Left Hemisphere Dominance Research Articles

Heschl’s gyrus and the temporal pole: The cortical lateralization of language

The left lateralization of language has been attributed to hemispheric specialization for processing rapidly changing information. While interhemispheric differences in auditory cortex organization support this view, the macrostructure of the entire cerebral cortex has not been thoroughly examined from this perspective. This study investigated hemispheric asymmetries in cortical surface area and thickness and their relationship to pronunciation scores from oral reading using the Human Connectome Project Young Adult dataset (N=1113). Heschl’s gyrus had the most left-lateralized surface area, while the temporal pole showed the strongest right-lateralization in thickness. These areas correspond to the core components of speech: sound and meaning. Notably, their structural features were the only ones also yielding a significant correlation with pronunciation scores. Additionally, Broca’s area’s posterior region (pars opercularis), involved in articulatory phonological processing, showed leftward lateralization, contrasting with the right-lateralized anterior portions. Left-hemisphere language areas were largely thinner and more extended than their right-sided homologs with a larger white-to-gray matter ratio. Cortical thickness was inversely related to surface area. The lateralization of auditory-related language areas and their structure’s correlation with pronunciation in oral reading supports a genetically based auditory foundation for language. A thinner, more efficient cortex with larger surface areas and increased myelination likely underlies the left-hemispheric dominance of language. Thinner, more extended brain areas have been linked to more myelination and wider cortical columns and intercolumnar space. This provides the potential for a fast network of interconnected, discrete information units able to support language’s demands of rapid categorical processing.

Asymmetry of Directed Brain Connectivity at Birth in Low-Risk Full-Term Newborns.

Functional connectivity hubs were previously identified at the source level in low-risk full-term newborns by high-density electroencephalography (HD-EEG). However, the directionality of information flow among hubs remains unclear. The aim of this study was to study the directionality of information flow among source level hubs in low-risk full-term newborns using HD-EEG. A retrospective analysis of HD-EEG collected from a prospective study. Subjects included 112 low-risk full-term (37-41 weeks' gestation) newborns born in a large delivery center and studied within 72 hours of life by HD-EEG. The directionality of information flow between hubs at the source level was quantified using the partial directed coherence in the delta frequency band. Descriptive statistics were used to identify the maximum and minimum information flow. Differences in information flow between cerebral hemispheres were assessed using Student t-test. There was higher information flow from the left hemisphere to the right hemisphere hubs (p < 0.05, t-statistic = 2). The brainstem had the highest information inflow and lowest outflow among all the hubs. The left putamen received the lowest information, and the right pallidum had the highest information outflow to other hubs. In low-risk full-term newborns, there is a significant information flow asymmetry already present, with left hemisphere dominance at birth. The relationship between these findings and the more prevalent left hemisphere dominance observed in full-term newborns, particularly in relation to language, warrants further study.

Development of Virtual Reality-Based Left Brain System

This paper proposes a virtual reality based Left Brain System named BrainUp World to improve left brain thinking. The left-brain system was employed with mobile virtual reality technology, hand motion tracking and haptic feedback system. The implementation of these systems is to enhance the experience and sense of embodiment. BrainUp World includes virtual reality-based brain training games to improve a person’s attention level, reasoning skill, auditory cognition, arithmetic skill, sequencing skill and memory. The hand tracking system was utilized with an IR camera to capture the hand orientation and return the gesture data to the VR application. A low-cost and lightweight haptic glove was invented which provides the sense of touch using vibrations while interacting with VR contents. An experimental study was conducted to assess the efficacy of BrainUp World compared to traditional PC-based training approaches. Participants were randomly assigned to either the VR-based or PC-based training group and underwent 6 different games to test a person’s attention level, reasoning skill, auditory cognition, arithmetic skill, sequencing skill, and memory. The results revealed a statistically significant improvement in left brain function in the VR-based training group compared to the PC-based group, with a T-score growth of 4.73. Analysis using ANOVA confirmed the significance of this difference (p-Value = 0.04). Notably, the study also identified age-related differences in thinking fluency, highlighting the importance of personalized cognitive training interventions. In conclusion, BrainUp World demonstrates the potential of VR technology in promoting left brain development, as evidenced by empirical findings from the conducted study. By offering immersive and interactive cognitive training experiences, VR-based systems hold promise for enhancing various aspects of cognitive function associated with left hemisphere dominance. Further research in this area is encouraged to explore the full potential of VR-based interventions for cognitive enhancement.

