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Biomedical subjects

H Shibasaki

Publications and source records attributed to H Shibasaki.

At least 217 records · Page 12Linked to original sources
PubMed1995

Myoclonus.

Genetic studies have suggested homogeneity between the Baltic-type and Mediterranean-type progressive myoclonic epilepsy. Magnetoencephalography was applied to elucidate the mechanism underlying the giant evoked responses in cortical reflex myoclonus. A new concept of negative myoclonus mediated by cortical reflex mechanism was proposed. Cortical myoclonus was demonstrated in various neurodegenerative or metabolic disorders, such as presenile or senile dementia, olivopontocerebellar atrophy, and myoclonus epilepsy associated with ragged-red fibres. Myoclonus in corticobasal degeneration is especially noteworthy because it has clinical and electrophysiological features of cortical reflex myoclonus, but its latency is shorter compared with the conventional cortical reflex myoclonus. Clinical features of 'palatal myoclonus' were reported by the name of 'palatal tremor'.

Adolescent↗
PubMed1995

Presence of Bereitschaftspotential preceding psychogenic myoclonus: clinical application of jerk-locked back averaging.

The method of jerk-locked back averaging was applied to six patients with clinically diagnosed psychogenic myoclonus. Five patients had a slow negative EEG shift corresponding to Bereitschaftspotential at the central region starting 0.7 to 2.1 seconds before the onset of the myoclonic jerk. One patient had no potential preceding the myoclonic jerk, whereas a small negative potential preceded the voluntary movement mimicking the jerk. The demonstration of Bereitschaftspotential before an apparently involuntary myoclonic jerk helps the clinical diagnosis of psychogenic myoclonus, although the absence of Bereitschaftspotential does not necessarily indicate that the movement is involuntary. Jerk-locked back averaging is clinically useful as a specific laboratory examination in this condition.

Adult↗
PubMed1995

[Cerebral blood flow and metabolism in Lafora disease].

An 18-year-old male manifesting intellectual deterioration and negative myoclonus was diagnosed as Lafora disease by the demonstration of Lafora bodies in the skin and muscle biopsy. The cortical evoked potential to electric stimulation of the median nerve at wrist showed the giant SEP, suggesting hyperexcitability of the sensory motor cortex. Cerebral blood flow, and cerebral glucose and oxygen metabolism were investigated by positron emission tomography (PET) in order to clarify the pathophysiological process in Lafora disease. The result showed diffusely decreased cortical glucose metabolic rate and cerebral blood flow, and moderately lowered oxygen metabolic rate. There was no increase in blood flow or glucose and oxygen metabolism in the sensorimotor cortex in spite of the presence of giant SEP. The ratio of the glucose to oxygen metabolism was not different from the mean value obtained from nine normal subjects. Based on these findings and review of the literature, it is unlikely that there is a significant deficit in cortical energy metabolism in patients with Lafora disease and it would be less plausible to have some enzymatic deficits in glucose metabolic process.

Adolescent↗
PubMed1995

SPECT imaging of dopamine D2 receptors with 2'-iodospiperone.

UNLABELLED: SPECT imaging of dopamine D2 receptors was performed using 123I-labeled 2'-iodospiperone (2'-ISP). METHODS: Iodine-123-2'-ISP was administered to 12 normal subjects. Serial SPECT scans were obtained in six normal subjects for kinetic studies and static SPECT images were obtained in four normal subjects. Two additional normal subjects had serial whole-body imaging to calculate radiation dosimetry. RESULTS: Serial SPECT scans demonstrated rapid initial brain uptake followed by gradual washout from the cerebral cortex and cerebellum, while the activity in the basal ganglia was stable for 2 hr and gradually decreased thereafter. There was fast clearance of blood activity with rapid conversion of 2'-ISP to the hydrophilic metabolites. The basal ganglia-to-frontal cortex ratio increased with time and plateaued between 2 and 4 hr postinjection. The basal ganglia-to-frontal cortex ratio obtained during this period demonstrated an age-dependent decrease similar to other D2 ligands. CONCLUSION: 2'-ISP can be used for mapping dopamine D2 receptors in human brain with SPECT. The relatively high background activity, however, suggests that further modification of the compound may be needed prior to widespread clinical use.

