Sunao Uchida

Correlation between electroencephalography and heart rate variability during sleep

Abstract It is known that autonomic nervous activities change in correspondence with sleep stages. However, the characteristics of continuous fluctuations in nocturnal autonomic nerve tone have not been clarified in detail. The study aimed to determine the possible correlation between the electroencephalogram (EEG) and autonomic nervous activities, and to clarify in detail the nocturnal fluctuations in autonomic nerve activities. Overnight EEGs and electrocardiograms of seven healthy males were obtained. These EEGs were analyzed by fast Fourier transformation algorithm to extract delta, sigma and beta power. Heart rate and heart rate variability (HRV) were calculated in consecutive 5‐min epochs. The HRV indices of low frequency (LF), high frequency (HF) and LF/HF ratio were calculated from the spectral analysis of R‐R intervals. The sleep stages were manually scored according to Rechtschaffen and Kales’ criteria. Low frequency and LF/HF were significantly lower during non‐rapid eye movement (NREM) than REM, and were lower in stages 3 and 4 than in stages 1 and 2. Furthermore, delta EEG showed inverse correlations with LF (r = − 0.44, P < 0.001) and LF/HF (r = − 0.41, P < 0.001). In contrast, HF differed neither between REM and NREM nor among NREM sleep stages. Detailed analysis revealed that correlation was evident from the first to third NREM, but not in the fourth and fifth NREM. Delta EEG power showed negative correlations with LF and LF/HF, suggesting that sympathetic nervous activities continuously fluctuate in accordance with sleep deepening and lightening.

Bayesian calibration of simultaneity in tactile temporal order judgment

Human judgment of the temporal order of two sensory signals is liable to change depending on our prior experiences. Previous studies have reported that signals presented at short intervals but in the same order as the most frequently repeated signal are perceived as occurring simultaneously. Here we report opposite perceptual changes that conform* to a Bayesian integration theory in judging the order of two stimuli delivered one to each hand.

Exercise effects on sleep physiology

This mini-review focuses on the effects of exercise on sleep. In its early days, sleep research largely focused on central nervous system (CNS) physiology using standardized tabulations of several sleep-specific landmark electroencephalogram (EEG) waveforms. Though coarse, this method has enabled the observation and inspection of numerous uninterrupted sleep phenomena. The research on the effects of exercise on sleep began, in the 1960s, with a focus primarily on sleep related EEG changes (CNS sleep). Those early studies found only small effects of exercise on sleep. However, more recent sleep research has explored not only CNS functioning, but somatic physiology as well. Sleep should be affected by daytime exercise, as physical activity alters endocrine, autonomic nervous system (ANS), and somatic functions. Since endocrinological, metabolic, and autonomic changes can be measured during sleep, it should be possible to assess exercise effects on somatic physiology in addition to CNS sleep quality, evaluated by standard polysomnographic (PSG) techniques. Additional measures of somatic physiology have provided enough evidences to conclude that the auto-regulatory, global regulation of sleep is not the exclusive domain of the CNS, but it is heavily influenced by inputs from the rest of the body.

Cortical oscillations in human medial temporal lobe during wakefulness and all-night sleep

We have recorded human medial temporal lobe electrocorticogram during wakefulness and natural sleep in epileptic patients with subdural electrodes. From these recordings, we have found gamma (30-150 Hz) [Neuroscience 90 (1999) 1149] and beta-1 (10-20 Hz) [NeuroReport 10 (1999) 3055] activities during wakefulness in human medial temporal lobe. In this paper, we will report changes of these frequencies across wake and natural sleep. Electrocorticograms during wake, slow wave sleep and rapid eye movement (REM) sleep were subjected to fast Fourier transformation analysis. During wake two spectral enhancements, beta-1 and gamma, were consistently observed across subjects. In the raw signal, beta-1 was observed as a regular rhythmic oscillation. In slow wave sleep, the beta-1 peak disappeared but gamma remained, although slightly reduced in power. During REM sleep, beta-1 appeared again, but the peak frequency was significantly lower than during wake (mean frequency: wake=16.6, REM=12.8 Hz). The gamma peak was also present in REM sleep. It has been known that the rhythmic slow activity (RSA) or theta is observed in some animals. However, it is unclear whether the human hippocampus displays similar activity. Since human beta-1 appears during wake and REM sleep when RSA is observed in other species, and since beta-1 is also a regular rhythmic oscillation, we propose that beta-1 may be the functional equivalent of hippocampal RSA (theta) observed in some animals. Functional significances of the gamma activity should be further investigated.

