Effect of alexithymia on the event-related theta-synchronization of human EEG during reception of emotional visual stimuli

The 62-channel EEG was recorded while control non-alexithymic (n = 21) and alexithymic (n = 20) participants viewed sequentially presented neutral, pleasant and unpleasant pictures and subjectively rated them after each presentation. The event-related synchronization (ERS) to these stimuli was assessed in the theta-1 (4-6 Hr) and theta-2 (6-8 Hz) frequency bands. The obtained findings indicate that alexithymia influences perception of only emotional stimuli. In the upper theta over anterior cortical regions alexithymia vs control individuals in response to both pleasant and unpleasant stimuli manifested decreased left hemisphere ERS in the early test period of 0-200 ms along with enhanced ERS in response to negative vs positive and neutral stimuli in the right hemisphere at 200-600 ms after stimulus onset. The findings provide the first EEG evidence that alexithymia construct, associated with a cognitive deficit in initial evaluation of emotion, is indexed by disrupted early frontal synchronization in the upper theta band that can be best interpreted to reflect disregulation during appraisal of emotional stimuli.     

Event-related synchronization and desynchronization of EEG during appraisal of threatening and pleasant visual stimuli in high anxious subjects

The 62-channel EEG was recorded while low (LA, n = 18) and high (HA, n = 18) trait-anxious subjects viewed sequentially presented neutral, threatening and pleasant IAPS stimuli. Event-related desynchronization (ERD) and synchronization (ERS) were studied in the delta, theta1, theta2, alpha1, alpha2, beta1, beta2, beta3, and gamma frequency bands. Between-group differences, related to stimulus emotionality, were linked to theta1 and theta2 bands. In the low theta at prefrontal sites in the test period of 100-700 ms after stimulus onset HA exhibited relative predominance of the left hemisphere in response to both threatening and pleasant stimuli, whereas LA yielded larger right than left hemisphere activity in response to all the three stimulus categories. In the upper theta band between group differences were associated with posterior cortical regions and the test period of 0-1000 ms after stimulus onset: HA exhibited the largest ERS to threatening, whereas LA prompted the largest ERS to pleasant stimuli. Finally, according to the ERD data, in the alpha1 band HA participants in comparison with LA revealed enhanced left hemisphere activation in response to all the stimulus categories. It is suggested that as it is indexed by theta-ERS relative predominance of the left hemisphere at prefrontal sites along with the largest bilateral activity of posterior cortical regions (i.e., enhanced higher order visual processing) to threatening stimuli could form the basis for general bias towards threatening information in HA at the very early stages of emotional processing.     

Reflection of the emotion manifestation in effects of evoked EEG synchronization and desynchronization

Event-related desynchronization (ERD) and synchronization (ERS) in response to neutral, positive and negative emotional IAPS stimuli were measured in narrow theta, alpha-1, alpha-2 and alpha-3 frequency bands in 22 healthy Ss. A high resolution 62-channel EEG was recorded while subjects viewed a sequence of pictures. The effects of valence discrimination related to hemispheric asymmetries are associated with increased theta and alpha-3 synchronization. Theta ERS revealed a significant valence by hemisphere interaction for anterior temporal leads in the time window of 100-700 ms after stimulus onset indicating a relatively greater right hemisphere ERS for negative and a left hemisphere ERS for positive stimuli in comparison to neutral those. In the alpha-3 band, negative stimuli induced a left hemisphere ERS increase (F7 site) in the time window of 800-1200 ms not observed for neutral and positive stimuli. The results obtained along with the earlier observations on EEG correlates of affective processing challenge the notion that effective anterior hemispheric asymmetries are reflected mainly in the wide alpha frequency band.     

