Modeling the neurocognitive dynamics of language across the lifespan.

Healthy aging is associated with a heterogeneous decline across cognitive functions, typically observed between language comprehension and language production (LP). Examining resting-state fMRI and neuropsychological data from 628 healthy adults (age 18-88) from the CamCAN cohort, we performed state-of-the-art graph theoretical analysis to uncover the neural mechanisms underlying this variability. At the cognitive level, our findings suggest that LP is not an isolated function but is modulated throughout the lifespan by the extent of inter-cognitive synergy between semantic and domain-general processes. At the cerebral level, we show that default mode network (DMN) suppression coupled with fronto-parietal network (FPN) integration is the way for the brain to compensate for the effects of dedifferentiation at a minimal cost, efficiently mitigating the age-related decline in LP. Relatedly, reduced DMN suppression in midlife could compromise the ability to manage the cost of FPN integration. This may prompt older adults to adopt a more cost-efficient compensatory strategy that maintains global homeostasis at the expense of LP performances. Taken together, we propose that midlife represents a critical neurocognitive juncture that signifies the onset of LP decline, as older adults gradually lose control over semantic representations. We summarize our findings in a novel synergistic, economical, nonlinear, emergent, cognitive aging model, integrating connectomic and cognitive dimensions within a complex system perspective.

Complex visual discrimination is impaired after right, but not left, anterior temporal lobectomy.

The prevailing view in human cognitive neuroscience associates the medial temporal lobes (MTLs) with declarative memory. Compelling experimental evidence has, however, demonstrated that these regions are specialized according to the representations processed, irrespective of the cognitive domain assessed. This account was supported by the study of patients with bilateral medial temporal amnesia, who exhibit impairments in perceptual tasks involving complex visual stimuli. Yet, little is known regarding the impact of unilateral MTL damage on complex visual abilities. To address this issue, we administered a visual matching task to 20 patients who underwent left (N = 12) or right (N = 8) anterior temporal lobectomy for drug-resistant epilepsy and to 38 healthy controls. Presentation viewpoint was manipulated to increase feature ambiguity, as this is critical to reveal impairments in perceptual tasks. Similar to control participants, patients with left-sided damage succeeded in all task conditions. In contrast, patients with right-sided damage had decreased accuracy compared with that of the other two groups, as well as increased response time. Notably, the accuracy of those with right-sided damage did not exceed chance level when feature ambiguity was high (i.e., when stimuli were presented from different viewpoints) for the most complex classes of stimuli (i.e., scenes and buildings, compared with single objects). The pattern reported in bilateral patients in previous studies was therefore reproduced in patients with right, but not left, resection. These results suggest that the complex visual-representation functions supported by the MTL are right-lateralized, and raise the question as to how the representational account of these regions applies to representations supported by left MTL regions.

TractLearn: A geodesic learning framework for quantitative analysis of brain bundles.

Deep learning-based convolutional neural networks have recently proved their efficiency in providing fast segmentation of major brain fascicles structures, based on diffusion-weighted imaging. The quantitative analysis of brain fascicles then relies on metrics either coming from the tractography process itself or from each voxel along the bundle. Statistical detection of abnormal voxels in the context of disease usually relies on univariate and multivariate statistics models, such as the General Linear Model (GLM). Yet in the case of high-dimensional low sample size data, the GLM often implies high standard deviation range in controls due to anatomical variability, despite the commonly used smoothing process. This can lead to difficulties to detect subtle quantitative alterations from a brain bundle at the voxel scale. Here we introduce TractLearn, a unified framework for brain fascicles quantitative analyses by using geodesic learning as a data-driven learning task. TractLearn allows a mapping between the image high-dimensional domain and the reduced latent space of brain fascicles using a Riemannian approach. We illustrate the robustness of this method on a healthy population with test-retest acquisition of multi-shell diffusion MRI data, demonstrating that it is possible to separately study the global effect due to different MRI sessions from the effect of local bundle alterations. We have then tested the efficiency of our algorithm on a sample of 5 age-matched subjects referred with mild traumatic brain injury. Our contributions are to propose: 1/ A manifold approach to capture controls variability as standard reference instead of an atlas approach based on a Euclidean mean. 2/ A tool to detect global variation of voxels' quantitative values, which accounts for voxels' interactions in a structure rather than analyzing voxels independently. 3/ A ready-to-plug algorithm to highlight nonlinear variation of diffusion MRI metrics. With this regard, TractLearn is a ready-to-use algorithm for precision medicine.

