Task-induced brain activity in aphasic stroke patients: what is driving recovery?

Abstract

Based on the interpretation and reinterpretation of published functional neuroimaging and clinical neuropsychological data, Geranmayeh et al. argue that recovery from aphasic stroke may be due as much to the function of high-order, domain-general networks as to recovery of language-specific networks. This distinction has implications for rehabilitation.

Between-session and within-session intra-individual variability in attention in aphasia

“…Similarly, Geranmayeh and colleagues have argued that the brain regions subserving domain-general systems, including attention, are often recruited to provide support for damaged language regions during treatment. According to this theory, upregulation of domain-general cognitive systems may modulate language networks, promoting language recovery, whereas damage to these same systems may negatively impact language recovery (Geranmayeh, Brownsett, & Wise, 2014). While these theories do not focus specifically on attention but more broadly on cognitive abilities in PWA, they help provide a rationale for future work on the role of specific cognitive abilities, such as attention, on the language rehabilitation process.…”

Neurophysiological Markers of Language Recovery in Subacute Stroke

“…Sentence level processing is considered to rely heavily on other cognitive functions, in particular verbal working memory (Caplan, Michaud, & Hufford, 2013). Therefore, the task-related prefrontal activity may actually reflect an increased requirement for attention and cognitive control mechanisms (Geranmayeh, Brownsett, & Wise, 2014) which are reduced in the acute phase, increased in the subacute phase and then return to normal activation patterns in the left hemisphere language areas in the chronic phase once support from the right hemisphere is no longer required (Saur et al, 2006) (this is covered in more depth in the discussion in Chapter 5). As such, while right hemisphere activation and specifically right IFG recruitment might be considered an early neural mechanism of recovery, it could be interpreted as a result of an increased nonlinguistic cognitive process that occurs in response to increased working memory or executive control demands (van Oers et al, 2010).…”

“…More recently, the interplay between domain-general cognitive systems and domain-specific language networks that are disrupted in aphasia has been investigated (see Geranmayeh et al, 2014 for a full review), demonstrating that the ability to activate domain general cognitive control networks has a direct influence on the potential outcome for aphasia recovery following treatment (Brownsett et al, 2013). Thus, recruitment of the domain-general right hemisphere regions in early post-stroke aphasia recovery can either be interpreted as a response to an increased requirement for cognitive control of language processes due to compromised functioning of the left hemisphere regions (Saur et al, 2006;Saur et al, 2010) or it may reflect an engagement of a domain-general network in response to impaired task performance and an increased requirement for greater topdown cognitive control (Geranmayeh et al, 2014).…”

“…A further limitation of the Saur et al (2006) study relates to the use of a sentence level task as sentence comprehension in aphasia is significantly reliant on other cognitive functions, particularly verbal working memory (Caplan et al, 2013). Since task-related activity observed in aphasia often reflects increased cognitive control and attention (Geranmayeh et al, 2014), there is a need to consider less cognitively demanding language tasks that can provide unique insights into aphasia recovery.…”

“…This presents a problem in the interpretation of brain activation as it is unclear whether the activity is indicative of an impaired performance or whether it is attributable to the neural deficit itself which underlies the impairment . In addition, the type of task employed required sentence comprehension which is known to rely significantly on other cognitive functions and in particular on verbal working memory (Caplan et al, 2013). Geranmayeh et al (2014 have suggested that much language-related brain activity observed in aphasia studies can be explained by the upregulation of regions more associated with attention and cognitive control and as such, they suggest that language tasks employed for aphasic patients need to be less cognitively demanding in order that mechanisms associated specifically with language processes can be clearly determined.…”