Brain Asymmetry Research Articles

Asymmetry-enhanced attention network for Alzheimer’s diagnosis with structural Magnetic Resonance Imaging

Background and objective:With the aging of the global population becoming severe, Alzheimer’s disease (AD) has become one of the world’s most common senile diseases. Many studies have suggested that the brain’s left–right asymmetry is one of the possible diagnostic landmarks for AD. However, most published approaches to classification problems may not adequately explore the asymmetry between the left and right hemispheres. At the same time, the relationship between asymmetry traits and other classifier features remains understudied. Methods:In this paper, we proposed an asymmetry enhanced attention network (ASEAN) for AD diagnosis that effectively combines the anatomical asymmetry characteristics of the brain to enhance the accuracy and stability of classification tasks. First, we proposed a multi-scale asymmetry feature extraction module (MSAF) that can extract the asymmetry features of the brain from various scales. Second, we proposed an asymmetry refinement module (ARM) that considers the dependency between feature maps to suppress the irrelevant regions of the asymmetric feature maps. In addition, a parameter-free attention module was introduced to infer 4D attention weights and improve the network’s representation capability. Results:The proposed method achieved performance improvements on two databases: Alzheimer’s Disease Neuroimaging Initiative (ADNI) and Australian Imaging, Biomarkers and Lifestyle (AIBL). For the classification tasks on ADNI, the proposed method achieves 92.1% accuracy, 96.2% sensitivity, and 91.3% specificity on the AD vs. CN (Cognitively Normal) task. Compared with state-of-the-art methods, the proposed method could achieve comparable results. Conclusion:The proposed model can extract long-range left–right brain similarity as complementary information and improve the model’s diagnostic performance. A large number of experiments also support the model’s validity. At the same time, this work provides a valuable reference for other neurological diseases, particularly those that exhibit left–right brain asymmetry during development.

Dissociable brain structural asymmetry patterns reveal unique phenome-wide profiles.

Broca reported ~150 years ago that particular lesions of the left hemisphere impair speech. Since then, other brain regions have been reported to show lateralized structure and function. Yet, studies of brain asymmetry have limited their focus to pairwise comparisons between homologous regions. Here, we characterized separable whole-brain asymmetry patterns in grey and white matter structure from n = 37,441 UK Biobank participants. By pooling information on left-right shifts underlying whole-brain structure, we deconvolved signatures of brain asymmetry that are spatially distributed rather than locally constrained. Classically asymmetric regions turned out to belong to more than one asymmetry pattern. Instead of a single dominant signature, we discovered complementary asymmetry patterns that contributed similarly to whole-brain asymmetry at the population level. These asymmetry patterns were associated with unique collections of phenotypes, ranging from early lifestyle factors to demographic status to mental health indicators.

Acute Effects of Cognitive Training Game on Functional Brain Asymmetry and Motor Performance in Golf Putting: A Pilot Study

ABSTRACT Neural and behavioral evidence has indicated that video games and mental training can enhance motor skills and attentional stability. The purpose of this study is to investigate the acute effect of a single session of cognitive game training on electroencephalography (EEG) activity and golf putting performance (10, 12 ft putts). A total of twelve participants (10 males, 2 females, aged 22–59) participated in this study. Seven participants were assigned to an experimental group. This group putted before and after a 10-min of cognitive game training; five additional participants were assigned to a control group, sitting quietly with limited physical movements. Measures of EEG signals (i.e., frontal alpha asymmetry, temporal alpha asymmetry) and performance outcomes (i.e., accuracy, quality of feel) were recorded before and after the intervention. The experimental group demonstrated a significantly increased quality of putting feel compared to the control group. Although functional brain asymmetry did not approach a significant level, it was speculated that this single session of cognitive game training might stimulate approaching attention to the target (i.e., hole) and reduce mental exertions which could explain why the experimental group showed a high quality of feel in their performance. Future work is still needed with larger sample size and controlled variables (e.g., eye-dominance, handedness) to examine the long-term effects of cognitive game training on motor performance in skilled and novice golfers, respectively.

Differences in temporal processing speeds between the right and left auditory cortex reflect the strength of recurrent synaptic connectivity.