Prediction of the clinical and naming status after anterior temporal lobe resection in patients with epilepsy.

By assessing the cognitive capital, neuropsychological evaluation (NPE) plays a vital role in the perioperative workup of patients with refractory focal epilepsy. In this retrospective study, we used cutting-edge statistical approaches to examine a group of 47 patients with refractory temporal lobe epilepsy (TLE), who underwent standard anterior temporal lobectomy (ATL). Our objective was to determine whether NPE may represent a robust predictor of the postoperative status, two years after surgery. Specifically, based on pre- and postsurgical neuropsychological data, we estimated the sensitivity of cognitive indicators to predict and to disentangle phenotypes associated with more or less favorable outcomes. Engel (ENG) scores were used to assess clinical outcome, and picture naming (NAM) performance to estimate naming status. Two methods were applied: (a) machine learning (ML) to explore cognitive sensitivity to postoperative outcomes; and (b) graph theory (GT) to assess network properties reflecting favorable vs. less favorable phenotypes after surgery. Specific neuropsychological indices assessing language, memory, and executive functions can globally predict outcomes. Interestingly, preoperative cognitive networks associated with poor postsurgical outcome already exhibit an atypical, highly modular and less densely interconnected configuration. We provide statistical and clinical tools to anticipate the condition after surgery and achieve a more personalized clinical management. Our results also shed light on possible mechanisms put in place for cognitive adaptation after acute injury of central nervous system in relation with surgery.

Speech rehabilitation in post-stroke aphasia using visual illustration of speech articulators: A case report study.

Recent studies on the remediation of speech disorders suggest that providing visual information of speech articulators may contribute to improve speech production. In this study, we evaluate the effectiveness of an illustration-based rehabilitation method on speech recovery of a patient with non-fluent chronic aphasia. The Ultraspeech-player software allowed visualization by the patient of reference tongue and lip movements recorded using ultrasound and video imaging. This method can improve the patient's awareness of their own lingual and labial movements, which can increase the ability to coordinate and combine articulatory gestures. The effects of this method were assessed by analyzing performance during speech tasks, the phonological processes identified in the errors made during the phoneme repetition task and the acoustic parameters derived from the speech signal. We also evaluated cognitive performance before and after rehabilitation. The integrity of visuospatial ability, short-term and working memory and some executive functions supports the effectiveness of the rehabilitation method. Our results showed that illustration-based rehabilitation technique had a beneficial effect on the patient's speech production, especially for stop and fricative consonants which are targeted (high visibility of speech articulator configurations) by the software, but also on reading abilities. Acoustic parameters indicated an improvement in the distinction between consonant categories: voiced and voiceless stops or alveolar, post-alveolar and labiodental fricatives. However, the patient showed little improvement for vowels. These results confirmed the advantage of using illustration-based rehabilitation technique and the necessity of detailed subjective and objective intra-speaker evaluation in speech production to fully evaluate speech abilities.

Hubs disruption in mesial temporal lobe epilepsy. A resting-state fMRI study on a language-and-memory network.

Mesial temporal lobe epilepsy (mTLE) affects the brain networks at several levels and patients suffering from mTLE experience cognitive impairment for language and memory. Considering the importance of language and memory reorganization in this condition, the present study explores changes of the embedded language-and-memory network (LMN) in terms of functional connectivity (FC) at rest, as measured with functional MRI. We also evaluate the cognitive efficiency of the reorganization, that is, whether or not the reorganizations support or allow the maintenance of optimal cognitive functioning despite the seizure-related damage. Data from 37 patients presenting unifocal mTLE were analyzed and compared to 48 healthy volunteers in terms of LMN-FC using two methods: pairwise correlations (region of interest [ROI]-to-ROI) and graph theory. The cognitive efficiency of the LMN-FC reorganization was measured using correlations between FC parameters and language and memory scores. Our findings revealed a large perturbation of the LMN hubs in patients. We observed a hyperconnectivity of limbic areas near the dysfunctional hippocampus and mainly a hypoconnectivity for several cortical regions remote from the dysfunctional hippocampus. The loss of FC was more important in left mTLE (L-mTLE) than in right (R-mTLE) patients. The LMN-FC reorganization may not be always compensatory and not always useful for patients as it may be associated with lower cognitive performance. We discuss the different connectivity patterns obtained and conclude that interpretation of FC changes in relation to neuropsychological scores is important to determine cognitive efficiency, suggesting the concept of "connectome" would gain to be associated with a "cognitome" concept.

