Task dependent cerebral lateralization of the 40 Hertz EEG rhythm

Cortical facilitation of tactile afferents during the preparation of a body weight transfer when standing on a biomimetic surface

Self-generated movement shapes tactile perception, but few studies have investigated the brain mechanisms involved in the processing of the mechanical signals related to the static and transient skin deformations generated by forces and pressures exerted between the foot skin and the standing surface. We recently found that standing on a biomimetic surface (i.e., inspired by the characteristics of mechanoreceptors and skin dermatoglyphics), that magnified skin-surface interaction, increased the sensory flow to the somatosensory cortex and improved balance control compared to standing on control (e.g., smooth) surfaces. In this study, we tested whether the well-known sensory suppression that occurs during movements is alleviated when the tactile afferent signal becomes relevant with the use of a biomimetic surface. Eyes-closed participants (n = 25) self-stimulated their foot cutaneous receptors by shifting their body weight toward one of their legs while standing on either a biomimetic or a control (smooth) surface. In a control task, similar forces were exerted on the surfaces (i.e., similar skin-surface interaction) by passive translations of the surfaces. Sensory gating was assessed by measuring the amplitude of the somatosensory-evoked potential over the vertex (SEP, recorded by EEG). Significantly larger and shorter SEPs were found when participants stood on the biomimetic surface. This was observed whether the forces exerted on the surface were self-generated or passively generated. Contrary to our prediction, we found that the sensory attenuation related to the self-generated movement did not significantly differ between the biomimetic and control surfaces. However, we observed an increase in gamma activity (30-50 Hz) over centroparietal regions during the preparation phase of the weight shift only when participants stood on the biomimetic surface. This result might suggest that gamma-band oscillations play an important functional role in processing behaviorally relevant stimuli during the early stages of body weight transfer.

Predictions of task using neural modeling

Introduction

A well-designed brain-computer interface (BCI) can make accurate and reliable predictions of a user's state through the passive assessment of their brain activity; in turn, BCI can inform an adaptive system (such as artificial intelligence, or AI) to intelligently and optimally aid the user to maximize the human-machine team (HMT) performance. Various groupings of spectro-temporal neural features have shown to predict the same underlying cognitive state (e.g., workload) but vary in their accuracy to generalize across contexts, experimental manipulations, and beyond a single session. In our work we address an outstanding challenge in neuroergonomic research: we quantify if (how) identified neural features and a chosen modeling approach will generalize to various manipulations defined by the same underlying psychological construct, (multi)task cognitive workload.

Methods

To do this, we train and test 20 different support vector machine (SVM) models, each given a subset of neural features as recommended from previous research or matching the capabilities of commercial devices. We compute each model's accuracy to predict which (monitoring, communications, tracking) and how many (one, two, or three) task(s) were completed simultaneously. Additionally, we investigate machine learning model accuracy to predict task(s) within- vs. between-sessions, all at the individual-level.

Results

Our results indicate gamma activity across all recording locations consistently outperformed all other subsets from the full model. Our work demonstrates that modelers must consider multiple types of manipulations which may each influence a common underlying psychological construct.

Discussion

We offer a novel and practical modeling solution for system designers to predict task through brain activity and suggest next steps in expanding our framework to further contribute to research and development in the neuroergonomics community. Further, we quantified the cost in model accuracy should one choose to deploy our BCI approach using a mobile EEG-systems with fewer electrodes-a practical recommendation from our work.

[EEG frequency and regional properties in patients with paranoid schizophrenia: effects of positive and negative symptomatology prevalence]

OBJECTIVE

EEG changes in schizophrenic patients are caused by a multitude of factors related to clinical heterogeneity of the disease, current state of patients, and conducted therapy. EEG spectral analysis remains an actual methodical approach for the investigation of the neurophysiological mechanisms of the disease. The goal of the investigation was the study of frequency and regional EEG correlating with the intensity of productive and negative disorders.

MATERIAL AND METHODS

Models of summary prevalence of positive/negative disorders and evidence of concrete clinical indices of the PANSS scale were used. Spectral characteristics of background EEG in the frequency range of 1-60 Hz were studied in 35 patients with paranoid schizophrenia free from psychoactive medication and in 19 healthy volunteers.

