Greater Left Hemisphere Activation Research Articles

Asymmetric hemisphere activation in tenderness: evidence from EEG signals

Emotions are processed asymmetrically by the human brain. Frontal alpha asymmetry (FAA) as measured by electroencephalographic (EEG) power in the alpha band (8–13 Hz), is a sensitive indicator of asymmetric brain activity in the frontal cortex. The current study aimed to analyze the frontal EEG asymmetries in terms of valence and motivational direction. We presented 37 participants with three film excerpts that were selected from the standard emotional film database to elicit three target emotions: tenderness, anger, and neutrality. Participants’ self-reports on their induced emotional responses and EEG signals were recorded and analyzed. The results showed that individuals displayed lower alpha power in the left hemisphere than the right hemisphere when they were watching a tender film, indicating that tenderness was positive and related to approach motivation. In contrast, when watching an angry movie, participants showed higher alpha power in the left hemisphere than the right hemisphere, suggesting that anger was negative and associated with withdrawal motivation. These findings help to link positive and approach-motivated tenderness with greater left hemispheric activation and state-anger with greater right hemispheric activation through the analysis of FAA.

Change in drawing placement: A measure of change in mood state reflective of hemispheric lateralization of emotion

The Valence Hypothesis of cerebral lateralization of emotion suggests greater right hemisphere activation during negative mood and greater left hemisphere activation during positive mood. This can manifest as visual field attentional bias. Here, study participants completed an assessment of current mood state (PANAS) and made a drawing (Drawing 1). To induce positive or negative mood, participants played a game; then, the winner read a script depicting a positive interpersonal interaction and the loser read a script depicting a negative interpersonal interaction. Participants then drew a second picture (Drawing 2) and completed the PANAS. We hypothesized that the game outcome would change current mood state and hemispheric activation, which would be reflected in drawing placement. The placement of Drawing 2 moved right for winners and left for losers. Winners experienced a greater increase in positive affect from Time 1 to Time 2 than losers and had decreased negative affect from Time 1. Losers had decreased positive affect from Time 1 and had a greater increase in negative affect from Time 1 to Time 2 than winners. Our results suggest that change in current mood state may be objectively observed by evaluating hemispatial bias reflective of brain hemispheric activation with drawings.

Transcranial Doppler Sonography Reveals Reductions in Hemispheric Asymmetry in Healthy Older Adults during Vigilance.

Given that older adults are remaining longer in the workforce, their ability to perform demanding cognitive tasks such as vigilance assignments needs to be thoroughly examined, especially since many vigilance assignments affect public safety (e.g., aviation, medicine and long distance driving). Previous research exploring the relation between aging and vigilance is conflicted, with some studies finding decreased vigilance performance in older adults but others finding no effect of age. We sought a better understanding of effects of age on vigilance by assessing neurophysiological change over the course of a vigil in young (aged 18–24) and healthy older (aged 66–77) adults. To measure temporal changes in cerebral blood flow, participants underwent functional transcranial doppler (fTCD) recording during a 1 h vigilance task. Based on research showing a compensatory effect of increased left hemisphere activation during vigilance in young adults and the “hemispheric asymmetry reduction in older adults” (HAROLD) model, we predicted that during vigilance our older adults would show greater left hemisphere activation but perform at a similar level compared to young adults. While cerebral blood flow velocity (CBFV) declined over time in both groups, only young adults showed the typical right-lateralized CBFV pattern. Older adults showed greater left hemisphere activation consistent with the HAROLD model. However, the increased left hemisphere activation did not appear to be compensatory as the older adults performed at a significantly lower level compared to young adults over the vigil. Findings are discussed in terms of the HAROLD model of healthy aging and the resource theory of vigilance.

End of the line: Line bisection, an unreliable measure of approach and avoidance motivation

Approach motivation leads to greater left hemisphere activation, whereas an avoidant motivational state activates the right hemisphere. Recent research, which served as the basis for the current experiment, suggests line bisection provides a simple measure of approach/avoidance lateralisation. Findings from Experiment 1 indicated that the landmark task was sensitive enough to identify lateral asymmetries evoked by happy and angry faces; however, follow-up experiments failed to replicate this finding. When task instructions were slightly modified or when a mixed design was used, motivation did not influence landmark task performance. The use of images in lieu of faces also failed to produce a significant effect. Importantly, a straight replication of Experiment 1 produced a null result. Line bisection does not appear to be a suitable measure of lateralised approach/avoidance biases, possibly due to the high individual variability inherent in visuospatial biases. Implications for null hypothesis significance testing are also discussed.

