Consuelo Arce

EEG Bands During Wakefulness, Slow-Wave, and Paradoxical Sleep As a Result of Principal Component Analysis in the Rat

Rat EEG has been empirically divided in bands that frequently do not correspond with EEG generators nor with the functional meaning of EEG rhythms. Power spectra from wakefulness (W), slow-wave sleep (SWS), and paradoxical sleep (PS) of Wistar rats were submitted to Principal Component Analyses (PCA) to investigate which frequencies are covariant. Three independent eigenvectors were identified for SWS: a band between 1-6, an intermediate band between 7-15, and a fast band between 16-32 Hz (90.74% of the variance); two independent eigenvectors were extracted for PS: slow frequencies between 1-6 covarying together with frequencies between 11-16 Hz, and activity between 6-10 covarying together with fast frequencies between 17-32 Hz (80.38% of the variance); four eigen-vectors were obtained for W: 3-7, 8-9, 10-21 and 21-32 Hz (81.47% of the variance). Vigilance states showed significant differences in AP from 1 to 22 Hz. PCA extracted broad bands different for each vigilance state, which included the most representative EEG activities characteristic of them. These results indicate that during SWS, slow oscillations include frequencies up to 6 Hz, and spindle oscillations frequencies down to 7 Hz. No alpha frequencies were identified as an independent band. Frequencies within theta and beta were gathered in the same eigenvector during PS and in different eigenvectors during W suggesting coordinated activation of hippocampal and cortical systems during PS. These bands are consistent with the underlying neurophysiological mechanisms of sleep and wakefulness and with firing frequencies of generators of rhythmic activity obtained in cellular studies in animals.

EEG oscillations during menstrual cycle.

12 sessions of EEG activity, one every second day, were recorded at F3, F4, C3, C4, P3, P4, O1 and O2 in 9 women with regular menstrual cycles. The following significant oscillations were observed: 1) absolute power was lower during periovulatory period; 2) absolute power of delta theta and alpha 1 was higher during premenstrual period whereas absolute power of alpha 2, beta 1 and beta 2 was higher during menstruation; 3) relative power of low alpha frequencies was lower and that of high frequencies was higher during premenstrual period; 4) interhemispheric correlation between frontals was higher during ovulation and between occipitals was higher during premenstrual phase; 5) no significant power asymmetries were observed. The present findings suggest higher activation of centro-parietal regions during menstruation and lower activation of frontal regions during premenstrual phase.

GENDER DIFFERENCES IN THE EEG DURING COGNITIVE ACTIVITY

EEG activity of 16 adult volunteers. 8 male and 8 females was monopolarly recorded at P3 and P4 at rest and during solution of three series of tasks: one analytic, one spatial and one mixed demanding both kinds of processing. The following main effects were observed: Men showed significantly higher beta relative power than women, while women showed significantly higher alpha relative power than men during all conditions. Alpha relative power decreased, while theta relative power increased during tasks solution in both sexes. Beta relative power was significantly higher at the left parietal only in men. Interparietal correlation was significantly higher in women than in men during all conditions and bands. For the theta band it increased from baseline values during tasks solution in men, while in women it decreased during the analytic task.

Within-subject reliability and inter-session stability of EEG power and coherent activity in women evaluated monthly over nine months

OBJECTIVE Quantitative EEG parameters during resting conditions are used as baseline in research on cognition and in serial-EEG recordings. Despite its increasing use in cognitive research and the numerous evidences of the existence of sex differences in EEG, EEG stability has been mainly investigated in men. Particularly, studies on stability of coherent activity are scarce. The aim of this study was to investigate within-subject reliability and inter-session stability of resting EEG over a nine-month period in women. METHODS Within-subject reliability and inter-session stability were analyzed for absolute power and inter- and intrahemispheric coherent activity at central and posterior regions, once a month, in resting conditions, with eyes open and closed. RESULTS Within-subject reliability was very high (r>0.89) for all subjects and EEG parameters. Inter-session stability was higher with eyes closed and for interhemispheric coherent activity, and poorer with eyes open especially in the alpha band. CONCLUSIONS Present results indicate high reliability of the pattern of power and coherent activity of each individual woman during rest, and group stability of EEG activity with eyes closed at least over a nine-month period. SIGNIFICANCE These results provide information on EEG stability in women over a long period.

