 %, P < 0.05). CONCLUSIONS: Bleeding from Dieulafoy lesion was well controlled by therapeutic endoscopic procedures. Hemoclipping was more effective for Dieulafoy lesion than epinephrine injection therapy, with less need for subsequent endoscopy.

Adult↗
PubMed2003

The effect of transcranial magnetic stimulation on movement selection.

OBJECTIVE: To attempt to replicate previous findings that showed an influence of transcranial magnetic stimulation of the cortical motor areas on the selection of motor programmes on the contralateral side. METHODS: Healthy volunteers were asked to choose to make a right or left index finger extension movement freely after hearing the click produced by transcranial magnetic stimulation. The stimulation was applied to the motor areas (test), including the motor cortex, vertex, and prefrontal cortex, and in the air (control). RESULTS: There was no preference for choosing the hand contralateral to the stimulation site, in either test or control trials. CONCLUSIONS: Previous results could not be reproduced. Simple magnetic stimulation of the motor areas is insufficient to affect voluntary selection of movement.

Adult↗
PubMed2001

Effect of levetiracetam on human corticospinal excitability.

OBJECTIVE: To investigate whether levetiracetam (LTC) alters corticospinal excitability in humans. BACKGROUND: Although the antiepileptic activity of LTC is well recognized, its mechanism of action has yet to be determined. Transcranial magnetic stimulation (TMS) has been used to investigate the pharmacologic effects of various antiepileptic drugs on human corticospinal excitability. METHODS: The authors performed TMS before and after double-blind administration of 3000 mg LTC or placebo in six healthy volunteers. TMS measurements included resting and active motor threshold (MT), recruitment curve of motor-evoked potential amplitudes, intracortical inhibition, and facilitation using the paired-pulse technique and silent period. F-wave and compound muscle action potential (CMAP) were also measured. RESULTS: In recruitment curve measurements, motor-evoked potential amplitude was reduced for LTC with high stimulation intensity (130% and 140% of resting MT) compared with placebo (p < 0.05 and p < 0.01), but not with relatively low stimulation intensity (110% and 120%). The changes in other TMS measurements as well as F-wave and CMAP after LTC did not differ significantly from those observed after placebo administration. CONCLUSION: These results suggest that LTC reduces the corticospinal neuronal response to magnetic stimulation, preferentially affecting less excitable neurons. The lack of change in F-wave and CMAP suggests that this effect is mainly derived from the motor cortex.

Adult↗
PubMed2000

Basilar artery vasospasm in postpartum cerebral angiopathy.

The reason cerebral edema in postpartum cerebral angiopathy (PPCA) occurs preferentially in the posterior brain is poorly understood. The authors present two patients with PPCA who showed vasospasm occurring earlier and more severely in the basilar artery than in the middle cerebral artery. Our patients demonstrate the difference in vascular change between the anterior and posterior cerebral vessels, explaining the susceptibility of the posterior brain to PPCA.

Adult↗
PubMed2000

The effect of long-term levodopa therapy on depression level in de novo patients with Parkinson's disease.

20) became non-depressed, while five patients (22%) among 23 initially non-depressed became depressed. With long-term levodopa therapy, the UPDRS-motor score significantly improved (35+/-15. 7-18+/-7.6), but the BDI score was unchanged (18+/-9.3-19+/-9.2). The initial BDI score was significantly and inversely correlated to the parkinsonian motor symptoms, but their percentage changes were not correlated to each other. These results provide strong support to previous observations that levodopa therapy does not alter parkinsonian depression as well as providing additional evidence to support the role of non-dopaminergic mechanisms in parkinsonian depression.

Depressive Disorder↗
PubMed2000

The brain lesion responsible for parkinsonism after carbon monoxide poisoning.

BACKGROUND: Parkinsonism is a common neurological sequela of carbon monoxide (CO) poisoning, but its pathophysiological mechanism has yet to be clarified. OBJECTIVES: To describe a married couple who were both affected by CO poisoning, but only 1 of whom developed CO-induced parkinsonism, and to discuss the possible underlying pathophysiological mechanism of CO-induced parkinsonism by comparing the neuroimaging findings of these patients. DESIGN AND SETTING: Case report from a clinical neurology department. PATIENTS: A married couple experienced CO poisoning simultaneously. One month later, only the husband gradually developed delayed sequelae, including parkinsonism and intellectual impairment. On detailed neurological examination, the husband showed mild but definite rigidity and bradykinesia, while no parkinsonian signs were observed in the wife. Neuropsychological examination revealed impaired memory and attention in both patients, but they were more severe in the husband than in the wife. Magnetic resonance imaging scans of the patients' brains disclosed diffuse high-intensity white matter signals in both patients and bilateral pallidal necrosis in the wife. Dopamine transporter imaging showed that the degree of dopamine neuronal loss was comparable between these patients. Magnetic resonance spectroscopy revealed more severe white matter damage in the husband than in the wife. Thirteen months later, neurological and neuropsychological examinations showed complete recovery from parkinsonism as well as intellectual impairment. Follow-up magnetic resonance spectroscopy also suggested remarkable improvements in white matter damage. CONCLUSION: These results support the role of white matter damage in producing parkinsonism after CO poisoning and highlight the possible usefulness of magnetic resonance spectroscopy in predicting delayed sequelae in patients after CO poisoning. Arch Neurol. 2000;57:1214-1218

