Fear is more right lateralized than happiness and anger: Evidence for the motivational hypothesis of emotional face perception?

Facial emotion processing (FEP) tends to be right hemisphere lateralized. This right-hemispheric bias (RHB) for FEP varies within and between individuals. The aim of the present research was to examine evidence pertaining to the prominent theories of FEP hemispheric bias as measured by a half-emotional half-neutral (no emotion) chimeric faces task. FEP hemispheric bias was indexed using laterality quotients (LQs) calculated from a Chimeric Faces Task completed by 427 adults recruited from the general population aged 18-67 years. Participants indicated which of two identical (but mirrored) emotional-neutral chimeric faces were more emotive. While all investigated emotions (fear, anger, and happiness) were right lateralized, fear was significantly more right lateralized than anger and happiness. These results provide evidence for both the right hemisphere hypothesis and the motivational hypothesis of emotion perception.

Hemisphere lateralization of graph theoretical network in end-stage knee osteoarthritis patients.

Hemisphere functional lateralization is a prominent feature of the human brain. However, it is not known whether hemispheric lateralization features are altered in end-stage knee osteoarthritis (esKOA). In this study, we performed resting-state functional magnetic imaging on 46 esKOA patients and 31 healthy controls (HCs) and compared with the global and inter-hemisphere network to clarify the hemispheric functional network lateralization characteristics of patients. A correlation analysis was performed to explore the relationship between the inter-hemispheric network parameters and clinical features of patients. The node attributes were analyzed to explore the factors changing in the hemisphere network function lateralization in patients. We found that patients and HCs exhibited "small-world" brain network topology. Clustering coefficient increased in patients compared with that in HCs. The hemisphere difference in inter-hemispheric parameters including assortativity, global efficiency, local efficiency, clustering coefficients, small-worldness, and shortest path length. The pain course and intensity of esKOA were positively correlated with the right hemispheric lateralization in local efficiency, clustering coefficients, and the small-worldness, respectively. The significant alterations of several nodal properties were demonstrated within group in pain-cognition, pain-emotion, and pain regulation circuits. The abnormal lateralization inter-hemisphere network may be caused by the destruction of regional network properties.

Insights on cognitive reorganization after hemispherectomy in Rasmussen's encephalitis. A narrative review.

Rasmussen's encephalitis is a rare neurological pathology affecting one cerebral hemisphere, therefore, posing unique challenges. Patients may undergo hemispherectomy, a surgical procedure after which cognitive development occurs in the isolated contralateral hemisphere. This rare situation provides an excellent opportunity to evaluate brain plasticity and cognitive recovery at a hemispheric level. This literature review synthesizes the existing body of research on cognitive recovery following hemispherectomy in Rasmussen patients, considering cognitive domains and modulatory factors that influence cognitive outcomes. While language function has traditionally been the focus of postoperative assessments, there is a growing acknowledgment of the need to broaden the scope of language investigation in interaction with other cognitive domains and to consider cognitive scaffolding in development and recovery. By synthesizing findings reported in the literature, we delineate how language functions may find support from the right hemisphere after left hemispherectomy, but also how, beyond language, global cognitive functioning is affected. We highlight the critical influence of several factors on postoperative cognitive outcomes, including the timing of hemispherectomy and the baseline preoperative cognitive status, pointing to early surgical intervention as predictive of better cognitive outcomes. However, further specific studies are needed to confirm this correlation. This review aims to emphasize a better understanding of mechanisms underlying hemispheric specialization and plasticity in humans, which are particularly important for both clinical and research advancements. This narrative review underscores the need for an integrative approach based on cognitive scaffolding to provide a comprehensive understanding of mechanisms underlying the reorganization in Rasmussen patients after hemispherectomy.

Location- and Object-Based Representational Mechanisms Account for Bilateral Field Advantage in Multiple-Object Tracking.

