Neuroplasticity of language networks in aphasia: advances, updates, and future challenges

Researchers have sought to understand how language is processed in the brain, how brain damage affects language abilities, and what can be expected during the recovery period since the early 19th century. In this review, we first discuss mechanisms of damage and plasticity in the post-stroke brain, both in the acute and the chronic phase of recovery. We then review factors that are associated with recovery. First, we review organism intrinsic variables such as age, lesion volume and location and structural integrity that influence language recovery. Next, we review organism extrinsic factors such as treatment that influence language recovery. Here, we discuss recent advances in our understanding of language recovery and highlight recent work that emphasizes a network perspective of language recovery. Finally, we propose our interpretation of the principles of neuroplasticity, originally proposed by Kleim and Jones (1) in the context of extant literature in aphasia recovery and rehabilitation. Ultimately, we encourage researchers to propose sophisticated intervention studies that bring us closer to the goal of providing precision treatment for patients with aphasia and a better understanding of the neural mechanisms that underlie successful neuroplasticity.P50 DC012283 - NIDCD NIH HHSPublished versio

Brain plasticity in aphasic patients: Intra- and inter-hemispheric reorganisation of the whole linguistic network probed by N150 and N350 components

The present study examined linguistic plastic reorganization of language through Evoked Potentials in a group of 17 non-fluent aphasic patients who had suffered left perisylvian focal lesions, and showed a good linguistic recovery. Language reorganisation was probed with three linguistic tasks (Phonological, Semantic, Orthographic), the early word recognition potential (N150) and the later phonological-related component (N350). Results showed the typical left-lateralised posterior N150 in healthy controls (source: left Fusiform Gyrus), that was bilateral (Semantic) or right sided (Phonological task) in patients (sources: right Inferior/Middle Temporal and Fusiform Gyri). As regards N350, controls revealed different intra- and inter-hemispheric linguistic activation across linguistic tasks, whereas patients exhibited greater activity in left intact sites, anterior and posterior to the damaged area, in all tasks (sources: Superior Frontal Gyri). A comprehensive neurofunctional model is presented, describing how complete intra- and inter-hemispheric reorganisation of the linguistic networks occurs after aphasic damage in the strategically dominant left perisylvian linguistic centres

Brain Plasticity in Aphasia

Dominant hemisphere for language function is the left hemisphere, however patients experiencing aphasia followed by damage to language areas often shows good recovery in the days to weeks to even years after brain injury. According to the duration from brain injury, recovery period of language function in aphasia can be divided into three overlapping periods (acute, subacute, and chronic phase) with different underlying neural mechanisms. During subacute period of weeks to months following brain injury, reorganization of neural network through brain plasticity occurring in the both hemisphere plays a crucial role in recovery of language function. Recently, the potential use of functional neuroimaging has been raised to explain the underlying neural mechanism for language recovery, however, the brain areas and various factors affecting brain reorganization are still controversial. This article reviews the clinical evidence for recovery of language function through brain plasticity and reorganization and the factors affecting the recovery of language function in aphasic patients following brain injuryope

MRI neuroimaging: language recovery in adult aphasia due to stroke

Thesis (Ph.D.)--Boston UniversityThis research focuses on the contribution of magnetic resonance imaging (MRI) to understanding recovery and treatment of aphasia in adults who have suffered a stroke. There are three parts. Part 1 presents the feasibility of the application of an overt, picture-naming, functional MRI (fMRI) paradigm to examine neural activity in chronic, nonfluent aphasia (four mild-moderate and one severe nonfluent/global patient). The advantages and disadvantages of an overt, object picture-naming, fMRI block-design paradigm are discussed. An overt naming fMRI design has potential as a method to provide insight into recovery from adult aphasia including plasticity of the brain after left hemisphere stroke and response to treatment. Part 2 uses the overt naming fMRI paradigm to examine changes in neural activity (neural plasticity) after a two-week series of repetitive transcranial magnetic stimulation (rTMS) treatments to improve picture naming in chronic nonfluent aphasia. An overview of rTMS and rationale for use of rTMS as a clinical treatment for aphasia is provided. Patterns of fMRI activation are examined in two patients with chronic nonfluent aphasia following a two-week series of 1 Hz rTMS treatments to suppress the right pars triangularis portion of the right hemisphere, Broca's homologue. One patient responded well, and the other did not. Differences in fMRI activation in response to the rTMS treatment for the two patients may be due to differences in the patients' lesion sites and extent of damage within each lesion site. Part 3 examines the area of the corpus callosum (CC) in 21 chronic nonfluent aphasia patients and 13 ageequivalent controls using structural MRI. Understanding brain morphology and potential atrophy of the CC in chronic stroke patients may shed light on alterations in the interhemispheric dynamics after stroke, especially patterns of brain reorganization during post-stroke language recovery. A decrease in interhemispheric connections has implications for mechanisms of language recovery and potential success with specific treatment methods. Future directions of both structural and functional neuroimaging to study language recovery in adult aphasia are discussed