Aspartic Acid↗
PubMed2000

Pure homonymous hemianopia due to anterior choroidal artery territory infarction.

The most consistently observed neurological deficits in the anterior choroidal artery (AChA) territory infarction are pure motor or sensorimotor syndromes. Visual field defects and higher cortical dysfunction are occasionally accompanied, but pure homonymous hemianopia without motor and sensory symptom has never been reported yet. We present 2 patients with pure homonymous hemianopia, whose MRI disclosed cerebral infarction in the well-known territory of the AChA. In most patients with ischemic stroke, pure homonymous hemianopia indicates infarction in the posterior circulation, particularly in the posterior cerebral artery territory. However, the present cases provide evidence that it can also be caused by infarction in the anterior circulation, i.e. the AChA.

Acute Disease↗
PubMed2000

Arterial pulsatility as an index of cerebral microangiopathy in diabetes.

BACKGROUND AND PURPOSE: This study was designed to evaluate cerebral hemodynamic changes related to diabetes mellitus (DM) with transcranial Doppler ultrasonography (TCD). METHODS: We measured the flow velocities and the Gosling pulsatility index (PI) of the middle cerebral artery (MCA), extracranial internal carotid artery (ICA), and basilar artery (BA) in 56 stroke-free, normotensive patients with type 2 DM and 70 age- and gender-matched healthy volunteers. Patients were divided into 2 groups according to the presence of microvascular complications such as retinopathy, nephropathy, and neuropathy. RESULTS: Patients showed slightly lower hematocrit and higher serum fibrinogen levels than control subjects, but other clinical profiles, including stroke risk factors except for diabetes, were comparable between patients and controls. The flow velocity of the ICA but not the MCA and BA in patients regardless of the complication was significantly higher than that in controls. The PIs of the MCA and ICA were significantly higher in patients with complication than those without complication, as well as in controls. The PI of the BA was also significantly higher, even in patients without complication, than in controls. The PIs of the MCA and ICA but not the BA were closely correlated with the duration of DM (r(2)=0.46 and 0.34, respectively). CONCLUSIONS: This study defines TCD findings of diabetes-related cerebral hemodynamic changes and suggests that the PI reflects microangiopathic changes of cerebral vessels.

Aged↗
PubMed1998

Dopaminergic influences on the P300 abnormality in Parkinson's disease.

This study was designed to evaluate the contribution of central dopaminergic mechanisms to the P300 event-related potential (P300) abnormality in Parkinson's disease. We measured the P300 in 37 non-demented patients with Parkinson's disease (19 de novo and 18 levodopa-treated) and 15 age-matched healthy volunteers. The P300 measurement was repeated in 14 de novo patients, after 6-12 months levodopa therapy. The severity of parkinsonian symptom was assessed using the UPDRS-motor scale. De novo patients showed prolonged P300 latency compared with levodopa-treated patients, as well as healthy volunteers. The levodopa therapy for 6-12 months significantly shortened the P300 latency and reduced the UPDRS-motor examination score in de novo patients. However, the percent changes in the P300 latency were not correlated with those in the UPDRS-motor examination score. These results indicate that the central dopaminergic mechanisms apart from those responsible for motor symptoms, may contribute to the P300 abnormality in Parkinson's disease.

Acoustic Stimulation↗
PubMed1998

The influence of white matter hyperintensities on the clinical features of Parkinson's disease.

This study was designed to investigate the influence of white matter hyperintensities (WMH) on clinical features of Parkinson's disease (PD) patients. The study subjects were 44 patients with PD who took a brain MRI. The severity of Parkinsonian symptoms was assessed in both 'on' and 'off' states, using the UPDRS-motor score. Thirteen patients (30%) showed WMH. The patients with WMH were significantly older than those without WMH (67 +/- 5.7 vs 60 +/- 6.4 years). In both 'off' and 'on' states, the gait scores were significantly higher in patients with WMH than in those without WMH (1.6 +/- 0.18 vs 1.1 +/- 0.12, P < 0.05), but other motor symptom (tremor, bradykinesia, rigidity) scores between the two patient groups were not statistically different. After taking a single dose of oral levodopa/benserazide (200mg/50mg), the patients with WMH showed significantly less improvement in bradykinesia score than those without WMH (25 +/- 4.1% vs 40 +/- 4.0%, P < 0.05), but the improvements in other symptoms were comparable between the two groups. These results suggest that WMH on MRI may influence Parkinsonian motor symptoms, particularly gait symptom and levodopa-responsiveness to bradykinesia symptom.