RESULTS

It was established that the main index of negative symptomatology in summary assessment was diffuse increase of spectral power of gamma and delta ranges. Deficient states with the predominance of volitional disorders were characterized by a lateralized increase of spectral power of beta-gamma ranges in the left hemisphere, and of delta range - in frontal areas of this hemisphere. Positive symptomatology was noticeably less reflected in EEG changes than negative ones.

CONCLUSION

An analysis of psychopathological symptom complexes revealed the significance of spatially structured EEG patterns in the beta range: for the delusion disturbances with psychic automatism phenomena - in frontal areas of the left hemisphere, and for the paranoid syndrome with primary interpretative delusion - in cortical areas of the right hemisphere.

Cortical γ responses: searching high and low

In this paper, a brief, preliminary attempt is made to frame a scientific debate about how functional responses at gamma frequencies in electrophysiological recordings (EEG, MEG, ECoG, and LFP) should be classified and interpreted. In general, are all gamma responses the same, or should they be divided into different classes according to criteria such as their spectral characteristics (frequency range and/or shape), their spatial-temporal patterns of occurrence, and/or their responsiveness under different task conditions? In particular, are the responses observed in intracranial EEG at a broad range of "high gamma" frequencies (~60-200Hz) different from gamma responses observed at lower frequencies (~30-80Hz), typically in narrower bands? And if they are different, how should they be interpreted? Does the broad spectral shape of high gamma responses arise from the summation of many different narrow-band oscillations, or does it reflect something completely different? If we are not sure, should we refer to high gamma activity as oscillations? A variety of theories have posited a mechanistic role for gamma activity in cortical function, often assuming narrow-band oscillations. These theories continue to influence the design of experiments and the interpretation of their results. Do these theories apply to all electrophysiological responses at gamma frequencies? Although no definitive answers to these questions are immediately anticipated, this paper will attempt to review the rationale for why they are worth asking and to point to some of the possible answers that have been proposed.

Assessment of language dominance by event-related oscillatory changes in an auditory language task: magnetoencephalography study

The authors investigated the oscillatory changes induced by auditory language task to assess hemispheric dominance of language. Magnetoencephalography studies were conducted during word listening in 6 normal right-handed volunteers and 13 epilepsy patients who underwent Wada test. We carried out a time-frequency analysis of event-related desynchronization (ERD)/event-related synchronization (ERS) and intertrial coherence. We localized ERD/ERS on each subject's magnetic resonance images using beamformer. We compared ERD/ERS values between the left and right side of regions of interest in inferior frontal and superior temporal areas. We assessed the target frequency range that correlated best with the Wada test results. In all normal subjects, gamma ERD was lateralized to the left side in both the inferior frontal and superior temporal areas. In epilepsy patients, the concordance rate of gamma ERD and the Wada test results was 76.9% for the inferior frontal area and 69.2% for the superior temporal area. Gamma ERD can be considered as an indicator of language function, although it was not sufficient to replace the Wada test in the evaluation of epilepsy patients. The gamma ERD value of the inferior frontal area was more reliable for the assessment of language dominance compared with that obtained in the superior temporal area.

Behavioral arrest: in search of the neural control system

Scientists have spent hundreds of years trying to understand how the brain controls movement. Why has there been so little interest in knowing how the brain STOPS movement? This review calls attention to behavioral phenomena in which an animal or human undergoes temporary total-body arrest of movement, that is, behavioral arrest (BA). These states can be actively induced by visual stimuli, by body and limb manipulations, and by drugs. Historically, these states have been considered as unrelated, and their literature does not cross-connect. What is known about the causal mechanisms is scant, limited mostly to implication of the brainstem in manipulation-induced BA and dopaminergic blockade in the striatum in the case of drug-induced BA. The possibility has not been experimentally tested that all of these states share with each other not only an active global immobility in which awkward postures are maintained, but also underlying neural mechanisms. This review identifies key brainstem, diencephalic, and basal forebrain areas that seem to be involved in causing BA. We review the evidence that suggest a possible role in BA for the following brain structures: entopeduncular nucleus, medullary and pontine reticular zones, parabrachial region, pedunculopontine nucleus and nearby areas, substantia nigra, subthalamic nucleus, ventromedial thalamic nucleus, and zona incerta. Such areas may operate as a BA control system. Confirmation of which brain areas operate collectively in BA would require testing of several kinds of BA in the same animals with the same kinds of experimental tests. Areas and mechanisms might be elucidated through a strategic combination of the following research approaches: imaging (fMRI, c-fos), lesions (of areas, of afferent and efferent pathways), chemical microstimulation, and electrical recording (of multiple units and field potentials, with an emphasis on testing coherence among areas). We suggest the working hypothesis that BA is created and sustained by coherent, perhaps oscillatory, activity among a group of basal forebrain and brainstem areas that collectively disrupt the normal spinal and supraspinal sequencing controls of reciprocal actions on the extensors and flexors that otherwise produce movement.

