Development of examination stress in subjects with various levels of cortical activation

The work is aimed at the study of neurophysiological mechanisms of examination stress in subjects with different levels of cortical activation. Spectral power and typical cortical connections of EEG rhythms were studied in students under conditions of stress before and immediately after examination as well as during usual academic semester. Students with relatively higher and relatively lower baseline alpha rhythm, i.e., with different levels of cortical activation revealed both similar and different EEG reactions. Before examination, in both groups of subjects the spectral power of EEG activity in the delta and thetal bands increased, and the number of connections in the bands of the alpha and beta 1 rhythms decreased as compared to usual baseline conditions. However, the EEG reactions in the theta 2 band in the two groups were oppositely directed. Significant changes in the beta 2 power were observed only in the group of subjects with higher baseline level of cortical activation.     

Respiratory instability during sleep onset.

It has been hypothesized that regulatory control in the respiratory system is state dependent. According to this view respiratory instability during sleep onset is a consequence of repeated fluctuations in arousal state. However, these speculations are based primarily on measurements during stable sleep, not during sleep onset itself. The aim of the present study was to assess changes in ventilation and gas tensions during sleep onset as a function of arousal state. Twenty-one subjects (12 males and 9 females, mean age 20 yr) were assessed over an average of 11.3 sleep onsets. The subject's state was classified as alpha, theta, body movement, or stage 2 sleep, and expiratory tidal volume, minute ventilation, respiratory rate, and end-tidal CO2 and O2 were measured by means of a face mask, valve, and pneumotachograph on a breath-by-breath basis. Respiratory instability during sleep onset was found to be a result of two factors. The first factor was a between-state effect in which transitions from alpha to theta were associated with falls, and from theta to alpha with increases, in ventilation. The magnitude of the change was a positive function of metabolic drive at the time of the state change (as indicated by alveolar PCO2 and PO2 levels). The second was a within-state effect in which ventilation fell during consecutive alpha breaths and increased during consecutive theta breaths. These changes were due to the influence of the relative hyperventilation of the alpha state and the relative hypoventilation of the theta state on metabolic drive.     

Psychophysiological mechanisms of stress in subjects with different representation of activation

The EEG spectral power was calculated in 102 students aged 18-25 years in three experimental conditions (during the common educational process, immediately before and after an examination). Before the examination (stress situation), predominant activation of the right anterior cortical quadrant (the area related with negative emotions, according to R. Davidson, 1993) was revealed by the asymmetry coefficient of the beta rhythm. Subjects with low amplitude of the alpha rhythm (more activated) manifested not only emotional but also autonomic disturbances, while only emotional signs were pronounced in students with high alpha (less activated). Increase in the theta rhythm spectral power during stress and its decrease in the poststress period were observed in the less activated persons, which is considered to be a normal reaction to emotionally negative stimuli. On the contrary, in students with low alpha the theta rhythm power in the stress situation was decreased pointing to their emotional instability. In this group, as distinct from the first one, the beta 2 rhythm recorded in the right anterior cortical quadrant did not decrease in the poststress situation. Together with the observed theta rhythm, decrease in the left-hemisphere and bilateral prefrontal areas in the stress situation, this deviation testifies to a predisposition to the reactive depression of these subjects.     

Bruxism and nocturnal groaning

Sleep bruxism (SB) is a sleep-related movement disorder, characterized by tooth grinding and/or clenching. The causes of SB range from psychosocial factors to an excessive sleep arousal response. Some studies showed that SB episodes during sleep are under the influences of transient activity of the brainstem arousal. Nocturnal groaning (NG) is a parasomnia characterized by an expiratory monotonous vocalization occurring during sleep, especially in REM sleep and during the second half of the night. The pathogenesis of NG remains still unclear and many hypotheses arose, ranging from the persistence of a vestigial ventilatory pattern rather than an expiratory upper airways' obstruction. Sleep microstructure fluctuation might modulate the NG, since the end of the NG episode usually is synchronized with a cortical arousal and an autonomic activation. Further studies should clarify the pathophysiology of SB and NG, especially when the two phenomena are associated.     

