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Individual variation in the experience and expression of pleasure may relate to differential patterns of lateral frontal activity. Brain electrical measures have been used to study the asymmetric involvement of lateral frontal cortex in positive emotion, but the excellent time resolution of these measures has not been used to capture second-by-second changes in ongoing emotion until now. The relationship between pleasure and second-by-second lateral frontal activity was examined with the use of hierarchical linear modeling in a sample of 128 children ages 6-10 years. Electroencephalographic activity was recorded during "pop-out toy," a standardized task that elicits pleasure. The task consisted of 3 epochs: an anticipation period sandwiched between 2 play periods. The amount of pleasure expressed during the task predicted the pattern of nonlinear change in lateral frontal activity. Children who expressed increasing amounts of pleasure during the task exhibited increasing left lateral frontal activity during the task, whereas children who expressed contentment exhibited increasing right/decreasing left activity. These findings indicate that task-dependent changes in pleasure relate to dynamic, nonlinear changes in lateral frontal activity as the task unfolds.
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An overview of the use of EEG to assess hemispheric differences in cognitive and affective processes is presented. Some of the advantages of using EEG to assess asymmetric hemispheric differences in the study of complex mental activity are described. Following this brief introduction, two conceptual issues which are central to studies of EEG asymmetries are introduced: (1) the distinction between hemispheric specialization and activation, and (2) the importance of rostral-caudal differences for the understanding of both specialization and activation. Three methodological issues in the use of EEG to assess hemispheric differences are then presented: (1) the use of asymmetry metrics, (2) muscle artifact, and (3) appropriate reference electrode location. Finally, some empirical examples of using EEG to assess affective and cognitive processes which illustrate these conceptual and methodological issues are described.
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Experienced Qigong meditators who regularly perform the exercises “Thinking of Nothing” and “Qigong” were studied with multichannel EEG source imaging during their meditations. The intracerebral localization of brain electric activity during the two meditation conditions was compared using sLORETA functional EEG tomography. Differences between conditions were assessed using t statistics (corrected for multiple testing) on the normalized and log-transformed current density values of the sLORETA images. In the EEG alpha-2 frequency, 125 voxels differed significantly; all were more active during “Qigong” than “Thinking of Nothing,” forming a single cluster in parietal Brodmann areas 5, 7, 31, and 40, all in the right hemisphere. In the EEG beta-1 frequency, 37 voxels differed significantly; all were more active during “Thinking of Nothing” than “Qigong,” forming a single cluster in prefrontal Brodmann areas 6, 8, and 9, all in the left hemisphere. Compared to combined initial–final no-task resting, “Qigong” showed activation in posterior areas whereas “Thinking of Nothing” showed activation in anterior areas. The stronger activity of posterior (right) parietal areas during “Qigong” and anterior (left) prefrontal areas during “Thinking of Nothing” may reflect a predominance of self-reference, attention and input-centered processing in the “Qigong” meditation, and of control-centered processing in the “Thinking of Nothing” meditation.

OBJECTIVE: High-density EEG recording offers increased spatial resolution but requires careful consideration of how the density of electrodes affects the potentials being measured. Power differences as a function of electrode density and electrolyte spreading were examined and a method for correcting these differences was tested. METHODS: Separate EEG recordings from 8 participants were made using a high-density electrode net, first with 6 of 128 electrodes active followed by recordings with all electrodes active. For a subset of 4 participants measurements were counterbalanced with recordings made in the reversed order by drying the hair after the high-density recordings and using a fresh dry electrode net of the same size for the low-density recordings. Mean power values over 6 resting eyes open/closed EEG recordings at the 6 active electrodes common to both recording conditions were compared. Evidence for possible electrolyte spreading or bridging between electrodes was acquired by computing Hjorth electrical distances. Spherical spline interpolation was tested for correcting power values at electrodes affected by electrolyte spreading for these participants and for a subset of participants from a larger previous study. RESULTS: For both the complete set and the counterbalanced subset, significant decreases in power at the 6 common electrodes for the high-density recordings were observed across the range of the standard EEG bands (1-44 Hz). The number of bridges or amount of electrolyte spreading towards the reference electrode as evidenced by small Hjorth electrical distances served as a predictor of this power decrease. Spherical spline interpolation increased the power values at electrodes affected by electrolyte spreading and by a significant amount for the larger number of participants in the second group. CONCLUSIONS: Understanding signal effects caused by closely spaced electrodes, detecting electrolyte spreading and correcting its effects are important considerations for high-density EEG recordings. A combination of scalp maps of power density and plots of small Hjorth electrical distances can be used to identify electrodes affected by electrolyte spreading. Interpolation using spherical splines offers a method for correcting the potentials measured at these electrodes.