Changes in power and coherence of brain activity in human sensorimotor cortex during performance of visuomotor tasks

Electrocorticograms (ECoG) were recorded using subdural grid electrodes in forearm sensorimotor cortex of six human subjects. The subjects performed three visuomotor tasks, tracking a moving visual target with a joystick-controlled cursor; threading pieces of tubing; and pinching the fingers sequentially against the thumb. Control conditions were resting and active wrist extension. ECoGs were recorded at 14 sites in hand- and arm-sensorimotor area, functionally identified with electrical stimulation. For each behavior we computed spectral power of ECoG in each site and coherence in all pair-wise sites. In three out of six subjects, gamma-oscillations were observed when the subjects started the tasks. All subjects showed widespread power decrease in the range of 11-20 Hz and power increase in the 31-60 Hz ranges during performance of the visuomotor tasks. The changes in gamma-range power were more vigorous during the tracking and threading tasks compared with the wrist extension. Coherence analysis also showed similar task-related changes in coherence estimates. In contrast to the power changes, coherence estimates increased not only in gamma-range but also at lower frequencies during the manipulative visuomotor tasks. Paired sites with significant increases in coherence estimates were located within and between sensory and motor areas. These results support the hypothesis that coherent cortical activity may play a role in sensorimotor integration or attention.

An integration of 40 Hz Gamma and phasic arousal: novelty and routinization processing in schizophrenia

OBJECTIVES

Frontal and lateralized schizophrenia disturbances were examined in terms of arousal-modulated changes in 40 Hz Gamma activity.

METHODS

Forty patients with schizophrenia and 40 age- and gender-matched controls were studied in a conventional auditory ERP oddball paradigm. We investigated sub-averaged Gamma activity based upon a simultaneous measure of electrodemal skin conductance response (phasic arousal) to differentiate novelty (large responses) from routinization (small or no responses). Both early Gamma (Gamma 1) and later induced Gamma (Gamma 2) activities were examined.

RESULTS

Patients with schizophrenia (compared with controls) had significantly reduced Gamma 1 amplitude in the right hemisphere for novelty processing and delayed Gamma 2 latency in the left hemisphere for both novelty and routinization. Overall, reduced Gamma 1 amplitude in patients with schizophrenia was also evident.

CONCLUSIONS

These findings indicate that the normal laterality of Gamma activity is specifically disturbed in schizophrenia in response to novel, but not routine (familiar) stimuli. The distinct pattern of findings suggests a dysregulation of activation across left and right hemispheres during initial attention and preparatory phases of information processing, in particular, in patients with schizophrenia.

Coherent EEG indicators of cognitive binding during ambiguous figure tasks

We tested the hypothesis that perception of an alternative image in ambiguous figures would be manifest as high-frequency (gamma) components that become synchronized over multiple scalp sites as a "cognitive binding" process occurs. For 171 combinations of data from 19 electrodes, obtained from 17 subjects and 10 replicate stimuli, we calculated the difference in correlation between the response to first seeing an ambiguous figure and when the alternative percept for that figure became consciously realized (cognitively bound). Numerous statistically significant correlation differences occurred in all frequency bands tested with ambiguous-figure stimulation, but not in two kinds of control data (a reaction-time test to sound stimuli and a no-task, mind-wandering test). Statistically significant correlation changes were widespread, involving frontal, parietal, central, and occipital regions of both hemispheres. Correlation changes were evident at each of five frequency bands, ranging up to 62.5 Hz. Most of the statistically significant correlation changes were not between adjacent sites but between sites relatively distant, both ipsilateral and contralateral. Typically, these correlation changes occurred in more than one frequency band. These results suggest that cognitive binding is a distinct mental state that is reliably induced by ambiguous-figure perception tasks. Coherent oscillations at multiple frequencies may reflect the mechanism by which such binding occurs. Moreover, different coherent frequencies may mediate different components of the total cognitive-binding process.

