Focusing attention on executive functioning in Aphasia

Despite ongoing debate pertaining to the number and nature of constituents as well as the strength and nature of relationships among such constituents, there is agreement that the cognitive domain of executive functioning (EF) is multidimensional, consisting of several top-down or supervisory processes that enable goal-directed and adaptive behaviour (Diamond, 2013; Logie, 2016). Thus, fundamental to our independence in participating in the myriad of complex activities and relationships we encounter on a daily basis is the integrity of our EF abilities.

Indeed, within the aphasia literature, an ever-growing body of evidence indicates that non-linguistic cognitive deficits, including EF impairments, commonly co-occur with aphasia and importantly, may influence language profiles and outcomes (e.g., Fucetola, Connor, Strube, & Corbetta, 2009; Murray, 2012; Villard & Kiran, 2016). Such ties between non-linguistic cognitive and language abilities in aphasia are to be expected given that such abilities rely, at least in part, on overlapping neural circuits and that most conceptualisations of cognition acknowledge interrelationships among its processes (Cahana-Amitay & Albert, 2015; Guilford & Hoepfner, 1971). Despite a rather rich history of delineating how certain non-linguistic cognitive domains, particularly memory, may mediate language processing among individuals with aphasia and thus should be considered within the clinical management of aphasia (Gordon, 1983; Salis, Kelly, & Code, 2015; Schuell, Jenkins, & Jimenez-Pabon, 1964), the robustness of EF abilities in aphasia has received less experiential attention, leaving a need for further explication of the theoretical and applied implications of EF deficits in aphasia. Accordingly, this special issue of Aphasiology represents a compilation of review and empirical papers with the common purpose of advancing researchers’ and clinicians’ understanding of the role EF abilities play in language symptoms and recovery among individuals with aphasia.

The first set of four papers not only explores the integrity of EF in individuals with aphasia, but also aims to characterise the relationship between EF and language abilities in this patient population. The issue begins with a study conducted by Dean and colleagues (2016) regarding anosognosia, an EF impairment well-established as a potent negative prognostic indicator for a number of acquired neurogenic disorders and more broadly, rehabilitation outcomes (e.g., Dockree, Tarleton, Carton, & FitzGerald, 2015; Leicht, Berwig, & Gertz, 2010). As Dean et al. (2016) note, however, compromised awareness of one’s language difficulties subsequent to the onset of aphasia has received relatively little empirical attention. Therefore, their investigation examined whether direct and indirect measures of awareness of aphasia hold parallel or complementary relationships with aphasia symptoms and other aspects of EF. Dean and colleagues identify some important differences between their direct and indirect awareness measures and describe the implications of such differences for cognitive constructs and clinical practice. With a similar focus on EF assessment procedures, in the next paper, Penn and colleagues (2016) examine the sensitivity of a test battery, consisting of a number of non-verbal EF measures, to the acute stages of recovery among bilingual individuals with aphasia in South Africa. Consistent with prior aphasia research (e.g., Baldo, Paulraj, Curran, & Dronkers, 2015; Murray, 2012), Penn et al. (2016) identify a variety of patterns of EF deficits and recovery among their participants who represent a range of aphasia profiles. Importantly, these authors offer a number of suggestions for EF assessment and aphasia management within the acute recovery phases as well as within multicultural and multilingual contexts.

The next two papers focus, at least in part, on the ongoing debate within research exploring non-linguistic cognitive deficits subsequent to onset of aphasia (Baldo et al., 2015; Mayer & Murray, 2012): Do such deficits represent domain-general or domain-specific difficulties? That is, with respect to EF, it is yet to be confirmed whether individuals with aphasia are challenged by the broad domain of EF or only those EF skills which support or alternately are supported by language processes (e.g., difficulties with both spatial and verbal reasoning vs. verbal reasoning only). To examine domain-general versus -domain-specific issues, Kuzmina and Weekes (2016) administer a number of verbal versus non-verbal cognitive control tasks along with language production and comprehension tasks to three participant groups: individuals with a non-fluent aphasia profile, individuals with a fluent aphasia profile and neurologically intact individuals. These researchers find that individuals with aphasia are challenged by executive control tasks, but also notably identify some differences between the non-fluent and fluent aphasic groups in terms of performance of the verbal versus non-verbal control tasks as well as the relationship between such impairments and language comprehension and production abilities. In the following paper, Murray (2017) utilises a design fluency measure to examine EF skills such as initiation, planning and self-monitoring that have been infrequently assessed in prior aphasia research; a relatively novel inclusion in this study’s methods is that both quantitative and qualitative analyses are used to characterise design fluency performances. Murray additionally explores the issue of domain-general versus domain-specific EF problems by comparing the performances of individuals with aphasia to those with right hemisphere brain damage on both the non-verbal, design fluency measure and a verbal fluency task. Murray finds that many, but not all, participants with aphasia demonstrate EF impairments and further suggests that the group comparisons as well as correlations among EF and language measures are indicative of domain-general cognitive difficulties.

The final two articles highlight the importance of considering EF when developing and providing intervention to individuals with aphasia. Nicholas and Tabor Connor (2016) review the involvement of EF in effective use of augmentative and alternative communication (AAC). With a primary focus on high-technology, speech-generating AAC devices and on use of AAC to promote communication expression, they identify specific skills within models of EF that support AAC use, and examine aphasia research that has similarly explored interactions between EF abilities and AAC use. They additionally offer cognitive assessment suggestions that may direct decision-making regarding AAC systems for individuals with aphasia. In the last paper of the special issue, Mayer and colleagues (2016) provide not only a critical review of management procedures designed to address EF deficits in individuals with aphasia, but also a case study that introduces a novel self-management treatment protocol. In their examination of process-based EF interventions, metacognitive strategy training and indirect treatment approaches (i.e., adapt language intervention to additionally target or accommodate for EF issues), Mayer et al. identify a dearth of studies exploring such approaches within the extant aphasia literature. Accordingly, they offer a description of their “Brain Budget” intervention, which combines EF strategy training within language-based activities, and the positive outcomes observed in their participant with aphasia and concomitant cognitive impairments including awareness issues.

Again, the purpose of this special issue of Aphasiology is to draw both empirical and clinical attention to the importance of understanding interactions between EF and language symptoms and outcomes in aphasia. Across the contributed papers, numerous gaps in the research literature have been identified that currently limit our understanding of the breadth and frequency of EF impairments in the broad aphasic population (e.g., acute and chronic phases of recovery; the spectrum of aphasia severity levels). Likewise, there remains a need to advance assessment procedures for quantifying and qualifying EF status, which circumvent or take into consideration the language challenges inherent in aphasia. As is the case for other neurogenic disorders (e.g., Eskes et al., 2015; Tate et al., 2014), research-vetted methods for addressing, directly or indirectly, EF impairments within the context of aphasia management are lacking. Accordingly, whereas the papers within this special issue describe, critique and/or advance contemporary research pertaining to EF in aphasia, clearly much more theoretical and applied attention and inquiry are warranted.

Disclosure statement

No potential conflict of interest was reported by the author.