This past year has seen significant advances in our understanding of the physiology of emotion. Attention continues to focus on the amygdala and its interconnections with prefrontal cortical regions. New evidence underscores the importance of lateralization for emotion. There are also new findings on the physiological predictors of individual differences in emotional behavior and experience, and on the role of autonomic arousal in emotional memory.
The brain circuitry underlying emotion includes several territories of the prefrontal cortex (PFC), the amygdala, hippocampus, anterior cingulate, and related structures. In general, the PFC represents emotion in the absence of immediately present incentives and thus plays a crucial role in the anticipation of the future affective consequences of action, as well as in the persistence of emotion following the offset of an elicitor. The functions of the other structures in this circuit are also considered. Individual differences in this circuitry are reviewed, with an emphasis on asymmetries within the PFC and activation of the amygdala as 2 key components of affective style. These individual differences are related to both behavioral and biological variables associated with affective style and emotion regulation. Plasticity in this circuitry and its implications for transforming emotion and cultivating positive affect and resilience are considered.
This article presents an overview of the author's recent electrophysiological studies of anterior cerebral asymmetries related to emotion and affective style. A theoretical account is provided of the role of the two hemispheres in emotional processing. This account assigns a major role in approach- and withdrawal-related behavior to the left and right frontal and anterior temporal regions of two hemispheres, respectively. Individual differences in approach- and withdrawal-related emotional reactivity and temperament are associated with stable differences in baseline measures of activation asymmetry in these anterior regions. Phasic state changes in emotion result in shifts in anterior activation asymmetry which are superimposed upon these stable baseline differences. Future directions for research in this area are discussed.
OBJECTIVE: The anterior cingulate cortex has been implicated in depression. Results are best interpreted by considering anatomic and cytoarchitectonic subdivisions. Evidence suggests depression is characterized by hypoactivity in the dorsal anterior cingulate, whereas hyperactivity in the rostral anterior cingulate is associated with good response to treatment. The authors tested the hypothesis that activity in the rostral anterior cingulate during the depressed state has prognostic value for the degree of eventual response to treatment. Whereas prior studies used hemodynamic imaging, this investigation used EEG. METHOD: The authors recorded 28-channel EEG data for 18 unmedicated patients with major depression and 18 matched comparison subjects. Clinical outcome was assessed after nortriptyline treatment. Of the 18 depressed patients, 16 were considered responders 4-6 months after initial assessment. A median split was used to classify response, and the pretreatment EEG data of patients showing better (N=9) and worse (N=9) responses were analyzed with low-resolution electromagnetic tomography, a new method to compute three-dimensional cortical current density for given EEG frequency bands according to a Talairach brain atlas. RESULTS: The patients with better responses showed hyperactivity (higher theta activity) in the rostral anterior cingulate (Brodmann's area 24/32). Follow-up analyses demonstrated the specificity of this finding, which was not confounded by age or pretreatment depression severity. CONCLUSIONS: These results, based on electrophysiological imaging, not only support hemodynamic findings implicating activation of the anterior cingulate as a predictor of response in depression, but they also suggest that differential activity in the rostral anterior cingulate is associated with gradations of response.
Two reports in the last issue of this journal attempted to replicate aspects of our previous studies on anterior electroencephalogram (EEG) asymmetry, affective style, and depression. In this commentary, an overview is provided of our model of anterior asymmetries, affective style, and psychopathology. Emphasis is placed on conceptualizing the prefrontal and anterior temporal activation patterns within a circuit that includes cortical and subcortical structures. The causal status of individual differences in asymmetric activation in the production of affective style and psychopathology is considered. Major emphasis is placed on EEG methods, particularly the need for multiple assessments to obtain estimates of asymmetric activation that better reflect an individual's true score. Issues specific to each of the two articles are also considered. Each of the articles has more consistency with our previously published data than the authors themselves suggest. Recommendations are made for future research to resolve some of the outstanding issues.