Correlation of high-frequency oscillations with the sleep-wake cycle and cognitive activity in humans

While several authors have suggested that high-frequency electroencephalogram activity (gamma, >30 Hz) correlates with conscious thought, others have suggested that electroencephalogram activity >30 Hz shows the same relationships to cognitive activity and sleep as activity in the conventional beta frequency band. The existence of coherence of gamma over large distances also remains controversial. We studied quantitatively the relationship of gamma activity to the sleep-wake cycle and cognitive tasks during wakefulness in humans using intracranial electroencephalogram. Gamma activity made up less than 1% of the total power spectrum. A significant relationship was observed between gamma activity and the sleep-wake cycle such that gamma was highest during wakefulness, intermediate during light and rapid eye movement sleep, and lowest during slow-wave sleep. As well, gamma was higher during rapid eye movement sleep with eye movements than during rapid eye movement sleep without eye movements. During a cognitive task experiment, while lower frequencies, including beta, showed a stepwise reduction with increasing task difficulty, gamma was observed to increase during cognitive tasks as compared to the resting state. The relationship between gamma and the sleep-wake cycle and cognitive tasks was independent of brain region and hemisphere. Coherence of gamma activity at distances of 5 mm and greater was not observed. Our data support previously reported findings that gamma activity has a significant relationship to the sleep-wake cycle. The findings of differences in gamma during REM sleep with and without eye movements suggest that the presence or absence of eye movements may reflect two different states of brain activity. Our findings of differences in the relationships of the beta and gamma bands to both the sleep-wake cycle and cognitive tasks demonstrate that various components of the high-frequency spectrum behave differently in some situations.

Human gamma band activity and perception of a gestalt

Neuronal oscillations in the gamma band (above 30 Hz) have been proposed to be a possible mechanism for the visual representation of objects. The present study examined the topography of gamma band spectral power and event-related potentials in human EEG associated with perceptual switching effected by rotating ambiguous (bistable) figures. Eleven healthy human subjects were presented two rotating bistable figures: first, a face figure that allowed perception of a sad or happy face depending on orientation and therefore caused a perceptual switch at defined points in time when rotated, and, second, a modified version of the Rubin vase, allowing perception as a vase or two faces whereby the switch was orientation-independent. Nonrotating figures served as further control stimuli. EEG was recorded using a high-density array with 128 electrodes. We found a negative event-related potential associated with the switching of the sad-happy figure, which was most pronounced at central prefrontal sites. Gamma band activity (GBA) was enhanced at occipital electrode sites in the rotating bistable figures compared with the standing stimuli, being maximal at vertical stimulus orientations that allowed an easy recognition of the sad and happy face or the vase-faces, respectively. At anterior electrodes, GBA showed a complementary pattern, being maximal when stimuli were oriented horizontally. The findings support the notion that formation of a visual percept may involve oscillations in a distributed neuronal assembly.

Psychophysiological correlates of hypnosis and hypnotic susceptibility

This article reviews and summarizes electroencephalographic (EEG)-based research on physiological and cognitive indicators of hypnotic responding and hypnotic susceptibility, with special attention to the author's programmatic research in this area. Evidence that differences in attention levels may account for hypnotic depth and individual differences in hypnotizability is provided with traditional EEG rhythms, event-related potentials, and 40-Hz EEG activity. The alteration of stimulus perception may be a secondary effect with respect to allocation of attentional resources. In both nonhypnosis and hypnosis conditions, high hypnotizables appeared to show greater task-related EEG hemispheric shifts than did low hypnotizables. Findings concerning cognitive and physiological correlates of hypnotic analgesia are discussed with respect to hemispheric functioning in the apparent control of focused and sustained attention. The conclusion is that although a definitive EEG-based signature for hypnosis and hypnotizability is not yet established, there are a number of promising leads.

Increased gamma-range activity in human sensorimotor cortex during performance of visuomotor tasks

OBJECTIVE

We documented changes in spectral power of human electrocorticograms (ECoG) during performance of sensorimotor tasks.