Adult↗
PubMed1995

Simple quantification of benzodiazepine receptor binding and ligand transport using iodine-123-iomazenil and two SPECT scans.

UNLABELLED: The feasibility of simplified procedures for the quantification of benzodiazepine receptor binding using [123I]iomazenil and SPECT was assessed. METHODS: Six normal male volunteers were studied. Following intravenous injection of 111 MBq [123I]iomazenil, serial dynamic SPECT scanning was performed for 120 min and the concentration of lipophilic compounds in the arterial plasma was determined by chloroform extraction. Kinetic parameters were estimated by a curve-fitting procedure using the following four models: three-compartment, four-parameter (K1-k4) (3C4P), three-compartment, three-parameter (fixed K1/k2) (3C3P), three-compartment, two-parameter (fixed K1/k2 and k4) (3C2P) and two-compartment, two-parameter (K1 and k2) (2C2P). Kinetic parameters were also calculated by a table look-up procedure with 3C2P using only two SPECT data acquisitions. Parametric images were generated based on the same procedure. RESULTS: In all models, the curve-fitting procedure gave similar outcomes for ligand transport (K1) and receptor density parameters (i.e., binding potential or distribution volume). The 3C4P parameters showed significant correlation between k2 and k3, while 3C3P did not show such a correlation, suggesting the stability of 3C3P. The 3C2P provided parameters essentially identical to those with the 3C3P, indicating the suitability of this model, while 2C2P gave similar distribution volume but obviously low K1. CONCLUSION: Table look-up procedures based on the 3C2P model permit quantification of benzodiazepine receptor binding using [123I]iomazenil with two SPECT scans. This method may be of clinical value in the diagnosis of various diseases.

Adult↗
PubMed1995

Ultra-high resolution SPECT system using four pinhole collimators for small animal studies.

UNLABELLED: We describe a newly developed ultra-high resolution SPECT system using four pinhole collimators for small animal studies. METHODS: The system utilizes a clinical four-head SPECT scanner with specially designed pinhole collimators. Four types of pinholes with different configurations were designed with different effective aperture sizes (1.0, 2.0 and 4.0 mm) and rotating radii (40 mm and 50 mm). The distance from the axis of rotation to the scintillator was fixed to 180 mm. A filtered backprojection algorithm was used to reconstruct SPECT images after fanbeam-to-parallel-beam data conversion. RESULTS: The system provided a reconstructed spatial resolution of 1.65 mm (FWHM) and sensitivity of 4.3 kcps/microCi/ml with the best type of pinholes, respectively. The 99mTc-HMPAO SPECT image in rat studies clearly visualized small brain structures, and the left ventricular myocardium and cardiac cavity were clearly separated with 99mTc-MIBI. Dynamic SPECT imaging of rat brain with [123I]iomazenil was also feasible. CONCLUSION: This ultra-high resolution SPECT system can be used to measure the regional distribution of radiolabeled tracers in small animals in vivo and may play a significant role in the development of new radiopharmaceuticals and in studies of various disease models using living animals.

Animals↗
PubMed1995

[Pathophysiology of involuntary movements--dystonia and myoclonus from viewpoint of brain activities].

Cortical myoclonus (CM) and focal dystonia (FD) are commonly characterized by co-contraction of agonist and antagonist muscles, enhancement by intentional movement, strong influence by sensory input, and spread to adjacent muscles. On the other hand, they are different in the nature of movements, speed of muscle contraction, speed of spread, and drug effects. There are abundant data indicating that CM is due to pathological hyperexcitability of the sensorimotor cortex (S1-M1), while, in FD, no definitive evidence to suggest cortical hyperexcitability has been found. Changes in regional cerebral blood flow (rCBF) studied by positron emission tomography (PET) during movements in patients with dystonia were inconsistent with regard to S1-M1, but the frontal cortex including the rostral SMA was shown to be overactivated, suggesting the thalamocortical disinhibition based on the basal ganglia disorders.