Arousal increases the representational capacity of cortical tissue

Arousal patently transforms the faculties of complex organisms. Although typical changes in cortical activity such as seen in EEG and LFP measurements are associated with change in state of arousal, it remains unclear what in the constitution of such state dependent activity enables this profound enhancement of ability. We put forward the hypothesis that arousal modulates cortical activity by rendering it more fit to represent information. We argue that representational capacity is of a dual nature—it requires not only that cortical tissue generate complex activity (i.e. spatiotemporal neuronal events), but also a complex cortical activity space (which is comprised of such spatiotemporal events). We explain that the topological notion of complexity—homology—is the pertinent measure of the complexity of neuronal activity spaces, as homological structure indicates not only the degree to which underlying activity is inherently clustered but also registers the effective dimensionality of the configurations formed by such clusters. Changes of this sort in the structure of cortical activity spaces can serve as the basis of the enhanced capacity to make perceptual/behavioral distinctions brought about by arousal. To show the feasibility of these ideas, we analyzed voltage sensitive dye imaging (VSDI) data acquired from primate visual cortex in disparate states of arousal. Our results lend some support to the theory: first as arousal increased so did the complexity of activity (that is the complexity of VSDI movies). Moreover, the complexity of structure of activity space (that is VSDI movie space) as measured by persistent homology—a multi scale topological measure of complexity—increased with arousal as well.     

Effectiveness of multiple-site EMG biofeedback in the reduction of arousal

During the training phase, 36 subjects received (a) EMG biofeedback from multiple muscle sites, (b) EMG biofeedback from the frontal site, or (c) no biofeedback. Results indicated that neither biofeedback procedure reduced self-reports of anxiety, but that multiple-site biofeedback was effective in reducing several indices of autonomic arousal (pulse rate, finger pulse volume, and skin temperature) while frontal biofeedback was not. During the generalization/stress phase, all subjects were threatened with and received electric shocks and were told to apply the relaxation techniques they learned during the training phase even though no additional biofeedback would be provided. Results indicated that multiple-site biofeedback was effective in reducing self-reports of anxiety and autonomic arousal but that frontal biofeedback was not. These results confirm previous data indicating that frontal biofeedback is not an effective procedure for controlling stress, but suggest that EMG biofeedback can be effective in reducing self-reported anxiety and autonomic arousal if a multiple muscle-site feedback procedure is employed.     

Fear conditioning in humans: the influence of awareness and autonomic arousal on functional neuroanatomy

The degree to which perceptual awareness of threat stimuli and bodily states of arousal modulates neural activity associated with fear conditioning is unknown. We used functional magnetic neuroimaging (fMRI) to study healthy subjects and patients with peripheral autonomic denervation to examine how the expression of conditioning-related activity is modulated by stimulus awareness and autonomic arousal. In controls, enhanced amygdala activity was evident during conditioning to both "seen" (unmasked) and "unseen" (backward masked) stimuli, whereas insula activity was modulated by perceptual awareness of a threat stimulus. Absent peripheral autonomic arousal, in patients with autonomic denervation, was associated with decreased conditioning-related activity in insula and amygdala. The findings indicate that the expression of conditioning-related neural activity is modulated by both awareness and representations of bodily states of autonomic arousal.     

Respiratory Sinus Arrhythmia Feedback in a Stressed Population Exposed to a Brief Stressor Demonstrated by Quantitative EEG and sLORETA

Previous investigations of electroencephalograms during relaxation have identified increases in slow wave band power, correlations between increased levels of alpha activity with lower levels of anxiety, and autonomic changes characterized by otherwise documented decreased sympathetic activity. This study was carried out to determine the overall changes in quantitative electroencephalographic activity and the current source as a result of an acute session of respiratory sinus arrhythmia (RSA) biofeedback in a population of subjects experiencing stress. This study’s findings provide physiological evidence of RSA feedback effect and suggest that RSA training may decrease arousal by promoting an increase of alpha band frequencies and decrease in beta frequencies overall and in areas critical to the regulation of stress. It was of interest that novices could achieve these objective alterations in EEG activity after minimal training and intervention periods considering that the previous literature on EEG and meditative states involve experienced meditators or participants who had been given extensive training. Additionally, these effects were present immediately following the training suggesting that the intervention may have effects beyond the actual practice.     