Probabilistic mapping of language networks from high frequency activity induced by direct electrical stimulation.

Direct electrical stimulation (DES) at 50 Hz is used as a gold standard to map cognitive functions but little is known about its ability to map large-scale networks and specific subnetwork. In the present study, we aim to propose a new methodological approach to evaluate the specific hypothesis suggesting that language errors/dysfunction induced by DES are the result of large-scale network modification rather than of a single cortical region, which explains that similar language symptoms may be observed after stimulation of different cortical regions belonging to this network. We retrospectively examined 29 patients suffering from focal drug-resistant epilepsy who benefitted from stereo-electroencephalographic (SEEG) exploration and exhibited language symptoms during a naming task following 50 Hz DES. We assessed the large-scale language network correlated with behavioral DES-induced responses (naming errors) by quantifying DES-induced changes in high frequency activity (HFA, 70-150 Hz) outside the stimulated cortical region. We developed a probabilistic approach to report the spatial pattern of HFA modulations during DES-induced language errors. Similarly, we mapped the pattern of after-discharges (3-35 Hz) occurring after DES. HFA modulations concurrent to language symptoms revealed a brain network similar to our current knowledge of language gathered from standard brain mapping. In addition, specific subnetworks could be identified within the global language network, related to different language processes, generally described in relation to the classical language regions. Spatial patterns of after-discharges were similar to HFA induced during DES. Our results suggest that this new methodological DES-HFA mapping is a relevant approach to map functional networks during SEEG explorations, which would allow to shift from "local" to "network" perspectives.

Speech recovery and language plasticity can be facilitated by Sensori-Motor Fusion training in chronic non-fluent aphasia. A case report study.

The rehabilitation of speech disorders benefits from providing visual information which may improve speech motor plans in patients. We tested the proof of concept of a rehabilitation method (Sensori-Motor Fusion, SMF; Ultraspeech player) in one post-stroke patient presenting chronic non-fluent aphasia. SMF allows visualisation by the patient of target tongue and lips movements using high-speed ultrasound and video imaging. This can improve the patient's awareness of his/her own lingual and labial movements, which can, in turn, improve the representation of articulatory movements and increase the ability to coordinate and combine articulatory gestures. The auditory and oro-sensory feedback received by the patient as a result of his/her own pronunciation can be integrated with the target articulatory movements they watch. Thus, this method is founded on sensorimotor integration during speech. The SMF effect on this patient was assessed through qualitative comparison of language scores and quantitative analysis of acoustic parameters measured in a speech production task, before and after rehabilitation. We also investigated cerebral patterns of language reorganisation for rhyme detection and syllable repetition, to evaluate the influence of SMF on phonological-phonetic processes. Our results showed that SMF had a beneficial effect on this patient who qualitatively improved in naming, reading, word repetition and rhyme judgment tasks. Quantitative measurements of acoustic parameters indicate that the patient's production of vowels and syllables also improved. Compared with pre-SMF, the fMRI data in the post-SMF session revealed the activation of cerebral regions related to articulatory, auditory and somatosensory processes, which were expected to be recruited by SMF. We discuss neurocognitive and linguistic mechanisms which may explain speech improvement after SMF, as well as the advantages of using this speech rehabilitation method.

What do patients with epilepsy tell us about language dynamics? A review of fMRI studies.

The objective of this review is to resume major neuroimaging findings on language organization and plasticity in patients with focal and refractory epilepsy, to discuss the effect of modulatory variables that should be considered alongside patterns of reorganization, and to propose possible models of language reorganization. The focal and refractory epilepsy provides a real opportunity to investigate various types of language reorganization in different conditions. The 'chronic' condition (induced by the epileptogenic zone or EZ) is associated with either recruitment of homologous regions of the opposite hemisphere or recruitment of intrahemispheric, nonlinguistic regions. In the 'acute' condition (neurosurgery and EZ resection), the initial interhemispheric shift (induced by the chronic EZ) could follow a reverse direction, back to the initial hemisphere. These different patterns depend on several modulatory factors and are associated with various levels of language performance. As a neuroimaging tool, functional magnetic resonance imaging enables the detailed investigation of both hemispheres simultaneously and allows for comparison with healthy controls, potentially creating a more comprehensive and more realistic picture of brain-language relations. Importantly, functional neuroimaging approaches demonstrate a good degree of concordance on a theoretical level, but also a considerable degree of individual variability, attesting to the clinical importance with these methods to establish, empirically, language localization in individual patients. Overall, the unique features of epilepsy, combined with ongoing advances in technology, promise further improvement in understanding of language substrate.