Aged↗
PubMed1998

Cerebral hemodynamic changes induced by sympathetic stimulation tests.

Sympathetic neuronal activity is primarily responsible for the neurogenic control of cerebral autoregulation. The stimulation of sympathetic nerves causes both large arterial constriction and small vessel dilation in experimental animals. However, the role of the sympathetic nervous system in the control of cerebral hemodynamics has yet to be clarified in humans. In order to assess the effect of sympathetic activation on human cerebral hemodynamics, we performed a simultaneous transcranial Doppler (TCD) monitoring of bilateral middle cerebral arterial flow velocity in 16 healthy male volunteers (mean age 26) during well-known sympathetic activation measures such as isometric hand-grip exercise (IHE) and cold pressor test (CPT). Blood pressure was checked manually before and at each minute during tests. The mean arterial pressure (MAP) was calculated as (systolic pressure + 2 X diastolic pressure)/3. There was a significant increase in MCA flow velocities during both sympathetic activation tests. The percent increase of diastolic velocity (36% with IHE and 24% with CPT) was significantly higher than systolic velocity (21% with IHE and 9% with CPT). The pulsatility index was significantly decreased during the tests (from 0.75 to 0.58 with IHE and from 0.81 to 0.63 with CPT). These results suggest that sympathetic activation increases MCA flow velocities, related with a reduction in small vessel resistance and/or a constriction of large arteries.

Adult↗
PubMed1998

Sympathetic skin response and cardiovascular autonomic function tests in Parkinson's disease.

Autonomic dysfunction commonly occurs in Parkinson's disease, but the pathogenesis of autonomic dysregulation remains uncertain. Autonomic functions regulating the cardiovascular system have been investigated in Parkinson's disease, but those involving the extremities has not been well demonstrated. To compare autonomic dysfunctions of the cardiovascular system with those of the extremities, we performed sympathetic skin response (SSR) and cardiovascular autonomic function tests (CAFT)-30 : 15 ratio, E : I ratio, Valsalva ratio, isometric exercise test (IET)--in 37 patients with Parkinson's disease and 33 age- and sex-matched healthy controls. The patients were asked to stop antiparkinsonian medications for at least 12 hours prior to the tests. SSR was measured at the right hand and foot after electrical stimulation of the right median and posterior tibial nerves. Absent SSR at either one or both extremities and CAFT beyond normal ranges were regarded as abnormal. Abnormal SSR was observed in 59% of patients, while abnormal CAFT were found in the range of 32%-81%. Patients with abnormal SSR showed more frequent and severe CAFT abnormalities than did patients with normal SSR. Among the CAFT, IET was well correlated with the SSR. The results suggest that parkinsonian sympathetic dysfunction involving either the cardiovascular system or the extremities may have the same pathophysiology.

Adult↗
PubMed1997

Blood flow velocity changes in the middle cerebral artery as an index of the chronicity of hypertension.

This study was designed to demonstrate cerebral hemodynamic changes related to hypertension using transcranial Doppler ultrasonography. We measured the flow velocities and the Gosling pulsatility index of the middle cerebral artery and the internal carotid artery in 94 stroke-free, hypertensive patients and 81 age- and gender-matched healthy controls. Compared with the control subjects, patients with a longer duration (> or = 5 years) of hypertension showed significantly lower flow velocities of the middle cerebral artery and a higher Gosling pulsatility index of the middle cerebral- and the internal carotid artery. These differences were not observed in patients with a shorter duration of hypertension (<5 years). In the patient group, the mean velocity of the middle cerebral artery was significantly and inversely correlated with the duration of hypertension. Decreased flow velocity with increased pulsatility observed in this study suggest that alterations in the small cerebral vessels and arterioles contribute primarily to cerebral hemodynamic changes occurring in long-standing hypertension and also suggest the possible usefulness of transcranial Doppler in monitoring the progression of cerebral atherogenesis related to hypertension.

Adult↗
PubMed1997

Locked-in syndrome with bilateral peduncular infarct.

Locked-in syndrome due to midbrain infarct is very rare. This report describes a patient with locked-in syndrome whose magnetic resonance images showed bilateral infarcts in the cerebral peduncle. Cerebral angiography disclosed bilateral irregular thrombotic narrowing of the vertebral and proximal basilar arteries with rostral basilar artery occlusion, a previously unreported findings.

Cerebral Angiography↗