Differences In Hemispheric Asymmetry Research Articles

Inter-hemispheric Asymmetry Patterns in the ADHD Brain: A Neuroimaging Replication Study.

Attention-deficit/ hyperactivity disorder (ADHD) is the most common neurodevelopment disorder in children, and many genetic markers have been linked to the behavioral phenotypes of this highly heritable disease. The neuroimaging correlates are similarly complex, with multiple combinations of structural and functional alterations associated with the disease presentations of hyperactivity and inattentiveness. Thus far, neuroimaging studies have provided mixed results in ADHD patients, particularly with respect to the laterality of findings. It is possible that hemispheric asymmetry differences may help reconcile the variability of these findings. We recently reported that inter-hemispheric asymmetry differences were more sensitive descriptors for identifying differences between ADHD and typically developing (TD) brains (n=849) across volumetric, morphometric, and white matter neuroimaging metrics. Here, we examined the replicability of these findings across a new data set (n=202) of TD and ADHD subjects at the time of diagnosis (medication naive) and after a six week course of either stimulant drugs, non-stimulant medications, or combination therapy. Our findings replicated our earlier work across a number of volumetric and white matter measures confirming that asymmetry is more robust at detecting differences between TD and ADHD brains. However, the effects of medication failed to produce significant alterations across either lateralized or symmetry measures. We suggest that the delay in brain volume maturation observed in ADHD youths may be hemisphere dependent. Future work may investigate the extent to which these inter-hemispheric asymmetry differences are causal or compensatory in nature.

Phonological ambiguity modulates resolution of semantic ambiguity during reading: An fMRI study of Hebrew.

The current fMRI study examined the role of phonology in the extraction of meaning from print in each hemisphere by comparing homophonic and heterophonic homographs (ambiguous words in which both meanings have the same or different sounds respectively, e.g., bank or tear). The analysis distinguished between the first phase, in which participants read ambiguous words without context, and the second phase in which the context resolves the ambiguity. Native Hebrew readers were scanned during semantic relatedness judgments on pairs of words in which the first word was either a homophone or a heterophone and the second word was related to its dominant or subordinate meaning. In Phase 1 there was greater activation for heterophones in left inferior frontal gyrus (IFG), pars opercularis, and more activation for homophones in bilateral IFG pars orbitalis, suggesting that resolution of the conflict at the phonological level has abolished the semantic ambiguity for heterophones. Reduced activation for all ambiguous words in temporo-parietal regions suggests that although ambiguity enhances controlled lexical selection processes in frontal regions it reduces reliance on bottom-up mapping processes. After presentation of the context, a larger difference between the dominant and subordinate meaning was found for heterophones in all reading-related regions, suggesting a greater engagement for heterophones with the dominant meaning. Altogether these results are consistent with the prominent role of phonological processing in visual word recognition. Finally, despite differences in hemispheric asymmetry between homophones and heterophones, ambiguity resolution, even toward the subordinate meaning, is largely left lateralized. (PsycINFO Database Record

Comparison of hemispheric asymmetry measurements for emotional recordings from controls

Four asymmetry measurements (conventional coherence function (CCF), cross wavelet correlation (CWC), phase lag index (PLI), and mean phase coherence (MPC)) have been compared to each other for the first time in order to recognize emotional states (pleasant (P), neutral (N), unpleasant (UP)) from controls in EEG sub-bands (delta (0–4 Hz), theta (4–8 Hz), alpha (8–16 Hz), beta (16–32 Hz), gamma (32–64 Hz)) mediated by affective pictures from the International Affective Picture Archiving System (IAPS). Eight emotional features, computed as hemispheric asymmetry between eight electrode pairs (Fp1 − Fp2, F7 − F8, F3 − F4, C3 − C4, T7 − T8, P7 − P8, P3 − P4, and O1 − O2), have been classified by using data mining methods. Results show that inter-hemispheric emotional functions are mostly mediated by gamma. The best classification is provided by a neural network classifier, while the best features are provided by CWC in time-scale domain due to non-stationary nature of electroencephalographic (EEG) series. The highest asymmetry levels are provided by pleasant pictures at mostly anterio-frontal (F3 − F4) and central (C3 − C4) electrode pairs in gamma. Inter-hemispheric asymmetry levels are changed by each emotional state at all lobes. In conclusion, we can state the followings: (1) Nonlinear and wavelet transform-based methods are more suitable for characterization of EEG; (2) The highest difference in hemispheric asymmetry was observed among emotional states in gamma; (3) Cortical emotional functions are not region-specific, since all lobes are effected by emotional stimuli at different levels; and (4) Pleasant stimuli can strongly mediate the brain in comparison to unpleasant and neutral stimuli.