Keeping track of multiple visually identical and independently moving objects is a remarkable feature of the human visual system. Theoretical accounts for this ability focus on resource-based models that describe parametric decreases of performance with increasing demands during the task (i.e., more relevant items, closer distances, higher speed). Additionally, the presence of two central tracking resources, one within each hemisphere, has been proposed, allowing for an independent maintenance of moving targets within each visual hemifield. Behavioral evidence in favor of such a model shows that human subjects are able to track almost twice as many targets across both hemifields compared with within one hemifield. A number of recent publications argue for two separate and parallel tracking mechanisms during standard object tracking tasks that allow for the maintenance of the relevant information in a location-based and object-based manner. Unique electrophysiological correlates for each of those processes have been identified. The current study shows that these electrophysiological components are differentially present during tracking within either the left or right hemifield. The present results suggest that targets are mostly maintained as an object-based representation during left hemifield tracking, while location-based resources are preferentially engaged during right hemifield tracking. Interestingly, the manner of representation does not seem to have an impact on behavioral performance within the subjects, while the electrophysiological component indicating object-based tracking does correlate with performance between subjects. We propose that hemifield independence during multiple-object tracking may be an indication of the underlying hemispheric bias for parallel location-based and object-based tracking mechanisms.

Multi-level fMRI analysis applied to hemispheric specialization in the language network, functional areas, and their behavioral correlations in the ABCD sample.

Prior research suggests that the organization of the language network in the brain is left-dominant and becomes more lateralized with age and increasing language skill. The age at which specific components of the language network become adult-like varies depending on the abilities they subserve. So far, a large, developmental study has not included a language task paradigm, so we introduce a method to study resting-state laterality in the Adolescent Brain Cognitive Development (ABCD) study. Our approach mixes source timeseries between left and right homotopes of the (1) inferior frontal and (2) middle temporal gyri and (3) a region we term "Wernicke's area" near the supramarginal gyrus. Our large subset sample size of ABCD (n = 6153) allows improved reliability and validity compared to previous, smaller studies of brain-behavior associations. We show that behavioral metrics from the NIH Youth Toolbox and other resources are differentially related to tasks with a larger linguistic component over ones with less (e.g., executive function-dominant tasks). These baseline characteristics of hemispheric specialization in youth are critical for future work determining the correspondence of lateralization with language onset in earlier stages of development.

Abnormal hemispheric specialization and inter-hemispheric functional cooperation in generalized anxiety disorder.

Abnormal hemispheric specialization and inter-hemispheric interactions may contribute to the pathogenesis of general anxiety disorder (GAD). The current study investigated these abnormalities in GAD patients based on the two analytic approaches and examined whether such abnormalities are correlated with anxiety symptom severity. Seventy-three patients with GAD and 60 matched healthy controls were recruited. All participants completed anxiety symptoms assessment and resting-state functional magnetic resonance imaging (rs-fMRI). The autonomy index (AI) and Connectivity between Functionally Homotopic voxels (CFH) were applied to measure and compared between groups. Compared to controls, patients showed stronger AI in the right middle temporal gyrus (MTG). Seed-based analysis revealed stronger functional connectivity (FC) of the right MTG with both right precuneus and right dorsolateral prefrontal cortex (dlPFC) in patients. Patients also exhibited greater CFH in right anterior cingulate cortex (ACC) but decreased CFH in bilateral postcentral gyrus (PCG) and superior occipital gyrus (SOG). Further there were significant correlations between these regional CFH and anxiety symptoms severity. GAD patients demonstrate right hemispheric specialization and aberrant inter-hemispheric functional cooperation, and abnormal inter-hemispheric coordination is associated with anxiety symptom severity. These findings provide a clue to understanding the neuropathological mechanisms of GAD.

Laterality and hemispheric specialization of self-face recognition.

Inspired by the pioneering work of Eran Zaidel beginning in the early 1970's on the role of the two cerebral hemispheres of the human brain in self-related cognition, we review research on self-face recognition from a laterality perspective. The self-face is an important proxy of the self, and self-face recognition has been used as an indicator of self-awareness more broadly. Over the last half century, behavioral and neurological data, along with over two decades of neuroimaging research evidence have accumulated on this topic, generally concluding a right-hemisphere dominance for self-face recognition. In this review, we briefly revisit the pioneering roots of this work by Sperry, Zaidel & Zaidel, and focus on the important body of neuroimaging literature on self-face recognition it has inspired. We conclude with a brief discussion of current models of self-related processing and future directions for research in this area.