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Two groups of subjects classified as high vs. low in the need for power (n power) were assessed for augmenting versus reducing in the event-related potential (ERP) elicited by neutral and power-related words. Words at four different intensity levels in each of these two classes were randomly presented and ERPs in response to each word class at each of the four intensity levels were computed from EEG recorded at Fz. The results indicated that the two groups responded differentially to the power-related vs. neutral words. HIgh n power subjects showed reduction in response to both power-related and neutral words while low n power subjects showed augmentation in response to the power-related words.
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Two groups of subjects classified as high vs. low in the need for power (n power) were assessed for augmenting versus reducing in the event-related potential (ERP) elicited by neutral and power-related words. Words at four different intensity levels in each of these two classes were randomly presented and ERPs in response to each word class at each of the four intensity levels were computed from EEG recorded at Fz. The results indicated that the two groups responded differentially to the power-related vs. neutral words. HIgh n power subjects showed reduction in response to both power-related and neutral words while low n power subjects showed augmentation in response to the power-related words.

Muscle or electromyogenic (EMG) artifact poses a serious risk to inferential validity for any electroencephalography (EEG) investigation in the frequency-domain owing to its high amplitude, broad spectrum, and sensitivity to psychological processes of interest. Even weak EMG is detectable across the scalp in frequencies as low as the alpha band. Given these hazards, there is substantial interest in developing EMG correction tools. Unfortunately, most published techniques are subjected to only modest validation attempts, rendering their utility questionable. We review recent work by our laboratory quantitatively investigating the validity of two popular EMG correction techniques, one using the general linear model (GLM), the other using temporal independent component analysis (ICA). We show that intra-individual GLM-based methods represent a sensitive and specific tool for correcting on-going or induced, but not evoked (phase-locked) or source-localized, spectral changes. Preliminary work with ICA shows that it may not represent a panacea for EMG contamination, although further scrutiny is strongly warranted. We conclude by describing emerging methodological trends in this area that are likely to have substantial benefits for basic and applied EEG research.
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In two prior studies, we investigated the neural mechanisms of spatial attention using a combined event-related potential (ERP) and positron emission tomography (PET) approach (Heinze et al. [1994]: Nature 392:543-546; Mangun et al. [1997]: Hum Brain Mapp 5:273-279). Neural activations in extrastriate cortex were observed in the PET measures for attended stimuli, and these effects were related to attentional modulations in the ERPs at specific latencies. The present study used functional magnetic resonance imaging (fMRI) and ERPs in single subjects to investigate the intersubject variability in extrastriate spatial attention effects, and to qualitatively compare this to variations in ERP attention effects. Activations in single subjects replicated our prior group-averaged PET findings, showing attention-related increases in blood flow in the posterior fusiform and middle occipital gyri in the hemisphere contralateral to attended visual stimuli. All subjects showed attentional modulations of the occipital P1 component of the ERPs. These findings in single subjects demonstrate the consistency of extrastriate attention effects, and provide information about the feasibility of this approach for integration of electrical and functional imaging data.
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Long-term Vipassana meditators sat in meditation vs. a control (instructed mind wandering) states for 25 min, electroencephalography (EEG) was recorded and condition order counterbalanced. For the last 4 min, a three-stimulus auditory oddball series was presented during both meditation and control periods through headphones and no task imposed. Time-frequency analysis demonstrated that meditation relative to the control condition evinced decreased evoked delta (2–4 Hz) power to distracter stimuli concomitantly with a greater event-related reduction of late (500–900 ms) alpha-1 (8–10 Hz) activity, which indexed altered dynamics of attentional engagement to distracters. Additionally, standard stimuli were associated with increased early event-related alpha phase synchrony (inter-trial coherence) and evoked theta (4–8 Hz) phase synchrony, suggesting enhanced processing of the habituated standard background stimuli. Finally, during meditation, there was a greater differential early-evoked gamma power to the different stimulus classes. Correlation analysis indicated that this effect stemmed from a meditation state-related increase in early distracter-evoked gamma power and phase synchrony specific to longer-term expert practitioners. The findings suggest that Vipassana meditation evokes a brain state of enhanced perceptual clarity and decreased automated reactivity.

