Biomedical subjects

M A Guevara

Publications and source records attributed to M A Guevara.

At least 19 recordsLinked to original sources

PubMed1998

Effect of diazepam and sex hormones on EEG of gonadectomized male and female rats.

Waking EEG was recorded from left and right parietals in 60 adult Wistar rats gonadectomized after puberty during 5 days, 1 as baseline, 1 with vehicle and 1 with 10 mg/kg i.m. of diazepam with hormonal treatment (either testosterone propionate, 5-alpha-dihydrotestosterone or vehicle in males and progesterone, estradiol benzoate or vehicle in females). Quantitative EEG analysis showed that: diazepam in gonadectomized males increased absolute power of alpha, beta 1 and beta 2, increased interparietal correlation of delta and decreased interparietal correlation of slow theta, fast theta and beta 1, whereas in gonadectomized females, diazepam additionally decreased slow and fast theta absolute power. EEG effects were not modified by testosterone propionate or 5-alpha-dihydrotestosterone treatment in males. Diazepam plus estradiol rendered the female EEG response similar to the gonadectomized or testosterone-treated males response; diazepam plus progesterone induced the same response in females as in gonadectomized females and additionally induced interparietal asymmetry and decreased interparietal correlation of all EEG bands. Present results and information on the effects of diazepam on interparietal coupling of EEG and demonstrate that the EEG response to diazepam in adult rats is sexually dimorphic and depends on sex as well as on activational effects of gonadal steroids.

Animals↗

PubMed1998

Characteristic frequency bands of the cortico-frontal EEG during the sexual interaction of the male rat as a result of factorial analysis.

The electrocorticogram (ECoG) from the prefrontal cortex was simultaneously recorded with the accelerometric signals of pelvic thrusting performed by male rats during sexual behavior. The changes in the prefrontal ECoG were precisely correlated in time with well defined elements of male rat copulation. Principal component analysis allowed to identify three distinct bands of frequencies in the frontal ECoG: the absolute power (AP) of the 4-16 Hz band was increased in the 500-ms periods before, during, and after the execution of pelvic thrusting in mount, intromission and ejaculation responses; the AP of the 18-24 Hz band was selectively increased during the execution of pelvic thrusting at the three copulatory responses, whereas the AP of the 26-32 Hz band was increased only during the pelvic moments of mount and intromission responses. These results show that the electroencephalographic activity of the prefrontal cortex of the male rat is related to the performance of sexual behavior, supporting the concept that this cortical area is involved in the organization of sequential behaviors, as sexual behavior.

Animals↗

PubMed1997

Stability of EEG inter- and intrahemispheric correlation in women.

EEG correlation and coherence analyses have been used to study functional relationships between cortical regions, and found to vary as a function of physiological conditions, sex hormones and cognitive processes. However, the utility of serial EEG studies is dependent upon the within-subject reliability of repeated EEG recordings. The present study was undertaken to assess the within-subject and within-group stability of EEG correlations in a group of young women (n = 9). EEG was recorded during relaxed wakefulness at F3, F4, C3, C4, P3, P4, O1 and O2 for 11 sessions, during 1 month. Ten artifact free 2-s epochs of EEG from each session were digitally filtered by means of a fast Fourier transform into 6 broad bands, and correlation coefficients between the EEG activity of every pair of derivations and bands were calculated in the time domain. All EEG features were submitted to principal component analysis and the first 5 components did not show significant differences between sessions (ANOVAs) for any band or pair of derivations. Alpha and beta showed higher variability whereas slow bands showed very little variability. The within-subject stability was assessed calculating multiple correlation coefficients between all EEG features of the eleven sessions of each subject: R-values ranged from 0.85 to 0.97. Present results indicate that the pattern of functional relationships between cortical regions during resting wakefulness is a stable characteristic for each woman at least over a 1 month period and that there are no significant group differences over sessions when menstrual phases are randomly distributed between women.

Adult↗

PubMed1997

Effect of spatial ability and sex on 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.

Adolescent↗

PubMed1997

Subcortical multiple unit activity changes during rat male sexual behavior.

Multiple unit activity (MUA) was recorded from the ventral tegmental area (VTA) and mesencephalic locomotor region (MLR) during copulatory behavior of freely moving male rats. Simultaneous accelerometric recordings of the copulatory pelvic thrusting performed by the male rat were taken to precisely correlate in time the changes in MUA with well defined elements of copulation. The baseline MUA firing rates recorded in the quiet-alert condition in the VTA and in the MLR were significantly increased during pursuit of the female by the male; significantly higher MUA firing rates were found in the VTA at the 500 ms periods before and during the execution of pelvic thrusting in mount, intromission, and ejaculation responses as compared to the baseline, and returned to this value when these responses ended. The maximum MUA firing rate in the MLR was obtained during the execution of pelvic thrusting in each copulatory response, and it remained significantly elevated, as compared to the baseline, after thrusting and at the postintromission and postejaculatory genital grooming, then decreasing to basal values at the initial part of the postejaculatory interval. The fact that the highest changes in MUA were related to pelvic thrusting suggests a major participation of both structures in the execution of motor copulatory responses.