Effect of age on lateralized auditory processing.

The lateralization of processing in the auditory cortex for different acoustic parameters differs depending on stimuli and tasks. Thus, processing complex auditory stimuli requires an efficient hemispheric interaction. Anatomical connectivity decreases with aging and consequently affects the functional interaction between the left and right auditory cortex and lateralization of auditory processing. Here we studied with magnetic resonance imaging the effect of aging on the lateralization of processing and hemispheric interaction during two tasks utilizing the contralateral noise procedure. Categorization of tones according to their direction of frequency modulations (FM) is known to be processed mainly in the right auditory cortex. Sequential comparison of the same tones according to their FM direction strongly involves additionally the left auditory cortex and therefore a stronger hemispheric interaction than the categorization task. The results showed that older adults more strongly recruit the auditory cortex especially during the comparison task that requires stronger hemispheric interaction. This was the case although the task difficulty was adapted to achieve similar performance as the younger adults. Additionally, functional connectivity from auditory cortex to other brain areas was stronger in older than younger adults especially during the comparison task. Diffusion tensor imaging data showed a reduction in fractional anisotropy and an increase in mean diffusivity in the corpus callosum of older adults compared to younger adults. These changes indicate a reduction of anatomical interhemispheric connections in older adults that makes larger processing capacity necessary when tasks require functional hemispheric interaction.

Show me your best side: Lateralization of social and resting behaviors in feral horses.

Growing evidence shows a variety of sensorial and motor asymmetries in social and non-social interactions in various species, indicating a lateralized processing of information by the brain. Using digital video cameras on tripods and drones, this study investigated lateralization in frequency and duration of social behavior patterns, in affiliative, agonistic, and resting contexts, in a feral population of horses (Equus ferus caballus) in Northern Portugal, consisting of 37 individuals organized in eight harem groups. Affiliative interactions (including grooming) were more often performed, and lasted longer, when recipients were positioned to the right side. In recumbent resting (animals lying down) episodes on the left side lasted longer. Our results of an affiliative behavior having a right side tendency, provide partial support to the valence-specific hypothesis of Ahern and Schwartz (1979) - left hemisphere dominance for positive affect, affiliative behaviors. Longer recumbent resting episodes on the left side may be due to synchronization. However, in both instances it is discussed how lateralization may be context dependent. Investigating the position asymmetries of social behaviors in feral equids will contribute to a better understanding of differential lateralization and hemispheric specialization from the ecological and evolutionary perspectives.

Face distortions in prosopometamorphopsia provide new insights into the organization of face perception.

Prosopometamorphopsia (PMO) is a striking condition of visual perception in which facial features appear distorted, for example drooping, swelling, or twisting. Although numerous cases have been reported, few of those investigations have carried out formal testing motivated by theories of face perception. However, because PMO involves conscious visual distortions to faces which participants can report, it can be used to probe fundamental questions about face representations. Here we review cases of PMO that address theoretical questions in visual neuroscience including face specificity, inverted face processing, the importance of the vertical midline, dissociable representations for each half of the face, hemispheric specialization, the relationship between face recognition and conscious face perception, and the reference frames that face representations are embedded within. Finally, we list and touch upon eighteen open questions that make clear how much is left to learn about PMO and the potential it has to provide important advances in face perception.

Development, and validation of non-speech dichotic listening test.

Background: Classic dichotic listening tests using speech stimuli result in right ear advantage, due to the dominant crossed pathway for speech and language. It is presumed that similar crossed dominance could exist for non-speech stimuli too. Hence, this is an attempt to develop and validate the dichotic non-speech test using environmental stimuli and explore the effect of focused attention on this test. Materials and method: Three lists of dichotic stimuli were created using these sounds with fifteen tokens in each list. Four professionals and non-professionals validated these materials. Normative estimation was obtained by administering the newly developed test on 70 adults and 70 children using a free-recall and forced-recall condition. Result: The results showed a significant difference between the left ear and right scores where the left ear score was better than the right, depicting left ear advantage (LEA) for free recall condition in both groups. In the forced recall condition, LEA was not seen; rather the mean score was significantly higher in the attended ear, irrespective of the stimuli presented to the right or left ear. The test-retest reliability in free recall was good in both the ears and moderate for forced right ear conditions. Conclusion: The novel test consistently showed LEA with good reliability and can be used to assess the hemispheric asymmetry in normal subjects and also in test batteries for the clinical population.

