Yoshikata Atsumi

Activation of the visual cortex imaged by 24-channel near-infrared spectroscopy

Near-infrared spectroscopy (NIRS) is a noninvasive technique for continuous monitoring of the amounts of total hemoglobin (total-Hb), oxygenated hemoglobin, (oxy-Hb) and deoxygenated hemoglobin (deoxy-Hb). The purpose of the present study was to demonstrate the utility of NIRS in functional imaging of the human visual cortex. A new NIRS imaging system enabled measurements from 24 scalp locations covering a 9 cm sq area. Topographic images were obtained from interpolations of the concentration changes between measurement points. Five healthy subjects between 25 and 49 years of age were investigated. After a resting baseline period of 50 s, the subjects were exposed to a visual stimulus for 20 s, followed by a 50 s resting period in a dimly lit, sound attenuating room. The visual stimulus was a circular, black and white, alternating checkerboard. In four of five subjects the visual cortex was the most activated area during visual stimulation. This is the first reported use of a NIRS-imaging system for assessing hemodynamic changes in the human visual cortex. The typical hemodynamic changes expected were observed; the total-Hb and oxy-Hb increased just after the start of stimulation and plateaued after 10 s of the stimulation period.

Dynamic relationships between sleep spindles and delta waves during a NREM period.

All-night sleep EEGs from 7 normal young male adults were analyzed by a waveform recognition method using FFT-IFFT band pass filters. The total durations of sleep spindles and sleep delta waves in each 20-s epoch were measured and plotted on an X-Y graph with lines connecting the points in time sequence (dynamic two-component plot). The relationship between these two measures within a single NREM period showed three dynamic phases and one stationary period. In the first phase, spindles increased while delta remained at low level or increased slightly. In the second phase delta increased greatly while spindles decreased. In the third phase, delta decreased while spindles remained at a low level. There was a stationary period between the second and third phases, when delta maintained a higher level and spindles maintained a lower level. These dynamic descriptions reflect the underlying physiological mechanisms more directly than static sleep stages. They should also permit finer analyses of sleep in psychiatric and neurological disorders.

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.

Activation of visual cortex in REM sleep measured by 24‐channel NIRS imaging

To visualize dreaming brain functions we studied hemodynamic changes in the visual cortex during the transition from non‐rapid eye movement (NREM) to rapid eye movement (REM) sleep, using a 24‐channel Near‐Infrared Spectroscopy (NIRS) imaging method. Results were compared to the activation in visual cortex by visual stimulation during wakefulness. Subjects were four healthy males between 25 and 49 years of age. Five all‐night polysomnographic and NIRS recordings were made. Increases in the oxygenated hemoglobin concentration in visual cortex were observed from nine of 14 REM periods. The activated areas were broader during REM sleep than during visual stimulation. These findings suggest that activation of visual cortex in REM sleep might represent dream‐related brain activity.

Influence of arousal level for functional magnetic resonance imaging (fMRI) study: simultaneous recording of fMRI and electroencephalogram.

Abstract Simultaneous recording of functional MRI (fMRI) and electroencephalogram (EEG) has been applied to several clinical fields, making it possible to monitor the arousal level of the subject during a cognitive task. The study confirmed that activated cerebral areas were different between high and low arousal levels during the smooth‐pursuit eye movement task. When arousal level was high, activations in the parietal eye field, frontal eye field (FEF), supplementary eye field (SMA), visual fields (V1) and occipito–temporal junction (V5) were found. In contrast, when arousal level was low, activations were found only in V1 and FEF. The results indicate that the monitoring of the arousal level of subjects using fMRI and EEG recordings simultaneously is crucial for detecting cortical activations during a cognitive task.

Eye Movement as an Indicator of Brain Function

Abstract: The level of consciousness between the alert and drowsy states was classified into four stages (Alert, Resting I, Resting II, Drowsy) by studying three factors of the EEG patterns on 23 normal subjects. The eye movements recorded by electro‐oculograph were divided into two groups, i.e. rapid eye movements (R type, r type) and slow eye movements (S type, s type). The occurrence of each type of eye movements was confirmed to change in close correspondence to the stages of consciousness.

Cerebral blood volume in the sleep measured by near‐infrared spectroscopy

Abstract We investigated the relationship between hemodynamic changes in the cortex measured by near‐infrared spectroscopy (NIRS) and the polysomnographic changes during sleep. Four healthy male volunteers participated in the study. Near‐infrared spectroscopy measuring and polysomnographic recordings were done simultaneously during sleep. In many case, oxy‐hemoglobin (oxy‐Hb) decreased and deoxy‐hemoglobin (deoxy‐Hb) increased during the transition from wakefulness to sleep, and oxy‐Hb increased toward deep sleep. Oxy‐Hb and deoxy‐Hb had larger fluctuations during REM sleep than those during non‐REM sleep. During REM sleep, oxy‐Hb often showed a lower level and deoxy‐Hb showed a higher level than those during the preceding and following non‐REM sleep.

Simultaneous recording of EEG and functional MRI

Abstract The simultaneous recording of the electroencephalogram (EEG) and functional magnetic resonance imaging (fMRI) provides a better understanding of the relationship between hemodynamic and electrical brain activation and is thought to be a powerful technique for studying brain function. However, the acquisition of EEG during fMRI experiments raises important practical issues for patient safety and for the artifacts of MRI images and EEG waveforms. It made it possible to acquire clear MRI images and EEG tracings with sufficient patient safety by using electrodes with register and with twisted leads. The simultaneous recording of fMRI and EEG has been applied to several clinical studies: epilepsy, sleep and ERP studies. It also makes it possible to monitor the arousal level of the subject during cognitive task. We confirmed that activated areas during pursuit eye movement tasks were different by the arousal level. Monitoring the arousal level of the subjects using fMRI and EEG simultaneous recording is thought to be crucial for the cognitive task.

Simultaneous recording by NIRS and VEP revealed the dominant response in left primary visual cortex

Introduction Visual evoked potential (VEP) is the response of electrical activity of neurons recorded during 0 (ETH) 300 msec after the stimulation. Functional MRI, PET and NIRS that were recently used for functional brain mapping record the hemodynamic change of the brain which occur a few seconds after the stimulation and continue for several seconds. It is very important to compare these two methodologies for combining conventional EEG studies with new findings in the brain mapping. In the present study simultaneous recording of the response of primary visual field (Vl) was done using conventional VEP and 22-channel NIRS.