High vs. low scorers on the Beck Depression Inventory (BDI) were compared on measures of resting EEG activation asymmetry from frontal and parietal brain regions. Depressed subjects showed greater relative right frontal activation compared with nondepressed subjects. Parietal asymmetry did not distinguish between the groups. These data support the hypothesis of right hemisphere hyperactivation in the frontal region of depressed individuals and are consistent with the growing body of literature which suggests that the left and right frontal regions may be differentially specialized for particular positive and negative affects.
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We assessed whether resting anterior asymmetry would discriminate individual differences in repressive-defensive coping styles. In 2 sessions, resting electroencephalogram was recorded from female adults during 8 60-s baselines. Subjects were classified as repressors or nonrepressors on the basis of scores on the Marlowe-Crowne Social Desirability Scale (MC), the State-Trait Anxiety Inventory (STAI), and the Beck Depression Inventory (BDI). In midfrontal and lateral frontal sites, repressors demonstrated relative left hemisphere activation when compared with other groups. The MC, but not the STAI or the BDI, contributed unique variance to frontal asymmetry. Relative left frontal activation may be linked to a self-enhancing regulatory style that promotes lowered risk for psychopathology.
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The influence of approach and avoidance tendencies on affect, reasoning, and behavior has attracted substantial interest from researchers across various areas of psychology. Currently, frontal electroencephalographic (EEG) asymmetry in favor of left prefrontal regions is assumed to reflect the propensity to respond with approach-related tendencies. To test this hypothesis, we recorded resting EEG in 18 subjects, who separately performed a verbal memory task under three incentive conditions (neutral, reward, and punishment). Using a source-localization technique, we found that higher task-independent alpha2 (10.5-12 Hz) activity within left dorsolateral prefrontal and medial orbitofrontal regions was associated with stronger bias to respond to reward-related cues. Left prefrontal resting activity accounted for 54.8% of the variance in reward bias. These findings not only confirm that frontal EEG asymmetry modulates the propensity to engage in appetitively motivated behavior, but also provide anatomical details about the underlying brain systems.
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Examined whether certain features of infant temperament might be related to individual differences in the asymmetry of resting frontal activation. EEG was recorded from the left and right frontal and parietal scalp regions of 13 normal 10-month-old infants. Infant behavior was then observed during a brief period of maternal separation. Those infants who cried in response to maternal separation showed greater right frontal activation during the preceding baseline period compared with infants who did not cry. Frontal activation asymmetry may be a state-independent marker for individual differences in threshold of reactivity to stressful events and vulnerability to particular emotions.
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Major depression is a heterogeneous condition, and the search for neural correlates specific to clinically defined subtypes has been inconclusive. Theoretical considerations implicate frontostriatal, particularly subgenual prefrontal cortex (PFC), dysfunction in the pathophysiology of melancholia--a subtype of depression characterized by anhedonia--but no empirical evidence has been found yet for such a link. To test the hypothesis that melancholic, but not nonmelancholic depression, is associated with the subgenual PFC impairment, concurrent measurement of brain electrical (electroencephalogram, EEG) and metabolic (positron emission tomography, PET) activity were obtained in 38 unmedicated subjects with DSM-IV major depressive disorder (20 melancholic, 18 nonmelancholic subjects), and 18 comparison subjects. EEG data were analyzed with a tomographic source localization method that computed the cortical three-dimensional distribution of current density for standard frequency bands, allowing voxelwise correlations between the EEG and PET data. Voxel-based morphometry analyses of structural magnetic resonance imaging (MRI) data were performed to assess potential structural abnormalities in melancholia. Melancholia was associated with reduced activity in the subgenual PFC (Brodmann area 25), manifested by increased inhibitory delta activity (1.5-6.0 Hz) and decreased glucose metabolism, which themselves were inversely correlated. Following antidepressant treatment, depressed subjects with the largest reductions in depression severity showed the lowest post-treatment subgenual PFC delta activity. Analyses of structural MRI revealed no group differences in the subgenual PFC, but in melancholic subjects, a negative correlation between gray matter density and age emerged. Based on preclinical evidence, we suggest that subgenual PFC dysfunction in melancholia may be associated with blunted hedonic response and exaggerated stress responsiveness.
