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Introduction Since its first description, the concept of reverse shoulder arthroplasty (RSA) has evolved. The term lateralization remains unclear and is used to describe implants that lateralize on the glenoid side, the humeral side, or both. The objective of this study was to provide a clear definition of lateralization and to measure the lateralization achieved by the most commonly used implants. Materials and methods Twenty-eight different configurations with 22 different implants were analyzed. Glenoid, humeral, and global lateralization was measured on digitized templates. Implant lateralization was normalized to the lateral offset of the Delta III. Each implant was defined as a combination of one of two glenoid categories (medialized glenoid (MG), lateralized glenoid (LG), and one of four humeral categories (medialized humerus (MH), minimally lateralized humerus (LH), lateralized humerus (LH+). In addition, implants were separated in categories of 5-mm increments for global offset (medialized RSA (M-RSA), minimally lateralized RSA (ML-RSA), lateralized RSA (L-RSA), highly lateralized RSA (HL-RSA), and very highly lateralized RSA (VHL-RSA). Results The global lateral offset of the Delta III was 13.1 mm; global lateral offset of all designs in this study varied between 13.1 and 35.8 mm. Regarding their global lateral offset, five implants are M-RSA (lateral offset < 18.1 mm), five ML-RSA (18.1–23.1 mm), seven L-RSA (23.1–28.1 mm), six HL-RSA (28.1–33.1 mm), and one VHL-RSA (33.1–38.1 mm). Conclusion There is high variability in the amount of lateralization provided by the majority of RSAs currently available. This descriptive analysis can help surgeons understand the features of implants in the market based on their lateralization in order to adapt the surgical technique depending on the expected lateral offset of the design being implanted.

One way to increase cognitive capacity is to avoid duplication of functions on the left and right sides of the brain. There is a convincing body of evidence showing that such asymmetry, or lateralization, occurs in a wide range of both vertebrate and invertebrate species. Each hemisphere of the brain can attend to different types of stimuli or to different aspects of the same stimulus and each hemisphere analyses information using different neural processes. A brain can engage in more than one task at the same time, as in monitoring for predators (right hemisphere) while searching for food (left hemisphere). Increased cognitive capacity is achieved if individuals are lateralized in one direction or the other. The advantages and disadvantages of individual lateralization are discussed. This paper argues that directional, or population-level, lateralization, which occurs when most individuals in a species have the same direction of lateralization, provides no additional increase in cognitive capacity compared to individual lateralization although directional lateralization is advantageous in social interactions. Strength of lateralization is considered, including the disadvantage of being very strongly lateralized. The role of brain commissures is also discussed with consideration of cognitive capacity.

recent evidence in natural and semi-natural settings has revealed a variety of left-right perceptual asymmetries among vertebrates. these include preferential use of the left or right visual hemifield during activities such as searching for food, agonistic responses, or escape from predators in animals as different as fish, amphibians, reptiles, birds, and mammals. there are obvious disadvantages in showing such directional asymmetries because relevant stimuli may be located to the animal's left or right at random; there is no a priori association between the meaning of a stimulus (e.g., its being a predator or a food item) and its being located to the animal's left or right. moreover, other organisms (e.g., predators) could exploit the predictability of behavior that arises from population-level lateral biases. it might be argued that lateralization of function enhances cognitive capacity and efficiency of the brain, thus counteracting the ecological disadvantages of lateral biases in behavior. however, such an increase in brain efficiency could be obtained by each individual being lateralized without any need to align the direction of the asymmetry in the majority of the individuals of the population. here we argue that the alignment of the direction of behavioral asymmetries at the population level arises as an “evolutionarily stable strategy” under “social” pressures occurring when individually asymmetrical organisms must coordinate their behavior with the behavior of other asymmetrical organisms of the same or different species.

It is widely acknowledged that the left and right hemispheres of human brains display both anatomical and functional asymmetries. For more than a century, brain and behavioral lateralization have been considered a uniquely human feature linked to language and handedness. However, over the past decades this idea has been challenged by an increasing number of studies describing structural asymmetries and lateralized behaviors in non-human species extending from primates to fish. Evidence suggesting that a similar pattern of brain lateralization occurs in all vertebrates, humans included, has allowed the emergence of different model systems to investigate the development of brain asymmetries and their impact on behavior. Among animal models, fish have contributed much to the research on lateralization as several fish species exhibit lateralized behaviors. For instance, behavioral studies have shown that the advantages of having an asymmetric brain, such as the ability of simultaneously processing different information and perform parallel tasks compensate the potential costs associated with poor integration of information between the two hemispheres thus helping to better understand the possible evolutionary significance of lateralization. However, these studies inferred how the two sides of the brains are differentially specialized by measuring the differences in the behavioral responses but did not allow to directly investigate the relation between anatomical and functional asymmetries. With respect to this issue, in recent years zebrafish has become a powerful model to address lateralization at different level of complexity, from genes to neural circuitry and behavior. The possibility of combining genetic manipulation of brain asymmetries with cutting-edge imaging technique and behavioral tests makes the zebrafish a valuable model to investigate the phylogeny and ontogeny of brain lateralization and its relevance for normal brain function and behavior.

