An Exploratory Study of Cerebellar Transcranial Direct Current Stimulation in Individuals With Chronic Stroke Aphasia

Protocol for Cerebellar Stimulation for Aphasia Rehabilitation (CeSAR): A randomized, double-blind, sham-controlled trial

In this randomized, double-blind, sham-controlled trial of Cerebellar Stimulation for Aphasia Rehabilitation (CeSAR), we will determine the effectiveness of cathodal tDCS (transcranial direct current stimulation) to the right cerebellum for the treatment of chronic aphasia (>6 months post stroke). We will test the hypothesis that cerebellar tDCS in combination with an evidenced-based anomia treatment (semantic feature analysis, SFA) will be associated with greater improvement in naming untrained pictures (as measured by the change in Philadelphia Picture Naming Test), 1-week post-treatment, compared to sham plus SFA. We will also evaluate the effects of cerebellar tDCS on naming trained items as well as the effects on functional communication, content, efficiency, and word-retrieval of picture description, and quality of life. Finally, we will identify imaging and linguistic biomarkers to determine the characteristics of stroke patients that benefit from cerebellar tDCS and SFA treatment. We expect to enroll 60 participants over five years. Participants will receive 15, 25-minute sessions of cerebellar tDCS (3-5 sessions per week) or sham tDCS combined with 1 hour of SFA treatment. Participants will be evaluated prior to the start of treatment, one-week post-treatment, 1-, 3-, and 6-months post-treatment on primary and secondary outcome variables. The long-term aim of this study is to provide the basis for a Phase III randomized controlled trial of cerebellar tDCS vs sham with concurrent language therapy for treatment of chronic aphasia. Trial registration: The trial is registered with ClinicalTrials.gov NCT05093673.

Non-invasive brain stimulation in the treatment of post-stroke aphasia: a scoping review

PURPOSE

Aphasia is an acquired language impairment that commonly results from stroke. Non-invasive brain stimulation (NIBS) might accelerate aphasia recovery trajectories and has seen mounting popularity in recent aphasia rehabilitation research. The present review aimed to: (1) summarise all existing literature on NIBS as a post-stroke aphasia treatment; and (2) provide recommendations for future NIBS-aphasia research.

MATERIALS AND METHODS

Databases for published and grey literature were searched using scoping review methodology. 278 journal articles, conference abstracts/posters, and books, and 38 items of grey literature, were included for analysis.

RESULTS

Quantitative analysis revealed that ipsilesional anodal transcranial direct current stimulation and contralesional 1-Hz repetitive transcranial magnetic stimulation were the most widely used forms of NIBS, while qualitative analysis identified four key themes including: the roles of the hemispheres in aphasia recovery and their relationship with NIBS; heterogeneity of individuals but homogeneity of subpopulations; individualisation of stimulation parameters; and much remains under-explored in the NIBS-aphasia literature.

CONCLUSIONS

Taken together, these results highlighted systemic challenges across the field such as small sample sizes, inter-individual variability, lack of protocol optimisation/standardisation, and inadequate focus on aphasiology. Four key recommendations are outlined herein to guide future research and refine NIBS methods for post-stroke aphasia treatment.

Effects of Cerebellar Non-Invasive Stimulation on Neurorehabilitation in Stroke Patients: An Updated Systematic Review

The cerebellum is emerging as a promising target for noninvasive brain stimulation (NIBS). A systematic review was conducted to evaluate the effects of cerebellar NIBS on both motor and other symptoms in stroke rehabilitation, its impact on functional ability, and potential side effects (PROSPERO number: CRD42022365697). A systematic electronic database search was performed by using PubMed Central (PMC), EMBASE, and Web of Science, with a cutoff date of November 2023. Data extracted included study details, NIBS methodology, outcome measures, and results. The risk of bias in eligible studies was also assessed. Twenty-two clinical studies involving 1016 participants were finally included, with a focus on outcomes related to post-stroke motor recovery (gait and balance, muscle spasticity, and upper limb dexterity) and other functions (dysphagia and aphasia). Positive effects were observed, especially on motor functions like gait and balance. Some efficiency was also observed in dysphagia rehabilitation. However, findings on language recovery were preliminary and inconsistent. A slight improvement in functional ability was noted, with no serious adverse effects reported. Further studies are needed to explore the effects of cerebellar NIBS on post-stroke non-motor deficits and to understand how cerebellar engagement can facilitate more precise treatment strategies for stroke rehabilitation.