Neural synchrony during response production and inhibition

Inhibition of irrelevant information (conflict monitoring) and/or of prepotent actions is an essential component of adaptive self-organized behavior. Neural dynamics underlying these functions has been studied in humans using event-related brain potentials (ERPs) elicited in Go/NoGo tasks that require a speeded motor response to the Go stimuli and withholding a prepotent response when a NoGo stimulus is presented. However, averaged ERP waveforms provide only limited information about the neuronal mechanisms underlying stimulus processing, motor preparation, and response production or inhibition. In this study, we examine the cortical representation of conflict monitoring and response inhibition using time-frequency analysis of electroencephalographic (EEG) recordings during continuous performance Go/NoGo task in 50 young adult females. We hypothesized that response inhibition would be associated with a transient boost in both temporal and spatial synchronization of prefrontal cortical activity, consistent with the role of the anterior cingulate and lateral prefrontal cortices in cognitive control. Overall, phase synchronization across trials measured by Phase Locking Index and phase synchronization between electrode sites measured by Phase Coherence were the highest in the Go and NoGo conditions, intermediate in the Warning condition, and the lowest under Neutral condition. The NoGo condition was characterized by significantly higher fronto-central synchronization in the 300-600 ms window, whereas in the Go condition, delta- and theta-band synchronization was higher in centro-parietal regions in the first 300 ms after the stimulus onset. The present findings suggest that response production and inhibition is supported by dynamic functional networks characterized by distinct patterns of temporal and spatial synchronization of brain oscillations.     

Representation of Cognitive Reappraisal Goals in Frontal Gamma Oscillations

Recently, numerous efforts have been made to understand the neural mechanisms underlying cognitive regulation of emotion, such as cognitive reappraisal. Many studies have reported that cognitive control of emotion induces increases in neural activity of the control system, including the prefrontal cortex and the dorsal anterior cingulate cortex, and increases or decreases (depending upon the regulation goal) in neural activity of the appraisal system, including the amygdala and the insula. It has been hypothesized that information about regulation goals needs to be processed through interactions between the control and appraisal systems in order to support cognitive reappraisal. However, how this information is represented in the dynamics of cortical activity remains largely unknown. To address this, we investigated temporal changes in gamma band activity (35–55 Hz) in human electroencephalograms during a cognitive reappraisal task that was comprised of three reappraisal goals: to decease, maintain, or increase emotional responses modulated by affect-laden pictures. We examined how the characteristics of gamma oscillations, such as spectral power and large-scale phase synchronization, represented cognitive reappraisal goals. We found that left frontal gamma power decreased, was sustained, or increased when the participants suppressed, maintained, or amplified their emotions, respectively. This change in left frontal gamma power appeared during an interval of 1926 to 2453 ms after stimulus onset. We also found that the number of phase-synchronized pairs of gamma oscillations over the entire brain increased when participants regulated their emotions compared to when they maintained their emotions. These results suggest that left frontal gamma power may reflect cortical representation of emotional states modulated by cognitive reappraisal goals and gamma phase synchronization across whole brain regions may reflect emotional regulatory efforts to achieve these goals. Our study may provide the basis for an electroencephalogram-based neurofeedback system for the cognitive regulation of emotion.     

Ability to Maintain Internal Arousal and Motivation Modulates Brain Responses to Emotions

Persistence (PS) is defined as the ability to generate and maintain arousal and motivation internally in the absence of immediate external reward. Low PS individuals tend to become discouraged when expectations are not rapidly fulfilled. The goal of this study was to investigate whether individual differences in PS influence the recruitment of brain regions involved in emotional processing and regulation. In a functional MRI study, 35 subjects judged the emotional intensity of displayed pictures. When processing negative pictures, low PS (vs. high PS) subjects showed higher amygdala and right orbito-frontal cortex (OFC) activity but lower left OFC activity. This dissociation in OFC activity suggests greater prefrontal cortical asymmetry for approach/avoidance motivation, suggesting an avoidance response to aversive stimuli in low PS. For positive or neutral stimuli, low PS subjects showed lower activity in the amygdala, striatum, and hippocampus. These results suggest that low PS may involve an imbalance in processing distinct emotional inputs, with greater reactivity to aversive information in regions involved in avoidance behaviour (amygdala, OFC) and dampened response to positive and neutral stimuli across circuits subserving motivated behaviour (striatum, hippocampus, amygdala). Low PS affective style was associated with depression vulnerability. These findings in non-depressed subjects point to a neural mechanism whereby some individuals are more likely to show systematic negative emotional biases, as frequently observed in depression. The assessment of these individual differences, including those that may cause vulnerability to depressive disorders, would therefore constitute a promising approach to risk assessment for depression.     

