Tadao Hori

Brain activity during expectancy of emotional stimuli : An fMRI study

We studied the neural activation associated with the expectancy of emotional stimuli using whole brain fMRI. Fifteen healthy subjects underwent fMRI scanning during which they performed a warned reaction task using emotional pictures carrying pleasant, unpleasant, or neutral content. The task involved an expected or unexpected condition. Data were analyzed by comparing the images acquired under the different conditions. In the expected condition, compared with the unexpected condition, significant activation was observed in the medial, inferior and dorsolateral prefrontal cortex. Whereas the expectancy of pleasant stimuli produced activation in the left dorsolateral and left medial prefrontal cortex as well as in the right cerebellum, the expectancy of unpleasant stimuli produced activation in the right inferior and right medial prefrontal cortex, the right amygdala, the left anterior cingulate cortex, and bilaterally in the visual cortex. These results suggest that the expectancy of emotional stimuli is mediated by the prefrontal area including the medial, inferior, and dorsolateral prefrontal cortex. Furthermore, our data suggest that left frontal activation is associated with the expectancy of pleasant stimuli and that right frontal activation is associated with the expectancy of unpleasant stimuli. Finally, our findings suggest that the amygdala and anterior cingulate cortex may play an important role in the expectancy of unpleasant stimuli and that the input of this negative information is modulated by these specific brain areas.

The effects of a 20 min nap in the mid-afternoon on mood, performance and EEG activity

OBJECTIVE The aim of the study is to examine the effects of a 20 min nap in the mid-afternoon on mood, performance and EEG activities. METHODS Seven young adults who had normal sleep-wake habits without habitual daytime napping participated in the study. They underwent Nap and No-nap conditions at intervals of 1 week. After a nocturnal sleep recording (00:00-08:00 h), their EEG recordings during relaxed wakefulness, and their mood, performance and self-ratings of performance level were measured every 20 min from 10:00 to 18:00 h. For the nap condition, they went to bed at 14:00 h and were awakened when 20 min had elapsed from the onset of sleep stage 1. For the No-nap condition, they took a rest without sleep by sitting on a semi-reclining chair. RESULTS All of the subjects were awakened from sleep stage 2 during the nap. The 20 min nap improved the subjective sleepiness, performance level and self-confidence of their task performance. The nap also suppressed EEG alpha activity during eyes-open wakefulness. CONCLUSIONS The results suggest that a short 20 min nap in the mid-afternoon had positive effects upon the maintenance of the daytime vigilance level.

The alerting effects of caffeine, bright light and face washing after a short daytime nap.

OBJECTIVE The present study examined whether the combination of a short daytime nap with caffeine, bright light and face washing was effective against mid-afternoon sleepiness. METHODS Ten young healthy adults participated in 5 experimental conditions; those experiments were-Nap only: taking a 20 min nap; Caffeine+Nap: taking 200 mg of caffeine followed by a nap; Nap+Bright-light: being exposed to 2000 lx of bright light for 1 min immediately after napping; Nap+Face-washing: washing their faces immediately after napping; and No-Nap: taking a rest without sleep. These naps were taken at 12:40 hours. The subjects engaged in computer tasks for 15 min before napping and for 1 h after napping. RESULTS Caffeine+Nap was the most effective for subjective sleepiness and performance level; its effects lasted throughout 1 h after napping. Nap+Bright-light was comparable with Caffeine+Nap, except for performance level. Nap+Face-washing showed mild and transient effects, however, it suppressed subjective sleepiness immediately after napping. CONCLUSIONS The effects of a short nap against mid-afternoon sleepiness could be enhanced by combining caffeine intake, exposure to bright light, or face washing. SIGNIFICANCE The present study would provide effective countermeasures against mid-afternoon sleepiness and sleepiness related accidents.

The effects of a 20-min nap at noon on sleepiness, performance and EEG activity

The prophylactic effects of a 20-min nap at noon on afternoon sleepiness were studied. Ten young adults who had normal sleep-wake habits without habitual daytime napping were subjected to nap and no-nap conditions at an interval of 1 week. After a nocturnal sleep recording (00.00-08.00 h), their EEG recordings during relaxed wakefulness, mood, performance, and self-ratings of performance level were measured every 20 min from 10.00 h to 18.00 h. For the nap condition, they went to bed at 12.20 h and were awakened when 20 min had elapsed from the onset of sleep stage 1. For the no-nap condition, they rested without sleeping by sitting on a semi-reclining chair. The nap did not improve task performance, however, it improved volition and the self-rating of task performance. It also suppressed subjective sleepiness and attenuated eyes-opened EEG alpha activities. The results suggest that a 20-min nap at noon had partial positive effects on the maintenance of the daytime arousal level.

Word imageability and N400 in an incidental memory paradigm

High imagery words are memorized better than low imagery words. To examine how these words are processed at encoding, event-related potentials (ERPs) were recorded in an incidental memory paradigm. Frequency-matched high and low imagery words (45 words each) were presented in a random order on a computer screen. Twelve university students were asked to rate the imageability of a words referent on a five-point scale. High imagery words elicited a larger N400 than low imagery words did. The N400 was more left-lateralized for low imagery words than for high imagery words, suggesting that some neural generators (probably in the right hemisphere) were not involved in the processing of low imagery words. Difference waveforms showed that the N400 was followed by a second negativity (N800), which was also larger for high imagery words and had a scalp distribution similar to that of the N400. Subsequent free recall showed a classical imagery effect that high imagery words were recalled better than low imagery words. These results suggest that the superiority of high imagery words over low imagery words in incidental memory results from more extensive activation of a semantic network distributed across the left and right hemispheres, the latter of which probably deals with imagery-related information that is not activated by low imagery words.

