Julieta Ramos-Loyo

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.

Event-related potentials and event-related oscillations during identity and facial emotional processing in schizophrenia.

Impairments in emotional recognition have been consistently reported in schizophrenic patients. The main aim of the present study was to evaluate time-sequenced responses in ERPs and event-related oscillations during emotional recognition of happiness and fear compared to facial identity recognition in schizophrenic patients (SCH) versus healthy controls (CON). Ten paranoid SCH and ten CON subjects performed three oddball paradigm tasks, evaluating face identity recognition and facial emotional recognition of happiness and fear. Event-related potentials and event-related theta and alpha oscillations were obtained for each task. N170 and P2 components appeared with higher amplitude in SCH than in CON at the occipital locations. An early prefrontally distributed P3a component was observed while doing the identity task with lower amplitude in SCH than in CON. Comparatively, P3b amplitude was lower in SCH than in CON over parietal leads in the identity and happiness tasks. Additionally, theta oscillations showed significantly lower RMS values in SCH between 250 and 500 ms post-stimuli in frontal and central regions. On the other hand, the grand-averaged alpha oscillations demonstrated higher RMS values in the occipital leads in SCH compared to CON and the opposite over the frontal regions. Results are interpreted in the framework of a functional disruption in the distributed neuronal networks involved both in facial identity and emotional recognition in schizophrenics as indexed by the brain oscillatory activity and related ERP components.

Sex differences in lipid peroxidation and fatty acid levels in recent onset schizophrenia

Sex differences in the symptomatology and course of illness have been reported among schizophrenic patients. Hence, the principal objective of the present study was to investigate sex differences in the concentrations of the lipid peroxidation metabolites MDA and 4-HNE, and in the membrane phospholipid levels of ARA, EPA and DHA in patients with schizophrenia. A total of 46 paranoid schizophrenics (25 women) with short-term evolution who were in an acute psychotic stage and 40 healthy controls (23 women) participated in the study. Psychopathology was evaluated by BPRS and PANSS. Lipid peroxidation sub-products (MDA, 4-HNE) and fatty acid levels (ARA, EPA, DHA) were determined in erythrocyte membranes. The men in both groups showed higher lipid peroxidation levels and those values were higher in schizophrenic patients than controls, with only EPA fatty acid concentrations found to be lower in the former than the latter. These results suggest that men may suffer greater oxidative neuronal damage than women, and that this could worsen the course of illness and result in greater disease severity.

Effects of musical tempi on visual attention ERPs.

The purpose of this work was to examine whether fast and slow musical tempi have different effects on selective attention evaluated through ERPs and task performance. A high demanding visual selective attention task was performed by the subjects: without music (BL) and with Bachs music in slow (ST) and fast tempi (FT). Difference waves were obtained substracting non-target from target. FT caused a reduction in reaction time and N2d and P3d latencies and in P3d amplitude. N2d latency was longer in ST than BL and FT. Music played in FT induced a faster stimuli evaluation and response than ST.

Emotional content of stimuli improves visuospatial working memory.

Processing and storage in visuospatial working memory (VSWM) seem to depend on attention-based mechanisms. In order to explore the effect of attention-attractive stimuli, such as emotional faces on VSWM performance, ERPs were obtained from 20 young adults while reproducing spatial sequences of six facial (happy and neutral) and non-facial control stimuli in inverse order. Behavioral performances revealed that trials with happy facial expressions resulted in a significantly higher amount of correct responses. For positive emotional facial stimuli, N170 amplitude was higher over right temporo-parietal regions, while P2 amplitude was higher over frontal and lower over parietal regions. In addition, LPP amplitude was also significantly higher for this type of stimuli. Both behavioral and electrophysiological results support the notion of the domain-general attention-based mechanism of VSWM maintenance, in which spatial to-be-remembered locations might be influenced by the emotional content of the stimuli.

Acute effect of callosotomy on cortical temporal coupling in humans: intraoperative electrocorticographic recording.

OBJECTIVE To investigate the acute role of the corpus callosum in inter- and intrahemispheric temporal coupling. METHODS Intraoperative electrocorticography (ECoG) makes it possible to investigate the acute role of the corpus callosum in cortical temporal coupling, or synchrony, without additional surgical intervention, thus avoiding the confounding effects of scalp recordings and the long-term reorganization of functional connectivity. ECoGs were recorded in three patients during callosotomies. Bilateral electrode grids were placed over the frontal cortex. ECoGs were recorded immediately before and after performing the anterior two-thirds callosal transection, were digitalized at a sampling rate of 512Hz, inspected for artifacts, and later analyzed offline. Cross-correlation between inter- and intrahemispheric electrode pairs were obtained for 1Hz bins and special broad bands obtained by principal component analysis for each patient pre- and post-callosotomy. RESULTS A statistically significant change was observed in intrahemispheric temporal coupling between electrode pairs that exceeded the confidence limit of correlation. CONCLUSIONS Present results show that interrupting the influence of the corpus callosum has an acute effect on intrahemispheric activity by decreasing temporal coupling between cortical areas. SIGNIFICANCE Intrahemispheric temporal coupling does not depend exclusively on ipsilateral cortico-cortical pathways or on subcortical influences, but also on callosal pathways.