Latent profiles of executive functioning in healthy young adults: evidence of individual differences in hemispheric asymmetry.

Two competing theoretical models of individual differences in executive functioning (EF) were examined: the Prefrontal Convexity Model and the Hemispheric Asymmetry Model. Neurologically healthy individuals (N=315; mean age 20.8) completed a modified switching task (MST) and the Attention Network Test (ANT) in a single testing session. Data analysis was conducted in two phases. In the first phase (model identification), latent profile analysis was applied to MST variables measuring the abilities to form, switch, and maintain mental sets under conditions designed to tax left or right hemisphere resources. In the second phase (model validation), participant clusters obtained from the first phase were compared on the ANT. The Model Identification phase yielded a 3-profile solution consistent with the Hemispheric Asymmetry Model. Profile 1 (N=203) was characterized by average EF performances. Profile 2 (N=43) revealed a set maintenance weakness under non-verbal conditions. Profile 3 (N=38) demonstrated weaknesses in cognitive flexibility combined with poor executive performances under verbal conditions. The Model Validation phase confirmed group differences. Profile 1 demonstrated average EF performances. Profile 2 demonstrated distractibility and decreased alertness, consistent with a right hemisphere weakness. Profile 3 demonstrated cognitive rigidity in the absence of external cues, consistent with a left hemisphere weakness. Individual differences in EF appear to follow a Hemispheric Asymmetry Model of EF among neurologically healthy adults. Investigating the relationship between hemispherically mediated executive functions and other individual difference factors known to confer health risk or resilience could inform numerous disciplines within the field of psychology.

Variation in semantic priming across age groups: An AERP study

Objective: To study the semantic priming effect on words across the life span by means of auditory event-related potentials (AERPs). Design: Participants heard a series of three words (S1, S2, and S3). The task was to indicate whether S2 was in the same semantic category as S3. Semantic priming was quantified as the difference between AERPs to the second word when it was semantically related to the first word (S2-R) or unrelated to the first word (S2-UR). Interest was focused entirely on the processing negativity (PN) component of the AERP to S2. The purpose of S3 was to delay the task decision so that the LPC generated by the decision would not confound the measurement of the PN component to S2. Sample: Ten children (9–11 years), 11 young adults (20–30 years), and 10 seniors (60–70 years). Results: The semantic priming effect was evident in the difference between peak amplitude of the PN component of the AERP to S2R and S2UR in all three groups. Children showed a clear asymmetry favoring the left hemisphere. In young adults, the asymmetry still favored the left hemisphere, but the degree of asymmetry was less robust. In the case of seniors, the priming effect was greater over the right hemisphere. Conclusion: Results suggest that all age groups benefit from contextual support, as evidenced by the semantic priming effect. However, differences in hemispheric asymmetry of activation indicate that perhaps seniors may need to recruit additional, but somewhat different brain resources to manage otherwise largely automatic tasks.

Corticospinal tract asymmetry and handedness in right- and left-handers by diffusion tensor tractography

Cerebral hemispheres represent both structural and functional asymmetry, which differs among right- and left-handers. The left hemisphere is specialised for language and task execution of the right hand in right-handers. We studied the corticospinal tract in right- and left-handers by diffusion tensor imaging and tractography. The present study aimed at revealing a morphological difference resulting from a region of interest (ROI) obtained by functional MRI (fMRI). Twenty-five healthy participants (right-handed: 15, left-handed: 10) were enrolled in our assessment of morphological, functional and diffusion tensor MRI. Assessment of brain fibre reconstruction (tractography) was done using a deterministic algorithm. Fractional anisotropy (FA) and mean diffusivity (MD) were studied on the tractography traces of the reference slices. We observed a significant difference in number of leftward fibres based on laterality. The significant difference in regard to FA and MD was based on the slices obtained at different levels and the laterality index. We found left-hand asymmetry and right-hand asymmetry, respectively, for the MD and FA. Our study showed the presence of hemispheric asymmetry based on laterality index in right- and left-handers. These results are inconsistent with some studies and consistent with others. The reported difference in hemispheric asymmetry could be related to dexterity (manual skill).

