The methodological quality of short-term/working memory treatments in post-stroke aphasia: a systematic review

Abstract

Background: Individuals with aphasia after stroke often present with concomitant short- term memory and working memory (STM/WM) impairments (Murray, Salis, Martin, & Dralle, 2018). These impairments can negatively influence language processing (e.g., Martin, Minkina, Kohen, & Kalinyak-Fliszar, 2018; Salis, Kelly, & Code, 2015; Zakariás, Salis, & Wartenburger, 2018). Research investigating the relationship between STM/WM and language processing has led to the promising hypothesis that treatments of STM/WM could lead to improvements in language functioning, a phenomenon known as general- ization. However, despite the growing number of STM/WM treatments in aphasia, little is known about their methodological rigor and quality, and whether treatment-related improvements of STM/WM generalize beyond STM/WM treatment tasks and to aspects of language (e.g., spoken sentence comprehension). Aims: (1) To identify and describe STM/WM treatments in stroke aphasia through a systematic review of relevant literature; (2) to appraise the methodological quality (i.e., internal and external validity) of these treatments; (3) to investigate whether STM/WM, language (e.g., spoken sentence comprehension, functional communication), and other everyday functions can benefit from STM/WM treatments in stroke aphasia. Methods & procedures: A systematic search of 13 databases was conducted in 2014 (February) and then updated in 2016 (December). Reference lists of included studies, conference abstracts, and relevant reviews were also screened for potentially eligible studies. Inclusion criteria were studies that had been published in English and included: (1) adult participants presenting with non-progressive, acquired aphasia as a result of stroke; (2) STM/WM tasks in their treatments; (3) STM/WM outcome data. We used the Risk of Bias in N-of-1 Trials (RoBiNT; Tate et al., 2015) quantitative scale to rate the internal and external validity of the included studies. Outcomes & results: The selection and inclusion process is summarized in Figure 1. The systematic search and inclusion/exclusion procedure yielded 17 included studies (mainly single case and case-series designs) with 37 participants. Table 1 summarizes the included studies (not included in the reference list), methodological quality scores, treatment procedures, and main outcomes. Methodological quality scores indicated poor internal and external validity across studies. The majority of studies reported improvements in STM/WM, which was based on inferential statistical or systematic visual analysis in 12 studies. Treatment effects on language were investigated in 16 studies, noting improvements on spoken sentence comprehension, spoken discourse produc- tion, everyday communication, and reading in some but not all studies. Only four studies investigated outcomes on STM/WM functioning in everyday life results of these studies are inconclusive. Conclusions: Methodological limitations make it difficult, at present, to draw firm conclusions about the effectiveness of STM/WM treatments in stroke aphasia. Results in terms of STM/WM, spoken sentence comprehension, and reading are promising, but further studies with more rigorous methodology and stronger experimental control are needed to determine the beneficial effects of this type of intervention. Future studies need to include outcome measures of memory functioning in everyday life, commu- nication, and psychosocial functioning to demonstrate clinically significant improve- ments after STM/WM treatments in aphasia.