A Comparison of Period Amplitude Analysis and FFT Power Spectral Analysis of All-Night Human Sleep EEG

Zero-cross and zero-derivative period amplitude analysis (PAA) data were compared with power spectral analysis (PSA) data obtained with the fast Fourier transform in all-night sleep EEG from 10 subjects. Although PAA zero-cross-integrated amplitude showed good agreement with PSA power in 0.3-2 Hz, zero-cross analysis appears relatively ineffective in measuring 2-4 Hz and above waves. However, PAA zero-derivative measures of peak-trough amplitude correlated well with PSA power in 2-4 Hz. Thus, while PAA appears able to measure the entire EEG spectrum, the analytic technique should be changed from zero cross to zero derivative at about 2 Hz in human sleep EEG. PAA and PSA both demonstrate robust and interrelated across-night oscillations in three frequency bands: delta (0.3-4 Hz); sigma (12-16 Hz); and fast beta (20-10 Hz). The frequencies between delta and sigma, and between sigma and fast beta, did not show clear across-night oscillations using either method, and the two methods showed lower epoch-to-epoch agreement in these intermediate bands. The causes of this reduced agreement are not immediately clear, nor is it obvious which method gives more valid results. We believe that the three strongly oscillating frequency bands represent fundamental properties of the human sleep EEG that provide important clues to underlying physiological mechanisms. These mechanisms are more likely to be understood if their dynamic properties are preserved and measured naturalistically rather than being forced into arbitrary sleep stages or procrustean models. Both PAA and PSA can be employed for such naturalistic studies. PSA has the advantages of applying the same analytic method across the EEG spectrum and rests on more fully developed theory. Combined zero-cross and zero-derivative PAA demonstrates EEG oscillations that closely parallel those observed with spectral power, and the PAA measures do not rely on assumptions about the spectral composition of the signal. In addition, both PAA techniques can measure the relative contributions of wave amplitude and incidence to total power: These waveform characteristics represent different biological processes and respond differentially to a wide range of experimental conditions.

Enhanced gamma (30–150 Hz) frequency in the human medial temporal lobe

We performed fast Fourier transformation power spectral analysis of the electrocorticogram in human medial temporal lobe during wakeful rest in six epileptic subjects. Compared with the electrocorticogram wave in the basal temporal lobe, which showed monotonic decline of spectral power across the frequency axis, the electrocorticogram wave in the parahippocampal gyrus was enhanced (or did not decline) in the gamma frequency range (30-150 Hz) in all subjects. Although it has been suggested that electrical oscillations of the hippocampus have functional roles in higher brain functions, namely learning and memory, the knowledge of hippocampal oscillations is largely limited to animal studies. The present results demonstrate that fast frequency oscillation is also present in the human medial temporal lobe, which has been reported in animal hippocampi. They also demonstrate the importance of recording very fast field potentials in human electrocorticograms. This fast oscillation is likely to play important functional roles related to learning and memory, possibly to induce long-term potentiation in the human medial temporal lobe.

Clonidine effects on all‐night human sleep: Opposite action of low‐ and medium‐dose clonidine on human NREM–REM sleep proportion