Assessing Language Lateralization through Gray Matter Volume: Implications for Preoperative Planning in Brain Tumor Surgery.

Functional MRI (fMRI) is widely used to assess language lateralization, but its application in patients with brain tumors can be hindered by cognitive impairments, compensatory neuroplasticity, and artifacts due to patient movement or severe aphasia. Gray matter volume (GMV) analysis via voxel-based morphometry (VBM) in language-related brain regions may offer a stable complementary approach. This study investigates the relationship between GMV and fMRI-derived language lateralization in healthy individuals and patients with left-hemisphere brain tumors, aiming to enhance accuracy in complex cases. The MRI data from 22 healthy participants and 28 individuals with left-hemisphere brain tumors were analyzed. Structural T1-weighted and functional images were obtained during three language tasks. Language lateralization was assessed based on activation in predefined regions of interest (ROIs), categorized as typical (left) or atypical (right or bilateral). The GMV in these ROIs was measured using VBM. Linear regressions explored GMV-lateralization associations, and logistic regressions predicted the lateralization based on the GMV. In the healthy participants, typical left-hemispheric language dominance correlated with higher GMV in the left pars opercularis of the inferior frontal gyrus. The brain tumor participants with atypical lateralization showed increased GMV in six right-hemisphere ROIs. The GMV in the language ROIs predicted the fMRI language lateralization, with AUCs from 80.1% to 94.2% in the healthy participants and 78.3% to 92.6% in the tumor patients. GMV analysis in language-related ROIs effectively complements fMRI for assessing language dominance, particularly when fMRI is challenging. It correlates with language lateralization in both healthy individuals and brain tumor patients, highlighting its potential in preoperative language mapping. Further research with larger samples is needed to refine its clinical utility.

Brain Laterality in Dyslexia Seen during Literacy Development and Early Training.

During the period in which children learn to read and write, a gradual shift from right to left hemisphere dominance for language is typically seen. However, in children with dyslexia, a deviant pattern is described in the literature. As part of a larger longitudinal study (The Bergen Longitudinal Dyslexia Study), the present study aimed to assess this development from an early age before children learn to read and write. Dichotic listening (DL), which is a non-invasive test, was used to assess the development of brain laterality in a Typical group and a Dyslexia group. The participants received yearly sessions of evidence-based literacy training at ages 5 to 7. The Typical group showed increasing ear scores and a shift from no ear advantage in the Pre-literacy stage (age 6), indicative of no hemisphere dominance, to a right ear advantage, indicative of a left hemisphere dominance, in the Emergent literacy stage (age 8) and the Literacy stage (age 11). The Dyslexia group showed a different pattern, with a significant right ear advantage at age 6, indicative of a right hemisphere dominance, and increasing ear scores at ages 8 and 11; however, no ear dominance was observed in the Literacy stage. The results point to an effect of relevant, evidence-based training affecting both right and left hemispheres in dyslexia, which should form a basis for further research.

Aphasia due to right hemisphere infarction in a patient with situs inversus after carotid artery stenting: a case report

BackgroundSitus inversus (SI) is a rare congenital anomaly in which systemic organs and vessels are positioned in a mirror image of their normal positions. An interesting issue regarding individuals with such a condition is whether they also have reversed brain asymmetries. Most of studies on this issue indicate that, similarly to many people with normal visceral alignment, patients with SI have a left hemispheric dominance for language functions.Case presentationWe report a rare occurrence of anomalous cerebral dominance for language in a patient with complete situs inversus. The right-handed patient developed aphasia after carotid stenting, and brain magnetic resonance imaging showed cerebral infarction in the right parietal lobe.ConclusionAnomalous cerebral dominance for language and visceral situs inversus in our patient both may result from a single, genetically coded atypicality of developmental gradient.

