Biomedical subjects

H Shibasaki

Publications and source records attributed to H Shibasaki.

At least 109 records · Page 6Linked to original sources

PubMed1999

Enhanced lateral premotor activity during paradoxical gait in Parkinson's disease.

Parkinson's disease (PD) patients often show marked improvement of hypokinetic gait when exposed to special stimuli. To investigate physiological mechanisms underlying this "paradoxical gait" induced by visual cues in PD patients, we examined regional cerebral blood flow changes during gait on a treadmill guided by two different visual cues, the lines oriented transversely to the direction of walk (TL) and the lines parallel to it (PL). Ten PD patients and 10 age-matched controls received injections of 99mTc-hexamethylpropyleneamine oxime twice, once during each walking condition. Brain perfusion images were obtained by single-photon emission computed tomography. When affected by TL, PD patients showed marked improvement of gait parameters, mainly reduction of cadence. In regional cerebral blood flow analysis, when TL was compared with PL, both groups had common activation in the posterior parietal cortex and cerebellar hemispheres. Especially in the right lateral premotor cortex, PD patients showed enhanced activation induced by TL to a significantly greater degree than the controls. The present study indicates that the network dedicated to visuomotor control, particularly the lateral premotor cortex, plays an important role in the development of the paradoxical gait induced by special visual stimuli in PD patients.

Aged↗

PubMed1999

Transient neural activity in the medial superior frontal gyrus and precuneus time locked with attention shift between object features.

To investigate the contribution of the superior frontal gyrus and precuneus to the cognitive process of attention set shift, we examined the correlation between change in neural activity in these areas and the timing of attention set shift using event-related functional magnetic resonance imaging. Seven subjects underwent a card-sorting task in which they matched a test card to one of two target cards according to color or shape. The subjects had to determine the correct category based only on feedback and shift the sorting principle when the feedback changed from "correct" to "incorrect." Transient increase of neural activity time locked with attention shift phases was detected in the medial superior frontal gyrus (the rostral part of the supplementary motor area) and precuneus. During the control task, in which the feedback and the motor responses were preserved without any attention shift, this type of change in neural activity was not observed. Our findings indicate that increase in neural activity in these brain areas may be closely related to attention set shift between object features and suggest that these areas may play a role in the shifting of cognitive sets.

Adult↗

PubMed1999

Temporal profile of visual evoked responses to pattern-reversal stimulation analyzed with a whole-head magnetometer.

Magnetoencephalography (MEG) has become accepted as a useful method for non-invasively studying brain functions, including visual perception. The present study used MEG to elucidate information processing following pattern-reversal stimulation by analyzing the origins and properties of visual evoked magnetic fields (VEFs). The VEFs of ten healthy adults were recorded in a magnetically shielded room using a 122-channel whole-head magnetometer. The visual stimulation of checkerboard-pattern reversal at 1.7 Hz was presented to the subject's right hemifield. Visual evoked potentials (VEPs) were recorded simultaneously, and 150 responses were each averaged for VEFs and VEPs. For the contrast profile study, pattern-reversal stimuli at five different contrast levels from 96% to 8% were used. In all subjects, the VEFs showed three components with latencies of approximately 95, 120, and 160 ms. The equivalent current dipoles for the first and the third components were located and were oriented close to each other in the left occipital lobe, but these dipoles were separated from that of the second component, which showed an opposite direction. Stimuli at a moderate contrast level markedly reduced the first component, but not the third. These findings indicate that the first and the third components of VEFs appear to originate from anatomically closely situated, almost identical, sources, but that their physiological properties differ.

Adult↗

PubMed1999

Cortical mechanisms underlying point localization of pain spot as studied by event-related potentials following CO2 laser stimulation in man.

To elucidate cortical mechanisms underlying point localization of a pain spot, we investigated event-related potentials (ERPs) while using a CO2 laser beam to apply a pain stimulus to the hand dorsum in 16 healthy men. The stimulus spot (pain spot) was shifted for each stimulus, while the subject was requested to identify the stimulated spot as accurately as possible and to use a pointer in the non-stimulated hand to indicate the corresponding spot on a figure of a hand that was projected onto a screen (localization condition). For the control condition, the subject pointed to a single predetermined spot, regardless of the location of the stimulation (control motor task condition). Electroencephalograms were recorded from 21 electrodes, referenced to the linked earlobes, and were averaged time-locked to the stimulus onset for each task separately. Under the control rest condition (neither point localization nor motor task), only two early components (N2 and P2) were recorded. During the control motor task condition (no point localization), in addition to N2 and P2, a steep negative-going slope was recorded at the fronto-central region. Exclusively during the localization condition, a positive peak (647 ms, 5.6 microV for the left and 634 ms, 5.7 microV for the right hand stimulation) was identified; this was maximal at the midline centro-parietal area and distributed symmetrically over the scalp. It is suggested that the late positive component detected exclusively during the localization task is related to the somatotopic point localization of the pain spot. From the distribution of this ERP, the task most likely involves bilateral activation of the superior parietal cortices.