In this experiment, we combined the measurement of observable facial behavior with simultaneous measures of brain electrical activity to assess patterns of hemispheric activation in different regions during the experience of happiness and disgust. Disgust was found to be associated with right-sided activation in the frontal and anterior temporal regions compared with the happy condition. Happiness was accompanied by left-sided activation in the anterior temporal region compared with disgust. No differences in asymmetry were found between emotions in the central and parietal regions. When data aggregated across positive films were compared to aggregate negative film data, no reliable differences in brain activity were found. These findings illustrate the utility of using facial behavior to verify the presence of emotion, are consistent with the notion of emotion-specific physiological patterning, and underscore the importance of anterior cerebral asymmetries for emotions associated with approach and withdrawal.
Ten-month-old infants viewed videotape segments of an actress spontaneously generating a happy or sad facial expression. Brain activity was recorded from the left and right frontal and parietal scalp regions. In two studies, infants showed greater activation of the left frontal than of the right frontal area in response to the happy segments. Parietal asymmetry failed to discriminate between the conditions. Differential lateralization of the hemispheres for affective processes seems to be established by 10 months of age.
This study compared the asymmetry of different features of brain electrical activity during the performance of a verbal task (word finding) and a spatial task (dot localization) that had been carefully matched on psychometric properties and accompanying motor activity. Nineteen right-handed subjects were tested. EEG was recorded from F3, F4, C3, C4, P3, and P4, referred to both CZ and computer-derived averaged-ears references, and Fourier transformed. Power in the delta, theta, alpha, and beta bands was computed. There were significant Task X Hemisphere effects in all bands for CZ-referenced data and for the alpha and beta bands for ears-referenced data. The effects were always either greater power suppression in the hemisphere putatively most engaged in task processing or greater power in the opposite hemisphere. Correlations between EEG and task performance indicated that CZ-referenced parietal alpha asymmetry accounted for the most variance in verbal task performance. Power within individual hemispheres or across hemispheres was unrelated to task performance. The findings indicate robust differences in asymmetrical brain physiology that are produced by well-matched verbal and spatial cognitive tasks.
The authors examined the hypothesis that rhesus monkeys with extreme right frontal electroencephalographic activity would have higher cortisol levels and would be more fearful compared with monkeys with extreme left frontal activity. The authors first showed that individual differences in asymmetric frontal electrical activity are a stable characteristic. Next, the authors demonstrated that relative right asymmetric frontal activity and cortisol levels are correlated in animals 1 year of age. Additionally, extreme right frontal animals had elevated cortisol concentrations and more intense defensive responses. At 3 years of age, extreme right frontal animals continued to have elevated cortisol concentrations. These findings demonstrate important relations among extreme asymmetric frontal electrical activity, cortisol levels, and trait-like fear-related behaviors in young rhesus monkeys.
Thirty-two participants were tested for both resting electroencephalography (EEG) and neuropsychological function. Eight one-minute trials of resting EEG were recorded from 14 channels referenced to linked ears, which was rederived to an average reference. Neuropsychological tasks included Verbal Fluency, the Tower of London, and Corsi's Recurring Blocks. Asymmetries in EEG alpha activity were correlated with performance on these tasks. Similar patterns were obtained for delta and theta bands. Factor analyses of resting EEG asymmetries over particular regions suggested that asymmetries over anterior scalp regions may be partly independent from those over posterior scalp regions. These results support the notions that resting EEG asymmetries are specified by multiple mechanisms along the rostral/caudal plane, and that these asymmetries predict task performance in a manner consistent with lesion and neuroimaging studies.