Production of co-speech gestures in the right hemisphere: Evidence from individuals with complete or anterior callosotomy.

INTRODUCTION: A right-hand preference for co-speech gestures in right-handed neurotypical individuals as well as the co-occurrence of speech and gesture has induced neuropsychological research to primarily target the left hemisphere when investigating co-speech gesture production. However, the substantial number of spontaneous left-hand gestures in right-handed individuals has, thus far, been unexplained. Recent studies in individuals with complete callosotomy and exclusive left hemisphere speech production show a reliable left-hand preference for co-speech gestures, indicating a right hemispheric generation. However, the findings raise the issue if the separate right hemisphere is able to also generate representational gestures. The present study challenges the proposition of a specific right hemispheric contribution to gesture production by differentiating gesture types including representational ones in individuals with complete callosotomy and by including individuals with anterior callosotomy in whom neural reorganization is less extensive. METHODS: Three right-handed individuals with complete commissurotomy (A.A., N.G., G.C.) and three right-handed individuals with anterior callosotomy (C.E., S.R., L. D), all with left hemisphere language dominance, and a matched right-handed neurotypical control group (n = 10) were examined in an experimental setting, including re-narration of a nonverbal animated cartoon and responding to intelligence questions. The participants' video-taped hand movement behavior was analyzed by two independent certified raters with the NEUROGES-ELAN system for nonverbal behavior and gesture. Unimanual right-hand and left-hand gestures were classified into eight gesture types. RESULTS: The individuals with complete and anterior callosotomy performed unimanual co-speech gestures with the left as well as the right hand, with no significant preference of one hand for gestures overall. Concerning the specific gesture types, the group with complete callosotomy showed a significant right-hand preference for pantomime gestures, which also applied to the callosotomy total group. The group with anterior callosotomy displayed a significant left-hand preference for form presentation gestures. As a trend, the callosotomy total group differed from the neurotypical group as they performed more left-hand egocentric deictic and left-hand form presentation gestures. DISCUSSION: The present study replicates the finding of a substantial left-hand use for unimanual co-speech gestures in individuals with complete callosotomy. The proposition of a right hemispheric contribution to gesture production independent from left hemispheric language production is corroborated by the finding that individuals with anterior callosotomy show a similar pattern of hand use for gestures. Representational gestures were displayed with either hand, suggesting that in particular right hemispheric spatial cognition can be directly expressed in gesture. The significant right-hand preference for pantomime gesture was outstanding and compatible with the established left hemispheric specialization for tool use praxis. The findings shed a new light on the left-hand gestures in neurotypical individuals, suggesting that these can be generated in the right hemisphere.

Hemispheric Differences in Self-evaluation Errors of Upper Extremity Movement in Patients with Chronic Stroke.

OBJECTIVE: There is growing evidence that the side of brain lesions results in distinct upper extremity deficits in motor control, movement behavior, and emotional and cognitive function poststroke. We investigated self-evaluation errors, which are the differences in scores between patient self-evaluation and clinician evaluations, and compared patients with left hemisphere damage (LHD) and right hemisphere damage (RHD) poststroke. METHOD: Twenty-eight patients with chronic stroke (LHD = 16) performed the actual amount of the test twice with a one-week interval. We videotaped the participants' movements, and participants with stroke and evaluators graded the quality of movement scores by watching video recordings. RESULTS: Self-evaluation errors were significantly lower in patients with LHD than in those with RHD (t = 2.350, p = .019). Interestingly, this error did not change after the clinician provided the correct score as feedback. Chi-squared analysis revealed that more patients with LHD underestimated their movements (χ2 = 9.049, p = .002), while more patients with RHD overestimated (χ2 = 7.429, p = .006) in the send evaluation. Furthermore, there were no correlations between self-evaluation error and age, cognitive function, physical impairment, ability to control emotions, or onset months poststroke. CONCLUSIONS: Patients with stroke and therapists evaluated the same movements differently, and this can be dependent on hemispheric damage. Therapists might need to encourage patients with LHD who underestimate their movement to ensure continuous use of their more-affected arm. Patients with RHD who overestimate their movement might need treatment to overcome impaired self-awareness, such as video recordings, to protect from unexpected dangerous situations.