Adult↗

PubMed1999

Synthesis of deuterium-labeled tetrahydrocortisol and tetrahydrocortisone for study of cortisol metabolism in humans.

A method is described for the preparation of multi-labeled tetrahydrocortisol (3alpha,11beta,17alpha,21-tetrahydroxy-5beta-[1, 2,3,4,5-2H5]pregnan-20-one, THF-d5), allo-tetrahydrocortisol (3alpha,11beta,17alpha,21-tetrahydroxy-5alpha-[1 ,2,3,4,5-2H5]pregnan-20-one, allo-THF-d5), and tetrahydrocortisone (3alpha,17alpha,21-trihydroxy-5beta-[1,2,3,4,5-2H5]pre gnane-11,20-dione, THE-d5) containing five non-exchangeable deuterium atoms in the steroid ring A. Reductive deuteration at C-1, C-2, C-3, C-4, and C-5 of prednisolone or prednisone was performed in CH3COOD with rhodium (5%) on alumina under the deuterium atmosphere. The isotopic purities of the labeled compounds as [2H5]-form were estimated to be 86.17 atom%D for THF-d5, 74.46 atom%D for allo-THF-d5 and 81.90 atom%D for THE-d5, based on the ion intensities in the region of the molecular ion of methoxime-trimethylsilyl (MO-TMS) derivatives measured by GC-MS.

Chromatography, Liquid↗

PubMed1999

Signal separation of background EEG and spike by using morphological filter.

A signal separation method for extracting background electroencephalogram (EEG) from EEG containing spikes was proposed. Morphological filters were designed for extracting spike waveforms, and then the background EEG was obtained by subtracting the detected spike waveforms from the EEG with spike. The proposed method was evaluated by using simulated EEG data, which consisted of a summation of EEG without spike and model waveform of typical spike. The background EEG separated by the method was processed by the automatic background EEG interpretation.

Adult↗

PubMed1999

Physiological variability of peak latency in evoked potentials: use of a property of asynchronous averaging.

A method for estimating the physiological variability of peak latency in an evoked potential, of whom the peak latency and amplitude varied, by using the property of asynchronous averaging was proposed. A point estimate of the physiological variability was obtained by minimizing the mean square error between a standard waveform and the asynchronously averaged waveform. An interval estimate was obtained by using the relationship between the signal-to-noise ratio and the standard deviation of the point estimate for the variability of peak latency. The proposed method was evaluated by using simulation data, and was successfully applied to actual P300 data of six normal subjects. The method gave accurate estimates for the physiological variability of peak latency of P300, and would also be effectively applicable to any other evoked potential records for estimating the physiological variability.

Adult↗

PubMed1999

Movement-related cortical potentials associated with voluntary relaxation of foot muscles.

OBJECTIVE: In our previous study of movement-related cortical potential (MRCP) in association with the voluntary relaxation of the hand muscle, Bereitschaftspotential (BP) was maximal at the vertex and symmetrically distributed, and Negative Slope (NS') was maximal over the contralateral central region. In order to clarify the generator sources of MRCP with voluntary muscle relaxation, we recorded MRCP in association with voluntary relaxation of the foot. METHODS: MRCP in association with plantar flexion of the foot caused by voluntary relaxation of the tibialis anterior muscle was recorded in 10 normal subjects. RESULTS: The BP started at about 1.7 s before the onset of the muscle relaxation, followed by NS' starting at about 650 ms before it. Both were maximal at the vertex and symmetrically distributed. There was no additional EEG activity in the lateral frontal areas, which are presumably located over the primary negative motor areas (PNMA). CONCLUSIONS: It is concluded that the voluntary muscle relaxation, similarly to the voluntary muscle contraction, involves the cortical preparatory activity at least in the primary motor area (M1) and probably the supplementary motor areas (SMAs). There is no evidence to suggest that the PNMA is also active prior to the voluntary muscle relaxation.

Adult↗

PubMed1999

Abnormal contingent negative variation in writer's cramp.