BACKGROUND: Studies using electroencephalogram (EEG) measures of activation asymmetry have reported differences in anterior asymmetry between depressed and nondepressed subjects. Several studies have suggested reciprocal relations between measures of anterior and posterior activation asymmetries. We hypothesized that depressed subjects would fail to show the normal activation of posterior right hemisphere regions in response to an appropriate cognitive challenge. METHODS: EEG activity was recorded from 11 depressed and 19 nondepressed subjects during the performance of psychometrically matched verbal (word finding) and spatial (dot localization) tasks. Band power was extracted from all epochs of artifact-free data and averaged within each condition. Task performance was also assessed. RESULTS: Depressed subjects showed a specific deficit in the performance of the spatial task, whereas no group differences were evident on verbal performance. In posterior scalp regions, nondepressed controls had a pattern of relative left-sided activation during the verbal task and relative right-sided activation during the spatial task. In contrast, depressed subjects failed to show activation in posterior right hemisphere regions during spatial task performance. CONCLUSIONS: These findings suggest that deficits in right posterior functioning underlie the observed impairments in spatial functioning among depressed subjects.
BACKGROUND: Asymmetric patterns of frontal brain activity and brain corticotropin-releasing hormone (CRH) systems have both been separately implicated in the processing of normal and abnormal emotional responses. Previous studies in rhesus monkeys demonstrated that individuals with extreme right frontal asymmetric brain electrical activity have high levels of trait-like fearful behavior and increased plasma cortisol concentrations. METHODS: In this study we assessed cerebrospinal fluid (CSF) CRH concentrations in monkeys with extreme left and extreme right frontal brain electrical activity. CSF was repeatedly collected at 4, 8, 14, 40, and 52 months of age. RESULTS: Monkeys with extreme right frontal brain activity had increased CSF CRH concentrations at all ages measured. In addition, individual differences in CSF CRH concentrations were stable from 4 to 52 months of age. CONCLUSIONS: These findings suggest that, in primates, the fearful endophenotype is characterized by increased fearful behavior, a specific pattern of frontal electrical activity, increased pituitary-adrenal activity, and increased activity of brain CRH systems. Data from other preclinical studies suggests that the increased brain CRH activity may underlie the behavioral and physiological characteristics of fearful endophenotype.
Motion correction of fMRI data is a widely used step prior to data analysis. In this study, a comparison of the motion correction tools provided by several leading fMRI analysis software packages was performed, including AFNI, AIR, BrainVoyager, FSL, and SPM2. Comparisons were performed using data from typical human studies as well as phantom data. The identical reconstruction, preprocessing, and analysis steps were used on every data set, except that motion correction was performed using various configurations from each software package. Each package was studied using default parameters, as well as parameters optimized for speed and accuracy. Forty subjects performed a Go/No-go task (an event-related design that investigates inhibitory motor response) and an N-back task (a block-design paradigm investigating working memory). The human data were analyzed by extracting a set of general linear model (GLM)-derived activation results and comparing the effect of motion correction on thresholded activation cluster size and maximum t value. In addition, a series of simulated phantom data sets were created with known activation locations, magnitudes, and realistic motion. Results from the phantom data indicate that AFNI and SPM2 yield the most accurate motion estimation parameters, while AFNI's interpolation algorithm introduces the least smoothing. AFNI is also the fastest of the packages tested. However, these advantages did not produce noticeably better activation results in motion-corrected data from typical human fMRI experiments. Although differences in performance between packages were apparent in the human data, no single software package produced dramatically better results than the others. The "accurate" parameters showed virtually no improvement in cluster t values compared to the standard parameters. While the "fast" parameters did not result in a substantial increase in speed, they did not degrade the cluster results very much either. The phantom and human data indicate that motion correction can be a valuable step in the data processing chain, yielding improvements of up to 20% in the magnitude and up to 100% in the cluster size of detected activations, but the choice of software package does not substantially affect this improvement.