NEREC, an effective brain mapping protocol for combined language and long-term memory functions.

Temporal lobe epilepsy can induce functional plasticity in temporoparietal networks involved in language and long-term memory processing. Previous studies in healthy subjects have revealed the relative difficulty for this network to respond effectively across different experimental designs, as compared to more reactive regions such as frontal lobes. For a protocol to be optimal for clinical use, it has to first show robust effects in a healthy cohort. In this study, we developed a novel experimental paradigm entitled NEREC, which is able to reveal the robust participation of temporoparietal networks in a uniquely combined language and memory task, validated in an fMRI study with healthy subjects. Concretely, NEREC is composed of two runs: (a) an intermixed language-memory task (confrontation naming associated with encoding in nonverbal items, NE) to map language (i.e., word retrieval and lexico-semantic processes) combined with simultaneous long-term verbal memory encoding (NE items named but also explicitly memorized) and (b) a memory retrieval task of items encoded during NE (word recognition, REC) intermixed with new items. Word recognition is based on both perceptual-semantic familiarity (feeling of 'know') and accessing stored memory representations (remembering). In order to maximize the remembering and recruitment of medial temporal lobe structures, we increased REC difficulty by changing the modality of stimulus presentation (from nonverbal during NE to verbal during REC). We report that (a) temporoparietal activation during NE was attributable to both lexico-semantic (language) and memory (episodic encoding and semantic retrieval) processes; that (b) encoding activated the left hippocampus, bilateral fusiform, and bilateral inferior temporal gyri; and that (c) task recognition (recollection) activated the right hippocampus and bilateral but predominant left fusiform gyrus. The novelty of this protocol consists of (a) combining two tasks in one (language and long-term memory encoding/recall) instead of applying isolated tasks to map temporoparietal regions, (b) analyzing NE data based on performances recorded during REC, (c) double-mapping networks involved in naming and in long-term memory encoding and retrieval, (d) focusing on remembering with hippocampal activation and familiarity judgment with lateral temporal cortices activation, and (e) short duration of examination and feasibility. These aspects are of particular interest in patients with TLE, who frequently show impairment of these cognitive functions. Here, we show that the novel protocol is suited for this clinical evaluation.

Finding the Words: How Does the Aging Brain Process Language? A Focused Review of Brain Connectivity and Compensatory Pathways.

As people age, there is a natural decline in cognitive functioning and brain structure. However, the relationship between brain function and cognition in older adults is neither straightforward nor uniform. Instead, it is complex, influenced by multiple factors, and can vary considerably from one person to another. Reserve, compensation, and maintenance mechanisms may help explain why some older adults can maintain high levels of performance while others struggle. These mechanisms are often studied concerning memory and executive functions that are particularly sensitive to the effects of aging. However, language abilities can also be affected by age, with changes in production fluency. The impact of brain changes on language abilities needs to be further investigated to understand the dynamics and patterns of aging, especially successful aging. We previously modeled several compensatory profiles of language production and lexical access/retrieval in aging within the Lexical Access and Retrieval in Aging (LARA) model. In the present paper, we propose an extended version of the LARA model, called LARA-Connectivity (LARA-C), incorporating recent evidence on brain connectivity. Finally, we discuss factors that may influence the strategies implemented with aging. The LARA-C model can serve as a framework to understand individual performance and open avenues for possible personalized interventions.

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.

Dynamic causal modeling of spatiotemporal integration of phonological and semantic processes: an electroencephalographic study.

Integration of phonological and lexicosemantic processes is essential for visual word recognition. Here we used dynamic causal modeling of event-related potentials, combined with group source reconstruction, to estimate how those processes translate into context-dependent modulation of effective connectivity within the temporal-frontal language network. Fifteen healthy human subjects performed a phoneme detection task in pseudo-words and a semantic categorization task in words. Cortical current densities revealed the sequential activation of temporal regions, from the occipital-temporal junction toward the anterior temporal lobe, before reaching the inferior frontal gyrus. A difference of activation between phonology and semantics was identified in the anterior temporal lobe within the 240-300 ms peristimulus time window. Dynamic causal modeling indicated this increase of activation of the anterior temporal lobe in the semantic condition as a consequence of an increase of forward connectivity from the posterior inferior temporal lobe to the anterior temporal lobe. In addition, fast activation of the inferior frontal region, which allowed a feedback control of frontal regions on the superior temporal and posterior inferior temporal cortices, was found to be likely. Our results precisely describe spatiotemporal network mechanisms occurring during integration of phonological and semantic processes. In particular, they support the hypothesis of multiple pathways within the temporal lobe for language processing, where frontal regions would exert a top-down control on temporal regions in the recruitment of the anterior temporal lobe for semantic processing.