Rapid Plasticity in the Prefrontal Cortex during Affective Associative Learning

MultiCS conditioning is an affective associative learning paradigm, in which affective categories consist of many similar and complex stimuli. Comparing visual processing before and after learning, recent MultiCS conditioning studies using time-sensitive magnetoencephalography (MEG) revealed enhanced activation of prefrontal cortex (PFC) regions towards emotionally paired versus neutral stimuli already during short-latency processing stages (i.e., 50 to 80 ms after stimulus onset). The present study aimed at showing that this rapid differential activation develops as a function of the acquisition and not the extinction of the emotional meaning associated with affectively paired stimuli. MEG data of a MultiCS conditioning study were analyzed with respect to rapid changes in PFC activation towards aversively (electric shock) paired and unpaired faces that occurred during the learning of stimulus-reinforcer contingencies. Analyses revealed an increased PFC activation towards paired stimuli during 50 to 80 ms already during the acquisition of contingencies, which emerged after a single pairing with the electric shock. Corresponding changes in stimulus valence could be observed in ratings of hedonic valence, although participants did not seem to be aware of contingencies. These results suggest rapid formation and access of emotional stimulus meaning in the PFC as well as a great capacity for adaptive and highly resolving learning in the brain under challenging circumstances.     

Temporal-Spatial Neural Activation Patterns Linked to Perceptual Encoding of Emotional Salience

It is well known that we continuously filter incoming sensory information, selectively allocating attention to what is important while suppressing distracting or irrelevant information. Yet questions remain about spatiotemporal patterns of neural processes underlying attentional biases toward emotionally significant aspects of the world. One index of affectively biased attention is an emotional variant of an attentional blink (AB) paradigm, which reveals enhanced perceptual encoding for emotionally salient over neutral stimuli under conditions of limited executive attention. The present study took advantage of the high spatial and temporal resolution of magnetoencephalography (MEG) to investigate neural activation related to emotional and neutral targets in an AB task. MEG data were collected while participants performed a rapid stimulus visual presentation task in which two target stimuli were embedded in a stream of distractor words. The first target (T1) was a number and the second (T2) either an emotionally salient or neutral word. Behavioural results replicated previous findings of greater accuracy for emotionally salient than neutral T2 words. MEG source analyses showed that activation in orbitofrontal cortex, characterized by greater power in the theta and alpha bands, and dorsolateral prefrontal activation were associated with successful perceptual encoding of emotionally salient relative to neutral words. These effects were observed between 250 and 550 ms, latencies associated with discrimination of perceived from unperceived stimuli. These data suggest that important nodes of both emotional salience and frontoparietal executive systems are associated with the emotional modulation of the attentional blink.     

Effects of aversive stimuli on prospective memory. An event-related fMRI study

Prospective memory (PM) describes the ability to execute a previously planned action at the appropriate point in time. Although behavioral studies clearly showed that prospective memory performance is affected by the emotional significance attributed to the intended action, no study so far investigated the brain mechanisms subserving the modulatory effect of emotional salience on PM performance. The general aim of the present study was to explore brain regions involved in prospective memory processes when PM cues are associated with emotional stimuli. In particular, based on the hypothesised critical role of the prefrontal cortex in prospective memory in the presence of emotionally salient stimuli, we expected a stronger involvement of aPFC when the retrieval and execution of the intended action is cued by an aversive stimulus. To this aim BOLD responses of PM trials cued by aversive facial expressions were compared to PM trials cued by neutral facial expressions. Whole brain analysis showed that PM task cued by aversive stimuli is differentially associated with activity in the right lateral prefrontal area (BA 10) and in the left caudate nucleus. Moreover a temporal shift between the response of the caudate nucleus that preceded that of aPFC was observed. These findings suggest that the caudate nucleus might provide an early analysis of the affective properties of the stimuli, whereas the anterior lateral prefrontal cortex (BA10) would be involved in a slower and more deliberative analysis to guide goal-directed behaviour.     

Bilateral Skin Conductance Responses to Emotional Faces

Skin conductance responses (SCR) measure objective arousal in response to emotionally-relevant stimuli. Central nervous system influence on SCR is exerted differentially by the two hemispheres. Differences between SCR recordings from the left and right hands may therefore be expected. This study focused on emotionally expressive faces, known to be processed differently by the two hemispheres. Faces depicting neutral, happy, sad, angry, fearful or disgusted expressions were presented in two tasks, one with an explicit emotion judgment and the other with an age judgment. We found stronger responses to sad and happy faces compared with neutral from the left hand during the implicit task, and stronger responses to negative emotions compared with neutral from the right hand during the explicit task. Our results suggest that basic social stimuli generate distinct responses on the two hands, no doubt related to the lateralization of social function in the brain.     