The neocortical infrastructure for language involves region-specific patterns of laminar gene expression

The language network of the human brain has core components in the inferior frontal cortex and superior/middle temporal cortex, with left-hemisphere dominance in most people. Functional specialization and interconnectivity of these neocortical regions is likely to be reflected in their molecular and cellular profiles. Excitatory connections between cortical regions arise and innervate according to layer-specific patterns. Here, we generated a gene expression dataset from human postmortem cortical tissue samples from core language network regions, using spatial transcriptomics to discriminate gene expression across cortical layers. Integration of these data with existing single-cell expression data identified 56 genes that showed differences in laminar expression profiles between the frontal and temporal language cortex together with upregulation in layer II/III and/or layer V/VI excitatory neurons. Based on data from large-scale genome-wide screening in the population, DNA variants within these 56 genes showed set-level associations with interindividual variation in structural connectivity between the left-hemisphere frontal and temporal language cortex, and with the brain-related disorders dyslexia and schizophrenia which often involve affected language. These findings identify region-specific patterns of laminar gene expression as a feature of the brain's language network.

Integrating brain function and structure in the study of the human attentional networks: a functionnectome study

Attention is a heterogeneous function theoretically divided into different systems. While functional magnetic resonance imaging (fMRI) has extensively characterized their functioning, the role of white matter in cognitive function has gained recent interest due to diffusion-weighted imaging advancements. However, most evidence relies on correlations between white matter properties and behavioral or cognitive measures. This study used a new method that combines the signal from distant voxels of fMRI images using the probability of structural connection given by high-resolution normative tractography. We analyzed three fMRI datasets with a visual perceptual task and three attentional manipulations: phasic alerting, spatial orienting, and executive attention. The phasic alerting network engaged temporal areas and their communication with frontal and parietal regions, with left hemisphere dominance. The orienting network involved bilateral fronto-parietal and midline regions communicating by association tracts and interhemispheric fibers. The executive attention network engaged a broad set of brain regions and white matter tracts connecting them, with a particular involvement of frontal areas and their connections with the rest of the brain. These results partially confirm and extend previous knowledge on the neural substrates of the attentional system, offering a more comprehensive understanding through the integration of structure and function.

Analysis of bihemispheric language function in pediatric neurosurgical patients using repetitive navigated transcranial magnetic stimulation.

Language dominance in the developing brain can vary widely across anatomical and pathological conditions as well as age groups. Repetitive navigated transcranial magnetic stimulation (rnTMS) has been applied to calculate the hemispheric dominance ratio (HDR) in adults. In this study, the authors aimed to assess the feasibility of using rnTMS to identify language lateralization in a pediatric neurosurgical cohort and to correlate the preoperative rnTMS findings with the postoperative language outcome. A consecutive prospectively collected cohort of 19 children with language-associated lesions underwent bihemispheric rnTMS mapping prior to surgery (100 stimulation sites on each hemisphere). In addition to feasibility and adverse effects, the HDR (ratio of the left hemisphere to right hemisphere error rate) was calculated. The anatomical surgical site and postoperative language outcome at 3 months after surgery were assessed according to clinical documentation. Repetitive nTMS mapping was feasible in all 19 children (mean age 12.5 years, range 4-17 years; 16 left-sided lesions) without any relevant adverse events. Thirteen children (68%) showed left hemispheric dominance (HDR > 1.1), and 2 children (11%) showed right hemispheric dominance (HDR < 0.9). In 4 children (21%), the bihemispheric error rates were nearly the same (HDR ≥ 0.9 and ≤ 1.1). Sixteen children underwent surgery (14 tumor/lesion resections and 2 hemispherotomies) and 3 patients continued conservative therapy. After surgery, 4 patients (25%) showed an improvement in language function, 10 (63%) presented with stable language function, and 2 (12.5%) experienced deterioration in language function. Of the 6 patients with right hemispheric language involvement, 4 (80%) had glial tumors, 1 (20%) had focal cortical dysplasia, and 1 (20%) experienced hypoxic brain injury. Children with right hemispheric language involvement (HDR ≤ 1.1) did not show any language deterioration postoperatively. Bihemispheric rnTMS language mapping as a noninvasive mapping technique to assess lateralization of language function in the pediatric neurosurgical population is safe and feasible. Why relevant right hemispheric language function (HDR ≤ 1.1) was associated with postoperative unaltered language function needs to be validated in future studies. Bihemispheric rnTMS language mapping strengthens risk-benefit considerations prior to pediatric tumor/epilepsy surgery in language-associated areas.