Fronto-thalamic networks and the left ventral thalamic nuclei play a key role in aphasia after thalamic stroke

Thalamic aphasia results from focal thalamic lesions that cause dysfunction of remote but functionally connected cortical areas due to language network perturbation. However, specific local and network-level neural substrates of thalamic aphasia remain incompletely understood. Using lesion symptom mapping, we demonstrate that lesions in the left ventrolateral and ventral anterior thalamic nucleus are most strongly associated with aphasia in general and with impaired semantic and phonemic fluency and complex comprehension in particular. Lesion network mapping (using a normative connectome based on fMRI data from 1000 healthy individuals) reveals a Thalamic aphasia network encompassing widespread left-hemispheric cerebral connections, with Broca's area showing the strongest associations, followed by the superior and middle frontal gyri, precentral and paracingulate gyri, and globus pallidus. Our results imply the critical involvement of the left ventrolateral and left ventral anterior thalamic nuclei in engaging left frontal cortical areas, especially Broca's area, during language processing.

Protocol for Cerebellar Stimulation for Aphasia Rehabilitation (CeSAR): A randomized, double-blind, sham-controlled trial

In this randomized, double-blind, sham-controlled trial of Cerebellar Stimulation for Aphasia Rehabilitation (CeSAR), we will determine the effectiveness of cathodal tDCS (transcranial direct current stimulation) to the right cerebellum for the treatment of chronic aphasia (>6 months post stroke). We will test the hypothesis that cerebellar tDCS in combination with an evidenced-based anomia treatment (semantic feature analysis, SFA) will be associated with greater improvement in naming untrained pictures (as measured by the change in Philadelphia Picture Naming Test), 1-week post treatment, compared to sham plus SFA. We will also evaluate the effects of cerebellar tDCS on naming trained items as well as the effects on functional communication, content, efficiency, and word-retrieval of picture description, and quality of life. Finally, we will identify imaging and linguistic biomarkers to determine the characteristics of stroke patients that benefit from cerebellar tDCS and SFA treatment. We expect to enroll 60 participants over five years. Participants will receive 15, 25-minute sessions of cerebellar tDCS (3-5 sessions per week) or sham tDCS combined with 1 hour of SFA treatment. Participants will be evaluated prior to the start of treatment, one-week post-treatment, 1-, 3-, and 6-months post treatment on primary and secondary outcome variables. The long-term aim of this study is to provide the basis for a Phase III randomized controlled trial of cerebellar tDCS vs sham with concurrent language therapy for treatment of chronic aphasia. Trial registration: The trial is registered with ClinicalTrials.gov NCT05093673.

Mixed Aphasia Caused by Bilateral Cerebellar Infarcts: a Case Report

Although neuroanatomical and physiological understanding of the cerebellum has evolved over recent decades and continues to develop, there is much that remains to be expounded upon, especially with regard to nonmotor roles. Neurocognitive and language processing is one area where involvement of the cerebellum is no longer in question, but the extent and mechanism of this relationship have yet to be defined. For example, which of the cerebellar hemispheres is involved continues to be debated. We present a case wherein a thrombus in the basilar artery led to bihemispheric cerebellar strokes with profound mixed effects on the patient's language and cognition. To the authors' knowledge, this is the first reported case of bilateral cerebellar strokes resulting in a mixed aphasia reported in scientific literature. This demonstrates the importance of continued research into a model for cerebellar function and the clinical impact of lesions to various cerebellar regions.

Effects of Cerebellar Transcranial Direct Current Stimulation in Patients with Stroke: a Systematic Review

BACKGROUND

The cerebellum is involved in regulating motor, affective, and cognitive processes. It is a promising target for transcranial direct current stimulation (tDCS) intervention in stroke.

OBJECTIVES

To review the current evidence for cerebellar tDCS (ctDCS) in stroke, its problems, and its future directions.

METHODS

We searched the Web of Science, MEDLINE, CINAHL, EMBASE, Cochrane Library, and PubMed databases. Eligible studies were identified after a systematic literature review of the effects of ctDCS in stroke patients. The changes in assessment scale scores and objective indicators after stimulation were reviewed.