Emotional intelligence and oscillatory responses to emotional facial expressions

Emotional intelligence-related differences in oscillatory responses to emotional facial expressions were investigated in 48 subjects (26 men and 22 women), age 18–30 years. Participants were instructed to evaluate emotional expression (angry, happy, and neutral) of each presented face on an analog scale ranging from ?100 (very hostile) to + 100 (very friendly). High emotional intelligence (EI) participants were found to be more sensitive to the emotional content of the stimuli. It showed up both in their subjective evaluation of the stimuli and in a stronger EEG theta synchronization at an earlier (between 100 and 500 ms after face presentation) processing stage. Source localization using sLORETA showed that this effect was localized in the fusiform gyrus upon the presentation of angry faces and in the posterior cingulate gyrus upon the presentation of happy faces. At a later processing stage (500–870 ms), event-related theta synchronization in high emotional intelligence subjects was higher in the left prefrontal cortex upon the presentation of happy faces, but it was lower in the anterior cingulate cortex upon the presentation of angry faces. This suggests the existence of a mechanism that can selectively increase the positive emotions and reduce negative emotions.     

Severity of depressive symptoms and oscillatory responses to emotional facial expressions

Differences in oscillatory responses to emotional facial expressions were studied in 40 subjects (19 men and 21 women aged from 18 to 30 years) varying in severity of depressive symptoms. Compared with perception of angry and neutral faces, perception of happy faces was accompanied by lower Δ synchronization in subjects with a low severity of depressive symptoms (Group 2) and higher Δ synchronization in subjects with a high severity of depressive symptoms (Group 1). Because synchronization of Δ oscillations is usually observed in aversive states, it was assumed that happy faces were perceived as negative stimuli by the Group 1 subjects. Perception of angry faces was accompanied by α desynchronization in Group 2 and α synchronization in Group 1. Based on Klimesch’s theory, the effect was assumed to indicate that the Group 1 subjects were initially set up for perception of negative emotional information. The effect of the emotional stimulus category was significant in Group 2 and nonsignificant in Group 1, testifying that the recognition of emotional information is hindered in depression-prone individuals.     

Regulation of the neural circuitry of emotion by compassion meditation: effects of meditative expertise

Recent brain imaging studies using functional magnetic resonance imaging (fMRI) have implicated insula and anterior cingulate cortices in the empathic response to another's pain. However, virtually nothing is known about the impact of the voluntary generation of compassion on this network. To investigate these questions we assessed brain activity using fMRI while novice and expert meditation practitioners generated a loving-kindness-compassion meditation state. To probe affective reactivity, we presented emotional and neutral sounds during the meditation and comparison periods. Our main hypothesis was that the concern for others cultivated during this form of meditation enhances affective processing, in particular in response to sounds of distress, and that this response to emotional sounds is modulated by the degree of meditation training. The presentation of the emotional sounds was associated with increased pupil diameter and activation of limbic regions (insula and cingulate cortices) during meditation (versus rest). During meditation, activation in insula was greater during presentation of negative sounds than positive or neutral sounds in expert than it was in novice meditators. The strength of activation in insula was also associated with self-reported intensity of the meditation for both groups. These results support the role of the limbic circuitry in emotion sharing. The comparison between meditation vs. rest states between experts and novices also showed increased activation in amygdala, right temporo-parietal junction (TPJ), and right posterior superior temporal sulcus (pSTS) in response to all sounds, suggesting, greater detection of the emotional sounds, and enhanced mentation in response to emotional human vocalizations for experts than novices during meditation. Together these data indicate that the mental expertise to cultivate positive emotion alters the activation of circuitries previously linked to empathy and theory of mind in response to emotional stimuli.     