OBJECTIVE: To investigate the physiological abnormality in writer's cramp, a focal dystonia which specifically affects writing. METHODS: We recorded brain potentials that precede hand and neck movements (contingent negative variation or CNV) in 11 patients and 11 age-matched normal subjects. A 1000 Hz tone burst (S1) was delivered to the right or left ear in random sequence, and 2 s after, a 2000 Hz tone burst (S2) was delivered to both ears simultaneously. For the response task to S2, the subjects were instructed to extend their fingers ipsilateral to the ear to which S1 was given in one experiment or to rotate the head to the side of the S1 presentation in another. All the patients had symptoms in the right hand only, and performed both tasks normally. CNV amplitudes were compared between normals and patients using unpaired t test. RESULTS: They showed normal CNV for neck movement but significantly decreased CNV amplitudes for movements both in the affected and unaffected hands. CONCLUSIONS: Our findings suggest that motor programming is specifically abnormal for the affected body part, including the asymptomatic contralateral limb, and that the clinical symptom may result from a deficient compensatory mechanism for abnormal motor programs or subroutines.

Adult↗

PubMed1999

Brain structures related to active and passive finger movements in man.

A PET study was performed in six normal volunteers to elucidate the functional localization of the sensory afferent component during finger movement. Brain activation during the passive movement driven by a servo-motor was compared with that during an auditory-cued active movement which was controlled kinematically in the same way as the passive one. A newly developed device was used for selectively activating proprioception with a minimal contribution from tactile senses. Active movement was associated with activation of multiple areas, including the contralateral primary sensorimotor cortex, premotor cortex, supplementary motor area (SMA), bilateral secondary somatosensory areas and basal ganglia and ipsilateral cerebellum. In contrast, only the contralateral primary and secondary somatosensory areas were activated by the passive movement. It is likely that the contribution of proprioceptive input to the activation of the premotor cortex, SMA, cerebellum and basal ganglia, if any, is small. However, the present results do not rule out the possibility that the cutaneous afferent input or the combination of cutaneous and proprioceptive input participates in the activation of those areas during the active movement.

Acoustic Stimulation↗

PubMed1999

The role of the hippocampus in auditory processing studied by event-related electric potentials and magnetic fields in epilepsy patients before and after temporal lobectomy.

To clarify the relationship between the hippocampus and the event-related responses in auditory information processing, we recorded event-related potentials (ERPs) and event-related magnetic fields (ERFs) associated with the auditory oddball paradigm in 12 patients with temporal lobe epilepsy before and after surgical treatment, and in eight age-matched healthy volunteers. Lesions in the patients were hippocampal sclerosis (8), cyst (2), cavernoma (1) and calcified arteriovenous malformation (1), all in the unilateral temporal lobe. Standard temporal lobectomy (8), selective amygdalohippocampectomy (2), selective hippocampectomy (1) and inferior lateral temporal resection (1) were carried out. ERPs were recorded in nine patients before surgery, in all 12 patients after surgery, and in all normal subjects. P300 was maximal at Pz in the patients both before and after surgery, and in normal subjects. The peak latency and amplitude of P300 measured at Pz in the patients either before or after surgery did not differ significantly from those in normal subjects. After surgery, only the amplitude of P300 over the anterior and mid-temporal area on the resected side was attenuated, while it was symmetric before surgery regardless of the side of epileptogenic focus. ERFs were recorded in three patients before surgery and in six normal subjects by using a whole-head neuromagnetometer. ERFs in response to the target stimuli at a latency of approximately 400 ms were recognized at the anterior, middle and posterior lateral channels on each hemisphere (M400). The latency and dipole moments for M400 did not differ significantly between the patients before surgery and the normal subjects. As a result of analysis using the time-varying multidipole model, three dipoles for M400 were estimated in two patients in whom ERFs were available before surgery for the analysis, and in normal subjects: mesial temporal area, superior temporal area and inferior parietal area on each hemisphere. After surgery, in four out of six patients in whom ERFs were recordable, M400 at the anterior temporal channels on the resected side disappeared, and the activity in the affected mesial temporal area was lost. In one patient who underwent inferior lateral temporal resection, M400 waveforms and its sources were preserved in all regions. There were no significant differences in the latency and dipole moments of the unaffected source of M400 before versus after surgery. These results suggest that the hippocampus contributes to the scalp-recorded P300 only at the corresponding anterior temporal region, and does not influence its general waveform and predominant distribution over the scalp.

Adult↗

PubMed1999

Focal ictal direct current shifts in human epilepsy as studied by subdural and scalp recording.

