Biomedical subjects

K Hyoki

Publications and source records attributed to K Hyoki.

6 recordsLinked to original sources

PubMed2004

Fluctuations of source locations of EEG activity during transition from alertness to sleep in Alzheimer's disease and vascular dementia.

Vascular dementia (VaD) differs from Alzheimer's disease (AD) in larger fluctuations of cognitive impairment, hypothetically because of deteriorated vigilance control. Vigilance levels are reflected by locations of EEG sources. Transition from alertness to sleep might be particularly sensitive to degradations of vigilance control. Twelve AD and 12 VaD patients (medication free, mean age 75.6 and 77.6 years, respectively, difference = n.s.), and 12 healthy elderly subjects (mean age 70.6 years), who served as controls, were studied (each group comprised 2 males and 10 females). A twenty-one-channel EEG was recorded from full alertness to the onset of sleep stage 2. Dipole source modeling, based on Fast Fourier Transform dipole approximation, yielded 3D source localizations in 7 EEG frequency bands. For each brain axis, means of source location differences between successive 20-second periods were calculated (fluctuation magnitude). EEG band-wise MANCOVAs (3 brain axes, 3 subject groups, covariate: age) showed differences in fluctuation magnitude between groups in the 10.5- to 12-Hz alpha(2) frequency band (p=0.0066). Post hoc ANCOVAs for the axes (3 subject groups, covariate: age) were significant on the superior-inferior axis: VaD patients had higher fluctuations than AD patients and controls, without significant difference between the latter two. Thus, larger source fluctuations in VaD might reflect the patients' decreased vigilance control, accounting for their increased fluctuations of cognitive impairment.

Aged↗

PubMed2002

Spatial organization of EEG activity from alertness to sleep stage 2 in old and younger subjects.

In order to elucidate brain mechanisms that contribute to the increased tendency for vigilance dysregulation in the elderly, we examined the spatial organization of brain electric activity [electroencephalogram (EEG)] during decreasing vigilance from alertness to onset of sleep stage 2, comparing 7 old and 10 younger, healthy subjects (60-79 and 18-41 years old, respectively). Two features were analyzed: (1) change of location of the brain electric source gravity centers of the EEG frequency bands, and (2) magnitude of fluctuation of these locations over time. Multichannel EEG was analyzed into source gravity center localizations for seven EEG frequency bands, using fast Fourier transform (FFT) Dipole Approximation (first principal component-single source modeling in the frequency domain). Multivariate analysis of covariance (MANCOVA) showed: source localizations were more anterior in old than younger subjects for beta-1 and more superior for all three beta bands; from alertness to sleep, delta and theta EEG sources (inhibitory activity) changed to more posterior and superior areas, and alpha-1 and -2 (routine activity) and beta-1 and -2 sources (excitatory activity) towards anterior and superior areas. Fluctuations of the source locations of delta and beta-2 were larger on the superior--inferior axis, and of beta-2 smaller on the left-right axis in the old than younger subjects. The results suggest functional specifications (inhibitory, routine, excitatory) of cortical positron emission tomography (PET) changes reported in sleep. In sum, aging exhibits changes in spatial organization of EEG-generating neuronal assemblies; during the transition wakefulness-to-sleep, aging affects the spatial-temporal dynamics of this organization. The latter is suggested to contribute to the increased risk for consciousness disturbances in the elderly.

Adolescent↗

PubMed1998

Quantitative electro-oculography and electroencephalography as indices of alertness.