Hemispheric engagement during the processing of affective adjectives—an ERP divided visual field study

ABSTRACT The study looked into the hemispheres’ involvement in emotional word encoding. It combined brain activity measures (ERPs) with behavioural data during the affective categorization task in the divided visual field presentation paradigm. Forty healthy right-handed student volunteers took part in the study, in which they viewed and evaluated 33 positive and 33 negative emotional adjectives presented to either the left or right visual field. We observed a marginally significant effect on the earlier time window (220–250 ms, the P2 component) with higher mean amplitudes evoked to the words presented to the right hemisphere, and then a strong effect on the 340–400 ms (the P3) with a reversed pattern (higher amplitudes for words presented to the left hemisphere). The latter effect was also visible in the error rates and RTs, with better overall performance for adjectives presented to the left hemisphere. There was also an effect on behavioural data of positive words only (higher error rates, shorter RTs). Thus, the study showed a particular “progression” pattern of hemispheric engagement: dependence of the initial stages of affective lexico-semantic processing on the right hemisphere, replaced by the left-hemispheric dominance for content evaluation and response programming stages.

Awake mapping for resection of cavernous angioma and arteriovenous malformations in the left dominant hemisphere

Awake mapping for resection of cavernous angioma and arteriovenous malformations in the left dominant hemisphere

Top-down modulation of dichotic listening affects interhemispheric connectivity: an electroencephalography study.

Dichotic listening (DL) has been extensively used as a task to investigate auditory processing and hemispheric lateralisation in humans. According to the "callosal relay model," the typical finding of a right ear advantage (REA) occurs because the information coming from the right ear has direct access to the left dominant hemisphere while the information coming from the left ear has to cross via the corpus callosum. The underlying neuroanatomical correlates and neurophysiological mechanisms have been described using diffusion tensor imaging (DTI) and lagged phase synchronization (LPS) of the interhemispheric auditory pathway. During the non-forced condition of DL, functional connectivity (LPS) of interhemispheric gamma-band coupling has been described as a relevant mechanism related to auditory perception in DL. In this study, we aimed to extend the previous results by exploring the effects of top-down modulation of DL (forced-attention condition) on interhemispheric gamma-band LPS. Right-handed healthy participants (n = 31; 17 females) performed three blocks of DL with different attention instructions (no-attention, left-ear attention, right-ear attention) during simultaneous EEG recording with 64 channels. Source analysis was done with exact low-resolution brain electromagnetic tomography (eLORETA) and functional connectivity between bilateral auditory areas was assessed as LPS in the gamma-band frequency range. Twenty-four participants (77%) exhibited a right-ear advantage in the no-attention block. The left- and right-attention conditions significantly decreased and increased right-ear reports, respectively. Similar to the previous studies, functional connectivity analysis (gamma-band LPS) showed significantly increased connectivity between left and right Brodmann areas (BAs) 41 and 42 during left ear reports in contrast with right ear reports. Our new findings notably indicated that the right-attention condition exhibited significantly higher connectivity between BAs 42 compared with the no-attention condition. This enhancement of connectivity was more pronounced during the perception of right ear reports. Our results are in line with previous reports describing gamma-band synchronization as a relevant neurophysiological mechanism involved in the interhemispheric connectivity according to the callosal relay model. Moreover, we newly added some evidence of attentional effects on this interhemispheric connectivity, consistent with the attention-executive model. Our results suggest that reciprocal inhibition could be involved in hemispheric lateralization processes.

The Right-Ear Advantage in Static and Dynamic Cocktail-Party Situations.