Resting-state activity in the left executive control network is associated with behavioral approach and is increased in substance dependence

BackgroundIndividuals with drug addictions report increased willingness to approach rewards. Approach behaviors are thought to involve executive control processes and are more strongly represented in the left compared to right prefrontal cortex. A direct link between approach tendencies and left hemisphere activity has not been shown in the resting brain. We hypothesized that compared to controls, substance dependent individuals (SDI) would have greater left hemisphere activity in the left executive control network (ECN) at rest. MethodsTwenty-five SDI and 25 controls completed a Behavioral Inhibition System/Behavioral Activation System (BIS/BAS) questionnaire and underwent a resting-state fMRI scan. Group independent component analysis was performed. We used template matching to identify the left and right ECN separately and compared the corresponding components across groups. Across group, BAS scores were correlated with signal fluctuations in the left ECN and BIS scores with right ECN. ResultsBAS scores were higher in SDI compared to controls (p<.003) and correlated with signal fluctuation in the left ECN. SDI showed significantly more activity than controls in the left prefrontal cortex of the left ECN. Conversely, SDI showed less activity than controls in the right prefrontal cortex of the right ECN. ConclusionsResults from this study suggest that approach tendencies are related to the left ECN, even during rest. Higher resting-state signal in the left ECN may play a role in heightened approach tendencies that contribute to drug-seeking behavior.

What happens when we get angry? Hormonal, cardiovascular and asymmetrical brain responses

This study aimed to evaluate neuroendocrine and cardiovascular responses together with changes in brain asymmetry following an anger mood induction laboratory task. Previous research has shown an increase in heart rate and blood pressure when anger is experienced. Increased testosterone and decreased cortisol in response to anger and aggressive behavior have also been reported. With regard to asymmetrical frontal brain activity and emotion, the valence model links negative affect (as anger) to the right hemisphere while the motivational direction model links approach-related emotions (as anger) to the left hemisphere. From the subjective perception and from the neuroendocrine and cardiovascular response of the subjects, we can conclude that the self-referent statement anger induction method by Engebretson et al. (1999) was able to generate an experience of an anger affect in 30 healthy men. Another question was to analyze the consequences of that experience upon perceptual asymmetry when measured with a non-emotional laterality task. Regarding dichotic listening, an enhanced REA (right ear advantage) was observed after anger which indicates greater left hemisphere activity, supporting the motivational direction model.

Hemispheric Asymmetry Profiles During Beginning Reading: Effects of Reading Level and Word Type

We evaluated how right- and the left-temporal lobe activation of first (1st LR), second (2ndLR), and third (3rdLR) level readers (N = 60; Age = 6–9 years) varied with reading level, word characteristics, and cognitive abilities by using electroencephalogram measurements while the children read high-frequency/high-imageability, high-frequency/low-imageability, and nonsense words. The ANOVA showed significant interaction effects: 1stLR had greater right-hemispheric activation than 3rdLR, who had greater left-hemispheric activation; for nonsense words, 1stLR had lower left-hemisphere activation than that of 2ndLR and 3rdLR. The electroencephalogram (EEG) measure of hemispheric asymmetry indicated a developmental effect on lateralized activity in the temporal lobes of beginning readers during word reading.

Hemispheric activation and interaction: Past activity affects future performance

Previous studies have shown that when hemispheric activation is modulated by a lateralised task performed concurrently with a second task, performance in the second task is affected by the side of the more active hemisphere. This effect is thought to be produced by competition for limited resources required to complete the two tasks and/or by a greater allocation of attention to the hemifield contralateral to the more active hemisphere. Little is known on how task performance is affected by the pattern of activation in the two cerebral hemispheres before a target task is conducted. The present study investigated how manipulation of hemispheric activity influenced performance of a non-lateralised task (letter matching). Greater left hemisphere activity interfered most with performance of the letter- matching task and was more pronounced in the early learning stage. Male participants were most affected by this effect. The results are discussed in relation to hemispheric interaction, functional lateralisation, and allocation of attention.

