Abstract
Clinical language performance and neurophysiological correlates of language processing were measured before and after intensive language therapy in patients with chronic (time post stroke >1 year) post stroke aphasia (PSA). As event-related potential (ERP) measure, the mismatch negativity (MMN) was recorded in a distracted oddball paradigm to short spoken sentences. Critical ‘deviant’ sentence stimuli where either well-formed and meaningful, or syntactically, or lexico-semantically incorrect. After 4 weeks of speech-language therapy (SLT) delivered with high intensity (10.5 h per week), clinical language assessment with the Aachen Aphasia Test battery demonstrated significant linguistic improvements, which were accompanied by enhanced MMN responses. More specifically, MMN amplitudes to grammatically correct and meaningful mini-constructions and to ‘jabberwocky’ sentences containing a pseudoword significantly increased after therapy. However, no therapy-related changes in MMN responses to syntactically incorrect strings including agreement violations were observed. While MMN increases to well-formed meaningful strings can be explained both at the word and construction levels, the neuroplastic change seen for ‘jabberwocky’ sentences suggests an explanation in terms of constructions. The results confirm previous reports that intensive SLT leads to improvements of linguistic skills in chronic aphasia patients and now demonstrate that this clinical improvement is associated with enhanced automatic brain indexes of construction processing, although no comparable change is present for ungrammatical strings. Furthermore, the data confirm that the language-induced MMN is a useful tool to map functional language recovery in PSA.
Highlights
Aphasia is an acquired language impairment that most commonly originates from stroke in the left hemisphere, affects approximately one third of all stroke patients, and leads to chronic disability (Pedersen et al, 2004; Berthier, 2005)
The mismatch negativity to grammatically well-formed and meaningful mini-constructions significantly increased over a 4 week therapy interval and a comparable increase was found for combinatorially regular ‘jabberwocky’ mini-constructions composed of a pronoun and an inflected but meaningless ‘pseudo-verb.’
In line with previous studies, our results show that language abilities in chronic aphasia patients significantly improve after intensive language training administered over a relatively short period of time (Pulvermüller et al, 2001b; Meinzer et al, 2008; Richter et al, 2008; Berthier et al, 2009; Breier et al, 2009; Kurland et al, 2012)
Summary
Aphasia is an acquired language impairment that most commonly originates from stroke in the left hemisphere, affects approximately one third of all stroke patients, and leads to chronic disability (Pedersen et al, 2004; Berthier, 2005). As language and communication difficulties are debilitating conditions, effective neurorehabilitation programs focusing on improving speech and language in patients with post stroke aphasia (PSA) are essential. In several randomized controlled clinical trials, intensive language action therapy (ILAT; Difrancesco et al, 2012), known as constraint-induced aphasia therapy (CIAT; Pulvermüller et al, 2001b), has proven to be highly effective in ameliorating language deficits in chronic PSA (Pulvermüller et al, 2001b; Maher et al, 2006; Meinzer et al, 2007; Berthier et al, 2009) as well as in subacute patients (Sickert et al, 2014). A better understanding of the neurobiological processes accompanying language deficits and rehabilitation may bear fruit in the development and advancement of neurorehabilitation programs (Berthier et al, 2009; Berthier and Pulvermüller, 2011; Cappa, 2011)
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