When presenting two competing speech stimuli, one to each ear, a right-ear advantage (REA) can often be observed, reflected in better speech recognition compared to the left ear. Considering the left-hemispheric dominance for language, the REA has been explained by superior contralateral pathways (structural models) and language-induced shifts of attention to the right (attentional models). There is some evidence that the REA becomes more pronounced, as cognitive load increases. Hence, it is interesting to investigate the REA in static (constant target talker) and dynamic (target changing pseudo-randomly) cocktail-party situations, as the latter is associated with a higher cognitive load than the former. Furthermore, previous research suggests an increasing REA, when listening becomes more perceptually challenging. The present study examined the REA by using virtual acoustics to simulate static and dynamic cocktail-party situations, with three spatially separated talkers uttering concurrent matrix sentences. Sentences were presented at low sound pressure levels or processed with a noise vocoder to increase perceptual load. Sixteen young normal-hearing adults participated in the study. The REA was assessed by means of word recognition scores and a detailed error analysis. Word recognition revealed a greater REA for the dynamic than for the static situations, compatible with the view that an increase in cognitive load results in a heightened REA. Also, the REA depended on the type of perceptual load, as indicated by a higher REA associated with vocoded compared to low-level stimuli. The results of the error analysis support both structural and attentional models of the REA.

Eye understand: Physiological measures as novel predictors of adaptive learning in horses

Striatal dopamine is a neurotransmitter that marks reward and mediates reward learning. Spontaneous Eye Blink Rate (SEBR) reflects striatal dopamine activity and could offer a novel, proxy measure of learning performance. Additionally, arousal affects performance in a range of cognitive tasks, but there is less evidence for the relationship between baseline arousal and learning. This study investigated whether SEBR predicts learning performance in an equine model. Further, it investigated novel physiological predictors of learning performance (eye temperature and heart rate variability). Nineteen horses completed a two-choice discrimination reversal learning (RL) task. Performance was measured using a Performance Index. SEBR and Heart Rate Variability (HRV) were measured at rest (home stable) and during RL. Infrared Thermography of eye temperature (IRT) was measured immediately before and after RL. SEBR did not change in response to RL despite being thought to reflect striatal dopamine activity. HRV was higher during RL than at rest though was not statistically significant (p = 0.06). Additionally, eye temperature decreased significantly during trials (left eye: p = 0.002; right eye: p = 0.05). These results indicate lower arousal in response to training, possibly similar to a ‘flow state’ in humans. Results of a negative binomial GLM revealed that SEBR was not associated with performance, however, positive predictors of learning performance included resting HRV (p = 0.009), HRV during the task (p = 0.002), and left eye temperature change (p < 0.0001). The association between left eye temperature and learning performance is consistent with lateralised blood flow to the left-brain hemisphere (responsible for learning targeted responses) and thought to be the first observation of this phenomenon during learning. Lower arousal may facilitate left-hemisphere dominance, creating the cognitive space to respond adaptively in RL. Left hemispheric dominance controls parasympathetic activity, potentially explaining the interactions observed here. Results suggest arousal both in the home and training environment may have important impacts on learning.

Correlation between thinking styles and academic achievement

The styles depend on the cerebral dominance of an individual in retaining and processing different modes of information in his/her thinking styles. Each student has his/her specific thinking style. Thinking styles may differ from one student to another. Parents and teachers must be aware of the thinking styles of their children and students. They must provide the thinking experiences by considering the learners' thinking styles. Thinking styles are one of the factors that decide the learners' academic achievement. Hence, this study attempted to study the correlation between thinking styles and academic achievement among student-teachers of B.Ed. Programme. A descriptive study has been applied for the conduction of the study. The study has been conducted on a representative sample of 100 student-teachers. Styles of learning and thinking developed by Venkataraman D and academic achievement test developed and validated by the researcher have been used to collect the data. The researcher used the statistical techniques mean, standard deviation and the product-moment correlation coefficient to analyze the data. The study revealed a weak negative correlation between left hemisphere dominance of thinking styles and academic achievement.