Bilinguals Have Different Hemispheric Lateralization in Visual Word Processing from Monolinguals

Previous bilingual studies showed reduced hemispheric asymmetry in visual tasks such as face perception in bilinguals compared with monolinguals, suggesting experience in reading one or two languages could be a modulating factor. Here we examined whether difference in hemispheric asymmetry in visual tasks can also be observed in bilinguals who have different language backgrounds. We compared the behavior of three language groups in a tachistoscopic English word sequential matching task: English monolinguals (or alphabetic monolinguals, A-Ms), bilinguals with an alphabetic-L1 and English-L2 (alphabetic-alphabetic bilinguals, AA-Bs), and bilinguals with Chinese-L1 and English-L2 (logographic-alphabetic bilinguals, LA-Bs). The results showed that AA-Bs had a stronger right visual field/ left hemispheric (LH) advantage than A-Ms and LA-Bs, suggesting that different language learning experiences can influence how visual words are processed in the brain. In addition, we showed that this effect could be accounted for by a computational model that implements a theory of hemispheric asymmetry in perception (i.e., the Double Filtering by Frequency theory; Ivry & Robertson, 1998); the modeling data suggested that this difference may be due to both the difference in participants' vocabulary size and the difference in word-to-sound mapping between alphabetic and logographic languages.

A critical re-examination of sexual dimorphism in the corpus callosum microstructure

Recent diffusion-tensor imaging (DTI) studies suggest sexual dimorphism in the micro-structural architecture of the corpus callosum. However, the corpus callosum is also found to be larger in males than in females, a fact that might introduce a systematic bias to the analysis of DTI parameters. Diffusion parameters obtained in the larger male corpus callosum could be less affected by partial-volume averaging with surrounding non-callosal tissue than respective parameters obtained in the smaller female corpus callosum, i.e. the sex of the subject and partial-volume effects would be confounded. The objective of the present DTI study was to re-examine microstructural sex differences in the corpus callosum, while controlling for corpus callosum size differences between sexes. We compared 41 female and 34 male participants using regional tract-based spatial statistics (TBSS) analysis. Clusters of significantly higher fractional anisotropy (FA) and lower diffusion strength in males compared to females were detected in the genu and truncus of the corpus callosum. However, only the sex difference located in the anterior genu subregions could be unequivocally interpreted. This was the only cluster where the diffusion parameters did not correlate with regional callosal size. The present results indicate a stronger inter-hemispheric connectivity between the frontal lobes in males than females, which might be related to sex differences in hemispheric asymmetry and brain size.

Do bilinguals have a different hemispheric lateralization in visual processing from monolinguals?

Previous bilingual studies showed reduced hemispheric asymmetry in visual tasks such as face perception in bilinguals compared with monolinguals, which suggested that hemispheric asymmetry in visual tasks could be modulated by experience in reading one or two languages. Here we examined whether difference in hemispheric asymmetry in visual tasks can also be observed in bilinguals who have different language backgrounds. We compared the behavior of three language groups in a tachistoscopic English word sequential matching task: English monolinguals (or alphabetic monolinguals, A-Ms), bilinguals with an alphabetic language L1 and English L2 (alphabetic-alphabetic bilinguals, AA-Bs), and bilinguals with a logographic language (Chinese) L1 and English L2 (logographic-alphabetic bilinguals, LA-Bs). The results showed that AA-Bs had a stronger right visual field/ left hemispheric (LH) advantage than A-Ms and LA-Bs, suggesting that different language learning experiences can influence how visual words are processed in the brain. In addition, we showed that this effect could be accounted for by a computational model that implements a theory of hemispheric asymmetry in perception (i.e. the Double Filtering by Frequency theory, Ivry & Robertson, 1998); the modeling data suggested that this difference may be due to both the difference in participants’ vocabulary size and the difference in word-to-sound mapping between alphabetic and logographic languages.

Preschoolers' Mental Rotation: Sex Differences in Hemispheric Asymmetry

Mental rotation performance has been found to produce one of the largest sex differences in cognition accompanied by sex differences in functional cerebral asymmetry. Although sex differences in mental rotation performance can be reliably demonstrated as early as age 5 years old, that is, long before puberty, no data exist as to whether preschooler's mental rotation performance is accompanied by sex differences in functional cerebral asymmetry. Based on the electrophysiological brain correlates of mental rotation, we observed a bilateral parietal brain activity for preschool boys whereas the preschool girls' brain activity was clearly lateralized toward the left hemisphere if and only if mental rotation was needed to solve the task. Thus, sex differences in functional cerebral asymmetry during mental rotation do not require hormonal changes that occur during puberty.