RESULTS

Eleven studies were included in the systematic review, comprising 169 stroke patients. Current evidence suggests that anode tDCS on the right cerebellar hemisphere does not appear to enhance language processing in stroke patients. Compared with the sham group, stroke patients showed a significant improvement in the verb generation task after cathodal ctDCS stimulation. However, with regard to naming, two studies came to the opposite conclusion. The contralesional anodal ctDCS is expected to improve standing balance but not motor learning in stroke patients. The bipolar bilateral ctDCS protocol to target dentate nuclei (PO10h and PO9h) had a positive effect on standing balance, goal-directed weight shifting, and postural control in stroke patients.

CONCLUSIONS

ctDCS appears to improve poststroke language and motor dysfunction (particularly gait). However, the evidence for these results was insufficient, and the quality of the relevant studies was low. ctDCS stimulation parameters and individual factors of participants may affect the therapeutic effect of ctDCS. Researchers need to take a more regulated approach in the future to conduct studies with large sample sizes. Overall, ctDCS remains a promising stroke intervention technique that could be used in the future.

Targeted neurorehabilitation strategies in post-stroke aphasia

BACKGROUND

Aphasia is a debilitating language impairment, affecting millions of people worldwide. About 40% of stroke survivors develop chronic aphasia, resulting in life-long disability.

OBJECTIVE

This review examines extrinsic and intrinsic neuromodulation techniques, aimed at enhancing the effects of speech and language therapies in stroke survivors with aphasia.

METHODS

We discuss the available evidence supporting the use of transcranial direct current stimulation (tDCS), repetitive transcranial magnetic stimulation, and functional MRI (fMRI) real-time neurofeedback in aphasia rehabilitation.

RESULTS

This review systematically evaluates studies focusing on efficacy and implementation of specialized methods for post-treatment outcome optimization and transfer to functional skills. It considers stimulation target determination and various targeting approaches. The translation of neuromodulation interventions to clinical practice is explored, emphasizing generalization and functional communication. The review also covers real-time fMRI neurofeedback, discussing current evidence for efficacy and essential implementation parameters. Finally, we address future directions for neuromodulation research in aphasia.

CONCLUSIONS

This comprehensive review aims to serve as a resource for a broad audience of researchers and clinicians interested in incorporating neuromodulation for advancing aphasia care.

Timing of transcranial direct current stimulation (tDCS) combined with speech and language therapy (SLT) for aphasia: study protocol for a randomized controlled trial

BACKGROUND

Studies suggest that language recovery in aphasia may be improved by pairing speech-language therapy with transcranial direct current stimulation. However, results from many studies have been inconclusive regarding the impact transcranial direct current stimulation may have on language recovery in individuals with aphasia. An important factor that may impact the efficacy of transcranial direct current stimulation is its timing relative to speech-language therapy. Namely, online transcranial direct current stimulation (paired with speech-language therapy) and offline transcranial direct current stimulation (prior to or following speech-language therapy) may have differential effects on language recovery in post-stroke aphasia. Transcranial direct current stimulation provided immediately before speech-language therapy may prime the language system whereas stimulation provided immediately after speech-language therapy may aid in memory consolidation. The main aim of this study is to investigate the differential effects of offline and online transcranial direct stimulation on language recovery (i.e., conversation) in post-stroke aphasia.

METHODS/DESIGN

The study is a randomized, parallel-assignment, double-blind treatment study. Participants will be randomized to one of four treatment conditions and will participate in 15 treatment sessions. All groups receive speech-language therapy in the form of computer-based script practice. Three groups will receive transcranial direct current stimulation: prior to speech-language therapy, concurrent with speech-language therapy, or following speech-language therapy. One group will receive sham stimulation (speech-language therapy only). We aim to include 12 participants per group (48 total). We will use fMRI-guided neuronavigation to determine placement of transcranial direct stimulation electrodes on participants' left angular gyrus. Participants will be assessed blindly at baseline, immediately post-treatment, and at 4 weeks and 8 weeks following treatment. The primary outcome measure is change in the rate and accuracy of the trained conversation script from baseline to post-treatment.

DISCUSSION

Results from this study will aid in determining the optimum timing to combine transcranial direct current stimulation with speech-language therapy to facilitate better language outcomes for individuals with aphasia. In addition, effect sizes derived from this study may also inform larger clinical trials investigating the impact of transcranial direct current stimulation on functional communication in individuals with aphasia.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03773406. December 12, 2018.