Handedness and religiosity, a two-nation study: Evidence that hemispheric functioning may influence religious beliefs

Prior research has reported that so-called consistent-handers are more religious than non-consistent-handers. This study analyzed data bearing on this possibility using large samples of college students from two different countries; Malaysia and the United States. When samples from both countries were separated by sex, no significant support for this prior research was found. However, when we analyzed our data with handedness dichotomized between right-handers and non-right-handers, some significant relationships were found. Among females in both countries, left- and mixed-handers expressed lower degrees of certainty about the existence of God and life-after-death. Also, right-handedness and religious service attendance were positively and significantly associated among Malaysian males. Among US males, however, belief in God was actually significantly stronger among right-handers than among left and mixed-handers. Assuming that right handedness is a rough proxy for left hemispheric dominance, our findings provide some support for the hypothesis that right hemispheric dominance is associated with orthodox religiosity at least among females.

33 Pre-Surgical Evaluation of Bilingual Epilepsy Patients; A Case Study Demonstrating the Importance of Bilingual Assessment

Objective:In the US, &gt;20% of individuals aged 5 years and older speak a language other than English at home, with rates of bi- and multilingualism increasing. Providing linguistically- and culturally- competent care to increasingly diverse populations is a necessary task for neuropsychologists. The need for close attention to bilingualism is even more glaring in the context of neurosurgical interventions, such as in intractable epilepsy. Pre-surgical epilepsy evaluations serve as a baseline for post-surgical change, inform lateralization and localization, and help determine cognitive risks associated with surgery. The importance of evaluating bilingual status and assessing cognitive abilities in both languages, if needed, in presurgical epilepsy evaluations is examined. We present the neuropsychological profile of a 10-year-old bilingual male with intractable epilepsy participating in a pre-surgical epilepsy evaluation.Participants and Methods:This right-handed male is a sequential language learner, exposed to Spanish at birth and English when he began kindergarten. His parent reported he was primarily English speaking. Developmental milestones were met within expected timeframes. Seizures began at age 5. He is prescribed Vimpat and Lamictal. vEEG during admission revealed right temporal-onset seizures. Neuropsychological assessment was conducted in English based on parent report; however, expressive language testing revealed significantly higher performance in Spanish (average) compared to English (exceptionally low). Subsequently, a bilingual provider was consulted, and supplemental Spanish verbal reasoning and verbal memory measures were administered.Results:The patient’s neuropsychological profile captured a significant difference between English and Spanish verbal abilities. WISC-V Similarities scaled scores (ss) were 5 and 11 in English and Spanish, respectively. Vocabulary scaled scores were 8 and 15 in English and Spanish, respectively. Regarding verbal memory, list learning was below average in English (ss = 5), but low average in Spanish (ss = 6). Contextual verbal memory was only administered in Spanish; scores were average (ss = 10). Verbal Fluency administered in English was low (phonemic fluency ss = 5, categorical fluency ss = 6). fMRI verbal tasks were performed in English and revealed left-sided language lateralization.Conclusions:In pre-surgical epilepsy evaluations of bilingual children, consideration of language is essential. Assessment of language dominance is a minimum requirement in bilingual families, followed by full bilingual evaluation if necessary. In this case, starkly different conclusions regarding lateralization and localization may have been made if the child had not been evaluated in both languages. In English, a significant split between verbal and non-verbal cognition was apparent, possibly suggesting involvement of the dominant left hemisphere. With Spanish testing, this split disappeared, with high average verbal skills. While a growing proportion of children in the US are bilingual, bilingual assessments are not commonly conducted in pre-surgical epilepsy evaluations. In fact, very little work has been done examining language functioning in bilingual epilepsy patients, particularly in children. With both epilepsy-and language-related factors at play in a developing brain, we encourage closer attention to these issues, particularly in the context of neurosurgical procedures.

Is There A Relationship Between Chewing Side Preference and Brain Laterality in Bruxers and Non-Bruxers?