Brain asymmetry in the sensitivity to spectrotemporal modulation is an established functional feature that underlies the perception of speech and music. The left auditory cortex (ACx) is believed to specialize in processing fast temporal components of speech sounds, and the right ACx slower components. However, the circuit features and neural computations behind these lateralized spectrotemporal processes are poorly understood. To answer these mechanistic questions we use mice, an animal model that captures some relevant features of human communication systems. In this study, we screened for circuit features that could subserve temporal integration differences between the left and right ACx. We mapped excitatory input to principal neurons in all cortical layers and found significantly stronger recurrent connections in the superficial layers of the right ACx compared to the left. We hypothesized that the underlying recurrent neural dynamics would exhibit differential characteristic timescales corresponding to their hemispheric specialization. To investigate, we recorded spike trains from awake mice and estimated the network time constants using a statistical method to combine evidence from multiple weak signal-to-noise ratio neurons. We found longer temporal integration windows in the superficial layers of the right ACx compared to the left as predicted by stronger recurrent excitation. Our study shows substantial evidence linking stronger recurrent synaptic connections to longer network timescales. These findings support speech processing theories that purport asymmetry in temporal integration is a crucial feature of lateralization in auditory processing.

Changes in and asymmetry of the proteome in the human fetal frontal lobe during early development

Inherent hemispheric asymmetry is important for cognition, language and other functions. Describing normal brain and asymmetry development during early development will improve our understanding of how different hemispheres prioritize specific functions, which is currently unknown. Here, we analysed developmental changes in and asymmetry of the proteome in the bilateral frontal lobes of three foetal specimens in the late first trimester of pregnancy. We found that during this period, the difference in expression between gestational weeks (GWs) increased, and the difference in asymmetric expression decreased. Changes in the patterns of protein expression differed in the bilateral frontal lobes. Our results show that brain asymmetry can be observed in early development. These findings can guide researchers in further investigations of the mechanisms of brain asymmetry. We propose that both sides of the brain should be analysed separately in future multiomics and human brain mapping studies.

Special Issue on Brain Asymmetry in Evolution

The brain is lateralized morphologically and functionally, with unique species-related specifications [...]

Brain Symmetry in Alpha Band When Watching Cuts in Movies

The purpose of this study is to determine if there is asymmetry in the brain activity between both hemispheres while watching cuts in movies. We presented videos with cuts to 36 participants, registered electrical brain activity through electroencephalography (EEG) and analyzed asymmetry in frontal, somatomotor, temporal, parietal and occipital areas. EEG power and alpha (8–13 Hz) asymmetry were analyzed based on 4032 epochs (112 epochs from videos × 36 participants) in each hemisphere. On average, we found negative asymmetry, indicating a greater alpha power in the left hemisphere and a greater activity in the right hemisphere in frontal, temporal and occipital areas. The opposite was found in somatomotor and temporal areas. However, with a high inter-subjects variability, these asymmetries did not seem to be significant. Our results suggest that cuts in audiovisuals do not provoke any specific asymmetrical brain activity in the alpha band in viewers. We conclude that brain asymmetry when decoding audiovisual content may be more related with narrative content than with formal style.

Conserved and diverged asymmetric gene expression in the brain of teleosts.

Morphological left-right brain asymmetries are universal phenomena in animals. These features have been studied for decades, but the functional relevance is often unclear. Studies from the zebrafish dorsal diencephalon on the genetics underlying the establishment and function of brain asymmetries have uncovered genes associated with the development of functional brain asymmetries. To gain further insights, comparative studies help to investigate the emergence of asymmetries and underlying genetics in connection to functional adaptation. Evolutionarily distant isogenic medaka inbred lines, that show divergence of complex traits such as morphology, physiology and behavior, are a valuable resource to investigate intra-species variations in a given trait of interest. For a detailed study of asymmetry in the medaka diencephalon we generated molecular probes of ten medaka genes that are expressed asymmetrically in the zebrafish habenulae and pineal complex. We find expression of eight genes in the corresponding brain areas of medaka with differences in the extent of left-right asymmetry compared to zebrafish. Our marker gene analysis of the diverged medaka inbred strains revealed marked inter-strain size differences of the respective expression domains in the parapineal and the habenulae, which we hypothesize may result from strain-specific gene loss. Thus, our analysis reveals both inter-species differences but also intra-species plasticity of gene expression in the teleost dorsal diencephalon. These findings are a starting point showing the potential to identify the genetics underlying the emergence and modulations of asymmetries. They are also the prerequisite to examine whether variance in habenular gene expression may cause variation of behavioral traits.