METHODS

In 6 human subjects, ECoGs were recorded simultaneously from 14 subdural cortical sites in forearm sensorimotor cortex. The subjects performed 3 visuomotor tasks: tracking a moving visual target with a joystick-controlled cursor, threading pieces of tubing, and pinching the fingers sequentially against the thumb. Control conditions consisted of passive resting and active extension of the wrist. For each site the spectral power of the ECoG during these behaviors was computed for 5 10 Hz ranges between 10 and 60 Hz.

RESULTS

All subjects showed power decreases in the range of 11-20 Hz and power increases in the 31-60 Hz range during performance of the visuomotor tasks, at sites in forearm sensorimotor cortex and adjacent areas. Simple wrist movements often produced little change in power. Three subjects showed episodes of explicit gamma oscillations during the visuomotor tasks. Different sites showed increases in gamma-range power for different tasks, indicating that the spatial distribution of the gamma activity is specific to the tasks. Cross-spectra showed that gamma activity could become synchronized between separate sites during particular tasks.

CONCLUSIONS

Synchronized gamma-range activity in human sensorimotor cortex increases with performance of manipulative visuomotor tasks, supporting the hypothesis that coherent gamma oscillations may play a role in sensorimotor integration or attention.

High-frequency brain activity: its possible role in attention, perception and language processing

Coherent high-frequency neuronal activity has been proposed as a physiological indicator of perceptual and higher cognitive processes. Some of these processes can only be investigated in humans and the use of non-invasive recording techniques appears to be a prerequisite for investigating their physiological substrate in the healthy human brain. After addressing methodological issues in the non-invasive recording of high-frequency responses, we summarize studies indicating co-occurrence of neuronal synchrony of single cells exhibiting rhythmic activity at high frequencies, oscillations in the local field potential and dynamics in high frequencies recorded using high-resolution electroencephalography (EEG) and magnetoencephalography (MEG). We then review EEG and MEG studies of attention, perception, and language processing in humans indicating that dynamics in the high-frequency range > 20 Hz reflect specific cognitive processes. Types of high-frequency (HF) activity can be distinguished according to their latency after stimulus onset, stimulus-locking, cortical topography and frequency. There appears to be a systematic relationship between specific cognitive processes and types of HF activity. The findings are related to recent theories about the generation of HF activity and their possible role in binding of stimulus features. Dynamics of HF cortical activity reflecting higher cognitive processes can be accounted for based on the assumption that the elements of cognitive processing, e.g. visual objects and words, are organized in the brain as distributed neuronal assemblies with defined cortical topographies generating well-timed spatio-temporal activity patterns.

The transient 40-Hz response, mismatch negativity, and attentional processes in humans

1. Recent experimental studies on the neurophysiological basis of auditory selective attention and sensory memory forming the sensory-data basis for tuning the selective-attention system in humans are reviewed. 2. The results demonstrate that the transient 40-Hz response is enhanced by selective attention, attenuated in the course of long-term stimulation, but is not affected by changes in auditory stimuli. 3. Therefore, the 40-Hz response seems to be closely related to selective and sustained attention, whereas it does not seem to be associated with passive attention, as it does not reflect the detection of changes in auditory stimuli. 4. Changes in auditory stimulation are registered by pre-attentive sensory memory, indexed by the mismatch negativity (MMN), a change-specific component of the event-related potentials (ERPs). By this time, the transient 40-Hz response has already terminated. The magnitude of stimulus change is reflected in MMN latency. These latency changes predict changes in attentive reaction time (RT). 5. Thus, the pre-attentive memory mechanism seems to govern attentive detection of changes in the auditory environment. 6. It is concluded that the transient 40-Hz response is related to active attention and MMN is related to passive attention.

Distributed gamma band responses in the brain studied in cortex, reticular formation, hippocampus and cerebellum

The transient evoked responses of auditory cortex, reticular formation, hippocampus and cerebellar cortex to auditory stimulation have been analysed in the gamma frequency band on cats with chronically implanted electrodes. We found gamma band transient responses consisting of wave packets with 3-4 oscillations in all of the studied brain structures in the first 100 ms of the poststimulus period. The responses were strongly time-locked to the stimulation time point. The observation that the gamma band responses exist simultaneously in various brain structures supports the tentative proposal of our group on the "diffuse gamma response system" of the brain, which seems to be an important, universal operator in brain function. Furthermore, it shows that in search for generalized approaches to brain phenomena it is important to analyse the simultaneous behavior of different brain structures.