Brain↗
PubMed1995

[Noninvasive study of cortical neuronal mechanism in voluntary movements: role of basal ganglia and cerebellum].

Voluntary movements can be classified into the two categories depending on how those are initiated; ones initiated internally, and others triggered or paced by external stimuli. Central neuronal mechanisms involved in those preparation and execution could be represented by movement-related cortical potentials (MRCP) or Bereitschaftspotential (BP), and contingent negative variation (CNV), respectively. The both potentials, as the field potentials, can be recorded with long time constant, and represent transient changes of the membrane potentials of the cortical neurons. In patients with the lesion at the cerebellar efferent system, the BP disappeared completely whereas the late CNV was normally seen. In patients with parkinsonism, in contrast, the late CNV was significantly smaller in amplitude in severe than in mild symptom group. Recent subdural recording in epilepsy patients demonstrated that the BP and late CNV were commonly generated from the primary and supplementary motor areas, and that late CNV also arose from the frontal association cortices (mesial, basal and lateral prefrontal areas). It is therefore suggested that subcortical generating mechanism is different for the late CNV and BP although both commonly share at least some cortical generators, and that the basal ganglia are most likely responsible for the generation of the late CNV and the cerebellar efferent system for the generation of the BP.

Basal Ganglia↗
PubMed1995

Pharmacokinetic studies of cortisol after oral administration of deuterium-labelled cortisol to a normal human subject.

A trace amount (5 mg) of stable isotopically labelled cortisol ([1,1,19,19,19-2H5]cortisol, cortisol-d5) was administered orally to a healthy human subject to examine the pharmacokinetic behaviour of exogenous cortisol and study the interconversion of cortisol to cortisone catalysed by 11 beta-hydroxysteroid dehydrogenase (11 beta-OHSD). The use of a gas chromatographic/mass spectrometric method allowed the simultaneous measurement of the plasma concentrations of endogenous and exogenous cortisol and cortisone. The amount administered was sufficiently small not to disturb or decrease the endogenous cortisol secretion by negative feedback. The appearance of cortisol-d5 and cortisone-d5 was very rapid. In a blood sample taken 10 min after administration of cortisol-d5, plasma concentrations of 154.8 ng ml-1 cortisol-d5 and 2.7 ng ml-1 cortisone-d5 were detected. A peak value of 196.6 ng ml-1 cortisol-d5 was observed 30 min after cortisol-d5 administration. The peak value of cortisone-d5 was 15.5 ng ml-1 40 min after cortisol-d5 administration, and thereafter cortisone-d5 declined in parallel with the slower decline phase of cortisol-d5. The plasma concentrations fell as low as 26.9 ng ml-1 for cortisol-d5 and 4.6 ng ml-1 for cortisone-d5 4 h after cortisol-d5 administration. The ratio of cortisone-d5 to cortisol-d5 approached a plateau 2 h after cortisol-d5 administration, reaching a constant value of approximately 0.15 thereafter. The higher value of the cortisone/cortisol concentration ratio (0.14-0.81; average 0.30) than the cortisone-d5/cortisol-d5 ratio may provide important information about the possibility that cortisone might be formed not only via the pathway of the cortisol conversion but also through other biotransformation processes.

Adrenal Cortex Hormones↗
PubMed1994

Spinal myoclonus resembling belly dance.