Preschoolers' mental rotation of letters: Sex differences in hemispheric asymmetry

Adults' mental rotation performance has been found to produce one of the largest sex differences in cognition accompanied by sex differences in functional cerebral asymmetry. In this study sex differences in mental rotation of letters were investigated with children as young as five years. Based on the electrophysiological brain correlates of mental rotation, we observed a bilateral brain activity for preschool girls whereas the preschool boys' brain activity was clearly lateralized towards the right hemisphere if and only if mental rotation was needed to solve the task. At the same time, we did not find any sex differences in mental rotation speed or accuracy. Thus, sex differences in functional hemispheric asymmetry during mental rotation do not require hormonal changes that occur during puberty.

Gender differences in hemispheric asymmetry for face processing

BackgroundCurrent cognitive neuroscience models predict a right-hemispheric dominance for face processing in humans. However, neuroimaging and electromagnetic data in the literature provide conflicting evidence of a right-sided brain asymmetry for decoding the structural properties of faces. The purpose of this study was to investigate whether this inconsistency might be due to gender differences in hemispheric asymmetry.ResultsIn this study, event-related brain potentials (ERPs) were recorded in 40 healthy, strictly right-handed individuals (20 women and 20 men) while they observed infants' faces expressing a variety of emotions. Early face-sensitive P1 and N1 responses to neutral vs. affective expressions were measured over the occipital/temporal cortices, and the responses were analyzed according to viewer gender. Along with a strong right hemispheric dominance for men, the results showed a lack of asymmetry for face processing in the amplitude of the occipito-temporal N1 response in women to both neutral and affective faces.ConclusionMen showed an asymmetric functioning of visual cortex while decoding faces and expressions, whereas women showed a more bilateral functioning. These results indicate the importance of gender effects in the lateralization of the occipito-temporal response during the processing of face identity, structure, familiarity, or affective content.

Behavioral and physiological findings of gender differences in global-local visual processing

Hemispheric asymmetries in global-local visual processing are well-established, as are gender differences in cognition. Although hemispheric asymmetry presumably underlies gender differences in cognition, the literature on gender differences in global-local processing is sparse. We employed event related brain potential (ERP) recordings during performance of a global-local reaction time task to compare hemispheric asymmetries and processing biases in adult men ( n = 15) and women ( n = 15). Women responded more quickly to local targets while men did not differentially respond to hierarchical stimuli. ERP data indicated that women had P100 responses that were selectively lateralized to the left hemisphere in response to local targets and N150 responses that were smaller for global targets. They also had P300 responses that were greater following local stimuli. The physiological data demonstrate that male-female performance differences arise from biologically based differences in hemispheric asymmetry. Findings are discussed in the context of existing literature regarding gender differences, hemispheric specialization, and the role of stimulus characteristics.

Asymmetry of fetal cerebral hemispheres: in utero ultrasound study

BACKGROUNDSlight morphological asymmetry of the cerebral hemispheres has been observed in fetal and newborn brains. In adults, sex differences in hemispheric asymmetry have also been reported.OBJECTIVETo establish whether cerebral hemisphere...

Differences in Hemispheric Asymmetry Between Dyslexic and Normal Children on a Lateralised Lexical Decision Task

The present experiment was conducted in order to further investigate the relationship between deficits in left hemisphere processing and phonetic decoding in dyslexic children. We administered a lateralised lexical decision task that manipulated wordness, length, and word regularity of grapheme-phoneme conversion. Right-handed male dyslexic children and normal control children were presented with words and pronounceable nonwords. Although there were no overall differences in hemispheric asymmetry between the groups, they did differ in laterality effects in accuracy when responding to nonwords and to phonetically regular words, with the normal children showing the right visual field advantage/ sensitivity (left hemisphere dominance/sensitivity), while the dyslexics failed to show any visual field advantage or sensitivity for these stimuli. Further, group differences were observed in left but not right hemisphere functioning. The results suggest that deficits in left hemisphere processing are apparent only when the dyslexics are attempting to utilise the rules of phonics. Support for the use of this paradigm for use with dyslexic children is also discussed.