High-frequency cortical responses reflect lexical processing: an MEG study

Meaningful words and matched pseudowords, such as moon vs. noom, are of equal perceptual complexity, but invoke different cognitive processes. To investigate high-frequency cortical responses to these stimuli, biomagnetic signals were recorded simultaneously over both hemispheres of right-handed individuals listening to words and pseudowords. Consistent with earlier EEG studies, evoked spectral responses recorded from the left hemisphere revealed depression of spectral power in the low gamma band (around 30 Hz) after pseudowords but not after words. Similar differences between stimulus categories were present in the beta range. These results indicate that distinct patterns of high-frequency cortical responses correspond to the different cognitive processes invoked by words and pseudowords. It is hypothesized that differential high-frequency cortical responses signal the activation or activation failure of distributed Hebbian cell assemblies representing words and other elements of cognitive processing.

Growth hormone-regulatory peptides (GHRH and somatostatin) and feeding: a model for the integration of central and peripheral function

The present paper provides an overview of findings that implicate growth hormone-releasing hormone (GHRH) and somatostatin (SS), the two peptides that regulate growth hormone secretion, in the central regulation of feeding. Evidence is presented that GHRH and SS increase food intake, in the rat, via a common centrally mediated mechanism involving the suprachiasmatic nucleus. Food intake is increased by increasing motivation to eat as evidenced by facilitation of operant behavior. Macronutrient-choice studies indicate that GHRH (and possibly SS) selectively facilitate protein consumption. Time of day is also important, with evidence that endogenous GHRH and SS-induced feeding is most strong in the early nocturnal period. GHRH and SS, together with other nutrient-specific signals, such as neuropeptide Y, noradrenaline and galanin, may determine the circadian expression of food intake in animals. Other behavioral and physiological effects of these peptides, both central and peripheral, are reviewed in the context of a possible mechanism by which these peptides integrate diverse, but complimentary, central and peripheral functions related to nutrition, metabolism and growth.

Electrophysiological evidence of lateralized disturbances in children with learning disabilities

This study used an electrophysiological measurement operation to investigate lateralized processing deficits associated with academic learning-disability subtypes. Fast frequency EEG activity in the 36-44 hertz (Hz) band was recorded from reading-disabled (RLD), arithmetic-disabled (ALD), and nondisabled control children engaged in verbal and nonverbal cognitive tasks. The control group, but neither LD group, exhibited a task-dependent shift in lateralization of 40 Hz EEG; the RLD subjects generated proportionately less left-hemisphere 40 Hz activity than control or ALD subjects during the verbal task; and the ALD subjects generated proportionately less right-hemisphere activity than control or RLD subjects during the nonverbal task. These results indicate that lateralized processing deficits are associated with different types of disabilities, and provide external validation of learning-disability classifications based on academic performance patterns.

A compound P300-40 Hz response of the cat hippocampus

In companion reports (Başar-Eroglu et al., in press a,b) it was shown that the hippocampal P300 response had a frequency content with prominent theta enhancement, especially near CA3 region. Moreover, frequency analysis revealed a marked component in the 40 Hz frequency range. In the present study, a detailed account about "40 Hz response accompanied by the N200-P300 compound response" is given. These results were obtained by use of digital adaptive filtering method described in previous studies (Başar et al., 1987, Başar, 1980). The physiological interpretation of the visual 40 Hz component gained tremendous importance since the discovery of Gray and Singer (1987, 1989) of 40 Hz oscillations in the visual cortex. Our analysis shows clearly that the 40 Hz response component is not only a cortical response pattern. Moreover, the 40 Hz response is accompanied by a P300 response and we discuss that it is also a universal building block of brain responsiveness. The 40 Hz response should be correlated with multimodal sensory and cognitive function.