Asymmetries and hemispheric interaction in the auditory system of elderly people.

Age-related changes of asymmetries in the auditory system and decreasing efficiency of hemispheric interaction have been discussed for some time. This mini-review discusses recent neuroimaging studies on alterations in lateralization of cortical processing and structural changes concerning the division of labor and interaction between hemispheres during auditory processing in elderly people with the focus on people without severe hearing loss. Several changes of asymmetries in anatomy, function and neurotransmitter concentration were observed in auditory cortical areas of older compared to younger adults. It was shown that connections between left and right auditory cortex are reduced during aging. Functionally, aging seems to lead to a reduction in asymmetry of auditory processing. However, the results do not always point into the same direction. Furthermore, correlations between function, anatomy and behavior in the left and right hemisphere appear to differ between younger and older adults. The changes in auditory cortex asymmetries with aging might be due to compensation of declining processing capacities, but at the same time these mechanisms could impair the balanced division of labor between the two hemispheres that is required for the processing of complex auditory stimuli such as speech. Neuroimaging studies are essential to follow the slow changes with aging as in the beginning no behavioral effects might be visible due to compensation. Future studies should control well for peripheral hearing loss and cognitive decline. Furthermore, for the interpretability of results it is necessary to use specific tasks with well-controlled task difficulty.

Abnormalities of hemispheric specialization in drug-naïve and drug-receiving self-limited epilepsy with centrotemporal spikes.

PURPOSE: Self-limited epilepsy with centrotemporal spikes (SLECTS) is a pediatric benign epilepsy but often accompanied by subsequent (in adulthood) functional changes such as language, which are thought to have distinct areas of hemispheric lateralization and functional differentiation. This study aimed to explore hemispheric specialization measured by resting-state functional magnetic resonance imaging (rs-fMRI) functional connectivity in drug-naïve and drug-receiving SLECTS. METHODS: Hemispheric specialization was quantified in three groups of children, including 21 drug-naïve patients (DNP) with SLECTS, 34 drug-receiving patients (DRP) with SLECTS and 36 demographically matched typical development (TD). RESULTS: Compared with the TD group, both the DNP and DRP groups exhibited significantly higher specialization in the left superior temporal gyrus, right parahippocampus, left putamen, and right caudate. The DNP group exhibited significantly higher hemispheric specialization in the right precentral gyrus and right inferior temporal gyrus, while the DRP group demonstrated significantly higher hemispheric specialization in the left postcentral gyrus and right hippocampus than the TD group. Furthermore, bilateral cerebellum_6 showed opposing hemispheric specialization trends in the two patient groups. Further meta-analytical mapping demonstrated that hemispheric specialization-related differential brain regions are primarily involved in language processing. CONCLUSION: Our findings showed that children with SLECTS had altered hemispheric specialization, mainly in language processing regions, suggesting both abnormal intrahemispheric segregation and interhemispheric integration in these children.

Increasing interhemispheric connectivity between human visual motion areas uncovers asymmetric sensitivity to horizontal motion.

Our conscious perceptual experience relies on a hierarchical process involving integration of low-level sensory encoding and higher-order sensory selection.1 This hierarchical process may scale at different levels of brain functioning, including integration of information between the hemispheres.2-5 Here, we test this hypothesis for the perception of visual motion stimuli. Across 3 experiments, we manipulated the connectivity between the left and right visual motion complexes (V5/MT+) responsible for horizontal motion perception2,3 by means of transcranial magnetic stimulation (TMS).4,5 We found that enhancing the strength of connections from the left to the right V5/MT+, by inducing spike-timing-dependent plasticity6 in this pathway, increased sensitivity to horizontal motion. These changes were present immediately and lasted at least 90 min after intervention. Notably, little perceptual changes were observed when strengthening connections from the right to the left V5/MT+. Furthermore, we found that this asymmetric modulation was mirrored by an asymmetric perceptual bias in the direction of the horizontal motion. Overall, observers were biased toward leftward relative to rightward motion direction. Crucially, following the strengthening of the connections from right to left V5/MT+, this bias could be momentarily reversed. These results suggest that the projections connecting left and right V5/MT+ in the human visual cortex are asymmetrical, subtending a hierarchical role of hemispheric specialization7-10 favoring left-to-right hemisphere processing for integrating local sensory input into coherent global motion perception.