A 63-year-old man presented with an 11-month history of progressive myoclonus in the right abdominal wall. Administration of clonazepam reduced the frequency and amplitude. When the therapy was discontinued, the frequency and amplitude of the myoclonus increased, and synchronous and weak myoclonus also was observed in the left abdomen. The trunk was twisted just after the appearance of the abdominal myoclonus associated with myoclonic jerks spreading from the rostral to caudal paraspinal muscles. Later in the clinical course, the myoclonus became stimulus sensitive and was induced by tendon tap given anywhere on the body, with the latency ranging from 50 to 150 ms irrespective of the sites of tapping. Myoclonus seen in the abdominal wall was segmental and considered to be of spinal origin. The reflex myoclonus had a 150-ms refractory period. It can be postulated that increased excitability of anterior horn cells at a certain segment might make a spino-bulbo-spinal reflex manifest at the corresponding segment. This myoclonus is considered to be a new form of spinal reflex myoclonus, because the abdominal myoclonic jerk seems to trigger another myoclonic jerk involving the paraspinal muscles.

Abdominal Muscles↗
PubMed1994

Cortical magnetic and electric fields associated with voluntary finger movements.

Multichannel recordings of both movement-related magnetic fields (MRMFs) and movement-related cortical potentials (MRCPs) were simultaneously recorded in association with voluntary unilateral self-paced index finger abduction movement in two normal volunteers. 1) Slow magnetic field (readiness field; RF) can be detected several hundred msec before the movement onset, and its field distribution indicates the existence of the largest generator source over the contralateral primary motor area. Taken together with the vertex-maximal Bereitschaftspotential which corresponds to the earlier part of the RF, the complexity of this magnetic field suggested by relatively low correlation value in single dipole model indicates the co-activation of other underlying generators besides this largest dipole. 2) The utilization of MRMF with MRCP facilitates the separation of two distinct electrophysiological events in proximity to the movement onset, which are difficult to be determined by the technique of MRCP only. Those are the motor field (MF) and the movement evoked field I (MEFI) in MRMF, and the parietal peak motor potential (ppMP) and the frontal peak motor potential (fpMP) in MRCP, which occur approximately 20 and 100 msec after EMG onset, respectively. These two subcomponents may imply the culmination of motor cortex and sensory feedback activation, respectively. Combined study of MRMF and MRCP will provide better definition of cortical events related to voluntary movement than the study of either modality alone.

Adult↗
PubMed1994

Dissociation between contingent negative variation and Bereitschaftspotential in a patient with cerebellar efferent lesion.

Contingent negative variation (CNV) and Bereitschaftspotential (BP) were from the scalp in a patient with a discrete infarct in the mesial tegmentum of the midbrain involving the decussation of the superior cerebellar peduncle. Bereitschaftspotential in association with hand movements was completely absent while CNV was normally present at the frontocentral midline. This indicates that CNV is, as opposed to BP, generated without cerebro-cerebellar interactivation, suggesting different generating mechanisms.

Cerebellar Diseases↗
PubMed1994

Automatic detection method of P300 waveform in the single sweep records by using a neural network.

Event-related potentials (ERPs) are responses related to the recognition of certain stimuli. P300 is the most important positive component in the ERP and appears around 300 ms after the target stimulus in the oddball paradigm. In our previous work, we proposed a method for the automatic detection of the P300 waveform in single-sweep records by using a correlation technique. However, determination of the threshold values of the P300 waveform for the correlation study was not an easy task. In skirting this problem, we developed an automatic method of detecting a single-sweep P300 waveform by using an artificial neural network. We selected appropriate characteristic parameters of positive peaks as input signals for the input layer units, and the weights between the layers were determined by using the back-propagation algorithm. The neural network for P300 detection was obtained automatically, based on the data of ERPs obtained from 11 healthy males, and gave substantial accuracy for P300 detection. Furthermore, by using this neural network we clarified the way in which the P300 waveform is judged visually by each inspector.

Acoustic Stimulation↗
PubMed1994

Cortical reflex negative myoclonus.