Convolutional Neural Networks-Based Framework for Early Identification of Dementia Using MRI of Brain Asymmetry.

Computer-aided diagnosis of health problems and pathological conditions has become a substantial part of medical, biomedical, and computer science research. This paper focuses on the diagnosis of early and progressive dementia, building on the potential of deep learning (DL) models. The proposed computational framework exploits a magnetic resonance imaging (MRI) brain asymmetry biomarker, which has been associated with early dementia, and employs DL architectures for MRI image classification. Identification of early dementia is accomplished by an eight-layered convolutional neural network (CNN) as well as transfer learning of pretrained CNNs from ImageNet. Different instantiations of the proposed CNN architecture are tested. These are equipped with Softmax, support vector machine (SVM), linear discriminant (LD), or [Formula: see text] -nearest neighbor (KNN) classification layers, assembled as a separate classification module, which are attached to the core CNN architecture. The initial imaging data were obtained from the MRI directory of the Alzheimer's disease neuroimaging initiative 3 (ADNI3) database. The independent testing dataset was created using image preprocessing and segmentation algorithms applied to unseen patients' imaging data. The proposed approach demonstrates a 90.12% accuracy in distinguishing patients who are cognitively normal subjects from those who have Alzheimer's disease (AD), and an 86.40% accuracy in detecting early mild cognitive impairment (EMCI).

Sunlight and lifestyle: linking prenatal light conditions and personality development in a wild bird

Even though personality is a major determinant of individual survival, the development of animal personality traits is still poorly understood. Beyond an individual's genetic background, personality may be shaped by the conditions experienced during embryonic development. Light is a salient and variable ecological factor that can affect organismal physiology, establish brain asymmetries and ultimately modulate postnatal phenotypes across multiple taxa. Exposure to light is known to vary among avian embryos due to changes in parental incubatory constancy, but whether differences in the prenatal light environment can influence offspring personality development has rarely been explored. Here, we investigated whether the prenatal light environment shapes a key dimension of animal personality, the shy–bold axis, in hatchlings of a semiprecocial seabird, the yellow-legged gull, Larus michahellis . In gulls, the prenatal light environment may be especially important for last-laid eggs, as parental attendance during late incubation is more variable for last-laid than for senior eggs. We manipulated the levels of embryonic exposure to light (within the natural range previously documented in the wild) during the last stages of egg incubation and assessed differences in boldness in newly hatched junior chicks. We then used structural equation modelling to explore whether the effect of prenatal light exposure on the shy–bold axis is linked to the establishment of brain asymmetries (lateralization) and/or changes in plasma corticosterone levels. Prenatal light exposure promoted bolder phenotypes in gull chicks, which may improve their individual performance when competing for parental resources. Prenatal light also promoted the lateralization of the begging behaviour in newly hatched chicks, which was negatively associated with boldness. Finally, light induced changes in glucocorticoid levels, but these changes did not impact chicks' personality. Our findings unambiguously confirm that the prenatal light environment strongly affects the development of shy–bold phenotypes in gull hatchlings through a complex multipath mechanism. • Can the prenatal environment shape animal personality? • Last-hatched gull eggs are highly exposed to sunlight during late incubation. • We explored whether prenatal exposure to light shapes boldness in hatchlings. • Prenatal light promoted bold phenotypes and brain lateralization in gull chicks. • These adjustments might improve chick performance under competitive disadvantage.

Neuroanatomical asymmetries in nonhuman primates in the homologs to Broca's and Wernicke's areas: a mini-review.

