Miguel Angel Guevara

EEG coherence or EEG correlation

In view of the widespread use of electroencephalographic correlation (r) and coherence (Coh) analyses in studying brain functional relationships, it seems important to illustrate results yielded by both methods. Although they are considered as equivalent, they show important differences. Results obtained from r and Coh were compared using: (a) 2 Hz sinusoidal signals, where phase and amplitude were artificially manipulated and, (b) Coh and r spectra obtained between each pair of derivations (C3, C4, F3, F4, T3 and T4) from wakefulness, stage 2, stage 4 and paradoxical sleep (n = 8). The following results were obtained: significant Pearson product-moment coefficients were obtained between r and Coh spectra in the range of 0.86 to 0.96 for interhemispheric and 0.60 to 0.90, for intrahemispheric paris; as a result of principal component analyses, the same three frequency bands were formed for r and Coh spectra with the exception of one single bin; similar results for r and Coh were obtained by two-way ANOVAs (physiological stages by derivations). In conclusion, as expected, a high degree of comparability between r and Coh was observed under normal physiological conditions and with the use of good quality recordings.

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.

Increase of the hippocampal theta activity in the Morris water maze reflects learning rather than motor activity

The change in the percentage of rat hippocampal high-frequency theta activity from being immobile and awake to swimming behaviour was calculated for three groups of rats, trained in either place learning, cue learning or egocentric learning in the Morris water maze. The place-learning-trained rats showed an increase in the percentage of theta activity, along with a significant reduction in escape latency over the last 3 days of training. No changes were observed in the other two groups. Because the motor activity displayed by the three groups of rats was similar, we suggest that the increase in the percentage of theta activity concomitant with place-learning training could be related to the processing of information by the hippocampus, rather than to the displayed motor activity.

Rapid eye movement sleep dreaming is characterized by uncoupled EEG activity between frontal and perceptual cortical regions

EEG coherent activity is involved in the binding of spatially separated but temporally correlated stimuli into whole events. Cognitive features of rapid eye movement sleep (REM) dreaming resemble frontal lobe dysfunction. Therefore, temporal coupling of EEG activity between frontal and perceptual regions was analyzed from 10 min prior to dream reports (8 adults) from stage-2 and REM sleep. EEG correlation between frontal and perceptual regions decreased and, among perceptual regions increased during REM. The temporal dissociation of EEG activity between executive and perceptual regions supplies an inadequate mechanism for the binding and interpretation of ongoing perceptual activity resulting in dream bizarreness.

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.

POTENCOR: a program to calculate power and correlation spectra of EEG signals.

This work describes a computer program (POTENCOR) that applying the Fast Fourier Transform and Pearson product-moment correlation, can calculate easily, fast and accurately the absolute and relative power as well as the inter- and intrahemispheric correlation between every pair of EEG signals for narrow bands and for broad bands. POTENCOR has three main advantages: (1) it allows calculation of inter- and intrahemispheric correlation spectra, for which to our knowledge, there is no commercial program available; (2) the absolute and relative power values are not affected by the number of points that constitutes the signal segment; and (3) in case of making the analysis by each segment the temporal evolution for each EEG parameter can be graphically represented. The utility and flexibility of this program has been confirmed in many clinical and experimental researches.

Differential alpha coherence hemispheric patterns in men and women during pleasant and unpleasant musical emotions

Potential sex differences in EEG coherent activity during pleasant and unpleasant musical emotions were investigated. Musical excerpts by Mahler, Bach, and Prodromidès were played to seven men and seven women and their subjective emotions were evaluated in relation to alpha band intracortical coherence. Different brain links in specific frequencies were associated to pleasant and unpleasant emotions. Pleasant emotions (Mahler, Bach) increased upper alpha couplings linking left anterior and posterior regions. Unpleasant emotions (Prodromidès) were sustained by posterior midline coherence exclusively in the right hemisphere in men and bilateral in women. Combined music induced bilateral oscillations among posterior sensory and predominantly left association areas in women. Consistent with their greater positive attributions to music, the coherent network is larger in women, both for musical emotion and for unspecific musical effects. Musical emotion entails specific coupling among cortical regions and involves coherent upper alpha activity between posterior association areas and frontal regions probably mediating emotional and perceptual integration. Linked regions by combined music suggest more working memory contribution in women and attention in men.

