Electroencephalographic pattern quantification and the arousal continuum

Sleepiness, alertness and performance during a laboratory simulation of an acute shift of the wake-sleep cycle

Monitoring the presence of sleepiness on the job and its effects on performance is of primary importance for improving schedule systems of shiftworkers. Shiftworkers, often involved in night-time operations and irregular work schedules, frequently complain of nocturnal sleepiness especially in conditions of abrupt shift of the wake-sleep cycle. In this study, the authors evaluated the effects of a laboratory simulation of acute night-shift changes on sleepiness, vigilance and performance, using Maintenance of Wakefulness Test, Multiple Sleep Latency Test and three pencil and paper tests: Digit Symbol Substitution Test, 'Deux Barrages' Test and a 3-Letter Cancellation Task. All of the tests were administered four times at 2-hourly intervals during the night after daytime sleep. Results showed that the ability to maintain wakefulness and to perform simple visuo-attentive tasks is substantially spared during the night. On the other hand, sleep tendency and performance on a more complex and monotonous task (Letter Cancellation Task) reveal, respectively, increasing sleepiness and degrading performance.

The relationship between quantified EEG and skin conductance level

Electroencephalographic measures (EEG) and skin conductance level (SCL) respectively reflect cerebral cortical activity and sympathetic autonomic activity. Such central and autonomic activities associated with arousal generally have been studied separately, despite their potential to reflect complementary dimensions of reticular-thalamo-hypothalamo-cortical activating networks. In this study, we examined the relationship between cortical (19 EEG sites) and autonomic (SCL) activities recorded simultaneously in 10 normal adults. Two second pre-stimulus EEGs and SCLs were assessed from an habituation paradigm which presented 22 trains of 7 tones in an 'ignore' condition. The mean SCLs of the epochs across subjects showed an initial rise (sensitization) followed by an exponential decline (habituation). Although EEG associated with the tones did not demonstrate such a distinct profile, EEG total power and band powers (beta, alpha and theta) associated with the trains showed a systematic increasing response profile. In the group data the mean SCLs within trains showed a significant correlation with alpha and beta band powers. Finer EEG band analyses indicated that beta 3 at Fz and alpha 2 at Cz showed the strongest separate linear correlations with SCL. beta 3 and alpha 1 at Fz were found to jointly covary with SCL. The findings indicate a substantive relationship between measures of cerebral function and autonomic arousal.

EEG asymmetry and heart rate during experience of hypnotic analgesia in high and low hypnotizables

This study evaluates the effects of hypnotic analgesia and hypnosis on bilateral EEG activity recorded from frontal, central and posterior areas during three painful electrical stimulation conditions: waking, hypnosis/no-analgesia, hypnosis/analgesia. Eight high-hypnotizable and eight low-hypnotizable (right handed) subjects participated in the experiment. The following measures were obtained: pain and distress tolerance ratings; EEG spectral amplitudes for the frequency bands: delta (0.5-3.75 Hz), theta 1 (4-5.75 Hz), theta 2 (6-7.75 Hz), alpha 1 (8-9.75 Hz), alpha 2 (10-12.75 Hz), beta 1 (13-15.75 Hz), beta 2 (16-31.75 Hz), total band (0.5-31.75 Hz), '40-Hz' (36-44 Hz); cardiac interbeat interval (ms); mid-frequency and high-frequency peaks from power spectral analysis of heart period variability. During hypnosis/analgesia, high hypnotizable subjects displayed significant reductions in pain and distress scores compared to hypnosis/no-analgesia and waking conditions. In each experimental condition these subjects displayed significant lower total and beta 1 amplitudes compared to low hypnotizables. High hypnotizables, on central and posterior recording sites, during both hypnosis/analgesia and hypnosis/no-analgesia conditions also showed total and delta EEG amplitude reductions in both hemispheres and a theta 1 amplitude reduction in the left hemisphere. However, for total, delta and beta 1 bands in the hypnosis/analgesia condition the amplitude reduction was more pronounced in the right hemisphere as shown by hemispheric asymmetry in favor of the left hemisphere. Low hypnotizables, on posterior recording sites, displayed a delta amplitude reduction during hypnosis/no-analgesia and hypnosis/analgesia conditions. These subjects also showed, for all recording sites, a reduction in theta 1 amplitude during hypnosis/no-analgesia compared to the waking condition. Lows, however, failed in evidencing amplitude differences between hypnosis/no-analgesia and hypnosis/analgesia conditions. During hypnotic analgesia the hemispheric asymmetry found in high hypnotizables was parallel to a significant reduction in the spectral mid-frequency peak of heart period variability which indicated a decrease in the level of sympathetic activity. In contrast, during hypnosis/no-analgesia the EEG amplitude reduction was not paralleled by a decrease in sympathetic activity.