Population-level lateralization in structure and function is a fundamental measure of the human nervous system. To what extent nonhuman primates exhibit similar patterns of asymmetry remains a topic of considerable scientific interest. In this mini-review, a brief summary of findings on brain asymmetries in nonhuman primates in brain regions considered to the homolog's to Broca's and Wernicke's area are presented. Limitations of existing and directions for future studies are discussed in the context of facilitating comparative investigations in primates.

Introduction to the special issue on symmetry in the life sciences - symmetry and asymmetry across biological scales.

In this special issue of Emerging Topics in Life Sciences, we present a series of mini-reviews of some of the most exciting research involving the concept of symmetry. This research spans the biological sciences from proteins to ecosystems. The reviews examine protein and floral symmetry, primate brain and behavioral asymmetries, geometric morphometrics, and various fluctuating asymmetries.

Interhemispheric asymmetry of the brain in patients with type 1 diabetes mellitus and cognitive impairment.

With an ageing of population and a splurging epidemic of diabetes mellitus (DM), the prevalence of complications associated with pathology of the central nervous system are expected to increase, which in the future may have serious consequences for public health. It is known that one of the main manifestations of brain damage in type 1 diabetes is cognitive impairment, which is possibly associated with the peculiarities of vascularization and interhemispheric asymmetry, which requires in-depth analysis using modern neuroimaging methods. The aim of the study is to assess the symmetry of structural, metabolic and neurovascularization changes in the brain in patients with type 1 diabetes and cognitive impairment. The study included 120 patients with type 1 diabetes aged 18 to 45 years suffering from cognitive impairment, and 30 people without cognitive decline and the control group (n=30) healthy people without diabetes. Neuropsychological testing included the Montreal Cognitive Dysfunction Assessment Scale (MoCA test). For neuroimaging methods, standard magnetic resonance imaging (MRI), magnetic resonance spectroscopy (MRS), contrast and non-contrast-enhanced perfusion were used. Statistical processing was carried out using the SPSS Statistic 2020 software. In patients with type 1 diabetes with cognitive impairment, as manifested by impaired memory and/or attention, perfusion imaging revealed the presence of brain asymmetry zones. Standard MRI allowed to demonstrate changes in the white, gray matter and hippocampus in the right hemisphere. The results obtained were refined taking into account the topical localization, so during the perfusion study, regions with asymmetric blood flow were identified - namely, the white matter of the frontal lobe and the gray matter in the occipital lobe. Spectroscopy of the brain revealed that it was in these areas of the brain that the most significant metabolic disorders were noted – in the form of significantly altered ratio of N-acetylaspartate (NAA)/choline (Cho) on the left, along with the asymmetry in phosphocreatine level (Cr 2) on the right. In conclusion, early preclinical predictive diagnostics with the use of modern neuroimaging methods allows for timely detection of impaired vascularization and brain metabolism in this group of patients, However, decreased perfusion in the region within the region of frontal lobe white matter and temporal lobe grey matter, and hippocampal cell metabolism by spectra should be highlighted among the parameters Cr right and NAA/Cho left.

A structural MRI study of global developmental delay in infants (

To use structural magnetic resonance imaging (3D-MRI) to evaluate the abnormal development of the cerebral cortex in infants with global developmental delay (GDD). The GDD group includes 67 infants aged between 112 and 699 days with global developmental delay and who underwent T1-weighted MRI scans in Shanxi Children's Hospital from December 2019 to March 2022. The healthy control (HC) group includes 135 normal developing infants aged between 88 and 725 days in Shanxi Children's Hospital from September 2020 to August 2021. Whole-brain T1-weighted MRI scans were carried out with a 3.0-T magnetic resonance scanner, which was later processed using InfantSurfer to perform MR image processing and cortical surface reconstruction. Two morphological features of the cortical surface of the 68 brain regions were computed, i.e., the cortical thickness (CT) and cortical surface area (SA), and compared between the GDD and HC groups. With regard to the CT, the HC group showed a rapid decrease at first and then a slow increase after birth, and the CT of the GDD group decreased slowly and then became relatively stable. The GDD group showed bilaterally higher hemispherical average CT than those in the HC group. In detail, for the left hemisphere, except in the entorhinal and temporal poles in which the average CT values of the two brain regions were lower than those of the HC group, the CT of the 26 brain regions in the GDD group was higher than those of the HC group (p < 0.05). For the right hemisphere, the CT of the entorhinal in the GDD group was lower than that in the HC group. Otherwise, the CT of the remaining 28 brain regions was higher than those in the HC group (p < 0.05). With regard to the SA, both groups showed a rapid increase after birth till 23 months and remained quite stable afterward. The GDD group shows lower SA bilaterally than that in the HC group. In detail, SA in the GDD group was lower in most cortical regions of both hemispheres than in the HC group (p < 0.05), except for the right temporal pole and entorhinal. When testing for brain asymmetry, we found that the HC group showed obvious asymmetry of CT and SA, while only a few cortical regions in the GDD group showed asymmetry.