Induced synchronization/desynchronization of the theta and alpha cortical electrical activity to a face stimuli with increasing visual working memory load

Using a cognitive set to emotional facial expression as a model, induced synchronization/desynchronization of the cortical theta- and alpha-activities were studied in adult healthy people under conditions of increased load on the working memory (additional task of the verbal stimuli recognition). A correlation was found between behavioral (increase in the set rigidity) and electrophysiological (decrease of the induced theta-rhythm synchronization) data. A hypothesis is suggested that the earlier revealed increase in the tonic prestimulus theta-activity and suppression of the poststimulus phasic activation of the cortico-hippocampal system are one of the mechanisms of the decrease in plasticity of the cognitive function of the emotional facial expression recognition under conditions of the increased load on the working memory. Reciprocal relations between two functional systems of the brain activity integration (cortico-hippocampal and fronto-thalamic) in the process of recognition of emotional facial expression are discussed.     

Cortical functional connectivity during the retention of affective pictures in working memory: EEG-source theta coherence analysis

The pattern of cortical functional connectivity in the source space was studied in a group of righthanded adult participants (N = 44:17 women, 27 men, aged M = 29.61 ± 6.45 years). Participants retained the traces of realistic pictures of positive, neutral, and negative emotional valences in their working memory (WM) while performing the same-different task. Within the framework of this task, participants had to compare the initial picture against a target picture that followed after a specified delay. The coherence (COH) between the pairs of cortical sources chosen in advance according to fMRI data was estimated in the theta frequency range for the period preceding the initial stimulus, during the retention of the initial stimulus in WM, and during the rest interval between successive trials. Two distinct sets of functional links were found. The links of the first type that presumably reflected the involvement of sustained attention were between the dorsal anterior cingulate cortex, the prefrontal areas, and temporal areas of the right hemispheres. When compared to the rest period, the links of this type showed strengthening not only during the retention period but also during the period preceding the initial picture. The links of the second type presumably reflected a progressive neocortex-to-hippocampus functional integration with increasing memory load and strengthened exclusively during the retention period. These links were between the parietal, temporal and prefrontal cortices in the lateral surface of both hemispheres with the additional inclusion of the posterior cingulate cortex and the medial parietal cortex in the left hemisphere. The impact of emotional valence on the strength and topography of the functional links of the second type was found. In the left hemisphere, the increase of strength of cortical interaction was more pronounced for the pictures of positive valence than for the pictures of either neutral or negative valences. When compared to the pictures of neutral valence, the retention of pictorial information of both positive and negative valence showed some extraneous integration of the cortical areas for the theta rhythm. This finding might be related to the additional load exerted by emotionally colored pictures onto the mechanisms of short-time retention of visual information.     

Analysis of elicited EEG synchronization and desynchronization in emotional activation: temporal and topographic characteristics

Event-related synchronization (ERS) and desynchronization (ERD) in delta, theta1, theta2, alpha1, alpha2, beta1, beta2, beta3, and gamma were measured in 20 healthy right-handed subjects in response to IAPS stimuli with low, moderate, and high arousal reactions. The 62-channel EEG was simultaneously recorded while subjects viewed sequentially presented pictures and subjectively rated them after each presentation. The results show that emotionally loaded stimuli induced higher ERS in the delta, theta1, theta2, beta1, beta3, and gamma bands along with combined ERD and ERS effects in alpha2 band. As to hemispheric asymmetries, the effects of emotional arousal were restricted not only to right parietal (theta1 and theta2 ERS, alpha2 ERD) but also to left frontal (theta2 ERS) regions. In terms of affective chronometry, lower theta was the first to catch the affective salience of incoming stimuli (time window 0-600 ms after the stimulus input). For theta2, alpha2, and gamma bands this process was delayed to 600-1000 ms.     

Emotional cues during simultaneous face and voice processing: electrophysiological insights

Both facial expression and tone of voice represent key signals of emotional communication but their brain processing correlates remain unclear. Accordingly, we constructed a novel implicit emotion recognition task consisting of simultaneously presented human faces and voices with neutral, happy, and angry valence, within the context of recognizing monkey faces and voices task. To investigate the temporal unfolding of the processing of affective information from human face-voice pairings, we recorded event-related potentials (ERPs) to these audiovisual test stimuli in 18 normal healthy subjects; N100, P200, N250, P300 components were observed at electrodes in the frontal-central region, while P100, N170, P270 were observed at electrodes in the parietal-occipital region. Results indicated a significant audiovisual stimulus effect on the amplitudes and latencies of components in frontal-central (P200, P300, and N250) but not the parietal occipital region (P100, N170 and P270). Specifically, P200 and P300 amplitudes were more positive for emotional relative to neutral audiovisual stimuli, irrespective of valence, whereas N250 amplitude was more negative for neutral relative to emotional stimuli. No differentiation was observed between angry and happy conditions. The results suggest that the general effect of emotion on audiovisual processing can emerge as early as 200 msec (P200 peak latency) post stimulus onset, in spite of implicit affective processing task demands, and that such effect is mainly distributed in the frontal-central region.     

