Abstract
Aphasic deficits are usually only interpreted in terms of domain-specific language processes. However, effective human communication and tests that probe this complex cognitive skill are also dependent on domain-general processes. In the clinical context, it is a pragmatic observation that impaired attention and executive functions interfere with the rehabilitation of aphasia. One system that is important in cognitive control is the salience network, which includes dorsal anterior cingulate cortex and adjacent cortex in the superior frontal gyrus (midline frontal cortex). This functional imaging study assessed domain-general activity in the midline frontal cortex, which was remote from the infarct, in relation to performance on a standard test of spoken language in 16 chronic aphasic patients both before and after a rehabilitation programme. During scanning, participants heard simple sentences, with each listening trial followed immediately by a trial in which they repeated back the previous sentence. Listening to sentences in the context of a listen–repeat task was expected to activate regions involved in both language-specific processes (speech perception and comprehension, verbal working memory and pre-articulatory rehearsal) and a number of task-specific processes (including attention to utterances and attempts to overcome pre-response conflict and decision uncertainty during impaired speech perception). To visualize the same system in healthy participants, sentences were presented to them as three-channel noise-vocoded speech, thereby impairing speech perception and assessing whether this evokes domain general cognitive systems. As expected, contrasting the more difficult task of perceiving and preparing to repeat noise-vocoded speech with the same task on clear speech demonstrated increased activity in the midline frontal cortex in the healthy participants. The same region was activated in the aphasic patients as they listened to standard (undistorted) sentences. Using a region of interest defined from the data on the healthy participants, data from the midline frontal cortex was obtained from the patients. Across the group and across different scanning sessions, activity correlated significantly with the patients’ communicative abilities. This correlation was not influenced by the sizes of the lesion or the patients’ chronological ages. This is the first study that has directly correlated activity in a domain general system, specifically the salience network, with residual language performance in post-stroke aphasia. It provides direct evidence in support of the clinical intuition that domain-general cognitive control is an essential factor contributing to the potential for recovery from aphasic stroke.
Highlights
Recovery from aphasic stroke can be both variable and unpredictable
This study provides evidence for the frequent clinical intuition that impaired function of these systems leads to a poorer prognosis in aphasia
Additional activity observed in the medial temporal lobes can be attributed to episodic memory encoding of the verbal message
Summary
Recovery from aphasic stroke can be both variable and unpredictable. The size of the lesion and the age of the patient only account for $40% of this variance (Lazar et al, 2008). Given the limited knowledge about the systems neuroscience of recovery and rehabilitation after focal brain injuries, it has been one of the goals of functional neuroimaging research to afford insight into the brain networks supporting recovery from aphasia (Musso et al, 1999; Leff et al, 2002; Abo et al, 2004; Fernandez et al, 2004; Naeser et al, 2004; Price and Crinion, 2005; Saur et al, 2006, 2010; Warren et al, 2009; see a review by Meinzer et al, 2011). Others have concluded that the contribution of ‘homologous’ language regions in the right hemisphere is unrelated to, or may even inhibit, recovery in the left hemisphere (Rosen et al, 2000; Thiel et al, 2001; Blank et al, 2003; Naeser et al, 2004, 2005; Winhuisen et al, 2007) or only contribute to recovery in the chronic stage (Mimura et al, 1998; Richter et al, 2008)
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