40-Hz EEG activity during hypnotic induction and hypnotic testing

The present study evaluates changes in left and right 40-Hz EEG production for 19 high and 20 low hypnotizable female Ss during the hypnotic induction and the administration of the Stanford Hypnotic Susceptibility Scale, Form C (SHSS:C) of the Weitzenhoffer and Hilgard (1962). Scalp recorded 40-Hz EEG density was obtained from the middle of the O1-P3-T5 and O2-P4-T6 triangles. As the hypnotic induction proceeded, high hypnotizable Ss exhibited a shift to greater right-hemisphere activity as compared to a waking-state rest condition. In contrast, low hypnotizable Ss, showed a reduction in left- and right-hemisphere activity. No differences between groups for SHSS:C ideomotor items were observed. A main effect for Hypnotizability among SHSS:C imaginative items was found. A Hypnotizability x Hemisphere x Trial interaction was found for both sensory distortion and imaginative SHSS:C items. A comparison was made between low versus high hypnotizable Ss of 40-Hz EEG activity while they passed the same item. The results of these comparisons indicate that differences in brain activity might be partially related to the differences between experiencing a hypnotic suggestion or failing to do so. Significant relationships between 40-Hz EEG production and hypnotizability and 40-Hz EEG production and level of amnesia were also found.

40-Hz EEG asymmetry during recall of emotional events in waking and hypnosis: differences between low and high hypnotizables

Sixteen high and thirteen low hypnotizable women, who had participated in our previous study (De Pascalis et al., 1987), were enrolled in a hypnotic session. After the hypnotic induction they were requested to recollect 2 positive and 2 negative personal life experiences. In our previous study subjects performed similar tasks in a waking-state. Hypnotizability was evaluated the first time with the Harvard Group Scale of Hypnotic Susceptibility (Form A) and, a second time, individually, with the Stanford Hypnotic Susceptibility Scale (Form C). The State Trait Anxiety Inventory, Maudsley Personality Inventory, and Tellegen Absorption Scale were administered. Upper-trapezius electromyogram (EMG) and bilateral electroencephalogram (EEG) activities within the 35-45 Hz band were recorded. Self-report rating scores for vividness of visual imagery and emotional feeling of the material recalled were evaluated. The 40-Hz EMG amplitude and the left and right hemisphere 40-Hz EEG densities were obtained. The data collected in hypnosis were compared with those in the waking-state. High hypnotizables, with respect to the lows, displayed significantly lower 40-Hz EEG density in the rest condition. High hypnotizables, while they were in hypnosis, showed an increase of 40-Hz EEG density during emotional recall compared with rest periods. In contrast, low hypnotizables, after hypnotic induction, showed no density change during tasks compared to the rest conditions. Different hemispheric trends were found between groups. Highs showed an increase of 40-Hz EEG density over both hemisphere during positive emotions and a density increase in the right and a density reduction in the left during negative ones. This hemispheric trend was found in waking and hypnotic conditions although in the hypnotic condition more pronounced hemispheric patterns were observed. The Tellegen Absorption Scale was found positively related to hypnotizability and with the level of 40-Hz density increase on the right hemisphere during emotional tasks. High hypnotizables, with respect to the lows, were able to access affects more readily. They also showed a greater hemispheric specificity in waking and hypnotic conditions.

Hemispheric activity of 40 Hz EEG during recall of emotional events: differences between low and high hypnotizables

This study evaluates individual differences in hypnotizability as reflected in waking-state hemispheric engagement during recollection of 3 positively and 3 negatively valenced personal life events. The State-Trait Anxiety Inventory, Maudsley Personality Inventory, Tellegen Absorption Scale and Harvard Group Scale of Hypnotic Susceptibility (Form A) were administered. Electromyogram (EMG) and bilateral electroencephalogram (EEG) activities within the 40-Hz band were recorded during rest and task conditions in 22 high and 21 low hypnotizable women. Self-report rating scores for vividness of visual imagery and emotional feeling of the material recalled were evaluated. The 40-Hz EMG amplitude and both hemisphere 40-Hz EEG densities were obtained. A 40-Hz EEG ratio, as a measure of hemispheric asymmetry, and a hemispheric specificity index were also computed. High hypnotizables showed significantly lower 40-Hz EEG density than low hypnotizables in all experimental conditions. The relationship between lateralization of 40-Hz EEG and emotional processing was moderated by hypnotizability. High hypnotizables, with respect to rest condition, showed an increase of density over both left and right hemispheres during two of the three positive emotional tasks, while they showed a depressed activity over the left and an increased activity over the right during negative emotional tasks. Low hypnotizables, on the other hand, did not exhibit differential hemispheric patterns that could be attributed to different emotional valences. The high group showed greater hemispheric specificity in the predicted direction than the low group. High subjects exhibited greater ratings of absorptive ability and emotional feeling than low subjects. Anxiety and EMG levels did not differ between groups. EMG was dependent on the type of emotion which showed greater activity in the negative emotion condition compared with the positive one.