Neural correlates of the perception of contrastive prosodic focus in French: a functional magnetic resonance imaging study.

This functional magnetic resonance imaging (fMRI) study aimed at examining the cerebral regions involved in the auditory perception of prosodic focus using a natural focus detection task. Two conditions testing the processing of simple utterances in French were explored, narrow-focused versus broad-focused. Participants performed a correction detection task. The utterances in both conditions had exactly the same segmental, lexical, and syntactic contents, and only differed in their prosodic realization. The comparison between the two conditions therefore allowed us to examine processes strictly associated with prosodic focus processing. To assess the specific effect of pitch on hemispheric specialization, a parametric analysis was conducted using a parameter reflecting pitch variations specifically related to focus. The comparison between the two conditions reveals that brain regions recruited during the detection of contrastive prosodic focus can be described as a right-hemisphere dominant dual network consisting of (a) ventral regions which include the right posterosuperior temporal and bilateral middle temporal gyri and (b) dorsal regions including the bilateral inferior frontal, inferior parietal and left superior parietal gyri. Our results argue for a dual stream model of focus perception compatible with the asymmetric sampling in time hypothesis. They suggest that the detection of prosodic focus involves an interplay between the right and left hemispheres, in which the computation of slowly changing prosodic cues in the right hemisphere dynamically feeds an internal model concurrently used by the left hemisphere, which carries out computations over shorter temporal windows.

Fear recognition impairment in early-stage Alzheimer's disease: when focusing on the eyes region improves performance.

A decline in the ability to identify fearful expression has been frequently reported in patients with Alzheimer's disease (AD). In patients with severe destruction of the bilateral amygdala, similar difficulties have been reduced by using an explicit visual exploration strategy focusing on gaze. The current study assessed the possibility of applying a similar strategy in AD patients to improve fear recognition. It also assessed the possibility of improving fear recognition when a visual exploration strategy induced AD patients to process the eyes region. Seventeen patients with mild AD and 34 healthy subjects (17 young adults and 17 older adults) performed a classical task of emotional identification of faces expressing happiness, anger, and fear in two conditions: The face appeared progressively from the eyes region to the periphery (eyes region condition) or it appeared as a whole (global condition). Specific impairment in identifying a fearful expression was shown in AD patients compared with older adult controls during the global condition. Fear expression recognition was significantly improved in AD patients during the eyes region condition, in which they performed similarly to older adult controls. Our results suggest that using a different strategy of face exploration, starting first with processing of the eyes region, may compensate for a fear recognition deficit in AD patients. Findings suggest that a part of this deficit could be related to visuo-perceptual impairments. Additionally, these findings suggest that the decline of fearful face recognition reported in both normal aging and in AD may result from impairment of non-amygdalar processing in both groups and impairment of amygdalar-dependent processing in AD.

When Age Tips the Balance: a Dual Mechanism Affecting Hemispheric Specialization for Language.

Aging engenders neuroadaptations, generally reducing specificity and selectivity in functional brain responses. Our investigation delves into the functional specialization of brain hemispheres within language-related networks across adulthood. In a cohort of 728 healthy adults spanning ages 18 to 88, we modeled the trajectories of inter-hemispheric asymmetry concerning the principal functional gradient across 37 homotopic regions of interest (hROIs) of an extensive language network, known as the Language-and-Memory Network. Our findings reveal that over two-thirds of Language-and-Memory Network hROIs undergo asymmetry changes with age, falling into two main clusters. The first cluster evolves from left-sided specialization to right-sided tendencies, while the second cluster transitions from right-sided asymmetry to left-hemisphere dominance. These reversed asymmetry shifts manifest around midlife, occurring after age 50, and are associated with poorer language production performance. Our results provide valuable insights into the influence of functional brain asymmetries on language proficiency and present a dynamic perspective on brain plasticity during the typical aging process.

Functional MRI assessment of orofacial articulators: neural correlates of lip, jaw, larynx, and tongue movements.