Autonomic nervous system responses to odours: the role of pleasantness and arousal

Perception of odours can provoke explicit reactions such as judgements of intensity or pleasantness, and implicit output such as skin conductance or heart rate variations. The main purpose of the present experiment was to ascertain: (i) the correlation between odour ratings (intensity, arousal, pleasantness and familiarity) and activation of the autonomic nervous system, and (ii) the inter-correlation between self-report ratings on intensity, arousal, pleasantness and familiarity dimensions in odour perception. Twelve healthy volunteers were tested in two separate sessions. Firstly, subjects were instructed to smell six odorants (isovaleric acid, thiophenol, pyridine, L-menthol, isoamyl acetate, and 1-8 cineole), while skin conductance and heart rate variations were being measured. During this phase, participants were not asked to give any judgement about the odorants. Secondly, subjects were instructed to rate the odorants on dimensions of intensity, pleasantness, arousal and familiarity (self-report ratings), by giving a mark between 1 (not at all intense, arousing, pleasant or familiar) and 9 (extremely intense, arousing, pleasant or familiar). Results indicated: (i) a pleasantness factor correlated with heart rate variations, (ii) an arousal factor correlated with skin conductance variations, and (iii) a strong correlation between the arousal and intensity dimensions. In conclusion, given that these correlations are also found in other studies using visual and auditory stimuli, these findings provide preliminary information suggesting that autonomic variations in response to olfactory stimuli are probably not modality specific, and may be organized along two main dimensions of pleasantness and arousal, at least for the parameters considered (i.e. heart rate and skin conductance).     

Cyclic Alternating Pattern Is Associated with Cerebral Hemodynamic Variation: A Near-Infrared Spectroscopy Study of Sleep in Healthy Humans

The cyclic alternating pattern (CAP), that is, cyclic variation of brain activity within non-REM sleep stages, is related to sleep instability and preservation, as well as consolidation of learning. Unlike the well-known electrical activity of CAP, its cerebral hemodynamic counterpart has not been assessed in healthy subjects so far. We recorded scalp and cortical hemodynamics with near-infrared spectroscopy on the forehead and systemic hemodynamics (heart rate and amplitude of the photoplethysmograph) with a finger pulse oximeter during 23 nights in 11 subjects. Electrical CAP activity was recorded with a polysomnogram. CAP was related to changes in scalp, cortical, and systemic hemodynamic signals that resembled the ones seen in arousal. Due to their repetitive nature, CAP sequences manifested as low- and very-low-frequency oscillations in the hemodynamic signals. The subtype A3+B showed the strongest hemodynamic changes. A transient hypoxia occurred during CAP cycles, suggesting that an increased CAP rate, especially with the subtype A3+B, which may result from diseases or fragmented sleep, might have an adverse effect on the cerebral vasculature.     

An ACTH 4-9 analog impairs selective attention in man

Male adults were tested in a dichotic listening task, providing electrophysiological measures of selective attention. Subjects were tested twice, 60 min after oral administration of either 40 mg of ACTH 4-9 analog, or placebo. Averaged auditory evoked potentials (AEPs) to tone pips when attended and when unattended, EEG spectra, heart rate and blood pressure, and behavioral performance were measured during task performance. ACTH 4-9 analog treatment impaired selective attention as indicated a) by a diminished difference between evoked potential waveforms to attended and to unattended tone pips, b) by an impaired behavioral signal detection performance. Furthermore, frontal EEG theta activity slowed down after ACTH 4-9 analog. With time on task, however, there was no decay, but an improvement of selective attention after peptide administration. Differences in attention could not be due to concurrent changes in general cortical and autonomic arousal as indicated by EEG alpha activity, blood pressure and heart rate. Since separate analyses of the AEPs revealed an increased processing of the unattended tone pips in the ACTH 4-9 analog sessions the impaired selective attention under ACTH 4-9 analog may be described as an inability to suppress processing of irrelevant or distracting stimuli.     

EEG Spectral Analysis of Relaxation Techniques

The acute central nervous system effects of relaxation techniques (RT) have not been systematically studied. We conducted a controlled, randomized study of the central nervous system effects of RT using spectral analysis of EEG activity. Thirty-six subjects were randomized to either RT or a music comparison condition. After listening to an RT audiotape or music audiotapes daily for 6 weeks, the acute central nervous system effects of RT and music were measured using power spectral analysis of alpha and theta EEG activity in all cortical regions. RT produced significantly greater increases in theta activity in multiple cortical regions compared to the music condition. These findings are consistent with widespread reductions in cortical arousal during RT. They extend previous findings and suggest that theta, and not alpha, EEG may be the most reliable marker of the central nervous system effects of RT. These findings demonstrate that RT produce greater reductions in central nervous system activity than a credible comparison condition. The findings suggest that RT represent a hypoactive central nervous system state that may be similar to Stage 1 sleep and that RT may exert their therapeutic effects, in part, through cerebral energy conservation/restoration.     

