Targeting Executive Function and Language Impairments with tACS Combined with Behavioral Intervention in Primary Progressive Aphasia: A Case-Series, Pilot Investigation

Abstract

Background/Objectives: Executive function (EF) impairments are found in a variety of neurodegenerative disorders, including in Primary Progressive Aphasia (PPA), which is primarily characterized by language impairments. The goal of this preliminary investigation was to evaluate the hypothesis that, by targeting domain-general EFs, domain-specific functions—specifically, language processing—might also be improved in this population. Methods: This case series included four Greek-speaking individuals with PPA who underwent behavioral and neurostimulation treatment daily for 15 consecutive sessions. Behavioral treatment was performed through Computerized Cognitive Training (CCT) that targeted various EF functions. Neurostimulation treatment included alpha-rhythm transcranial alternating current stimulation (tACS) over the left dorsolateral prefrontal cortex (DLPFC), previously implicated in EF functioning. EF and language performance was assessed before (pre-) and after (post-) treatment and was also compared against the performance of healthy control individuals. Results: The pre- to post-treatment comparisons showed improvements primarily in EF functions, with heterogeneous improvements in language functions across the four cases. Except for one task (N-back), in which all four patients showed numerical improvement, the pattern of numerical gains differed across patients. Conclusions: While the treatment protocol targeted EF functioning, improvements were found for both EF and language processes (albeit more variable across patients). These results support the hypothesis that improvement in domain-general functions may lead to improvements in domain-specific functions as well. These preliminary findings can be used as guiding evidence for the design of future, large-scale clinical trials that will allow us to generalize conclusions to the broader PPA population.