Low-frequency Alpha Research Articles

The effects of age and gender on sleep EEG power spectral density in the middle years of life (ages 20–60 years old)

The effects of age and gender on sleep EEG power spectral density were assessed in a group of 100 subjects aged 20 to 60 years. We propose a new statistical strategy (mixed-model using fixed-knot regression splines) to analyze quantitative EEG measures. The effect of gender varied according to frequency, but no interactions emerged between age and gender, suggesting that the aging process does not differentially influence men and women. Women had higher power density than men in delta, theta, low alpha, and high spindle frequency range. The effect of age varied according to frequency and across the night. The decrease in power with age was not restricted to slow-wave activity, but also included theta and sigma activity. With increasing age, the attenuation over the night in power density between 1.25 and 8.00 Hz diminished, and the rise in power between 12.25 and 14.00 Hz across the night decreased. Increasing age was associated with higher power in the beta range. These results suggest that increasing age may be related to an attenuation of homeostatic sleep pressure and to an increase in cortical activation during sleep.

EEG Responses to Low-Level Chemicals in Normals and Cacosmics

Recent studies from the University of Arizona indicate that normal subjects, both college students and the elderly, can register the presence of low-intensity odors in the electroencephalogram (EEG) in the absence of conscious awareness of the odors. The experimental paradigm involves subjects sniffing pairs of bottles, one containing an odorant (e.g. isoamyl acetate) dissolved in an odorless solvent (water or liquid silicone), the other containing just the solvent, while 19 channels of EEG are continuously recorded. For the low-intensity odor conditions, concentrations are adjusted downward (decreased) until subjects correctly identify the odor bottle at chance (50%). The order of odorants, concentrations, and hand holding the control bottle, are counterbalanced within and across subjects. Three previous experiments found that alpha activity (8-12 hz) decreased in midline and posterior regions when subjects sniffed the low-intensity odors. The most recent study suggests that decreased theta activity (4-8 hz) may reflect sensory registration and decreased alpha activity may reflect perceptual registration. In a just completed experiment involving college students who were selected based on combinations of high and low scores on a scale measuring cacosmia (chemical odor intolerance) and high and low scores on a scale measuring depression, cacosmic subjects (independent of depression) showed greater decreases in low-frequency alpha (8-10 hz) and greater increases in low-frequency beta (12-16 hz) to the solvent propylene glycol compared to an empty bottle. Topographic EEG mapping to low-intensity odorants may provide a useful tool for investigating possible increased sensitivity to specific chemicals in chemically sensitive individuals.

Alpha frequency in schizophrenia: an association with enlarged cerebral ventricles.

Low alpha frequency (less than 10.2 Hz) occurred more frequently in medication-free schizophrenic patients than in normal control subjects, as determined by quantitative EEG analysis. Furthermore, those patients with low alpha frequency had significantly larger lateral ventricles, as measured by CT scan, than did other schizophrenic patients (mean +/- SD ventricle-brain ratios = 9.8 +/- 1.9 versus 5.0 +/- 2.4; p less than 0.01). This finding suggests the existence of a relationship between cerebral structural pathology and the alpha rhythm that may be based on involvement of alpha-generating structures which border the cerebral ventricles. Future EEG studies of schizophrenia may resolve these questions in the context of other brain findings.

Low-temperature enhancement of the thermopower of La-Al, Ca-Al and Ca-Al-Ga glassy metal alloys

Enhancements of the low-temperature thermopower of several La-based and Ca-based glassy alloys are compared with the predictions for the electron-phonon enhancement. The agreement is reasonably good for the La-based alloys, but unexpected structure is observed for the Ca-based alloys. The measurements suggest that the low-frequency alpha 2( omega )F( omega ) is proportional to omega beta with beta >1 for these alloys.

The choice of feedback stimulus can determine the success of alpha feedback training.

ABSTRACTThe experimenter's choice of auditory feedback stimulus may determine the success of alpha feedback training, The stimulus medium of the feedback message may interfere with or enhance the person's ability to increase alpha activity. Forty undergraduates were randomly assigned to one of two feedback stimulus groups or one of two stimulus control groups. The two auditory stimuli used for feedback produced dramatically different effects on the spectral power in high and low frequency alpha during training, whereas the stimulus controls showed little change from eyes open baselines. The experiences associated with the auditory stimuli before training and the alpha levels for the pre and post stimulus baselines were significant predictors of alpha changes during training. These results suggest that the feedback stimulus may influence how alpha information is received and utilized by affecting arousal, attentional capacity, and control strategies, or may directly influence the generators of the alpha rhythm.

EEG correlates of sustained attention: Hemispheric and sex differences

Subjects were presented with sets of four digits, and had to respond only when all the digits in a set were odd. The EEG was measured from occipital-parietal derivations over the left and right hemispheres, and the energy within each of five frequency bands was integrated over 3-sec epochs corresponding to the presentation of individual sets of digits. The EEG abundance was found to be lower the more a digit set resembled a signal, but hemisphere differences in this effect tended to be small and to occur only in certain frequency bands. The effect for stimulus type changed over time in some frequency bands, but there were no differences between the hemispheres in this change. Nor were sex differences in lateralization found. Reaction time was found to correlate positively with (a) EEG abundance, and (b) EEG differentiation of stimuli, in the theta and low alpha frequency bands.