Three patients with progressive myoclonic epilepsy (PME), two of them clinically manifesting only negative myoclonus and the other manifesting both positive and negative myoclonus, were electrophysiologically investigated, and compared with two other patients with PME presenting with only positive myoclonus. Electric stimulation of the median nerve during sustained active wrist extension in the three patients with negative myoclonus often elicited a short lapse of the posture in the stimulated hand associated with a silent period in the muscle discharge with or without being preceded by an abrupt increase in the muscle discharge (C reflex). The occurrence of the stimulus-induced silent period was significantly correlated with that of the giant somatosensory evoked potentials (SEPs), and in two patients the silent period was elicited also in the opposite (non-stimulated) hand when the giant SEP was recorded at the hemisphere ipsilateral to the stimulus as well. In one patient, the duration of the silent period was positively correlated with the amplitude of the cortical SEP. Furthermore, the duration of the induced silent period was closely related to the recovery function of SEP in each individual case. In contrast, in the two patients manifesting only positive myoclonus, the silent period was not elicited by the peripheral stimulation, and the somatosensory cortex was hyperexcitable immediately after the peripheral stimulus. Thus, this stimulus-sensitive negative myoclonus is mediated by a transcortical reflex mechanism, and corresponds to the negative form of the cortical reflex myoclonus ('cortical reflex negative myoclonus').

Adult↗
PubMed1994

Generator mechanism of pain-related evoked potentials following CO2 laser stimulation of the hand: scalp topography and effect of predictive warning signal.

In order to clarify the generator mechanism of pain-related evoked potentials (pain EPs), we studied the scalp topography of the pain EPs following CO2 laser stimulation of hand dorsum by using balanced sternovertebral electrodes as the noncephalic reference in 11 normal volunteers. We also examined the effects of predictive warning signal (light-emitting diode) on the pain EPs. In both the warned and unwarned conditions, all of the 22 hand stimulations showed a large negative component (N2) at the peak latency of about 213 ms followed by a large positive component (P2) at the peak latency of about 329 ms. A preceding small negative component (N1) at the peak latency of about 148 ms was detected in 12 of the 22 hand stimulations in the warned condition and in 13 of the 22 hand stimulations in the unwarned condition. P2 was significantly larger and occurred earlier in the warned condition than in the unwarned condition, whereas other components did not differ between the two conditions, suggesting that an increased attention of the subject to the stimulus influenced the generator mechanism of the P2 component. With regards to the scalp topography, N2 was maximal at Cz and widespread transversely to both sides, whereas P2 was maximal at Cz or Pz and spread more posteriorly than N2. These findings suggest that P2 is generated by a different mechanism from N2 and is most likely associated with pain-related cognitive function. N1 was localized to the contralateral central and midtemporal areas, confirming that the nociceptive inputs are perceived in the sensory cortex in humans. The question as to whether the N1 component is generated in the hand area of the primary somatosensory cortex or in the secondary somatosensory cortex, or in both areas, remains to be solved.

Adult↗
PubMed1994

Automatic detection of P300 in single sweep records of auditory event-related potential.

In the conventional recording of event-related potentials (ERPs) by the "oddball" paradigm, the subject may employ different strategies for processing one stimulus from the other even within the same session because of variable psychological state. Hence, "averaging" may not necessarily be suitable for recording ERP. We have therefore established a method for single trial recording of auditory ERPs by processing the EEG data through discrete Fourier transform followed by inverse discrete Fourier transform with the low pass filter of 8 Hz (digital filter). Each single sweep response of the processed data was visually evaluated as to whether it contained P300 or not by three investigators who were made completely blind with respect to the category of each response. As the result, a positive peak at a latency of 200-500 ms was recognized in the single sweep responses to target stimuli at a significantly greater frequency (40-60%) than in those to nontarget stimuli (0-18%). Then a new method for the automatic detection of P300 was established based on the data of 11 subjects belonging to the training group, by taking into account, in addition to the correlation coefficient analysis in which the template was computed specifically for each subject, other criteria with respect to the amplitude and waveforms, so that a good agreement with the results of visual inspection as to the presence or absence of P300 could be achieved for both target and nontarget responses. This automatic analysis method was successfully applied to five other subjects of the test group. The peak latency and amplitude of the detected positive peaks significantly varied among single target responses even within the same session. The reaction time significantly correlated positively with the peak latency of the detected positive peaks and negatively with the amplitude of those peaks, supporting the usefulness of the present method.

Adult↗