The neural face perception network is distributed across both hemispheres. However, the dominant role in humans is virtually unanimously attributed to the right hemisphere. Interestingly, there are, to our knowledge, no imaging studies that systematically describe the distribution of hemispheric lateralization in the core system of face perception across subjects in large cohorts so far. To address this, we determined the hemispheric lateralization of all core system regions (i.e., occipital face area - OFA, fusiform face area - FFA, posterior superior temporal sulcus - pSTS) in 108 healthy subjects using functional magnetic resonance imaging (fMRI). We were particularly interested in the variability of hemispheric lateralization across subjects and explored how many subjects can be classified as right-dominant based on the fMRI activation pattern. We further assessed lateralization differences between different regions of the core system and analyzed the influence of handedness and sex on the lateralization with a generalized mixed effects regression model. As expected, brain activity was on average stronger in right-hemispheric brain regions than in their left-hemispheric homologues. This asymmetry was, however, only weakly pronounced in comparison to other lateralized brain functions (such as language and spatial attention) and strongly varied between individuals. Only half of the subjects in the present study could be classified as right-hemispheric dominant. Additionally, we did not detect significant lateralization differences between core system regions. Our data did also not support a general leftward shift of hemispheric lateralization in left-handers. Only the interaction of handedness and sex in the FFA revealed that specifically left-handed men were significantly more left-lateralized compared to right-handed males. In essence, our fMRI data did not support a clear right-hemispheric dominance of the face perception network. Our findings thus ultimately question the dogma that the face perception network – as measured with fMRI – can be characterized as “typically right lateralized”.

Introduction The complications of the conventional medialized design for reverse total shoulder arthroplasty (RSA) are increased scapular notching, and decreased external rotation and deltoid wrapping. Currently, lateralization design RSA, which avoid scapular notching and improve impingement-free range of motion, is commonly used. Especially, humeral lateralization design was most commonly used and glenoid lateralization design was preferred for glenoid abnormities. We compared mid-term clinical and radiologic outcomes of glenoid and humeral lateralization RSA in an Asian population in this study. Materials and Methods We enrolled 124 shoulders of 122 consecutive patients (mean age 73.8 ± 6.8 years) who received glenoid or humeral lateralization RSA from May, 2012 to March, 2019. We divided these patients into two groups according to RSA using either glenoid or humeral lateralization design. These different designs were introduced consecutively in Korea. The clinical and radiological results of 60 glenoid lateralization RSA (Group I, 60 patients) and 64 humeral lateralization RSA (Group II, 62 patients) were retrospectively evaluated and also were compared between the two groups. All patients were followed for mean 3 years. Results The clinical and radiologic outcomes of the two groups did not differ significantly, including scapular notching ( p  = 0.134). However, humeral lateralization RSA showed a larger glenoid-tuberosity (GT) distance ( p  = 0.000) and less distalization shoulder angle (DSA) ( p  = 0.035). The complication rate did not differ significantly either. But, revision surgery was performed for 2 humeral loosening in the Group II. Conclusion The clinical and radiologic outcomes of the two groups did not differ significantly, including scapular notching at mid-term follow-up. However, humeral lateralization design showed larger GT distance and less DSA. Humeral lateralization design RSA could preserve the normal shoulder contour due to a larger GT distance (more lateralization) and provide less deltoid tension due to less DSA (less distalization of COR).