The associations between 40 Hz-EEG and the middle latency response of the auditory evoked potential

The study of the 40 Hz activity of the brain which was begun by Adrian (1942) has been furthered for the past years with several new approaches: A neural model for the generation of 40 Hz activity in attention has been published by Freeman (1975) whereas new possibilities in clinical applications and exploration of cognitive processes in an extended manner was proposed by Galambos and coworkers (1981). The present study demonstrates the relation between 40 Hz spontaneous activity in human EEG-recordings and the middle latency response of the auditory evoked potentials. The applied signal analysis method allows also a single trial analysis of EEG-EP epochs which can be extended in studies on cognitive processes. A perspective concerning the middle latency response of the auditory AEP is also given.

Task-related EEG asymmetries: a comparison of alpha blocking and beta enhancement

Alpha and beta content of spectrally analyzed EEG were used to assess differential hemispheric engagement during two linguistic tasks (semantic and phonetic) and one acoustic task involving detection of target items embedded within the same stimulus series. Beta content of the EEG increased reliably in the left hemisphere during the linguistic tasks, whereas the expected attenuation or blocking of alpha did not occur reliably. These data suggest that left hemisphere beta enhancement rather than alpha blocking is a more efficient index of differential hemispheric engagement during language processing.

Lateralized cortical/cognitive processing and bilateral electrodermal activity: effects of sensory mode and sex

Forty-eight subjects were assigned to four equal-size cells defined by sex and familial handedness (presence versus absence of an immediate family member who is left-handed or ambidextrous). Subjects were presented a series of 40 stimuli, each of which was designed to represent the intersection of a sensory mode (visual versus auditory) and hemisphere mode (verbal versus spatial). The dependent measures were the number of stimulus-specific and nonspecific responses with magnitude larger on the lefthand. On the whole, results are supportive of the contralateral inhibitory process hypothesized by LaCroix and Comper (1979). Nonspecific response data appear to be sensitive to hemispheric manipulation as observed previously in this laboratory. Sensory mode appears to be an important determinant of lateralized phasic magnitude differences, with males showing the most striking verbal-spatial distinctions during visual mode presentation.

A 40-Hz auditory potential recorded from the human scalp

Computer techniques readily extract from the brainwaves an orderly sequence of brain potentials locked in time to sound stimuli. The potentials that appear 8 to 80 msec after the stimulus resemble 3 or 4 cycles of a 40-Hz sine wave; we show here that these waves combined to form a single, stable, composite wave when the sounds are repeated at rates around 40 per sec. This phenomenon, the 40-Hz event-related potential (ERP), displays several properties of theoretical and practical interest. First, it reportedly disappears with surgical anesthesia, and it resembles similar phenomena in the visual and olfactory system, facts which suggest that adequate processing of sensory information may require cyclical brain events in the 30- to 50-Hz range. Second, latency and amplitude measurements on the 40-Hz ERP indicate it may contain useful information on the number and basilar membrane location of the auditory nerve fibers a given tone excites. Third, the response is present at sound intensities very close to normal adult thresholds for the audiometric frequencies, a fact that could have application in clinical hearing testing.

Some quantitative hemispheric EEG measures reflecting the affective profile of students differing in university academic success

Quantitative measurements of the integrated epoch based EEG amplitudes obtained from two groups of university students differing in academic success during an eyes close, relaxed state revealed significantly higher right/left amplitude variance ratios and more right hemispheric non-Gaussian cumulated amplitude distributions among unsuccessful students. These data, which resemble patterns often found in depression, are consistent with, and appear to reflect specific affective differences that emerge using a concurrently administered, conventional psychometric inventory (Beck Depression Inventory) as well as a subjective self-assessment questionnaire. The results of this study may be useful in further elaborating the nature in which right hemispheric brain processes serve to mediate affective behavior, as well as influence academic performance.