Stereotyping, Self-Affirmation, and the Cerebral Hemispheres

The authors used the processing characteristics of the left and right cerebral hemispheres to gain some insight into the relation between self-affirmation and stereotyping. In Study 1, self-affirmation led to greater stereotyping (of a librarian) and to greater left hemisphere activation, which in turn mediated the self-affirmation/stereotyping relationship. Study 2 replicated these results but also found that self-affirmation decreased stereotyping for a stigmatized target. However, relative hemisphere activation did not mediate this self-affirmation/stereotyping relationship. These studies showed that self-affirmation can either increase or decrease stereotyping depending on the status of the target and that relative hemisphere activation may provide clues as to underlying processes of stereotyping. In both studies, relative hemisphere activation was assessed using a line bisection task. Discussion focuses on possible mechanisms of different kinds of stereotyping and on the ways in which a consideration of relative hemisphere activation could help researchers gain insights into those mechanisms.

Motor Sequence Complexity and Performing Hand Produce Differential Patterns of Hemispheric Lateralization

Studies in brain damaged patients conclude that the left hemisphere is dominant for controlling heterogeneous sequences performed by either hand, presumably due to the cognitive resources involved in planning complex sequential movements. To determine if this lateralized effect is due to asymmetries in primary sensorimotor or association cortex, whole-brain functional magnetic resonance imaging was used to measure differences in volume of activation while healthy right-handed subjects performed repetitive (simple) or heterogeneous (complex) finger sequences using the right or left hand. Advanced planning, as evidenced by reaction time to the first key press, was greater for the complex than simple sequences and for the left than right hand. In addition to the expected greater contralateral activation in the sensorimotor cortex (SMC), greater left hemisphere activation was observed for left, relative to right, hand movements in the ipsilateral left superior parietal area and for complex, relative to simple, sequences in the left premotor and parietal cortex, left thalamus, and bilateral cerebellum. No such volumetric asymmetries were observed in the SMC. Whereas the overall MR signal intensity was greater in the left than right SMC, the extent of this asymmetry did not vary with hand or complexity level. In contrast, signal intensity in the parietal and premotor cortex was greater in the left than right hemisphere and for the complex than simple sequences. Signal intensity in the caudal anterior cerebellum was greater bilaterally for the complex than simple sequences. These findings suggest that activity in the SMC is associated with execution requirements shared by the simple and complex sequences independent of their differential cognitive requirements. In contrast, consistent with data in brain damaged patients, the left dorsal premotor and parietal areas are engaged when advanced planning is required to perform complex motor sequences that require selection of different effectors and abstract organization of the sequence, regardless of the performing hand.

Complementary hemispheric specialization for word and accent detection

When we hear a familiar word pronounced in a foreign accent, which parts of the brain identify the word and which identify the accent? Here we present converging evidence from PET blood flow, event-related scalp potentials, and behavioral responses during dichotic listening, showing homologous and complementary hemispheric specialization for word and accent detection. Accuracy of detecting target words was greater when stimuli were presented to the right ear, indicating left hemisphere specialization, with no ear advantage for detecting target accents. Detection of words also produced increased blood flow in a left frontal area associated with motor and phonetic processing, and a left temporal area associated with semantic memory. Homologous areas of the right hemisphere, together with right prefrontal and precuneus regions, showed increased blood flow during detection of accents. Separate analyses for each detection task indicated that voxels whose activity maximally correlated with accuracy were in the left hemisphere for word detection, but in the right hemisphere for accent detection. Voxels whose activity maximally correlated with inaccuracy were in the opposite hemisphere for both tasks, strengthening the interpretation that between-task differences in brain activation are related to lateralized specializations for task performance. ERP waveforms and reaction times suggested that greater left hemisphere activation during word detection preceded greater right hemisphere activation during accent detection. The results are interpreted as supporting left hemisphere specialization for extraction of the linguistic, phonetic, and semantic information contained in speech, and right hemisphere specialization for pragmatics, the social context of linguistic communication.

