Unveiling the neuroplastic capacity of the bilingual brain: insights from healthy and pathological individuals.

Research on the neural imprint of dual-language experience, crucial for understanding how the brain processes dominant and non-dominant languages, remains inconclusive. Conflicting evidence suggests either similarity or distinction in neural processing, with implications for bilingual patients with brain tumors. Preserving dual-language functions after surgery requires considering pre-diagnosis neuroplastic changes. Here, we combine univariate and multivariate fMRI methodologies to test a group of healthy Spanish-Basque bilinguals and a group of bilingual patients with gliomas affecting the language-dominant hemisphere while they overtly produced sentences in either their dominant or non-dominant language. Findings from healthy participants revealed the presence of a shared neural system for both languages, while also identifying regions with distinct language-dependent activation and lateralization patterns. Specifically, while the dominant language engaged a more left-lateralized network, speech production in the non-dominant language relied on the recruitment of a bilateral basal ganglia-thalamo-cortical circuit. Notably, based on language lateralization patterns, we were able to robustly decode (AUC: 0.80 ± 0.18) the language being used. Conversely, bilingual patients exhibited bilateral activation patterns for both languages. For the dominant language, regions such as the cerebellum, thalamus, and caudate acted in concert with the sparsely activated language-specific nodes. In the case of the non-dominant language, the recruitment of the default mode network was notably prominent. These results demonstrate the compensatory engagement of non-language-specific networks in the preservation of bilingual speech production, even in the face of pathological conditions. Overall, our findings underscore the pervasive impact of dual-language experience on brain functional (re)organization, both in health and disease.

A novel cognitive neurosurgery approach for supramaximal resection of non-dominant precuneal gliomas: a case report.

Despite mounting evidence pointing to the contrary, classical neurosurgery presumes many cerebral regions are non-eloquent, and therefore, their excision is possible and safe. This is the case of the precuneus and posterior cingulate, two interacting hubs engaged during various cognitive functions, including reflective self-awareness; visuospatial and sensorimotor processing; and processing social cues. This inseparable duo ensures the cortico-subcortical connectivity that underlies these processes. An adult presenting a right precuneal low-grade glioma invading the posterior cingulum underwent awake craniotomy with direct electrical stimulation (DES). A supramaximal resection was achieved after locating the superior longitudinal fasciculus II. During surgery, we found sites of positive stimulation for line bisection and mentalizing tests that enabled the identification of surgical corridors and boundaries for lesion resection. When post-processing the intraoperative recordings, we further identified areas that positively responded to DES during the trail-making and mentalizing tests. In addition, a clear worsening of the patient's self-assessment ability was observed throughout the surgery. An awake cognitive neurosurgery approach allowed supramaximal resection by reaching the cortico-subcortical functional limits. The mapping of complex functions such as social cognition and self-awareness is key to preserving patients' postoperative cognitive health by maximizing the ability to resect the lesion and surrounding areas.

"Neural dynamics supporting longitudinal plasticity of action naming across languages: MEG evidence from bilingual brain tumor patients".

Previous evidence suggests that distinct ventral and dorsal streams respectively underpin the semantic processing of object and action knowledge. Recently, we found that brain tumor patients with dorsal gliomas in frontoparietal hubs show a selective longitudinal compensation (post-vs. pre-surgery) during the retrieval of lexico-semantic information about actions (but not objects), indexed by power increases in beta rhythms (13-28 Hz). Here, we move one-step further and ask whether a similar organizational principle also stands across the different languages a bilingual speaks. To test this hypothesis, we combined a picture-naming task with MEG recordings and evaluated highly proficient Spanish-Basque bilinguals undergoing surgery for tumor resection in left frontoparietal regions. We assessed patients before and three months after surgery. At the behavioral level, we observed a similar performance across sessions irrespectively of the language at use, suggesting overall successful function preservation. At the oscillatory level, we found longitudinal selective power increases in beta for action naming in Spanish and Basque. Nevertheless, tumor resection triggered a differential reorganization of the L1 and the L2, with the latter one additionally recruiting the right hemisphere. Overall, our results provide evidence for (i) the specific involvement of frontoparietal regions in the semantic retrieval/representation of action knowledge across languages; (ii) a key role of beta oscillations as a signature of language compensation and (iii) the existence of divergent plasticity trajectories in L1 and L2 after surgery. By doing so, they provide new insights into the spectro-temporal dynamics supporting postoperative recovery in the bilingual brain.

Association of Notch-1, osteopontin and stem-like cells in ENU-glioma malignant process.

Notch-1 and osteopontin (OPN) mediate angiogenesis and glioma stem-like cell (GSLC) maintenance. However, the relationship between these molecules and GSLCs during the development of glioma is unknown. We investigate the expression of Notch-1, OPN and vascular endothelial growth factor (VEGF) associated to the stemness markers nestin and CD133 in three stages of murine gliomas induced by N-ethyl-N-nitrosourea (ENU). Notch-1 and OPN overexpress in the intermediate stage (II), which corresponds to the "angiogenesis switch". Nestin+ cells appear in all stages of ENU-glioma but CD133 only from stage II on. In stage III, neoplastic cells expressing nestin, CD133 and nestin/CD133 reside in spheroid-like aggregates (SAs) and in the neoangiogenic border. These aggregates show Notch-1 and VEGF+ surrounding cells and a significant size and density increase with respect to stage I (3.3 ± 1.5 to 22.4 ± 6.3 µm2, n° = 0.3 ± 0.1 to 4.2 ± 0.9, from stage I to stage III, respectively). OPN expression increases in correlation to the glioma malignancy from 4.5 ± 1.8% (I) to 12.3 ± 1.2% of OPN+ cells (III). It predominates in astrocyte-like cells of the neoangiogenic border, displaying co-location with VEGF and CD133. The OPN immunopositivity distribution correlates with the CD133 distribution. In conclusion, OPN co-expressing with CD133 contributes to the identification of GSLCs in the neoangiogenic border, while Notch-1 is present around SAs in advanced stages. The ENU-glioma, mainly in stage II, is a useful tool for assessing new antitumour therapies against these molecules.