The basis and impact of functional asymmetries in the brain, particularly language lateralization, are not fully understood, and the relationship between functional and structural asymmetries remains largely untested. This study investigated the degree to which asymmetries in hemispheric language laterality are concordant with asymmetries in gray matter (GM) structure and whether the hemispheric organization of memory is influenced by functional language asymmetries. Structural and functional MR data was acquired from 261 individuals, including those with unilateral temporal lobe epilepsy (LTLE = 96, RTLE = 69) and matched with healthy participants (HPs = 96). Functional language laterality indices (LIs) were calculated using two methods: (1) standard LIs from the frontal, temporal, and parietal lobes and (2) targeted LIs (T‐LIs) from individually defined activation peaks. Structural LIs (ST‐LIs) were derived from the GM volumes underlying these functional LIs. We observed significant shifts in language laterality in LTLE compared to HPs in 8 out of 12 brain regions. Strong correlations were observed between functional LIs and their structural counterparts. Discriminant analyses demonstrated that targeted LIs and ST‐LIs more effectively distinguished TLE patients from HPs, with ST‐LIs being the most powerful discriminator. Partial least squares analyses showed verbal and visual memory have a direct dependence on targeted LIs in HPs and LTLE, with this effect more pronounced in HPs. In RTLE, verbal memory showed a similar dependency. These findings underscored the importance of individualized, region‐specific measures for understanding language laterality, its relation to structural underpinnings, and its impact on the organization of other cognitive functions such as memory. This study highlights the strong correlation between functional language lateralization and gray matter structure, revealing how hemispheric asymmetries in language influence memory organization. Targeted language laterality indices (LIs) provide effective discrimination between temporal lobe epilepsy patients and matched healthy participants, with the patients displaying signs of atypical language organization.

Leftward language production and rightward spatial attention are salient features of functional organization in most humans, but their anatomical basis remains unclear. Interhemispheric connections and intrahemispheric white matter asymmetries have been proposed as important factors underlying functional lateralization. To investigate the role of white matter connectivity in functional lateralization, we first identified 96 left-handers using visual half field naming tasks. They were then divided into atypical and typical functional dominance based on the lateralization of brain activation in a word generation task (for language production) and a landmark task (for spatial attention). Using a novel fixel-based framework, we obtained fiber-specific properties of white matter pathways. Results showed, first, that differences between two language dominance groups occurred in the asymmetry of the superior longitudinal fasciculus-III (SLF-III), whereas differences between two spatial attention dominance groups occurred in the rostrum and rostral body of the corpus callosum. However, the directions of functional lateralization were not associated with the directions of white matter asymmetries. Second, the degree of language lateralization was predicted by SLF-III asymmetry and the rostral body of the corpus callosum, whereas the degree of spatial attention lateralization was predicted by the rostrum of the corpus callosum. Notably, the degree of each functional lateralization was negatively correlated with the anterior and middle callosal connections, supporting the excitatory model of the corpus callosum. The results suggest that language lateralization is shaped by a combined effect of intra- and interhemispheric connections, whereas spatial attention lateralization relies more on interhemispheric connections.

Children with autism often show atypical brain lateralization for speech and language processing, however, it is unclear what linguistic component contributes to this phenomenon. Here we measured event-related potential (ERP) responses in 21 school-age autistic children and 25 age-matched neurotypical (NT) peers during listening to word-level prosodic stimuli. We found that both groups displayed larger late negative response (LNR) amplitude to native prosody than to nonnative prosody; however, unlike the NT group exhibiting left-lateralized LNR distinction of prosodic phonology, the autism group showed no evidence of LNR lateralization. Moreover, in both groups, the LNR effects were only present for prosodic phonology but not for phoneme-free prosodic acoustics. These results extended the findings of inadequate neural specialization for language in autism to sub-lexical prosodic structures.

Research on a growing number of vertebrate species has shown that the left and right sides of the brain process information in different ways and that lateralized brain function is expressed in both specific and broad aspects of behaviour. This paper reviews the available evidence relating strength of lateralization to behavioural/cognitive performance. It begins by considering the relationship between limb preference and behaviour in humans and primates from the perspectives of direction and strength of lateralization. In birds, eye preference is used as a reflection of brain asymmetry and the strength of this asymmetry is associated with behaviour important for survival (e.g., visual discrimination of food from non-food and performance of two tasks in parallel). The same applies to studies on aquatic species, mainly fish but also tadpoles, in which strength of lateralization has been assessed as eye preferences or turning biases. Overall, the empirical evidence across vertebrate species points to the conclusion that stronger lateralization is advantageous in a wide range of contexts. Brief discussion of interhemispheric communication follows together with discussion of experiments that examined the effects of sectioning pathways connecting the left and right sides of the brain, or of preventing the development of these left-right connections. The conclusion reached is that degree of functional lateralization affects behaviour in quite similar ways across vertebrate species. Although the direction of lateralization is also important, in many situations strength of lateralization matters more. Finally, possible interactions between asymmetry in different sensory modalities is considered.