Crossed Aphasia in a Patient with Anaplastic Astrocytoma of the Non-Dominant Hemisphere

Aphasia describes a spectrum of speech impairments due to damage in the language centers of the brain. Insult to the inferior frontal gyrus of the dominant cerebral hemisphere results in Broca\u27s aphasia - the inability to produce fluent speech. The left cerebral hemisphere has historically been considered the dominant side, a characteristic long presumed to be related to a person\u27s handedness . However, recent studies utilizing fMRI have shown that right hemispheric dominance occurs more frequently than previously proposed and despite a person\u27s handedness. Here we present a case of a right-handed patient with Broca\u27s aphasia caused by a right-sided brain tumor. This is significant not only because the occurrence of aphasia in right-handed-individuals with right hemispheric brain damage (so-called crossed aphasia ) is unusual but also because such findings support dissociation between hemispheric linguistic dominance and handedness. © 2017, EduRad. All rights reserved

Fokus auf der Untersuchung des Einflusses biometrischer Faktoren auf das Ergebnis der nTMS Messung sprachrelevanter Areale neurochirurgischer Patienten

Objective: Navigated transcranial magnetic stimulation (nTMS) is a non-invasive mapping tool to locate functional areas of the brain, gaining importance as a preoperative diagnostic device. This is a summary of three studies, Schwarzer et al., Rosenstock et al. and Zdunczyk et al., whose aim it is to increase the accuracy and usability of nTMS in different neurosurgical patient groups. They intend to describe neurophysiological data gained through nTMS as a supportive measure for surgical planning to increase patient safety and improve outcome. Methods: All patients and healthy subjects were examined via bihemispheric nTMS. Schwarzer et al. ascertained a baseline picture naming performance and used repetitive nTMS (rnTMS) to induce speech disruptions to identify individual language areas in patients with language eloquent lesions. Nine biometric factors were analyzed for correlation with elevated error occurrence. Rosenstock et al. concentrated on the primary motor cortex of patients with motor-eloquent glioma and performed correlation analyses to test the association of nTMS-related variables and postoperative motor outcome. Zdunczyk et al. examined patients with degenerative cervical myelopathy (DCM) and healthy volunteers to see differences in neurophysiological nTMS data due to disease severity. Results: Schwarzer et al. showed a significant increase in error occurrence with increased severity of cognitive impairment (p8mm (p=0.014). New postoperative deficits could be seen in patients with pathological excitability of the motor cortex (resting motor threshold ratio 110%, p=0.031). Patients with DCM had a reduced corticospinal excitability estimated by the recruitment curve (p=0.022), and patients with mild symptoms showed an increased activation on non- primary motor areas (p<0.005). Patients with severe symptoms showed a higher cortical inhibition (p<0.05) and a reduced motor area (p<0.05). Conclusion: Most patients are eligible for rnTMS language mapping. A new protocol for language mapping is proposed for secure identification of patients eligible for reliable rnTMS in Schwarzer et al. Rosenstock et al. introduce a new risk stratification model, based on objective functional-anatomical and neurophysiological measures, which enables physicians to counsel patients about the risk of functional deterioration or the potential for recovery and supports surgical planning. Zdunczyk et al. propose a new concept for functional compensation for DCM on the cortical and spinal level: the corticospinal reserve capacity. nTMS is a viable diagnostic tool to characterize this and its parameters serve as valuable prognostic factors.Fragestellung: Navigierte transkranielle Magnetstimulation (nTMS) ist eine nicht-invasive Untersuchungsmethode, um kortikale Funktionsareale zu identifizieren, welche zunehmend an Bedeutung als präoperatives diagnostisches Mittel gewinnt. Dies ist eine Zusammenfassung dreier Studien, Schwarzer et al., Rosenstock et al. und Zdunczyk et al. Die Studien haben als Ziel, die Benutzerfreundlichkeit und Genauigkeit von nTMS für unterschiedliche neurochirurgische Patientengruppen zu verbessern. Neurophysiologische Parameter wurden mittels nTMS erhoben, um die operative Planung zu unterstützen und das individuelle Patientenrisiko korrekt einzuschätzen und zu verbessern. Methodik: Alle Patienten und Probanden wurden bihemisphärisch mittels nTMS untersucht. Schwarzer et al. erhoben vorher die individuelle Fähigkeit zur Objektbenennung (baseline) und nutzten repetitive nTMS (rnTMS), um Sprachunterbrechungen hervorzurufen und somit Kortexareale bei Patienten mit sprachrelevanten Hirnläsionen zu identifizieren. Neun biometrische Patienteneigenschaften wurden in ein Verhältnis mit der Fehleranfälligkeit gesetzt. Rosenstock et al. untersuchten den primär motorischen Kortex bei Gliompatienten und analysierten den Zusammenhang von nTMS-ermittelten Parametern mit dem postoperativen Patientenzustand. Zdunczyk et al. betrachteten Patienten mit degenerativer zervikaler Myelopathie (DCM), sowie gesunde Probanden und ermittelten die unterschiedlichen nTMS-Parameter in Abhängigkeit von der Symptomschwere. Ergebnisse: Die meisten biometrischen Faktoren zeigten keinen statistischen Zusammenhang mit dem Stimulationsergebnis bei Schwarzer et al. Je schwerer der Aphasiegrad und die kognitiven Einschränkungen waren, desto mehr Sprachfehler wurden in der rnTMS Untersuchung gemacht (je p8mm zwischen Tumor und kortikospinalem Trakt keine neuen permanenten postoperativen Defizite auftraten (p=0.014). Neue postoperative Defizite traten bei Patienten mit präoperativ pathologischer Kortexerregbarkeit (Ruhemotorschwellenverhältnis RMT 110%, p=0.031) auf. DCM Patienten wiesen eine reduzierte kortikospinale Erregbarkeit, gekennzeichnet durch ein Abflachen der recruitment curve, auf (p=0.022). Ein vergrößertes motorisch relevantes Kortexareal mit Aktivierung sekundärer Motorareale zeigte sich bei Patienten mit milder Symptomatik (p<0.005), während bei schwer betroffenen Patienten eine erhöhte kortikale Hemmung (CSP, p<0.05) und reduzierte motorische Kortexfläche auffiel (p<0.05). Schlussfolgerung: Schwarzer et al. stellen ein neues Prüfungsprotokoll für die Eignung von Patienten für ein reliables rnTMS Ergebnis vor, wobei die statistische Analyse ergab, dass die meisten Patienten für eine reliable rnTMS Sprachuntersuchung geeignet sind. Rosenstock et al. präsentieren ein neues Risikostratifikationsmodell für Patienten mit motorisch relevanten Gliomen, wodurch der Operateur anhand von funktionell-anatomischen und neurophysiologischen Parametern das individuelle Patientenrisiko für den postoperativen Verlauf einschätzen kann. Zdunczyk et al. beschreiben einen möglichen funktionellen Kompensationsmechanismus bei DCM Patienten auf kortikaler und spinaler Ebene: die kortikospinale Reservekapazität. Die durch nTMS ermittelten Parameter lassen damit objektivierbare prognostische Aussagen zu