Compared with complex coordinated orofacial actions, few neuroimaging studies have attempted to determine the shared and distinct neural substrates of supralaryngeal and laryngeal articulatory movements when performed independently. To determine cortical and subcortical regions associated with supralaryngeal motor control, participants produced lip, tongue and jaw movements while undergoing functional magnetic resonance imaging (fMRI). For laryngeal motor activity, participants produced the steady-state/i/vowel. A sparse temporal sampling acquisition method was used to minimize movement-related artifacts. Three main findings were observed. First, the four tasks activated a set of largely overlapping, common brain areas: the sensorimotor and premotor cortices, the right inferior frontal gyrus, the supplementary motor area, the left parietal operculum and the adjacent inferior parietal lobule, the basal ganglia and the cerebellum. Second, differences between tasks were restricted to the bilateral auditory cortices and to the left ventrolateral sensorimotor cortex, with greater signal intensity for vowel vocalization. Finally, a dorso-ventral somatotopic organization of lip, jaw, vocalic/laryngeal, and tongue movements was observed within the primary motor and somatosensory cortices using individual region-of-interest (ROI) analyses. These results provide evidence for a core neural network involved in laryngeal and supralaryngeal motor control and further refine the sensorimotor somatotopic organization of orofacial articulators.

Missing links: The functional unification of language and memory (L∪M).

The field of neurocognition is currently undergoing a significant change of perspective. Traditional neurocognitive models evolved into an integrative and dynamic vision of cognitive functioning. Dynamic integration assumes an interaction between cognitive domains traditionally considered to be distinct. Language and declarative memory are regarded as separate functions supported by different neural systems. However, they also share anatomical structures (notably, the inferior frontal gyrus, the supplementary motor area, the superior and middle temporal gyrus, and the hippocampal complex) and cognitive processes (such as semantic and working memory) that merge to endorse our quintessential daily lives. We propose a new model, "L∪M" (i.e., Language/union/Memory), that considers these two functions interactively. We fractionated language and declarative memory into three fundamental dimensions or systems ("Receiver-Transmitter", "Controller-Manager" and "Transformer-Associative" Systems), that communicate reciprocally. We formalized their interactions at the brain level with a connectivity-based approach. This new taxonomy overcomes the modular view of cognitive functioning and reconciles functional specialization with plasticity in neurological disorders.

Comparing the selectivity of vowel representations in cortical auditory vs. motor areas: A repetition-suppression study.

A computational model of speech perception, COSMO (Laurent et al., 2017), predicts that speech sounds should evoke both auditory representations in temporal areas and motor representations mainly in inferior frontal areas. Importantly, the model also predicts that auditory representations should be narrower, i.e. more focused on typical stimuli, than motor representations which would be more tolerant of atypical stimuli. Based on these assumptions, in a repetition-suppression study with functional magnetic resonance imaging data, we show that a sequence of 4 identical vowel sounds produces lower cortical activity (i.e. larger suppression effects) than if the last sound in the sequence is slightly varied. Crucially, temporal regions display an increase in cortical activity even for small acoustic variations, indicating a release of the suppression effect even for stimuli acoustically close to the first stimulus. In contrast, inferior frontal, premotor, insular and cerebellar regions show a release of suppression for larger acoustic variations. This "auditory-narrow motor-wide" pattern for vowel stimuli adds to a number of similar findings on consonant stimuli, confirming that the selectivity of speech sound representations in temporal auditory areas is narrower than in frontal motor areas in the human cortex.

Cognitive outcome after left functional hemispherectomy on dominant hemisphere in patients with Rasmussen encephalitis: beyond the myth of aphasia. Patient series.

BACKGROUND: Rasmussen encephalitis is a rare chronic neurological pathology frequently treated with functional hemispherectomy (or hemispherotomy). This surgical procedure frees patients of their severe epilepsy associated with the disease but may induce cognitive disorders and notably language alterations after disconnection of the left hemisphere. OBSERVATIONS: The authors describe longitudinally 3 cases of female patients with Rasmussen encephalitis who underwent left hemispherotomy in childhood and benefited from a favorable cognitive outcome. In the first patient, the hemispherotomy occurred at a young age, and the recovery of language and cognitive abilities was rapid and efficient. The second patient benefited from the surgery later in childhood. In addition, she presented a reorganization of language and memory functions that seem to have been at the expense of nonverbal ones. The third patient was a teenager during surgery. She benefited from a more partial cognitive recovery with persistent disorders several years after the surgery. LESSONS: Recovery of cognitive functions, including language, occurs after left hemispherotomy, even when performed late in childhood. Therefore, the surgery should be considered as early as possible to promote intercognitive reorganization.