Three experiments were performed testing the effects of a variety of impedance cardiograph electrode types and recording arrangements on recorded electroencephalography (EEG) using either a monopolar single-ear reference or a physically linked ears reference. EEG was recorded either alone or concurrently with an impedance cardiograph. When the cardiograph was recorded using a spot electrode for the top current-inducing electrode, there was an overall decrease in power density of the EEG, and this effect was dependent on the location of the recording electrode. This effect was diminished when the top cardiograph spot electrode was replaced by a mylar-coated neck band electrode and EEG was recorded using a monopolar, single-ear reference. However, there tended to be an overall increase in log power density of the EEG in each frequency band below 60 Hz when less technologically advanced EEG amplifiers were used. This effect was diminished if the EEG was recorded using a physically linked ears reference. Recommendations for the concurrent recording of EEG and impedance cardiography are discussed.
The corticotrophin-releasing hormone (CRH) system integrates the stress response and is associated with stress-related psychopathology. Previous reports have identified interactions between childhood trauma and sequence variation in the CRH receptor 1 gene (CRHR1) that increase risk for affective disorders. However, the underlying mechanisms that connect variation in CRHR1 to psychopathology are unknown. To explore potential mechanisms, we used a validated rhesus macaque model to investigate association between genetic variation in CRHR1, anxious temperament (AT) and brain metabolic activity. In young rhesus monkeys, AT is analogous to the childhood risk phenotype that predicts the development of human anxiety and depressive disorders. Regional brain metabolism was assessed with (18)F-labeled fluoro-2-deoxyglucose (FDG) positron emission tomography in 236 young, normally reared macaques that were also characterized for AT. We show that single nucleotide polymorphisms (SNPs) affecting exon 6 of CRHR1 influence both AT and metabolic activity in the anterior hippocampus and amygdala, components of the neural circuit underlying AT. We also find evidence for association between SNPs in CRHR1 and metabolism in the intraparietal sulcus and precuneus. These translational data suggest that genetic variation in CRHR1 affects the risk for affective disorders by influencing the function of the neural circuit underlying AT and that differences in gene expression or the protein sequence involving exon 6 may be important. These results suggest that variation in CRHR1 may influence brain function before any childhood adversity and may be a diathesis for the interaction between CRHR1 genotypes and childhood trauma reported to affect human psychopathology.
This study was designed to test the hypothesis that Japanese subjects exhibit different patterns of resting EEG asymmetry compared with Westerners. EEG was recorded from the left and right temporal and parietal scalp regions in bilingual Japanese and Western subjects during eyes-open and eyes-closed rest periods before and after the performance of a series of cognitive tasks. Alpha activity was integrated and digitized. Japanese subjects were found to exhibit greater relative right-sided parietal activation during the eyes closed condition. This difference was found to be a function of greater left hemisphere activation among the Westerners. Various possible contributors to this cross-cultural differences are discussed.
Facial expression, EEG, and self-report of subjective emotional experience were recorded while subjects individually watched both pleasant and unpleasant films. Smiling in which the muscle that orbits the eye is active in addition to the muscle that pulls the lip corners up (the Duchenne smile) was compared with other smiling in which the muscle orbiting the eye was not active. As predicted, the Duchenne smile was related to enjoyment in terms of occurring more often during the pleasant than the unpleasant films, in measures of cerebral asymmetry, and in relation to subjective reports of positive emotions, and other smiling was not.
Asymmetry of waking electroencephalography (EEG) alpha power in frontal regions has been correlated with waking emotional reactivity and the emotional content of dream reports. Little is known regarding alpha asymmetry during sleep. The present study was performed to compare alpha power and alpha power asymmetry in various brain regions across states of sleep and wakefulness. Waking and sleep EEG were recorded in a group of patients undergoing polysomnographic evaluation for possible sleep disorders. Alpha EEG asymmetry in frontal and temporal regions was significantly correlated in waking versus sleep, particularly during rapid eye movement (REM) sleep. These results suggest that patterns of frontal alpha asymmetry are stable across sleep and waking and may be related to emotional reactivity during dreaming. During sleep, alpha power was highest during slow-wave sleep and lowest during REM sleep. Implications of these data for understanding the functional significance of alpha power during waking and sleeping are considered.
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.
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.