Effect of cochlear implant side on early speech processing in adults with single-sided deafness.

OBJECTIVE: In binaurally deaf subjects, speech processing particularly benefits from a cochlear implant (CI) in the right ear, which is contralateral to the commonly left speech-dominant hemisphere. However, it is unclear whether such effects of implantation side also occur in speech processing in patients with single-sided deafness (SSD). METHODS: Lateralization of N1 responses was analyzed with a high-density electroencephalogram (EEG) in fourteen adults with postlingually acquired left or right SSD who received a CI in adulthood. During recording, patients performed a speech and a pure-tone discrimination task. Lateralization of N1 responses was assessed by side-specific global field power (GFP) and compared (a) between normal hearing and CI-implanted ears within subjects and (b) between implantation sides across subjects. RESULTS: N1 responses were stronger in the contralateral than in the ipsilateral hemisphere during stimulation of the normal hearing ear (except for left speech stimulation), and was bilateral symmetric with CI stimulation on either side. A significant correlation between speech discrimination performance and left lateralization was found across subjects for the left CI ear. CONCLUSIONS: CI stimulation altered auditory processing across hemispheres. Speech discrimination in left CI-implanted SSD patients improved with left lateralization of the N1 response. SIGNIFICANCE: Side-specific rehabilitation in SSD patients might improve speech processing across hemispheres.

Is there hemispheric specialization in the chronic pain brain?

Organismal bilateral symmetry is associated with near-identical halves of the central nervous system, with certain functions displaying specialization through one brain hemisphere. The processing of pain in the brain as well as brain plasticity in the context of painful injuries have garnered much attention in recent decades. Noninvasive brain imaging studies in pain-free human subjects have identified multiple brain regions that are linked to the sensory and affective components of pain. Longlasting adaptations in brains of chronic pain sufferers have likewise been described, suggesting a mechanism for pain chronification. Invasive molecular and biochemical studies in animal models have expanded on these findings, with added emphasis on the role of specific genes and molecules involved. To date, the extent of hemispheric asymmetry in the context of pain is not well-understood. This topical review evaluates the evidence of hemispheric specialization observed in humans and rodent models of pain and compares it to findings where such asymmetry is absent. Our review shows conflicting information regarding the existence of pain-related asymmetry, and if so, the side to which it can be localized. This could be due to the heterogeneity of pain processing pathways, heterogeneity in study parameters, as well as differences in data reporting. With the advent of progressively sophisticated non-invasive tools that can be used in human subjects, in addition to more precise methods to visualize and control specific brain regions or neuronal ensembles in animal models, we predict that the next few decades will witness a better understanding of the supraspinal control and processing of chronic pain, including the role of each of its hemispheres.

Neonatal manual specialization in language and music conditions: Consistency with the hemispheric specialization adult model.

The main purpose of this study was to test in neonates the influence of the sound environment, i.e., language versus music, on asymmetric hand movement activity in the presence of a target object. Based on hemispheric specialization, our hypothesis was that infants would use their right hand more in the speech context (left hemisphere) and their left hand more in the music context (right hemisphere). The study involved 19 full-term 3-day-old neonates. An object was presented successively in the two sound environments in counterbalance order for 120 s each. Left and right movements and mouth activity were scored during the target object presentation. Results show that neonates moved their left hand twice as much as their right hand in the music condition than in the language condition, and they moved their right hand a longer time in the language condition than in the music condition. The average number of sucking bursts was significantly higher in the language condition than in the music condition. We discuss the results in terms of manual specialization in relation to the development of hemispheric specialization.