Abstract  Norepinephrine (NE) is considered to play a permissive role in the occurrence of rapid eye movement (REM) sleep. Clonidine is an NE α‐2‐receptor agonist, which has been considered to act mainly on the autoreceptors of presynaptic noradrenergic neurons to reduce their release of NE. However, previous studies of clonidine effects on REM sleep have produced controversial results and the effects of clonidine remain uncertain. To clarify the pharmacological effects of clonidine on human sleep, the sleep electroencephalograms (EEG) recorded from 15 young normal subjects after a single administration of either a low (25 µg) or medium (150 µg) dose of clonidine were examined, and fast Fourier transformation (FFT) spectral analyses of the C3‐A2 EEG were performed. Low‐dose clonidine significantly increased the amount of REM sleep and decreased the amount of non‐REM (NREM) sleep during the second one‐third of the drug nights compared to the corresponding hours of baseline night recordings. In contrast, medium‐dose clonidine significantly decreased REM and increased NREM on drug nights compared to baseline nights in the entire night. The opposite actions of low and medium doses of clonidine on NREM‐REM proportion may indicate that low‐dose clonidine mainly affects the α‐2‐receptors on locus coeruleus‐NE neurons presynaptically, reducing the release of NE, whereas medium‐dose clonidine acts more post‐synaptically.

Sigma (12-16 Hz) and beta (20-28 HZ) EEG discriminate NREM and REM sleep

All night sleep EEG from ten normal students were subjected to FFT spectral analyses. Delta (0.3-3 Hz), sigma (12-16 Hz) and beta (20-28 Hz) EEG showed strongly oscillating patterns across the night. The scattergram of sigma versus beta revealed two separate clusters. One cluster demonstrated a positive linear correlation between sigma and beta. The second cluster showed a range of beta, but a stable, low level of sigma activity. Points in the former cluster consisted of those from NREM epochs, and in the latter, from REM epochs. The present results suggest that REM and NREM EEG are composed of two sets of EEG frequency components, perhaps reflecting different neuronal pools.

Theta oscillation in the human anterior cingulate cortex during all-night sleep: An electrocorticographic study

Ten epileptic patients each with subdural electrodes surgically attached to the anterior cingulate cortex (ACC; two cases), the orbitofrontal cortex (OFC; seven cases), or both (one case) were included in this study. We recorded each patients ACC or OFC electrocorticogram (ECoG) during the time period that the patient was awake and naturally asleep. We performed a Fast Fourier Transformation (FFT) power spectral analysis on each ECoG to examine its frequency component. We found that the ACC showed regular and continuous theta oscillation (5-7Hz) during wakefulness and rapid eye movement (REM) sleep, but not during slow wave sleep. Theta waves observed in REM sleep were not as distinct as those found in wakefulness. We also discovered that the orbitofrontal signals represented spectral peaks in the theta band only during wakefulness. This suggests the coexistence of theta oscillation in the ACC. Considering our previous observations of gamma and beta oscillations in the human hippocampus, we hypothesize that the human limbic system manifests two oscillatory activities. The results obtained in this study suggest that electrophysiological activity in the ACC could be related to particular psychological functions in wakefulness and in REM sleep. These results are useful in elucidating the human brain mechanism.

Suppression of gamma activity in the human medial temporal lobe by sevoflurane anesthesia

We have reported the presence of continuous gamma (30–150 Hz) activity in the human medial temporal lobe (MTL). Since the MTL is involved in learning and memory, we speculated that MTL gamma activity is related to such higher brain functions. It is thus of interest to learn how this activity changes during different states of consciousness. In this study, we recorded electrocorticographic (ECoG) activity directly from the surface of the MTL after various doses of sevoflurane anesthesia. Five epileptic patients underwent electrode placement operations in which electrodes were attached to the surfaces of the MTL and the basal temporal lobe (BTL). Immediately following the operation ECoG was recorded from each patient under four concentrations of sevoflurane anesthesia (1.5, 2.0, 2.5 and 3.0%). Fast Fourier Transform (FFT) analysis was performed on the MTL ECoGs. Under the lowest sevoflurane concentration, MTL gamma activity was observed in all patients. However, gamma activity was progressively suppressed by increased concentrations of sevoflurane, in a dose-dependent manner. Sevoflurane has been known to reduce neuronal excitability in the rat hippocampus in vitro, probably by changing GABAergic inhibition. The reduction of MTL gamma in the present study may be the result of such a mechanism. Although memory function was not tested in this study, the amount of MTL gamma activity may be related to residual memory function during anesthesia.