Aphasie: evidenzbasierte Therapieansätze

Investigating the neural mechanisms of transcranial direct current stimulation effects on human cognition: current issues and potential solutions

Transcranial direct current stimulation (tDCS) has been studied extensively for its potential to enhance human cognitive functions in healthy individuals and to treat cognitive impairment in various clinical populations. However, little is known about how tDCS modulates the neural networks supporting cognition and the complex interplay with mediating factors that may explain the frequently observed variability of stimulation effects within and between studies. Moreover, research in this field has been characterized by substantial methodological variability, frequent lack of rigorous experimental control and small sample sizes, thereby limiting the generalizability of findings and translational potential of tDCS. The present manuscript aims to delineate how these important issues can be addressed within a neuroimaging context, to reveal the neural underpinnings, predictors and mediators of tDCS-induced behavioral modulation. We will focus on functional magnetic resonance imaging (fMRI), because it allows the investigation of tDCS effects with excellent spatial precision and sufficient temporal resolution across the entire brain. Moreover, high resolution structural imaging data can be acquired for precise localization of stimulation effects, verification of electrode positions on the scalp and realistic current modeling based on individual head and brain anatomy. However, the general principles outlined in this review will also be applicable to other imaging modalities. Following an introduction to the overall state-of-the-art in this field, we will discuss in more detail the underlying causes of variability in previous tDCS studies. Moreover, we will elaborate on design considerations for tDCS-fMRI studies, optimization of tDCS and imaging protocols and how to assure high-level experimental control. Two additional sections address the pressing need for more systematic investigation of tDCS effects across the healthy human lifespan and implications for tDCS studies in age-associated disease, and potential benefits of establishing large-scale, multidisciplinary consortia for more coordinated tDCS research in the future. We hope that this review will contribute to more coordinated, methodologically sound, transparent and reproducible research in this field. Ultimately, our aim is to facilitate a better understanding of the underlying mechanisms by which tDCS modulates human cognitive functions and more effective and individually tailored translational and clinical applications of this technique in the future.

Stimulating aged brains with transcranial direct current stimulation: Opportunities and challenges

Ageing involves significant neurophysiological changes that are both systematic while at the same time exhibiting divergent trajectories across individuals. These changes underlie cognitive impairments in elderly while also affecting the response of aged brains to interventions like transcranial direct current stimulation (tDCS). While the cognitive benefits of tDCS are more variable in elderly, older adults also respond differently to stimulation protocols compared to young adults. The age-related neurophysiological changes influencing the responsiveness to tDCS remain to be addressed in-depth. We review and discuss the premise that, in comparison to the better calibrated brain networks present in young adults, aged systems perform further away from a homoeostatic set-point. We argue that this age-related neurophysiological deviation from the homoeostatic optimum extends the leeway for tDCS to modulate the aged brain. This promotes the potency of immediate tDCS effects to induce directional plastic changes towards the homoeostatic equilibrium despite the impaired plasticity induction in elderly. We also consider how age-related neurophysiological changes pose specific challenges for tDCS that necessitate proper adaptations of stimulation protocols. Appreciating the distinctive properties of aged brains and the accompanying adjustment of stimulation parameters can increase the potency and reliability of tDCS as a treatment avenue in older adults.

Computerized Training in Poststroke Aphasia: What About the Long-Term Effects? A Randomized Clinical Trial

BACKGROUND

Poststroke aphasia is a very disabling disorder, which may affect speech expression, comprehension, and reading or writing. Treatment of aphasia should be initiated as soon as possible after the brain injury; however, the improvement of language functions can occur also in the chronic phase.

MATERIALS AND METHODS

Thirty-two patients were randomly assigned to either an experimental group (17 patients) treated with computerized rehabilitation training (Power-Afa, Maddaloni, Campania, Italy) or a control group (15 patients), submitted to conventional speech therapy. Patients were trained 3 times a week for 8 weeks, (i.e., 24 sessions of 45 minutes each), and assessed at baseline (T0), at the end of each training (T1), and 3 months after the end of the treatment (T2).

RESULTS

The experimental group had a significant improvement from T0 to T1 in all the outcomes, whereas for the control group patients such an improvement was significant only concerning Functional Independence Measure and ideomotor praxis. Notably, the improvements in cognitive and language functions were maintained at 3-month follow-up only in the experimental group.

CONCLUSIONS

The software Power-Afa can be considered a valuable tool in improving the linguistic and cognitive recovery in patients affected by poststroke aphasia in the chronic phase. Further studies with larger samples and longer follow-up periods are needed to confirm such promising findings.