Cingulate transcranial direct current stimulation in adults with HIV

BACKGROUND

Neuronal dysfunction plays an important role in the high prevalence of HIV-associated neurocognitive disorders (HAND) in people with HIV (PWH). Transcranial direct current stimulation (tDCS)-with its capability to improve neuronal function-may have the potential to serve as an alternative therapeutic approach for HAND. Brain imaging and neurobehavioral studies provide converging evidence that injury to the anterior cingulate cortex (ACC) is highly prevalent and contributes to HAND in PWH, suggesting that ACC may serve as a potential neuromodulation target for HAND. Here we conducted a randomized, double-blind, placebo-controlled, partial crossover pilot study to test the safety, tolerability, and potential efficacy of anodal tDCS over cingulate cortex in adults with HIV, with a focus on the dorsal ACC (dACC).

METHODS

Eleven PWH (47-69 years old, 2 females, 100% African Americans, disease duration 16-36 years) participated in the study, which had two phases, Phase 1 and Phase 2. During Phase 1, participants were randomized to receive ten sessions of sham (n = 4) or cingulate tDCS (n = 7) over the course of 2-3 weeks. Treatment assignments were unknown to the participants and the technicians. Neuropsychology and MRI data were collected from four additional study visits to assess treatment effects, including one baseline visit (BL, prior to treatment) and three follow-up visits (FU1, FU2, and FU3, approximately 1 week, 3 weeks, and 3 months after treatment, respectively). Treatment assignment was unblinded after FU3. Participants in the sham group repeated the study with open-label cingulate tDCS during Phase 2. Statistical analysis was limited to data from Phase 1.

RESULTS

Compared to sham tDCS, cingulate tDCS led to a decrease in Perseverative Errors in Wisconsin Card Sorting Test (WCST), but not Non-Perseverative Errors, as well as a decrease in the ratio score of Trail Making Test-Part B (TMT-B) to TMT-Part A (TMT-A). Seed-to-voxel analysis with resting state functional MRI data revealed an increase in functional connectivity between the bilateral dACC and a cluster in the right dorsal striatum after cingulate tDCS. There were no differences in self-reported discomfort ratings between sham and cingulate tDCS.

CONCLUSIONS

Cingulate tDCS is safe and well-tolerated in PWH, and may have the potential to improve cognitive performance and brain function. A future study with a larger sample is warranted.

Cerebellar tDCS does not modulate language processing performance in healthy individuals

Clinical and neuroscientific studies in healthy volunteers have established that the cerebellum contributes to language comprehension and production. Yet most evidence is correlational and the exact role of the cerebellum remains unclear. The aim of this study was to investigate the role of the right cerebellum in unimpaired language comprehension and production using non-invasive brain stimulation. In this double-blind, sham-controlled experiment, thirty-six healthy participants received anodal or sham transcranial direct current (tDCS) stimulation to the right cerebellum while performing a lexical decision, sentence comprehension, verbal fluency and a non-language control task. Active tDCS did not modulate performance in any of the tasks. Additional exploratory analyses suggest difficulty-specific performance modulation in the sentence comprehension and lexical decision task, with tDCS improving performance in easy trials of the sentence comprehension task and difficult trials in the lexical decision task. Overall, our findings provide no evidence for the involvement of the right posterior cerebellum in language processing. Further research is needed to dissociate the influence of task difficulty of the underlying cognitive processes.

Consensus Paper: Novel Directions and Next Steps of Non-invasive Brain Stimulation of the Cerebellum in Health and Disease

The cerebellum is involved in multiple closed-loops circuitry which connect the cerebellar modules with the motor cortex, prefrontal, temporal, and parietal cortical areas, and contribute to motor control, cognitive processes, emotional processing, and behavior. Among them, the cerebello-thalamo-cortical pathway represents the anatomical substratum of cerebellum-motor cortex inhibition (CBI). However, the cerebellum is also connected with basal ganglia by disynaptic pathways, and cerebellar involvement in disorders commonly associated with basal ganglia dysfunction (e.g., Parkinson's disease and dystonia) has been suggested. Lately, cerebellar activity has been targeted by non-invasive brain stimulation (NIBS) techniques including transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) to indirectly affect and tune dysfunctional circuitry in the brain. Although the results are promising, several questions remain still unsolved. Here, a panel of experts from different specialties (neurophysiology, neurology, neurosurgery, neuropsychology) reviews the current results on cerebellar NIBS with the aim to derive the future steps and directions needed. We discuss the effects of TMS in the field of cerebellar neurophysiology, the potentials of cerebellar tDCS, the role of animal models in cerebellar NIBS applications, and the possible application of cerebellar NIBS in motor learning, stroke recovery, speech and language functions, neuropsychiatric and movement disorders.