Unpleasantness and physiological responses in using sanitary napkins

This study investigated the physiological and psychological effects of sanitary napkins (SN) on women in hemorrhage treatment during the menstrual phase. Mesh and non-woven napkins were employed, and the effects were studied during the follicular and menstrual phases; mesh SN presented a higher textural surface-roughness. In both phases, the increases in systolic and diastolic blood pressure were significantly dependent on the application intervals. The low-frequency component of systolic blood pressure variability significantly increased, while the salivary secretion rate decreased with the use of mesh SN during the follicular phase compared with non-woven SN. In addition, the heart rate during the menstrual phase significantly increased in subjects after the replacement of mesh SN compared with non-woven SN. In cases of wearing the unpleasant mesh SN, electroencephalography (EEG) manifested bilateral enhancements in beta and alpha2 waves in the frontal areas increased arousal level during both phases. From the above findings, napkin use increased physiological loading and wearing napkins with higher textural surface-roughness tended to increase activities of the autonomic nervous system and brain arousal level.     

Cholinergic input uncouples Ca2+ changes from K+ conductance activation and amplifies intradendritic Ca2+ changes in hippocampal neurons

Muscarinic synaptic activation is known to be involved in cortical arousal as well as learning. Although simple increases in the electrical responsiveness of neurons might be the basis of arousal, the linkage of muscarinic transmission to the synaptic plasticity that might underlie learning is lacking. Most models of synaptic plasticity involve postsynaptic Ca2+ changes as a trigger for subsequent processes. We imaged muscarinic effects on free Ca2+ accumulation during intracellular recordings from CA3 pyramidal neurons in the guinea pig hippocampal slice. Muscarinic activation, either by repetitive stimulation of cholinergic fibers or by bath-applied carbachol, strongly increased intradendritic Ca2+ accumulation during directly evoked repetitive firing, in part by blocking a Ca(2+)-dependent K+ conductance. The effects of repetitive stimulation of cholinergic fibers were enhanced by the acetylcholine-esterase blocker eserine and blocked by the muscarinic antagonist atropine. These findings demonstrate a novel muscarinic reinforcement of Ca2+ changes during excitation, which are probably significant for synapse modification.     

Alexithymia impact on EEG activity of anterior and posterior regions of the right hemisphere while experiencing positive and negative emotions

The present study was aimed to assess the influence of alexithymia (an emotional disorder associated with difficulties in identification and describing personal feelings) on regional activity while experiencing positive or negative emotional activation. The 62-channels EEG was recorded in non-alexithymic (n = 27) and alexithymic (n = 17) subjects viewing emotional film clips. Effects of alexithymia were found in the upper theta, low and upper alpha frequency bands; for all the bands the alexithymics exhibited greater reactivity of the right hemisphere, suggesting enhanced avoidance motivational tendencies, negative effect and autonomic arousal. The present phenomenon suggests engagement of additional cognitive resources in identification of emotional feelings. Such a 'cognitive effort' can be a result of impaired referential links and deficit of symbolic processing of emotions.     

Changes in the brain's electrical activity during habituation to verbal stimulus in subjects with high and low levels of personal anxiety

Brain electrical activity during habituation to repeated verbal stimulus was recorded in subjects with high and low levels of personal anxiety. During habituation of subjects with low anxiety, the spectral power of EEG alpha and theta bands increased in the frontal cortical areas. Such a reaction was not observed in subjects with high anxiety level. Moreover, during habituation traces, the latency of P300 of the auditory evoked potential increased. This parameter did not depend on anxiety level. The amplitude of P300 in the right temporal region was shown to be related to anxiety level: it increased after habituation in subjects with low anxiety and did not change in subjects with high anxiety.     

Can the Neural Basis of Repression Be Studied in the MRI Scanner? New Insights from Two Free Association Paradigms

Background

The psychodynamic theory of repression suggests that experiences which are related to internal conflicts become unconscious. Previous attempts to investigate repression experimentally were based on voluntary, intentional suppression of stimulus material. Unconscious repression of conflict-related material is arguably due to different processes, but has never been studied with neuroimaging methods.