In order to clarify further the characteristics of ictal direct current (DC) shifts in human epilepsy, we investigated them by subdural and scalp recording in six and three patients, respectively, both having mainly neocortical lobe epilepsy (five with frontal lobe epilepsy, two with parietal lobe epilepsy and two with temporal lobe epilepsy). By using subdural electrodes made of platinum, ictal DC shifts were observed in 85% of all the recorded seizures (89 seizures) among the six patients, and they were localized to just one or two electrodes at which the conventional initial ictal EEG change was also observed. They were closely accompanied by the electrodecremental pattern in all patients except for one in whom 1 Hz rhythmic activity was superimposed on clear negative slow shifts. Seizure control after resection of the cortex, including the area showing DC shifts, was favourable irrespective of histological diagnosis. Scalp-recorded ictal slow shifts were observed in 23% of all the recorded seizures (60 seizures) among the three patients. They were, like the subdurally recorded ones, mainly surface-negative in polarity, closely related to the electrodecremental pattern and consistent in their location. It seems that scalp-recorded DC shifts were detected particularly when seizures were clinically intense, while no slow shifts were observed in small seizures. It is concluded that at least subdurally recorded ictal slow shifts are clinically useful before epilepsy surgery to delineate more specifically an epileptogenic area as well as to further confirm the conventional initial ictal EEG change, and that scalp-recorded ictal slow shifts also have high specificity although their low sensitivity is to be taken into account.

Adolescent↗

PubMed1999

Cognitive motor control in human pre-supplementary motor area studied by subdural recording of discrimination/selection-related potentials.

To clarify the functional role of human pre-supplementary motor area (pre-SMA) in 'cognitive' motor control as compared with other non-primary motor cortices (SMA-proper and lateral premotor areas) and prefrontal area, we recorded epicortical field potentials by using subdural electrodes in five epileptic patients during presurgical evaluation, whose pre-SMA, SMA-proper, prefrontal and lateral premotor areas were defined by electric cortical stimulation and recent anatomical orientations according to the bicommissural plane and callosal grid system. An S1-Go/NoGo choice and delayed reaction task (S1-choice paradigm) and a warned choice Go/NoGo reaction task (S2-choice paradigm) with inter-stimulus intervals of 2 s were employed. The results showed (i) transient potentials with onset and peak latencies of about 200 and 600 ms, respectively, after S1 in the S1-choice paradigm mainly at pre-SMA and to a lesser degree at the prefrontal and lateral premotor areas, but not in the S2-choice paradigm. At SMA-proper, a similar but much smaller potential was seen after S1 in both S1- and S2-choice paradigms and (ii) slow sustained potentials between S1 and S2 in both S1- and S2-choice paradigms in all of the non-primary motor areas investigated (pre-SMA, SMA-proper and lateral premotor areas) and prefrontal area. It is concluded that pre-SMA plays a more important role in cognitive motor control which involves sensory discrimination and decision making or motor selection for the action after stimuli, whereas SMA-proper is one of the main generators of Bereitschaftspotential preceding self-paced, voluntary movements. In the more general anticipation of and attention to the forthcoming stimuli, non-primary motor cortices including pre-SMA, SMA-proper and lateral premotor area, and the prefrontal area are commonly involved.

Adult↗

PubMed1999

Mechanisms underlying gait disturbance in Parkinson's disease: a single photon emission computed tomography study.

Single photon emission computed tomography was used to evaluate regional cerebral blood flow changes during gait on a treadmill in 10 patients with Parkinson's disease and 10 age-matched controls. The subjects were injected with [99mTc]hexamethyl-propyleneamine oxime twice: while walking on the treadmill, which moved at a steady speed, and while lying on a bed with their eyes open. On the treadmill, all subjects walked at the same speed with their preferred stride length. The patients showed typical hypokinetic gait with higher cadence and smaller stride length than the controls. In the controls, a gait-induced increase in brain activity was observed in the medial and lateral premotor areas, primary sensorimotor areas, anterior cingulate contex, superior parietal cortex, visual cortex, dorsal brainstem, basal ganglia and cerebellum. The Parkinson's disease patients revealed relative underactivation in the left medial frontal area, right precuneus and left cerebellar hemisphere, whereas they showed relative overactivity in the left temporal cortex, right insula, left cingulate cortex and cerebellar vermis. This is the first experimental study showing that the dorsal brainstem, which corresponds to the brainstem locomotor region in experimental animals, is active during human bipedal gait. The reduced brain activity in the medial frontal motor areas is a basic abnormality in motor performance in Parkinson's disease. The underactivity in the left cerebellar hemisphere, in contrast to the overactivity in the vermis, could be associated with a loss of lateral gravity shift in parkinsonian gait.

Aged↗

PubMed1999