Even though both electro-oculography (EOG) and EEG have been widely used for assessing alertness, the relationship between these two measures has not yet been clarified at various alertness levels. We estimated the frequencies of eye movements faster than 15 degrees/s (NoEM15) and EEG power at every 0.5 Hz step frequency point, quantitatively as well as continuously from alert to very light sleep (Stage 1) in 14 healthy adults. We devised a new EOG derivation for a computerized analysis, because conventional EOG recordings suffer from EEG contamination and have been analyzed manually. EOG electrodes were attached to the left orbitale in this study. The eye movements were detected as peaks in differentiated EOG signals. Significant correlations were found between NoEM15 and EEG powers at several frequency points, mainly in the alpha and beta bands. Though fluctuating EEG components in close correspondence to the frequency of the eye movements varied depending on the individual, EEG power at the peak frequency of the awake state was most closely associated with the eye movements. A broad band power that centers at the peak frequency may be a better measure for alertness assessment than powers in fixed bands.

Adolescent↗

PubMed1993

Horizontal component of electro-oculogram as a parameter of arousal in dementia: relationship between intellectual improvement and increasing arousal under pharmacotherapy.

Although nootropics and metabolically active compounds sometimes attenuate intellectual deficits of dementia patients, this mechanism has not been discussed or investigated. The authors hypothesized that these compounds act to enhance attention and/or concentration by increasing the arousal level, and then improve intellectual functions. Based on this hypothesis, the authors investigated the arousal level and the improvement of intellectual functions in ten patients with Alzheimer type dementia and ten patients with multi-infarct dementia before and after 3 months pharmacotherapy using bifemelane hydrochloride. They then analyzed whether the increases in arousal level involves or relates to the improvement of intellectual functions. On the 20 patients, psychological tests were carried out, and the arousal level was evaluated using the frequency of rapid eye movements in the electro-oculogram (EOG) before and after 3 months administration of bifemelane hydrochloride. As a result, a significant positive correlation was observed between the improvement on the Hasegawa's dementia scale and the rate of increase in rapid eye movements in the EOG. The EOG monitoring can be a great help in establishing an objective evaluation method on drug efficacy.

Aged↗

PubMed1993

Responders and non-responders to bifemelane hydrochloride in Alzheimer-type and multi-infarct dementia.

Although metabolically active compounds sometime attenuate cognitive deficits of dementia patients, this mechanism has not been discussed or investigated. We hypothesized that these compounds improve cognitive disorders not by directly acting on this cognitive function, but by increasing the arousal level. Based on this hypothesis, we investigated the change of arousal levels and the improvement of intellectual functions in 10 patients with Alzheimer-type dementia (ATD) and 10 patients with multi-infarct dementia (MID) before and 3 months after pharmacotherapy using bifemelane hydrochloride. For each patient, a psychological test battery was carried out and the arousal level was evaluated using the frequency of rapid eye movements in the electro-oculogram (EOG) and the frequency analysis of electroencephalogram (EEG) before and after the treatment. Evaluation of the cognitive improvement was made and eight out of the 20 patients were regarded as responders to the treatment. The frequency of small rapid eye movements (SREM) in the EOG increased significantly only in responders and the rate of change in SREM appearance in responders was significantly different from that in non-responders. This finding suggests that a part of the intellectual improvement in ATD and MID results from the increased level of arousal.

Aged↗

PubMed1993

[The correlation between changes in EEG and eye movement (EOG) accompanied by lowered arousal level].

We investigated the correlation between the components of spontaneous eye movement (EOG) and EEG in six healthy individuals. The study was conducted in three periods; from the resting to drowsy stage, from the drowsy to spontaneous awakening stage, and in the forced waking stage. EEG, as registered from bipolar electrodes attached between the left parietal region (P3) and the left occipital region (O1), was monitored continuously by the FFT method with a segment of 12.8 seconds. Rapid eye movement and slow eye movement were observed simultaneously. In conclusion, even when the arousal level varies considerably, there is a close correlation between frequency of rapid eye movement and EEG patterns of 10.16 integral of 10.94 Hz & 17.97 integral of 19.53 Hz (simple correlation p < 0.01). Additionally, during the forced waking period (after stage 2), delta and theta bands increased in cases along with sleepiness. Even if the depth of sleep was the same, one's mood upon awakening was determined by the frequency of slow waves before awakening.

Adult↗