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The relationships between brain electrical and metabolic activity are being uncovered currently in animal models using invasive methods; however, in the human brain this relationship remains not well understood. In particular, the relationship between noninvasive measurements of electrical activity and metabolism remains largely undefined. To understand better these relations, cerebral activity was measured simultaneously with electroencephalography (EEG) and positron emission tomography using [(18)f]-fluoro-2-deoxy-D-glucose (PET-FDG) in 12 normal human subjects during rest. Intracerebral distributions of current density were estimated, yielding tomographic maps for seven standard EEG frequency bands. The PET and EEG data were registered to the same space and voxel dimensions, and correlational maps were created on a voxel-by-voxel basis across all subjects. For each band, significant positive and negative correlations were found that are generally consistent with extant understanding of EEG band power function. With increasing EEG frequency, there was an increase in the number of positively correlated voxels, whereas the lower alpha band (8.5-10.0 Hz) was associated with the highest number of negative correlations. This work presents a method for comparing EEG signals with other more traditionally tomographic functional imaging data on a 3-D basis. This method will be useful in the future when it is applied to functional imaging methods with faster time resolution, such as short half-life PET blood flow tracers and functional magnetic resonance imaging.
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Developments in technologic and analytical procedures applied to the study of brain electrical activity have intensified interest in this modality as a means of examining brain function. The impact of these new developments on traditional methods of acquiring and analyzing electroencephalographic activity requires evaluation. Ultimately, the integration of the old with the new must result in an accepted standardized methodology to be used in these investigations. In this paper, basic procedures and recent developments involved in the recording and analysis of brain electrical activity are discussed and recommendations are made, with emphasis on psychophysiological applications of these procedures.
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Recent years have seen an explosion of interest in using neural oscillations to characterize the mechanisms supporting cognition and emotion. Oftentimes, oscillatory activity is indexed by mean power density in predefined frequency bands. Some investigators use broad bands originally defined by prominent surface features of the spectrum. Others rely on narrower bands originally defined by spectral factor analysis (SFA). Presently, the robustness and sensitivity of these competing band definitions remains unclear. Here, a Monte Carlo-based SFA strategy was used to decompose the tonic ("resting" or "spontaneous") electroencephalogram (EEG) into five bands: delta (1-5Hz), alpha-low (6-9Hz), alpha-high (10-11Hz), beta (12-19Hz), and gamma (>21Hz). This pattern was consistent across SFA methods, artifact correction/rejection procedures, scalp regions, and samples. Subsequent analyses revealed that SFA failed to deliver enhanced sensitivity; narrow alpha sub-bands proved no more sensitive than the classical broadband to individual differences in temperament or mean differences in task-induced activation. Other analyses suggested that residual ocular and muscular artifact was the dominant source of activity during quiescence in the delta and gamma bands. This was observed following threshold-based artifact rejection or independent component analysis (ICA)-based artifact correction, indicating that such procedures do not necessarily confer adequate protection. Collectively, these findings highlight the limitations of several commonly used EEG procedures and underscore the necessity of routinely performing exploratory data analyses, particularly data visualization, prior to hypothesis testing. They also suggest the potential benefits of using techniques other than SFA for interrogating high-dimensional EEG datasets in the frequency or time-frequency (event-related spectral perturbation, event-related synchronization/desynchronization) domains.
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This research assessed whether individual differences in anterior brain asymmetry are linked to differences in basic dimensions of emotion. In each of 2 experimental sessions, separated by 3 weeks, resting electroencephalogram (EEG) activity was recorded from female adults during 8 60-s baselines. Mean alpha power asymmetry across both sessions was extracted in mid-frontal and anterior temporal sites. Across both regions, groups demonstrating stable and extreme relative left anterior activation reported increased generalized positive affect (PA) and decreased generalized negative affect (NA) compared with groups demonstrating stable and extreme relative right anterior activation. Additional correlational analyses revealed robust relations between anterior asymmetry and PA and NA, particularly among subjects who demonstrated stable patterns of EEG activation over time. Anterior asymmetry was unrelated to individual differences in generalized reactivity.
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Reliable individual differences in electrophysiological measures of prefrontal activation asymmetry exist and predict dispositional mood and other psychological and biological indices of affective style. Subjects with greater relative right-sided activation report more dispositional negative affect and react with greater intensity to negative emotional challenges than their left-activated counterparts. We previously established that such individual differences in measures of prefrontal activation asymmetry were related to basal NK function, with left-activated subjects exhibiting higher levels of NK function than right-activated subjects. The present study was designed to replicate and extend these earlier findings. Subjects were tested in five experimental sessions over the course of 1 year. During the first two sessions, baseline measures of brain electrical activity were obtained to derive indices of asymmetric activation. During sessions 3 and 4, blood samples were taken during a nonstressful period in the semester and then 24 h prior to the subjects' most important final examination. During session 5, subjects were presented with positive and negative film clips 30 min in duration. Blood samples were obtained before and after the film clips. Subjects with greater relative right-sided activation at baseline showed lower levels of basal NK function. They also showed a greater decrease in NK function during the final exam period compared to the baseline period. Subjects with greater relative left-sided activation showed a larger increase in NK function from before to after the positive film clip. These findings indicate that individual differences in electrophysiological measures of asymmetric prefrontal activation account for a significant portion of variance in both basal levels of, and change in NK function.