Objective: There is no consensus on the etiology of unilateral mastication. While some studies argue that environmental factors such as missing teeth, teeth with restoration, pain, dental caries and temporomandibular disorder affect chewing side preference, others claim that brain laterality associated with hand, foot, ear and eye preferences also influences a chewing side preference. The aim of this study was to evaluate the relationship between the direction of unilateral chewing preference and brain laterality in fully dentate bruxers and non-bruxers (fully dentate or with missing and/or restored teeth).&#x0D; Methods: Brain laterality of the subjects (n=132) was determined based on responses to questions about extremity and sensory preferences. The reliable visual analogue scale (VAS), Kazazoglu’s method and the sunflower seed shell cracking test were used to determine chewing side preference (CSP).&#x0D; Results: CSP as determined by VAS was not associated with brain laterality. While extremity and sensory preferences were predominantly right-sided (dominant left hemisphere) in all groups, the frequency of the left-side chewing was found to be high only among bruxers (p&gt;0.05). No significant association was found between the results of VAS and other techniques (p&gt;0.05). &#x0D; Conclusion: The left-side CSP is observed more commonly in bruxers, suggesting that different central and peripheral mechanisms may be involved in bruxers.

The brain lateralization and development of math functions: progress since Sperry, 1974.

In 1974, Roger Sperry, based on his seminal studies on the split-brain condition, concluded that math was almost exclusively sustained by the language dominant left hemisphere. The right hemisphere could perform additions up to sums less than 20, the only exception to a complete left hemisphere dominance. Studies on lateralized focal lesions came to a similar conclusion, except for written complex calculation, where spatial abilities are needed to display digits in the right location according to the specific requirements of calculation procedures. Fifty years later, the contribution of new theoretical and instrumental tools lead to a much more complex picture, whereby, while left hemisphere dominance for math in the right-handed is confirmed for most functions, several math related tasks seem to be carried out in the right hemisphere. The developmental trajectory in the lateralization of math functions has also been clarified. This corpus of knowledge is reviewed here. The right hemisphere does not simply offer its support when calculation requires generic space processing, but its role can be very specific. For example, the right parietal lobe seems to store the operation-specific spatial layout required for complex arithmetical procedures and areas like the right insula are necessary in parsing complex numbers containing zero. Evidence is found for a complex orchestration between the two hemispheres even for simple tasks: each hemisphere has its specific role, concurring to the correct result. As for development, data point to right dominance for basic numerical processes. The picture that emerges at school age is a bilateral pattern with a significantly greater involvement of the right-hemisphere, particularly in non-symbolic tasks. The intraparietal sulcus shows a left hemisphere preponderance in response to symbolic stimuli at this age.

H - 24 The Role of Bilingual Neuropsychologists in Presurgical Epilepsy Evaluations: La Evaluación Comprensiva en Español.

As neuropsychologists continually work to establish clinical standards of practice for evaluation of linguistically and culturally diverse children with epilepsy (Berrios-Siervo et al., 2023), this case study supports efforts to document complex assessment procedures with an adolescent who recently immigrated from Mexico to the U.S. A 16-year-old, right-handed, primarily Spanish-speaking, Hispanic male with intractable epilepsy (complex partial seizures) was referred for a presurgical neuropsychological evaluation. Medication was initiated in Mexico at age 11years, but increased frequency and severity of seizures prompted immigration to the U.S. at age 14 for further treatment. EEG and brain MRI indicated left hemisphere involvement. Magnetoencephalography results indicated right-hemisphere dominance for receptive language. Functional MRI (fMRI) indicated left-hemisphere dominance. Subsequent Wada and bilateral language mapping results supported left-hemisphere dominance. Personal history was significant for anxiety and depressed mood. Bilingual neuropsychologists completed a presurgical evaluation, fMRI, stereo EEG language mapping, and Wada in Spanish. He was seizure-free 6months post selective left temporal resection. He recently completed his1-year post-op evaluation. Baseline testing indicated average neurocognitive functioning, with select relative weaknesses lacking strong evidence for lateralization/localization. Post-operative consultation/ evaluation at 6 and 12months, respectively, revealed the patient was doing well academically with perceived improvements in attention and memory and minimal language difficulties. Reported improvements in mood were attributed to family reunification and increased social engagement. In addition to pre/post-surgical assessment in Spanish, bilingual neuropsychologists are uniquely positioned to contribute to the establishment of culturally-informed, standardized approaches to essential aspects of the presurgical workup (e.g., language mapping, Wada).