Animals↗

PubMed1997

Computer programs to analyze brain electrical activity during copulatory pelvic thrusting in male rats.

Two microcomputer programs have been developed to simultaneously record and analyze the brain electrical activity: multiple unit activity (MUA) and electroencephalogram (EEG), and the accelerometric signals generated in relation to the pelvic thrusting that performs the male rat during the copulatory responses of mount, intromission, and ejaculation. CAPTUMUL is a program allowing the on line capture of the different signals and the further off line delimitation of the brain signals occurring in exact temporal relation with the accelerometric record of motor responses. The ANAMUA program allows the off line analysis of the neuronal firing rate in MUA records at different discrimination levels according to the amplitude of the neuronal spikes, and compare these data in various behavioral situations. The use of these programs provides a way of correlating in time the changes of brain electrical activity occurring in animals in free-movement with the brief motor events of copulation as well as with other behaviors (i.e., genital grooming, sniffing, running, walking). Advantages of this software include the recording of sequential events, a better and rapid handling of data and a reliable method to analyze the MUA with different discrimination levels according to the amplitude of the neuronal spikes.

Animals↗

PubMed1996

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.

Adult↗

PubMed1996

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.

Algorithms↗

PubMed1996

Time course of reaction time and EEG while performing a vigilance task during total sleep deprivation.

Nine young adult male (23-30 years old) paid volunteers were subjected to total sleep deprivation (TSD), after two consecutive nights in the laboratory, for 40 hours (from 0800 hours on the first day to 2400 hours on the following day). Oral temperature (OT), reaction time (RT) in a visual vigilance task, and electroencephalogram (EEG; C3, C4, T3, and T4) while performing the task were recorded every 2 hours during TSD and after recovery sleep. One second of EEG, before target and non-target stimuli for every subject and condition was visually inspected, and artifact-free epochs were Fourier transformed. Absolute power (AP) was calculated for 4-20 Hz (full band) and for theta, alpha 1, alpha 2, and beta 1. Analyses of variance (ANOVAs), with TSD and time-of-day as factors, showed the following significant results. TSD induced an increase in RT and AP of the full band at C3 and C4, of all bands at C3, of theta at T3, and of beta 1 at T4 (p < 0.009 for all comparisons). No time-of-day effects nor interactions were found. OT was not affected by TSD. All variables returned to baseline values after recovery sleep. RT and EEG power showed a linear increase with accumulating hours of wakefulness. The increment in RT also correlated with the increase in EEG power. The results demonstrate that the increment in RT is associated with the increase in AP, particularly in the left central cortex; that the EEG may be used to identify sleepiness; and that EEG during task performance is more sensitive to TSD than during relaxed wakefulness.

Adult↗

PubMed1995

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.

Adolescent↗

PubMed1995

Inter- and intrahemispheric EEG correlation during sleep and wakefulness.

Inter- (INTERr) and intrahemispheric (INTRAr) electroencephalographic (EEG) correlations were assessed in eight young male adults during wakefulness with eyes closed before going to sleep, and during stage 2, stage 4 and paradoxical sleep (PS) on the second night spent at the laboratory. Pearson product-moment correlations were calculated between EEG signals of every pair of electrodes (C3, C4, F3, F4, T3, T4) for six bands and for every 0.5 Hz from 1.5 to 15 Hz. Previous results of higher INTERr during sleep compared to during wakefulness were confirmed for the delta and theta bands during stage 2 sleep and PS and for sleep spindles during stage 2 sleep. The present results extend these findings to INTERr between F3 and F4 and during stage 4 sleep. INTRAr of 1.5-6.5 and 11-15 Hz was significantly higher during stages 2 and 4, whereas during PS INTRAr did not change. 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 sleep, whereas during PS only inter-hemispheric differentiation is attenuated but intrahemispheric differentiation maintains similar levels of wakefulness. The attenuation of cortical differentiation may be of relevance for the understanding of mental activity changes during sleep.

Adult↗

PubMed1995

EEG interhemispheric correlation after callosotomy: one case study.