Methods

We used functional magnetic resonance imaging (fMRI) in addition with skin conductance recordings during two free association paradigms to identify the neural mechanisms underlying forgetting of freely associated words according to repression theory.

Results

In the first experiment, free association to subsequently forgotten words was accompanied by increases in skin conductance responses (SCRs) and reaction times (RTs), indicating autonomic arousal, and by activation of the anterior cingulate cortex. These findings are consistent with the hypothesis that these associations were repressed because they elicited internal conflicts. To test this idea more directly, we conducted a second experiment in which participants freely associated to conflict-related sentences. Indeed, these associations were more likely to be forgotten than associations to not conflict-related sentences and were accompanied by increases in SCRs and RTs. Furthermore, we observed enhanced activation of the anterior cingulate cortex and deactivation of hippocampus and parahippocampal cortex during association to conflict-related sentences.

Conclusions

These two experiments demonstrate that high autonomic arousal during free association predicts subsequent memory failure, accompanied by increased activation of conflict-related and deactivation of memory-related brain regions. These results are consistent with the hypothesis that during repression, explicit memory systems are down-regulated by the anterior cingulate cortex.     

Electrodermal and cardiovascular manifestations of emotions in children

The purpose of this paper is to analyze the current state of developmental researches in the area of psychophysiology of emotions in preschool and elementary school children. Electrodermal and cardiovascular activity measures are considered as the sources of indices of the autonomic nervous system activation during emotion-eliciting stimulation in children. We discuss the question of sensitivity of phasic and tonic autonomic measures for the identification of occurrence of emotion, mapping it along with valence and arousal dimensions in affective space, and to further differentiate emotions by their physiological manifestations. Considered are the conceptual and methodological issues related to psychophysiological measurements and developmental factors affecting the emotional reactivity in children. Special attention is devoted to the developmental aspects of psychophysiological studies on emotion such as the maturation of organs, integration of the autonomic and central nervous systems, age and gender-related changes in autonomic reactivity, and development of inhibitory control. Summarized are main findings relevant to psychophysiology of emotions in preschool and early school-age children and suggested are most perspective directions of their integration in the framework of modern theories of emotion.     

The EEG activity after lesions of the diencephalic part of the zona incerta in rats

Neocortical and hippocampal EEG activity was recorded in 23 rats subjected to the bilateral electrolytic lesions of the diencephalic zona incerta (ZI). The aim was to find whether damage to ZI can replicate insomnia and disturbances in cortical EEG desynchronization and hippocampal theta rhythm found after lesions of the lateral hypothalamic (LH) area. No effect of the ZI lesions on waking-sleep cycle was found. The amplitude and frequency of cortical waves and hippocampal theta rhythm during waking were changed only in some rats. These changes were small, short-lasting and bidirectional (toward and increase or decrease in different subjects). Both the amplitude and frequency of paradoxical sleep theta were depressed in part of animals. Thus the marked EEG changes after LH lesions can not be attributed to simultaneous damage of the adjacent subthalamic region. However, the ZI seems to constitute a part of a larger system regulating cortical arousal and hippocampal theta rhythm.     

Neural Activations during Visual Sequence Learning Leave a Trace in Post-Training Spontaneous EEG

Recent EEG studies have shown that implicit learning involving specific cortical circuits results in an enduring local trace manifested as local changes in spectral power. Here we used a well characterized visual sequence learning task and high density-(hd-)EEG recording to determine whether also declarative learning leaves a post-task, local change in the resting state oscillatory activity in the areas involved in the learning process. Thus, we recorded hd-EEG in normal subjects before, during and after the acquisition of the order of a fixed spatial target sequence (VSEQ) and during the presentation of targets in random order (VRAN). We first determined the temporal evolution of spectral changes during VSEQ and compared it to VRAN. We found significant differences in the alpha and theta bands in three main scalp regions, a right occipito-parietal (ROP), an anterior-frontal (AFr), and a right frontal (RFr) area. The changes in frontal theta power during VSEQ were positively correlated with the learning rate. Further, post-learning EEG recordings during resting state revealed a significant increase in alpha power in ROP relative to a pre-learning baseline. We conclude that declarative learning is associated with alpha and theta changes in frontal and posterior regions that occur during the task, and with an increase of alpha power in the occipito-parietal region after the task. These post-task changes may represent a trace of learning and a hallmark of use-dependent plasticity.