Brain Asymmetry and Its Effects on Gait Strategies in Hemiplegic Patients: New Rehabilitative Conceptions.

Brain asymmetry is connected with motor performance, suggesting that hemiparetic patients have different gait patterns depending on the side of the lesion. This retrospective cohort study aims to further investigate the difference between right and left hemiplegia in order to assess whether the injured side can influence the patient’s clinical characteristics concerning gait, thus providing insights for new personalized rehabilitation strategies. The data from 33 stroke patients (17 with left and 16 with right hemiplegia) were retrospectively compared with each other and with a control group composed of 20 unaffected age-matched individuals. The 3D gait analysis was used to assess kinematic data and spatio-temporal parameters. Compared to left hemiplegic patients, right hemiplegic patients showed worse spatio-temporal parameters (p < 0.05) and better kinematic parameters (p < 0.05). Both pathological groups were characterized by abnormal gait parameters in comparison with the control group (p < 0.05). These findings show an association between the side of the lesion—right or left—and the different stroke patients’ gait patterns: left hemiplegic patients show better spatio-temporal parameters, whereas right hemiplegic patients show better segmentary motor performances. Therefore, further studies may develop and assess new personalized rehabilitation strategies considering the injured hemisphere and brain asymmetry.

Fronto—Parietal Regions Predict Transient Emotional States in Emotion Modulated Response Inhibition via Low Frequency and Beta Oscillations

The current study evaluated the impact of task-relevant emotion on inhibitory control while focusing on midline cortical regions rather than brain asymmetry. Single-trial time-frequency analysis of electroencephalography recordings linked with response execution and response inhibition was done while thirty-four participants performed the emotion modulated stop-signal task. To evaluate individual differences across decision-making processes involved in inhibitory control, a hierarchical drift-diffusion model was used to fit data from Go-trials for each of the 34 participants. Response threshold in the early processing stage for happy and disgust emotions could be distinguished from the later processing stage at the mid-parietal and mid-frontal regions, respectively, by the single-trial power increments in low frequency (delta and theta) bands. Beta desynchronization in the mid-frontal region was specific for differentiating disgust from neutral emotion in the early as well as later processing stages. The findings are interpreted based on the influence of emotional stimuli on early perceptual processing originating as a bottom-up process in the mid-parietal region and later proceeding to the mid-frontal region responsible for cognitive control processing, which resulted in enhanced inhibitory performance. The results show the importance of mid-frontal and mid-parietal regions in single-trial dynamics of inhibitory control processing.

Cognitive and Neurophysiological Models of Brain Asymmetry

Asymmetry is an inherent characteristic of brain organization in both humans and other vertebrate species, and is evident at the behavioral, neurophysiological, and structural levels. Brain asymmetry underlies the organization of several cognitive systems, such as emotion, communication, and spatial processing. Despite this ubiquity of asymmetries in the vertebrate brain, we are only beginning to understand the complex neuronal mechanisms underlying the interaction between hemispheric asymmetries and cognitive systems. Unfortunately, despite the vast number of empirical studies on brain asymmetries, theoretical models that aim to provide mechanistic explanations of hemispheric asymmetries are sparse in the field. Therefore, this Special Issue aims to highlight empirically based mechanistic models of brain asymmetry. Overall, six theoretical and four empirical articles were published in the Special Issue, covering a wide range of topics, from human handedness to auditory laterality in bats. Two key challenges for theoretical models of brain asymmetry are the integration of increasingly complex molecular data into testable models, and the creation of theoretical models that are robust and testable across different species.

