Enhancing Language Recovery in Post-Stroke Aphasia with the Nurostym.

A stroke is a life-altering event, and one of its most devastating consequences can be aphasia, a language disorder that affects comprehension and expression. For over half a century, speech and language therapy (SLT) has been the mainstay of treatment. However, its effectiveness, particularly in cases of chronic post-stroke aphasia, has been limited. Recent research has explored alternative approaches, and a promising avenue is the use of non-invasive brain stimulation (NIBS) techniques. 

Omae et al. (2024) recently investigated the efficacy of amplitude modulated transcranial alternating current stimulation (tACS), through use of the Nurostym device, in enhancing language recovery in post-stroke aphasia. They targeted Broca's area, a key region for language production, and its homotopic region in the right hemisphere, which has been implicated in facilitating language recovery post-stroke. The rationale behind this approach stems from previous neuroimaging studies showing that the right hemisphere may play a compensatory role in language recovery by releasing interhemispheric inhibition from the damaged left hemisphere. Additionally, phase synchrony within the low beta-band frequency between Broca's area and the right hemisphere has been positively correlated with language function in post-stroke aphasia. 

AM-tACS offers a unique advantage over traditional tACS by utilising both high-frequency sinusoidal carrier waves and low-frequency amplitude modulation. This modulation has been shown to enhance neuronal oscillations and synchrony between stimulated regions without inducing phosphene perception, a common limitation of beta band tACS. 

In a meticulously designed N-of-1 study, a 76-year-old man with chronic post-stroke aphasia underwent three types of interventions: real AM-tACS on Broca's area and the right homotopic region, sham AM-tACS, and real AM-tACS on Broca's area and the left parietal area (as a control condition). The stimulation sites were confirmed using a Brainsight neuronavigation system with the patient’s head MRI. Short-term and long-term assessments were conducted to evaluate language function, including naming ability, verbal fluency, and the aphasia quotient. 

Remarkably, the results demonstrated significant improvements in language function following real AM-tACS, with sustained effects observed even a month after the intervention. Importantly, the increase in language function was accompanied by enhanced synchrony between Broca's area and the right homotopic region, suggesting a mechanistic link between interhemispheric connectivity and language recovery. 

Omae et al. (2024) highlight the potential of combining AM-tACS with SLT to induce long-lasting improvements in language function in post-stroke aphasia. By targeting specific functional networks, such as the interhemispheric language network, NIBS techniques like AM-tACS offer a promising avenue for enhancing the efficacy of rehabilitation programs. 

Omae, E., Shima, A. and Tanaka, K. et al. (2024). Case report: An n-of-1 study using amplitude modulated transcranial alternating current stimulation between Broca’s area and the right homotopic area to improve post-stroke aphasia with increased inter-regional synchrony. Frontiers in Human Neuroscience 18. DOI: 10.3389/fnhum.2024.1297683