Role of corpus callosum in interhemispheric coherent activity during sleep

OBJECTIVE To investigate to what extent the increase in interhemispheric coherent activity observed from wakefulness to sleep depends on the integrity of the corpus callosum (CC). METHODS Interhemispheric coherent activity was analyzed in two epileptic patients selected for callosotomy because of multifocal refractory epilepsy, before and 4 months after callosotomy. One patient underwent complete callosotomy and another was subjected to callosotomy of the anterior 2/3, which offered the possibility of comparing the role of the CC in the coherent activity increase from wakefulness to sleep, between anterior regions with interrupted CC communication (in the two patients) and posterior regions with intact communication (in one of them). Results were compared with a group of normal subjects. RESULTS Both patients showed increased coherent activity from wakefulness to sleep after surgery. CONCLUSIONS Results demonstrate that interhemispheric coherent activity, despite an attenuation after surgery, is higher during SWS than during wakefulness after sectioning the CC; however, they have to be taken with caution because they come from two patients only. SIGNIFICANCE Present results show that the increase in coherent activity during sleep does not depend exclusively on callosal integrity but also on state-dependent influences from sleep-promoting mechanisms, probably spread throughout the thalamo-cortical network.

Patterns of Covariant Power and Coherent Eeg Activity During Rest in Young Adults

Functional cortical organization is not dependent on cognition only, but also reflects basic intrinsic individual characteristics stable over time and across physiological conditions that suggest the existence of self-organization patterns operating even during rest. The aim of the present study was to investigate the pattern of functional organization of EEG broad bands and coherent activity during rest by means of Principal Component Analysis (PCA) with closed and open eyes of 28 men and women. PCA revealed patterns of covariant oscillatory activity and functionally related regions with covariant coherent activity present during resting conditions, different for open and closed eyes. Different patterns of covariant oscillations within alpha frequencies were identified consistent with current notions on overlapping frequencies with different origin and behavioral context. Covariant coherent cortical networks were revealed congruent with functional systems described during cognitive processes; one, linking regions involved in visuo-motor coordination, another in language, and a third one in visuo-spatial processes suggesting that strong functional links are present during rest.

Sex differences in emotional contexts modulation on response inhibition.

The aim of the present study was to explore sex differences in the effects that emotional contexts exert on the temporal course of response inhibition using event-related potentials (ERP). Participants performed a Go-NoGo response inhibition task under 3 context conditions: with 1) neutral background stimuli, and 2) pleasant, and 3) unpleasant emotional contexts. No sex differences were found in relation to accuracy. Women showed higher N2NoGo amplitudes than men in both emotional contexts; whereas during inhibition men tended to show higher P3NoGo amplitudes than women in the unpleasant context. Both groups experienced a relevant effect of the presence of the unpleasant context during inhibition processing, as shown by the enhancement of the N2NoGo amplitudes in frontal regions compared to results from the neutral and pleasant conditions. In addition, women showed differences between the pleasant and unpleasant contexts, with the latter inducing higher amplitude values. Only in men did inhibition accuracy correlate with higher N2NoGo and lower P3NoGo amplitudes in the emotional context conditions. These findings suggest that when an inhibition task is performed in an emotionally-neutral background context no sex differences are observed in either accuracy or ERP components. However, when the emotional context was introduced -especially the unpleasant one- some gender differences did become evident. The higher N2NoGo amplitude at the presence of the unpleasant context may reflect an effect on attention and conflict monitoring. In addition, results suggest that during earlier processing stages, women invested more resources to process inhibition than men. Furthermore, men who invested more neural resources during earlier stages showed better response inhibition than those who did it during later processing stages, more closely-related to cognitive and motor inhibition processes.

Feedback-related negativity is enhanced in adolescence during a gambling task with and without probabilistic reinforcement learning.

Feedback-related negativity (FRN) is a negative deflection that appears around 250 ms after the gain or loss of feedback to chosen alternatives in a gambling task in frontocentral regions following outcomes. Few studies have reported FRN enhancement in adolescents compared with adults in a gambling task without probabilistic reinforcement learning, despite the fact that learning from positive or negative consequences is crucial for decision-making during adolescence. Therefore, the aim of the present research was to identify differences in FRN amplitude and latency between adolescents and adults on a gambling task with favorable and unfavorable probabilistic reinforcement learning conditions, in addition to a nonlearning condition with monetary gains and losses. Higher rate scores of high-magnitude choices during the final 30 trials compared with the first 30 trials were observed during the favorable condition, whereas lower rates were observed during the unfavorable condition in both groups. Higher FRN amplitude in all conditions and longer latency in the nonlearning condition were observed in adolescents compared with adults and in relation to losses. Results indicate that both the adolescents and the adults improved their performance in relation to positive and negative feedback. However, the FRN findings suggest an increased sensitivity to external feedback to losses in adolescents compared with adults, irrespective of the presence or absence of probabilistic reinforcement learning. These results reflect processing differences on the neural monitoring system and provide new perspectives on the dynamic development of an adolescent’s brain.