Functional Brain Asymmetry and Menopausal Treatments: Is There a Link?

Background and Objectives: The human brain presents a functional asymmetry for every cognitive function, and it is possible that sexual hormones could have an impact on it. Visual–spatial attention, one of the most lateralized functions and one that is mainly dependent on the right hemisphere, represents a sentinel for functional cerebral asymmetry (FCA). The aim of this study was to evaluate whether menopausal hormone therapy (MHT) or phytoestrogens could modulate FCA in postmenopausal women. Materials and Methods: We enrolled postmenopausal women who were taking MHT or soy isoflavones or receiving no therapy and asked them to perform the line bisection test at study enrollment and after 18 and 36 months. Results: Ninety women completed the follow-up. At zero time, women who had not been subjected to therapy showed a leftward deviation (F = −3.0), whereas, after 36 months, the test results showed a rightward deviation (F = 4.5; p < 0.01). Women taking MHT showed a leftward deviation at the start (F = −3.0) and a persistent leftward deviation after 36 months (F = −4.0; p = 0.08). Conversely, women taking soy isoflavones started with a leftward deviation (F = −3.0) that became rightward (F = 3.0), with a significant difference shown after 36 months (p < 0.01). Conclusions: Our data suggest that hormonal modulation improves the interplay between the two hemispheres and reduces FCA. We propose, therefore, that the functions of the right hemisphere are mainly affected by aging and that this could be one of the reasons why the right hemisphere is more susceptible to the effects of MHT.

Structural Brain Asymmetries for Language: A Comparative Approach across Primates

Humans are the only species that can speak. Nonhuman primates, however, share some ‘domain-general’ cognitive properties that are essential to language processes. Whether these shared cognitive properties between humans and nonhuman primates are the results of a continuous evolution [homologies] or of a convergent evolution [analogies] remain difficult to demonstrate. However, comparing their respective underlying structure—the brain—to determinate their similarity or their divergence across species is critical to help increase the probability of either of the two hypotheses, respectively. Key areas associated with language processes are the Planum Temporale, Broca’s Area, the Arcuate Fasciculus, Cingulate Sulcus, The Insula, Superior Temporal Sulcus, the Inferior Parietal lobe, and the Central Sulcus. These structures share a fundamental feature: They are functionally and structurally specialised to one hemisphere. Interestingly, several nonhuman primate species, such as chimpanzees and baboons, show human-like structural brain asymmetries for areas homologous to key language regions. The question then arises: for what function did these asymmetries arise in non-linguistic primates, if not for language per se? In an attempt to provide some answers, we review the literature on the lateralisation of the gestural communication system, which may represent the missing behavioural link to brain asymmetries for language area’s homologues in our common ancestor.

Cerebral Polymorphisms for Lateralisation: Modelling the Genetic and Phenotypic Architectures of Multiple Functional Modules

Recent fMRI and fTCD studies have found that functional modules for aspects of language, praxis, and visuo-spatial functioning, while typically left, left and right hemispheric respectively, frequently show atypical lateralisation. Studies with increasing numbers of modules and participants are finding increasing numbers of module combinations, which here are termed cerebral polymorphisms—qualitatively different lateral organisations of cognitive functions. Polymorphisms are more frequent in left-handers than right-handers, but it is far from the case that right-handers all show the lateral organisation of modules described in introductory textbooks. In computational terms, this paper extends the original, monogenic McManus DC (dextral-chance) model of handedness and language dominance to multiple functional modules, and to a polygenic DC model compatible with the molecular genetics of handedness, and with the biology of visceral asymmetries found in primary ciliary dyskinesia. Distributions of cerebral polymorphisms are calculated for families and twins, and consequences and implications of cerebral polymorphisms are explored for explaining aphasia due to cerebral damage, as well as possible talents and deficits arising from atypical inter- and intra-hemispheric modular connections. The model is set in the broader context of the testing of psychological theories, of issues of laterality measurement, of mutation-selection balance, and the evolution of brain and visceral asymmetries.