Self-serving biases in causal attributions as a function of altered activation asymmetry.

The method of induced lateral orientation of attention was selectively used to alter the balance of activation of the brain toward one cerebral hemisphere or the other. The goal was to extend earlier research which showed greater personal optimism for future events during left hemisphere activation to the related phenomenon of causal attributions. As predicted, there was significantly greater self-serving bias (attribution of internal, stable, and global causes for positive events and external, unstable, and specific causes for negative events) during left hemisphere than during right hemisphere relative activation. This was true for achievement but not for affiliation events. These effects were explained in terms of the increased positive affect which correlates with greater left hemisphere activation. Selective activation of the left hemisphere as a means temporarily to alter attributional style was discussed as a possible tool in the treatment of learned helplessness and depression.

Evoked Potential Correlates of Right Hemisphere Involvement in Language Recovery Following Stroke

A probe evoked potentials procedure was used to assess the relative engagement of both cerebral hemispheres during a language task in the following four groups of dextral adults: left hemisphere (LH)-damaged aphasics recovering from stroke, dysarthrics, right hemisphere (RH)-damaged nonaphasic patients, and normal control subjects. In agreement with previous findings using the probe procedure, the present results indicate greater task-specific RH activation in recovering aphasics and, to a lesser degree, dysarthric patients and greater LH activation in both nonaphasic, RH-damaged patients and normal control subjects. On the basis of these data, we suggest that increasing participation of the nondominant hemisphere may subserve restitution of language in adults sustaining LH lesions.

Worry: An electrocortical analysis

Worry has been described as uncontrollable verbally-mediated analytic cognitive activity, or thoughts, concerning future events. To date, worry and the treatment of worry have been assessed primarily by self-report of cognitive activity. The current study assessed worriers and nonworriers during worry and a brief relaxation treatment using EEG alpha and beta measures. Worry was found to be associated with high, overall cortical activation as well as relatively greater left hemisphere activation. Progressive relaxation was associated with attenuation of worriers' left hemisphere asymmetric EEG activation. EEG alpha measures indicated less activation during and after progressive muscular relaxation than during a self-relaxation condition. Implications for theory and assessment of cognitive anxiety are discussed.

Spontaneous EEG correlates of intellectual functioning in talented and handicapped adolescents.

EEG correlates of intellectual functioning were investigated in 35 academically talented and 20 academically handicapped adolescents. EEG data from Ertl's Brainwave Analyzer were factor-analyzed and factor scores entered into regression equations predicting four primary mental abilities, verbal, numerical, reasoning, spatial, and two sequential tests of educational progress, reading and mathematics. Analysis indicated that (1) frequency ratio, with relatively greater left-hemisphere activity was the most important EEG variable related to mental functioning in the talented group; (2) while EEG period and alpha ratio were the two most important EEG variables related to intellectual functioning in the mentally handicapped group; (3) hemispheric symmetry was of some importance for both groups, with greater symmetry being associated with superior performance. Contrary to Ertl's neural efficiency theory, (1) neural information transfer rate was significantly positively (not negatively as predicted) related to intellectual performance (for the handicapped group only), and (2) alpha was significantly related to intellectual functioning (for the handicapped group only). Further research is needed to extend and confirm the above findings dealing with persons scoring in the normal IQ range and during mentally active as well as resting conditions.

Eye Movements in Schizophrenic vs Normal Subjects-Reply

In Reply.— Dr Levick and Dr Voneida question both the appropriateness of studying initial lateral eye movements (LEMs) in a face-to-face experimental design and the interpretation of our results. Although Gur et al 1 originally demonstrated that LEMs are influenced by the experimenters' location, more recently Gur and Gur 2 reexamined this issue in greater detail. Using an experimenter behind the subject as well as in a face-to-face paradigm, they found that subjects performed better on verbal questions when the initial LEM was to the right (ie, presumed greater left-hemisphere activity) and the experimenter behind the subject. Similarly, performance on spatial questions was slightly, but not significantly, more accurate with initial left LEMs. When the experimenter was in front of the subject, performance on spatial questions was significantly better when the subject's initial eye movements were to the left. Thus, Gur and Gur 2 concluded that direction of gaze in normal