High interhemispheric EEG correlation (INTERr) or coherence has been interpreted as a consequence of callosal interconnections. The EEG of a callosotomized (two anterior thirds) 32-yr.-old patient was recorded during relaxed wakefulness with eyes closed. 100 2-sec. artifact-free epochs were digitally filtered into traditional broad bands and INTERr was calculated by means of Pearson product-moment coefficients. INTERr between anterior regions, where they should be expected, showed very few differences between data of this patient and those of two control groups of healthy persons. Only a few differences were observed between posterior regions where the callosum was intact. These results suggest that the role of the callosum is not crucial for INTERr and that subcortical influences and functional differentiation between hemispheres may be more plausible explanations for INTERr.

Adult↗

PubMed1995

Effect of total sleep deprivation on reaction time and waking EEG activity in man.

Nine paid volunteers were sleep deprived over a period of 40 hours. Every 2 hours during total sleep deprivation (TSD) and after recovery sleep, oral temperature (OT), reaction time (RT) in a vigilance task and electroencephalogram (EEG) with eyes open and closed (C3, C4, T3 and T4) were recorded. Ten artifact-free samples from each condition were Fourier transformed. Absolute power was calculated for six bands. Analyses of variance with deprivation and time of day as factors showed the following significant results: 1) TSD induced an increase in RT, of theta power in all derivations, of beta power in both centrals and a decrease of alpha power with eyes closed; OT was not affected. 2) All bands showed a peak of power at 1800 hours, 2 hours in advance of the OT acrophase at 2000 hours. All variables recovered baseline values after 1 night of sleep. Significant linear correlations of hours of wakefulness with EEG and RT, and of EEG power with OT and RT, were observed. The present findings show a linear increase in EEG power and RT with TSD, and a diurnal oscillation of EEG power, which is independent of TSD.

Adult↗

PubMed1994

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.

Adult↗

PubMed1994

Effects of intrathecal administration of adrenergic agonists on the frequency of copulatory pelvic thrusting of the male rat.

The effects of the intrathecal perispinal administration of adrenergic agonists on the characteristics of frequency, duration, and vigor of pelvic thrusting displayed by male rats during copulation was assessed by an accelerometric technique. A different dose of one drug (noradrenaline, clonidine or isoproterenol) and saline as control was administered at the lumbosacral level of the spinal cord to sexually active male rats in tests of sexual behavior performed at weekly intervals. The intrathecal administration of noradrenaline (alpha-adrenoceptor agonist) increased the frequency of pelvic thrusting in mount and intromission responses, whereas both the alpha 2-adrenoceptor agonist clonidine (25 micrograms) and the beta-adrenoceptor agonist isoproterenol (40 micrograms) reduced the frequency of pelvic thrusting in these responses as compared to values obtained under the intrathecal administration of saline. On the other hand, the duration of the thrusting trains and the potency or vigor of pelvic thrusting in mounts and intromissions did not differ from values obtained under saline treatment. These findings indicate a possible participation of noradrenaline in the modulation of the spinal mechanisms involved in the generation of rhythmic pelvic thrusting performed by the male rat during copulation.

Adrenergic Agonists↗

PubMed1993

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.

Adolescent↗

PubMed1992

Changes in the waking EEG as a consequence of sleep and sleep deprivation.

Electroencephalographic (EEG) activity was monopolarly recorded during resting wakefulness in 10 volunteers under the following conditions: at night before going to sleep, at night before total sleep deprivation, in the morning after waking, in the morning after sleep deprivation and at night after having slept during the day. Absolute and relative power and inter- and intrahemispheric correlation were established. After diurnal and nocturnal sleep as compared to sleep deprivation, we obtained the following significant results: interhemispheric correlations were higher; intrahemispheric correlations were lower; absolute power of alpha 2, beta 1 and beta 2 was lower; and relative power of alpha 2 and beta 2 was lower. EEG changes as a consequence of sleep or lack of sleep are dependent on prior sleep and/or wakefulness and not on circadian phase. EEG activity during wakefulness is a sensitive parameter and a useful tool to assess the consequences of sleep on brain functional organization.

Adult↗

PubMed1990

The late event related potentials CNV and PINV in normal and dyslexic subjects.

The most prominent ERP to occur during intervals of preparation and anticipation is the contingent negative variation (CNV) or expectancy wave. The resolution of this wave is called the postimperative negative variation (PINV). The purpose of this study was to distinguish the characteristics of the CNV and the PINV in a group of children with reading disabilities or dyslexia and to compare them from a group of normal readers. Nine righthanded boys aged between 10-13 years with reading disabilities were studied. The children were matched with a group of nine normal readers. Four derivations were used: frontal, central, parietal and occipital zones, with reference to linked ears. Data were analyzed using multivariate procedures. Significant differences between groups in CNV amplitude and in PINV amplitude and latency at the left parietal site were observed. We discuss the participation of this zone and we consider processes like expectancy, attention and brain activity signal processing in the differences mentioned.

Adolescent↗