Different functionality of the medial and orbital prefrontal cortex during a sexually motivated task in rats

This study was designed to analyze whether the electroencephalographic (EEG) activity of the medial (mPFC) and orbital prefrontal cortex (oPFC) was modified during the performance of male rats in a T maze under two different conditions, sexually motivated (with previous intromission and females in the goal boxes of the lateral arms) or sexually non-motivated (without previous intromission and with empty goal boxes). Relative power (RP) of three EEG band frequencies, and inter-hemispheric correlation (r) were calculated and a comparison was made between rats under motivated and non-motivated conditions. In the mPFC of sexually motivated males, an increase of the RP in the 6-7 Hz band as well as a decrease in the 8-11 Hz band was observed in relation to an awake-quiet state and during the walk in the maze stem. Similarly, an increase in the r of the 6-7 Hz band was observed during the walk in the maze stem and when remaining near to a receptive female, when compared to non-motivated males. In the oPFC, only the RP of the 6-7 Hz band was increased during the walk in the maze stem of the motivated males. These data suggest that, among sexually motivated males, the mPFC is involved both in anticipatory and motor execution during the performance of the T maze task, whereas the oPFC is only involved in the motor execution of the T maze. These results are in line with other studies suggesting that the mPFC and oPFC are functionally distinct, regions which may work together during certain behaviors and physiological conditions.

Electrical activity of prefrontal cortex and ventral tegmental area during rat maternal behavior.

Maternal behavior is a motivated behavior that includes pup-directed sequential motor acts. The dopaminergic (DAergic) brain systems have been proposed to play an important role in voluntary maternal acts, however, not much is known about the way these systems function during the performance of this behavior. The electroencephalogram (EEG) is a sensitive tool that allows determination of the simultaneous functioning of different structures in relation to specific cognitive processes or motor acts. The present study recorded the function of the two structures that constitute the mesoprefrontal DAergic system, ventral tegmental area (VTA) and prefrontal cortex (PFC) by EEG during the performance of various maternal behaviors. Bilateral EEG from the VTA and medial PFC (mPFC) was simultaneously recorded during typical maternal acts and was compared to that recorded during non-maternal behaviors in freely moving female rats. Three different frequency bands (6-7, 8-11, and 12-21 Hz) were obtained from principal component analysis applied to the EEG for both structures. In the left and right mPFC and VTA, absolute power (AP) of the 8-11 Hz band showed a significant increase during pup retrieval compared to the EEG during walking. In the left and right mPFC and VTA, AP of the three bands showed a significant increase during pup licking with respect to forepaw licking. No differences in the EEG were found during inactive nursing behaviors compared to the awake quiet condition. The mPFC and VTA presented characteristic EEG patterns during active maternal behaviors but not during inactive maternal behaviors. This provides electrical evidence of the involvement of these structures in the performance of maternal behavior.

Brain activity and temporal coupling related to eye movements during REM sleep : EEG and MEG results

EEG and MEG REM sleep gamma activity was studied immediately before rapid eye movement onset (PRE-EM), during REM sleep with eye movements away from eye movement onset -phasic-REM (Ph-REM)--and during REM sleep without eye movements, or tonic REM (T-REM). For this purpose, activity was segmented into three different time windows: of 62.5, 250 and 500 ms. Two strategies were used: one a statistical comparison of changes between T-REM, Ph-REM and PRE-EM; the other a descriptive approach using principal component analysis. Significant findings showed that both EEG and MEG gamma activity are higher directly before eye movement onset in PRE-EM periods and during Ph-REM than during T-REM; temporal coupling of electrical activity between the frontal and parietal regions is decreased, while temporal coupling between the right frontal and midline is increased. Just before eye movement onset, larger recording sites become related. For the first time, results showed a close temporal link between power and temporal coupling of fast oscillations andrapid eye movements in REM sleep, indicating increased activation, uncoupling between the left frontal executive areas and posterior sensory association regions and increased coupling between the right frontal attentional and midline alerting systems. Brain activity is reorganized by phasic events.