Spatiotemporal changes of EEG activity during waking-sleeping transition period

To evaluate the spatiotemporal changes of EEG during waking-sleeping transition or hypnagogic period, spectral analysis of the five scalp EEG on the midline (Fpz, Fz, Cz, Pz and Oz) referenced to the left ear lobe was carried out on seven young male subjects. Power spectra from consecutive samples of 5.12 sec period with 0.2 Hz resolution were studied from 10 min before the manually scored stage 1 onset to 30 min after the onset of stage 1. The average power spectra over 1 min segments and corresponding coefficient of variation (CV) were determined for the frequency bands of delta (1-3 Hz), theta (4-7 Hz), alpha (8-12 Hz), sigma (13-15 Hz) and beta (16-19 Hz). The latency score was defined as the time elapsed from the onset of stage 1 to the first epoch when the frequency band power, using the ANOVA significantly increased (or decreased) in comparison with the average level at the onset of stage 1. Median latency scores for each band were similar to the Cz scores, with a ranking, from early to late, of: alpha (2 min), theta (3 min), delta (5 min) and sigma (5 min). Significant change was not observed on the beta band activity. In terms of the EEG areas, the shortest latency was found in the theta band activity of the Fz EEG (2 min), and the longest was the sigma band activity of the Fpz and Oz EEG (8 min). The average stage 2 latency was 3.5 min when it was measured as time elapsed between the onset of stage 1 and 2. The average curves of delta, theta and alpha band CVs, started to increase just before or immediately after stage 1 onset and continued to increase for about 10 min. If the increased CV or unsteadiness of EEG activity is taken as a characteristic of the hypnagogic period, hypnagogic states may be considered to have continued until about 10 min after the stage 1 onset. Delta-theta activity showed a rapid rise in power after the onset of stage 1 for all areas. Delta power at the occipital, however, increased more gradually, and consistently remained at a lower level. The differences of delta power between Oz and other four electrode sites became clear at 7 min after the onset of stage 1. These regional differences may reflect the termination of hypnagogic effects.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of a daytime nap in the aged.

This study evaluated the effects of the daytime nap on performance, mood and physiological measures in aged individuals. Participants were six healthy aged persons (M = 72.2 years old) who habitually napped in the afternoon three or more times a week. They participated under two conditions with an interval of 1 week. In the nap condition, the subjects went to bed at 13:00 h and slept for 30 min. In the rest condition, they just watched television. In both conditions, electroencephalogram (EEG), blood pressure, mood and performance were measured before and after a nap or rest. The daytime nap improved performance, decreased subjective sleepiness and fatigue, and attenuated EEG alpha band activity. Moreover, following a nap diastolic blood pressure significantly decreased. These findings suggest that a habitual daytime nap helps aged individuals to maintain their daytime physiological, psychological and behavioral arousal at an adequate level.

Changes in Alpha Band Eeg Activity in the Frontal Area after Stimulation with Music of Different Affective Content

This study investigated the stimulating effects of music. Twelve-channel EEGs (Fp1, Fp2, F7, F8, Fz, C3, C4, Pz, T5, T6, O1, O2) were recorded on 10 students during periods of baseline, premusic rest, music (stimulating or calming), and postmusic rest. The amplitude of the alpha-2 (9.6 to 11.4 Hz) band was lower during the rest session than that during the baseline session. In the music period the amplitude of alpha-2 band increased during both the stimulating and calm music. The frontal interhemispheric coherence values (F7-F8) of the alpha-2 band increased during the stimulating music session, while the coherence values did not change during the calm music. These findings implied close relationships between the interhemispheric transmission of information in the frontal areas and positive attention to stimulating music.

Effects of short nap and exercise on elderly people having difficulty in sleeping.

The purpose of the present study was to examine the effects of short nap and exercise on the sleep quality of elderly people who reported difficulty in sleeping. ‘Interventions’ such as short nap after lunch and moderate‐intensity exercise in the evening were carried out for 4 weeks. After the ‘interventions’, wake time after sleep onset significantly decreased and sleep efficiency significantly increased, which showed that sleep quality was improved. The frequency of nodding in the evening significantly decreased. These results demonstrated that the proper awakening maintenance in the evening was effective in improving sleep quality. After the ‘intervention’, mental health was also improved with improving sleep quality.

The vanishing point of the mismatch negativity at sleep onset

OBJECTIVE To determine when the mismatch negativity (MMN) disappears at sleep onset, event-related potentials (ERPs) were recorded continuously from wakefulness to sleep. METHODS Ten healthy young students were told to fall asleep ignoring the tones presented through a loudspeaker above their head. Standard (1000 Hz, P=0.90), high deviant (1200 Hz, P=0.05), and low deviant (1050 Hz, P=0.05) tones were presented in a quasirandom order with a fixed stimulus onset asynchrony of 500 ms. ERP waveforms were obtained separately for 5 successive stages characterized by typical electroencephalographic (EEG) patterns of the sleep onset period. The EEG staging was made manually with very short (5 s) scoring epochs. RESULTS The MMN appeared in wakefulness and in the early phase of stage 1 sleep (EEG stage II) but disappeared when low-voltage theta waves emerged after alpha flattening (EEG stage III). Instead, P240 and N360 developed particularly for high deviant tones. CONCLUSIONS Concurrently with the disappearance of alpha waves, the automatic change detection system in wakefulness seems to stop operating and a different sleep-specific system becomes dominant.