Wavelike Properties of the Alpha Rhythm

Apparent similarities between brain waves and physical waves are considered. The distribution of power in the alpha rhythm over frequency and spatial wavelength is measured in several subjects. This is accomplished by means of spatial-temporal Fourier analyses of scalp surface potentials using multichannel recordings from electrodes placed along the midline. It is found that the spectrum of midline alpha oscillations peaks for long wavelengths (?20 cm). A dispersion relation relating frequency to spatial wavelength apparently exists for frequencies near the peak alpha frequency. That is, in all 13 records, frequency components just above the peak alpha frequency have shorter midline wavelengths than low alpha frequency components. The relationship of these results to theoretical descriptions of the EEG and to other experiments is discussed.

Relationship between EEG, personality and vigilance

The dependence of alpha frequencies upon vigilance performance and upon the personality variables of rigidity, extraversion and neurotic tendency was investigated. The EEG was recorded from bipolar derivations F3-C3, P3-O1 and T5-O1 during various resting and task periods. The independent evaluation of records from the latter two positions and the correlation of these with other data gave the following results: 1. 1. Good vigilance correlates positively with low (8–9 c/sec) and negatively with high (12–13 c/sec) alpha frequencies during both task performance and the subsequent resting stage. 2. 2. Good vigilance correlates negatively with the alpha index in the subsequent resting period. 3. 3. Rigidity correlates positively with the error score in the vigilance task and negatively with the percentage of correct responses. 4. 4. Rigidity correlates negatively with low 5. (8–9 c/sec) and positively with high (12–13 c/sec) alpha frequencies. 6. 5. Neurotic tendency correlates positively with intermediate (19-11 c/sec) alpha frequencies during the vigilance task and with the alpha index during and after this task. 7. 6. Neurotic tendency, however, correlates negatively with the intermediate (10–11 c/sec) alpha frequencies during the resting period prior to the task. 8. 7. Poor performance (error score) on the arithmetic tasks correlates negatively with the alpha index during the resting stages. 9. 8. Poor performance (error score) on the arithmetic tasks correlates positively with the low (8–9 c/sec) alpha frequencies during the vigilance task. The results suggest that good vigilance is associated with the lower alpha frequencies and poor vigilance with the higher ones. Rigidity appears to be associated with high alpha frequencies and poor performance. When neurotic tendency is high, performance of the vigilance task causes an increase rather than a decrease in 10–11 c/sec waves.

Behavior of Noise Figure in Junction Transistors

It is well-known that generator resistance and dcemitter current are two major factors in determining the noise figure of junction transistors. Other important factors are base resistance, low-frequency alpha, and alpha cutoff frequency. A method of calculating the noise figure in terms of these parameters, the frequency variation of the noise figure, and the conditions for minimizing the noise figure are presented. The results provide means for specifying transistor and circuit parameters to meet noise requirements. In the absence of "excess" or 1/f noise, the noise figure as a function of frequency for the common base, common collector, and common emitter configurations is constant up to √1-a0 fa. Here a0 is the low-frequency alpha and fa the alpha cutoff frequency. Above this frequency the noise figure increases toward an asymptote of 6 decibels per octave. Calculations show that for minimum noise figure the base resistance and emitter current should be small, a0 should be close to one, fa should be large, and the driving source resistance has an optimum value. This work is based on a simplified version of a transistor noise equivalent circuit developed by van der Ziel.

The electroencephalogram in manic-depressive psychosis.

The main object of this investigation is to verify the claim of Pauline Davis (1941) that manic-depressive depressed psychotics (M.D.D.s) tend to possess frequencies of alpha rhythm in the E.E.G. at 10 c./sec. or slower, whilst manic-depressive manic patients (M.D.M.s) tend to show alpha frequencies at 10 c./sec. or faster; furthermore that there is no shift in alpha frequency corresponding to change in psychotic phase or in degree of phase. These claims are of importance in relation to a recent paper by Mundy-Castle (1951b) in which a significant correlation was reported between ratings of the Heymans-Wiersma temperament variable secondary function and mean frequencies of alpha rhythm in normal adults, since both Heymans (1929) and Wiersma (1932) maintained that M.D.D.s possessed a high degree of secondary function and M.D.M.s a low degree of this variable. To explain this in more detail, secondary function is postulated as being present in individuals in different degrees varying over a continuous scale ranging from domination of the conscious field by secondary function to domination by primary experience (relative lack of secondary function). Individuals displaying the former may be referred to as secondary functioning, their behaviour being characterized by steadiness of action, continuity of interest, evenness of mood and psychic tempo, reduced stimulability and a tendency for mental events to perseverate. Individuals in whom secondary function is relatively lacking (it can never be wholly absent) may be termed primary functioning, their behaviour being characterized by impulsiveness, mobility, high stimulability and a quick and variable psychic tempo. The Heymans-Wiersma temperament scheme has been developed extensively by Biesheuvel (1935, 1949). Mundy-Castle's study revealed that subjects rated as secondary functioning possessed low alpha frequencies whilst those rated as primary functioning possessed high alpha frequencies. The present investigation should help to elucidate the view of Heymans and Wiersma concerning secondary function and manic-depressive psychosis.