Behavioural clusters and predictors of performance during recovery from stroke

We examined the patterns and variability of recovery post-stroke in multiple behavioral domains. A large cohort of first time stroke patients with heterogeneous lesions was studied prospectively and longitudinally at 1-2 weeks, 3 months and one year post-injury with structural MRI to measure lesion anatomy and in-depth neuropsychological assessment. Impairment was described at all timepoints by a few clusters of correlated deficits. The time course and magnitude of recovery was similar across domains, with change scores largely proportional to the initial deficit and most recovery occurring within the first three months. Damage to specific white matter tracts produced poorer recovery over several domains: attention and superior longitudinal fasciculus II/III, language and posterior arcuate fasciculus, motor and corticospinal tract. Finally, after accounting for the severity of the initial deficit, language and visual memory recovery/outcome was worse with lower education, while the occurrence of multiple deficits negatively impacted attention recovery

Magnetoencephalography in Stroke Recovery and Rehabilitation

Magnetoencephalography (MEG) is a non-invasive neurophysiological technique used to study the cerebral cortex. Currently, MEG is mainly used clinically to localize epileptic foci and eloquent brain areas in order to avoid damage during neurosurgery. MEG might, however, also be of help in monitoring stroke recovery and rehabilitation. This review focuses on experimental use of MEG in neurorehabilitation. MEG has been employed to detect early modifications in neuroplasticity and connectivity, but there is insufficient evidence as to whether these methods are sensitive enough to be used as a clinical diagnostic test. MEG has also been exploited to derive the relationship between brain activity and movement kinematics for a motor-based brain-computer interface. In the current body of experimental research, MEG appears to be a powerful tool in neurorehabilitation, but it is necessary to produce new data to confirm its clinical utility

ERP correlates of word production before and after stroke in an aphasic patient

No abstract available

Action Observation for Neurorehabilitation in Apraxia

Neurorehabilitation and brain stimulation studies of post-stroke patients suggest that action-observation effects can lead to rapid improvements in the recovery of motor functions and long-term motor cortical reorganization. Apraxia is a clinically important disorder characterized by marked impairment in representing and performing skillful movements [gestures], which limits many daily activities and impedes independent functioning. Recent clinical research has revealed errors of visuo-motor integration in patients with apraxia. This paper presents a rehabilitative perspective focusing on the possibility of action observation as a therapeutic treatment for patients with apraxia. This perspective also outlines impacts on neurorehabilitation and brain repair following the reinforcement of the perceptual-motor coupling. To date, interventions based primarily on action observation in apraxia have not been undertaken