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OBJECTIVE: In this case study, we describe the effects of a particular individual's concentration/meditation technique on autonomic nervous system activity and the innate immune response. The study participant holds several world records with regard to tolerating extreme cold and claims that he can influence his autonomic nervous system and thereby his innate immune response. METHODS: The individual's ex vivo cytokine response (stimulation of peripheral blood mononuclear cells with lipopolysaccharide [LPS]) was determined before and after an 80-minute full-body ice immersion during which the individual practiced his concentration/meditation technique. Furthermore, the individual's in vivo innate immune response was studied while practicing his concentration/mediation technique during human endotoxemia (intravenous administration of 2 ng/kg LPS). The results from the endotoxemia experiment were compared with a historical cohort of 112 individuals who participated in endotoxemia experiments in our institution. RESULTS: The ex vivo proinflammatory and anti-inflammatory cytokine response was greatly attenuated by concentration/meditation during ice immersion, accompanied by high levels of cortisol. In the endotoxemia experiment, concentration/meditation resulted in increased circulating concentrations of catecholamines, and plasma cortisol concentrations were higher than in any of the previously studied participants. The individual's in vivo cytokine response and clinical symptoms after LPS administration were remarkably low compared with previously studied participants. CONCLUSIONS: The concentration/meditation technique used by this particular individual seems to evoke a controlled stress response. This response is characterized by sympathetic nervous system activation and subsequent catecholamine/cortisol release, which seems to attenuate the innate immune response.
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A growing body of literature has documented the differential role of the frontal regions of the two cerebral hemispheres in certain positive and negative affective processes. This corpus of evidence has led to the hypothesis of a possible differential effect of diazepam on asymmetry of frontal activation. To examine this question, nine infant rhesus monkeys were tested on two occasions during which brain electrical activity was recorded from left and right frontal and parietal scalp regions. During one session, recordings were obtained under a baseline restraint condition and then after an injection of diazepam (1 mg/kg). In the other session, following the same baseline restraint condition, a vehicle injection was given. In response to diazepam, the animals showed an asymmetrical decrease in power in the 4-8 Hz frequency band, which was most pronounced in the left frontal region. No change in electroencephalogram (EEG) activity was observed in response to vehicle. Asymmetry in parietal EEG activity was also unchanged by diazepam. Diazepam also produced overall reductions in power across different frequency bands in both frontal and parietal regions. Good test-retest stability of EEG measures of activation asymmetry was also found between the two testing sessions separated by three months. The possible proximal cause of the asymmetrical change in frontal brain electrical activity in response to diazepam, as well as the implications of these findings for understanding the mechanism of action of benzodiazepines are discussed.
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Based on previous findings in humans and rhesus monkeys suggesting that diazepam has asymmetrical effects on frontal lobe activity and other literature supporting a role for the benzodiazepine system in the mediation of individual differences in anxiety and fearfulness, the relation between asymmetrical changes in scalp-recorded regional brain activity in response to diazepam and the temperamental dimension of behavioral inhibition indexed by freezing time in 9 rhesus monkeys was examined. Animals showed greater relative left-sided frontal activation in response to diazepam compared with the preceding baseline. The magnitude of this shift was strongly correlated with an aggregate measure of freezing time (r = .82). The implications of these findings for understanding the role of regional differences in the benzodiazepine system in mediating individual differences in fearfulness are discussed.
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Baseline resting electroencephalogram activity was recorded with 3 different reference montages from 15 clinically depressed and 13 control subjects. Power in all frequency bands was extracted by fast Fourier transformation. There was a significant Group X Hemisphere interaction in the mid-frontal region, for the alpha band power only. Depressed subjects had less left-sided activation (i.e., more alpha activity) than did normal control subjects. This pattern of diminished left-sided frontal activation is interpreted as indicating a deficit in approach mechanisms in depressed subjects.
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