Analysis of functional brain connections for positive–negative emotions using phase locking value

In this study, we investigate the brain networks during positive and negative emotions for different types of stimulus (audio only, video only and audio + video) in \(\alpha , \beta\), and \(\gamma\) bands in terms of phase locking value, a nonlinear method to study functional connectivity. Results show notable hemispheric lateralization as phase synchronization values between channels are significant and high in right hemisphere for all emotions. Left frontal electrodes are also found to have control over emotion in terms of functional connectivity. Besides significant inter-hemisphere phase locking values are observed between left and right frontal regions, specifically between left anterior frontal and right mid-frontal, inferior-frontal and anterior frontal regions; and also between left and right mid frontal regions. ANOVA analysis for stimulus types show that stimulus types are not separable for emotions having high valence. PLV values are significantly different only for negative emotions or neutral emotions between audio only/video only and audio only/audio + video stimuli. Finding no significant difference between video only and audio + video stimuli is interesting and might be interpreted as that video content is the most effective part of a stimulus.     

Effects of emotional expression of an irrelevant face image on recognition of visual stimuli

Psychophysiological experiments were performed on 34 healthy subjects. We analyzed the accuracy and latency of motor response in recognizing two types of complex visual stimuli, animals and objects, which were presented immediately after a brief presentation of face images with different emotional expressions: anger, fear, happiness, and a neutral expression. We revealed the dependence of response latency on emotional expression of the masked face. The response latency was lower when the test stimuli were preceded by angry or fearful faces compared to happy or neutral faces. These effects depended on the type of stimulus and were more expressive when recognizing objects compared to animals. We found that the effects of emotional faces were related to personal features of the subjects that they exhibited in the emotional and communicative blocks of Cattell’s test and were more expressive in more sensitive, anxious, and pessimistic introverts. The mechanisms of the effects of unconsciously perceived emotional information on human visual behavior are discussed.     

Reflection of the Emotional Significance of Visual Stimuli in the Characteristics of Evoked EEG Potentials

Healthy subjects (n = 88) were asked to passively visualize positive and passive emotiogenic visual stimuli and also stimuli with a neutral emotional content. Images of the International Affective Picture System (IAPS) were used. Amplitude/time characteristics of the components of evoked EEG potentials (EPs), P1, N1, P2, N2, and P3 and topographic distribution of the latter components were analyzed. The latencies, amplitudes, and topography of the EP waves induced by presentation of positive and negative stimuli were found to be different from the respective values for the EPs induced by neutral stimuli. The level and pattern of these differences typical of different EP components were dissimilar and depended on the sign of the emotions. Specificities related to the valency of an identified stimulus were observed within nearly all stages of processing of visual signals, for the negative stimuli, beginning from an early stage of sensory analysis corresponding to the development of wave Р1. The latencies of components Р1 in the case of presentation of emotiogenic negative stimuli and those of components N1, N2, and Р3 in the case of presentation of the stimuli of both valencies were shorter than the latencies observed at neutral stimuli. The amplitude of component N2 at perception of positive stimuli was, on average, lower, while the Р3 amplitude at perception of all emotiogenic stimuli was higher than in the case of presentation of neutral stimuli. The time dynamics of topographic peculiarities of processing of emotiogenic information were complicated. Activation of the left hemisphere was observed during the earliest stages of perception, while the right hemisphere was activated within the intermediate stages. Generalized activation of the cortex after the action of negative signals and dominance of the left hemisphere under conditions of presentation of positive stimuli were observed only within the final stages. As is supposed, emotiogenic stimuli possess a greater biological significance than neutral ones, and this is why the former attract visual attention first; they more intensely activate the respective cortical zones, and the corresponding visual information is processed more rapidly. The observed effects were more clearly expressed in the case of action of negative stimuli; these effects involved more extensive cortical zones. These facts are indicative of the higher intensity of activating influences of negative emotiogenic stimuli on neutral systems of the higher CNS structures.