Work hours, sleepiness and the underlying mechanisms

Severe subjective and physiological sleepiness occur in night work, afflict almost all individuals and are associated with a performance impairment severe enough to explain night-work accident data. The alertness deficit is caused by the displacement of work to the circadian phase which is least conducive to alert behaviour, by extension of the time spent awake and by the reduction of sleep length (due to circadian interference with sleep). Sleepiness will be extreme when the three causes are operative simultaneously. The three factors may be used quantitatively to predict sleepiness.

Work hours and sleepiness

The present paper finds that shift work is associated with severe sleepiness on the night shift and to some extent on the morning shift. This sleepiness is at least as severe as that seen in hypersomnia and is associated with a strongly increased risk of accidents. The reason for night shift sleepiness is work at the circadian nadir, extended periods of wakefulness, and truncated sleep. Much of the sleepiness in shift work may be predicted using a quantitative model.

40-Hz EEG activity during hypnotic induction and hypnotic testing

The present study evaluates changes in left and right 40-Hz EEG production for 19 high and 20 low hypnotizable female Ss during the hypnotic induction and the administration of the Stanford Hypnotic Susceptibility Scale, Form C (SHSS:C) of the Weitzenhoffer and Hilgard (1962). Scalp recorded 40-Hz EEG density was obtained from the middle of the O1-P3-T5 and O2-P4-T6 triangles. As the hypnotic induction proceeded, high hypnotizable Ss exhibited a shift to greater right-hemisphere activity as compared to a waking-state rest condition. In contrast, low hypnotizable Ss, showed a reduction in left- and right-hemisphere activity. No differences between groups for SHSS:C ideomotor items were observed. A main effect for Hypnotizability among SHSS:C imaginative items was found. A Hypnotizability x Hemisphere x Trial interaction was found for both sensory distortion and imaginative SHSS:C items. A comparison was made between low versus high hypnotizable Ss of 40-Hz EEG activity while they passed the same item. The results of these comparisons indicate that differences in brain activity might be partially related to the differences between experiencing a hypnotic suggestion or failing to do so. Significant relationships between 40-Hz EEG production and hypnotizability and 40-Hz EEG production and level of amnesia were also found.

EEG correlates of emotional tasks related to attentional demands

This research brings together two separate areas: that of EEG processes associated with positive and negatively valenced emotional material; and that of traditional psychophysiological research related to the "intake" and "rejection" of environmental stimuli. Forty males on each of two days were presented with tasks reflecting both attentional demands and affectual processing. Heart rate and bilateral EEG measures from frontal, parietal and temporal sites were recorded. Using a FFT (fast Fourier transform) electrocortical activity in the 2-7 Hz, 8-15 Hz, and 16-24 Hz was determined and analyzed. The results suggest emotional valence (i.e. positive and negative) and attentional demands (i.e. intake vs rejection) are differentially represented in terms of EEG functioning. An interaction of attentional demand with hemisphere was found for EEG alpha activity in the temporal and parietal areas. For emotional valence there was a significant main effect for EEG beta activity in both the temporal and parietal areas. Differential hemispheric activity was found using a factor analytic technique (PARAFAC) with positively valenced tasks being associated with right temporal beta. Heart rate changes for the attentional dimension were consistent with previous research.

EEG theta waves and psychological phenomena: a review and analysis

In this paper, studies which have explored the relation between EEG theta waves and psychological phenomena in normal human subjects are reviewed. It is noted that increases in theta activity occur in conjunction with several kinds of psychological processes. The importance of ocnsidering properties of theta activity, such as amplitude, rhythmicity and scalp topography when analyzing the relation between theta and psychological processes is emphasized. Although there is some evidence for a relationship between theta and psychological processes, it is concluded that the degree to which properties of theta activity are systematically related to specific psychological processes is not yet known.

Alpha and theta EEG in vigilance

During a 1-hr. vigilance session Ss were required to detect specified digit triads in an uninterrupted random digit series. EEG was recorded continuously with sampled epochs analyzed by computer for autocorrelation and period analysis. Correlogram ratios indicated progressively decreasing arousal through the session but did not distinguish responses from detection failures. Incidence of alpha waves by period analysis also did not identify errors, but incidence of theta waves dropped significantly just prior to failures and did not do so around responses.