Differences in Hemispheric Asymmetry Between Dyslexic and Normal Children on a Lateralised Lexical Decision Task

Differences in Hemispheric Asymmetry Between Dyslexic and Normal Children on a Lateralised Lexical Decision Task

Auditory ERP components and mismatch negativity in dysphasic children

Auditory event-related potentials (ERPs) and especially the mismatch negativity component (MMN) were examined in 14 dysphasic and 12 normal children (aged 7–13). The ERPs were elicited by sine tone stimuli using the passive oddball paradigm and short ISI (350 msec). We measured the peak latency and peak amplitude of MMN responses to frequency (500/553 Hz) and duration (50/110 msec or 50/500 msec) differences. In the dysphasic group the peak amplitude of the frequency MMN was significantly attenuated. The duration MMN showed a significant difference between the two groups only for stimuli with highly contrasting values (50/500 msec). In normal subjects we found a negative correlation between the peak latency of the frequency MMN and age. The maturational changes of long-latency ERPs were non-significant in dysphasic children. Evidence of differences in hemispheric asymmetry between the two groups was observed.

Is right hemisphere decline in the perception of emotion a function of aging?

The hypothesis that the right cerebral hemisphere declines more quickly than the left cerebral hemisphere in the normal aging process was tested using accuracy and intensity measures in a facial recognition test and using response time and response bias measures in a tachistoscopic paradigm. Elderly and younger men and women (N = 60) participated in both experiments. Experiment 1 required facial affect identification and intensity ratings of 50 standardized photographs of 5 affective categories: Happy, Neutral, Sad, Angry, and Fearful. The elderly were significantly less accurate in identifying facial affective valence. This effect was found using negative and neutral expressions. Results for happy expressions, however, were consistent with the younger group. In Experiment 2, age differences in hemispheric asymmetry were evaluated using presentation of affective faces in each visual field. Following prolonged experience with the affective stimuli during Experiment 1, the elderly showed heightened cerebral asymmetry for facial affect processing compared to the younger group. Both groups showed a positive affective bias to neutral stimuli presented to the left hemisphere. Elderly and younger subjects scored significantly higher on Vocabulary and Block Design subtests of the WAIS-R, respectively. Overall, the findings suggest that the elderly have more difficulty processing negative affect, while their ability to process positive affect remains intact. The results lend only partial support to the right hemi-aging hypothesis.

Gender differences in the normal lateralization of the supratemporal cortex: MRI surface-rendering morphometry of Heschl's gyrus and the planum temporale.

Gender differences in hemispheric asymmetry for language functioning have been reported in the neuropsychological literature. Despite numerous reports of anatomic asymmetries in corresponding cortical regions, the possibility of gender dimorphism in the putative neuroanatomical substrate of language has not been systematically examined in vivo. We assessed asymmetry of the planum temporale (PT), a supratemporal region of auditory association cortex, in 12 normal, right-handed females and 12 age-matched right-handed males with the aid of MRI surface-rendering morphometry. Bilateral areas were also assessed for Heschl's gyrus (HG), a supratemporal region of primary auditory cortex where no asymmetry was anticipated. We found a significant interaction between gender and hemisphere for the PT, with males having significantly larger left versus right PTs. Left-right differences in PT area were not significant among females (10 of 12 males showed leftward lateralization of the PT, vs 5 of 12 females). No main effect of gender was found for total (left + right) PT area, and no asymmetries or gender effects were detected for HG. This finding of gender dimorphism in PT area is consistent with evidence for reduced asymmetry among females in the lateralization of language functions attributable to the supratemporal cortex. The implications for theories about interactions between sex hormones and the development of brain asymmetries are discussed.

Cerebral asymmetry in autonomic conditioning to facial expressions: Sex differences

In the present experiment, sex differences in hemispheric asymmetry during classical conditioning to emotional stimuli are reported. 125 subjects (62 females and 63 males) were shown a slide of a happy face in the right (or left) visual half field (VHF), and simultaneously a slide of an angry face in the left (or right) VHF. Eight groups were formed by the combination of male and female subjects; left and right VHF positions of the angry/happy faces; and the administration/omission of the shock unconditioned stimulus (UCS). Dependent measures were skin conductance responses recorded from both hands. The results during extinction showed a significant larger SCR magnitude to the shock compared to the no-shock groups only for the female subjects. CS position during conditioning was also important in revealing differential responding to either the happy or angry faces. A right hemisphere effect was found for the angry face CS for both the male and female subjects, however with a greater difference for the females.