Effect of spatial ability and sex inter- and intrahemispheric correlation of EEG activity

Inter- and intrahemispheric correlation of the EEG activity at rest was computed in two groups of men and women, between 17 and 21 years old, with extreme degrees of spatial ability (SA) evaluated by the Spatial Relations Subtest of the Differential Aptitudes Test (DAT). Interhemispheric (INTERr) and intrahemispheric (INTRAr) EEG correlations were computed by means of Pearson product-moment coefficients for 5 EEG bands after digitally filtering with an FFT. Women showed significantly higher INTERr of alpha 1 between left and right centrals, lower INTRAr between right frontal and right central regions and lower INTRAr within the left than in the right hemisphere. High SA subjects showed lower INTERr between left and right frontal derivations and higher INTRAr between frontal and parietal and between central and parietal regions of both hemispheres. Sex interacted with SA in INTRAr of alpha between right frontal and right temporal regions with high SA women showing lower INTRAr than low SA women and than men. The present results indicate a different inter- and intrahemispheric functional organization in men and women and in subjects with high and low spatial ability.

Eeg Activity During Cognitive Performance in Women

EEG activity of 20 female volunteers was monopolarly recorded at P3, P4, C3 and C4 during four resting periods and three series of cognitive tasks: one analytic, one spatial and one demanding analytical and spatial processing or mixed task. Relative power and inter and intrahemispheric correlations were analysed. Beta relative power was significantly higher during the resting periods at the right parietal and the same pattern of asymmetry was maintained during the three series of tasks. Alpha relative power decreased and theta increased during the three series of tasks regardless of their cognitive nature as compared to baseline. Interhemispheric correlation for theta frequencies, and intrahemispheric correlation for the full band were significantly different during task solution. There were no significant differences between left and right intrahemispheric correlations.

Inter and intrahemispheric EEG correlation as a function of sleep cycles

1. Inter (INTERr) and intrahemispheric (INTRAr) EEG correlation were assessed in 8 young male adults during wakefulness (W) with eyes closed before going to sleep, and during stage 2 (S2), stage 4 (S4) and paradoxical sleep (PS) of the first three sleep cycles during the second night spent at the laboratory. 2. Pearson product-moment correlation were calculated between EEG signals of each pair of electrodes (C3, C4, F3, F4, T3, T4) for every 0.5 Hz from 1.5 to 15 Hz. 3. INTERr and INTRAr of 1.5-6.5 and 11-15 Hz were significantly higher during stage 2 and 4; INTERr of 1.5-6.5 Hz was also higher during PS in cycle 1 and 2, whereas INTERr and INTRAr of 7-10.5 Hz were lower than during wakefulness. 4. INTRAr of S2 and S4 approximated, whereas INTRAr oF PS moved away from W over successive sleep cycles. 5. These data show that cortical changes during sleep are also observed in functional differentiation between cortical sites. Inter and intrahemispheric differentiation is attenuated during stage 2 and 4 while during PS only interhemispheric differentiation is attenuated but intrahemispheric differentiation is accentuated compared to wakefulness. This pattern of cortical differentiation may be of relevance for the understanding of mental activity changes during sleep.

Effect of spatial ability and sex on EEG power in high school students

Performance at eight cognitive tests and EEG spectral power at rest was computed in 2 groups of men and women, between 17 and 21 years of age, with extreme degrees of spatial ability (SA) evaluated by the spatial relations subtest of the DAT: a low spatial ability group (10 men, 10 women) with scores below percentile 30 and a high spatial ability group (10 men, 10 women) with scores above percentile 80. Ten EEG artifact free samples, 4.096 sec each, were analyzed and absolute (AP) and relative power (RP) were obtained for 5 frequency bands using an FFT. EEG was submitted to principal component analysis and two way ANOVAs. High SA showed lower AP in the entire spectrum with eyes open and closed, and lower alpha 1 RP with eyes open than low SA group regardless of sex. The difference between low and high SA was better explained by high alpha AP at all derivations and high theta AP at right derivations and at left central and occipital regions. Women showed higher beta 1 and beta 2 AP at all derivations except at temporal regions than men regardless of SA scores.