Does Inner Speech Improve Access to Overt Speech in Aphasia Following Stroke? An fMRI Study Utilising Computerised Rehabilitation Software.

15 million people worldwide have a stroke each year, with 152,000 in the United Kingdom. Recent estimates suggest that roughly 33% of patients suffering a stroke develop aphasia, a loss or impairment of language function caused by brain damage, which can have a significant impact on all aspects of an individual's life, as well as that of their carers. Aphasia can often be long-term, or chronic, affecting patients at least a year or more after their initial stroke.

Few studies have systematically investigated the effects of rehabilitation on brain mechanisms recruited to support recovery in stroke. Studies in this area are highly heterogeneous. The heterogeneity largely stems from 'lesion-related or language deficit-related differences in the patients studied'. Participants across and sometimes within the few studies conducted in this area vary with regard to the type of aphasia or time-following-stroke. These studies also boast differences including the type and dosage of treatment, the type of scanning task used to evaluate the desired effects of treatment, and the type of data analysis employed. Results from these studies have, unsurprisingly, indicated dissimilar neural outcomes associated with neuropsychological gains, such as increased right hemisphere (contra-lateral) involvement, or, in contrast, increased peri-lesional activation. There is, therefore, no consensus of how 'successful therapies' (that is, those that elicit some kind of language gain, either in comprehension or production) impact the language networks of the brain.

"It is well known that individuals with aphasia differ greatly with often varying language patterns and associated lesions, and even study participants carefully selected for their deficit patterns are seldom, if ever, homogeneous" . People with aphasia will, and do, differ markedly. Given this predicament, it becomes necessary to systematically control the other parts of the study, which includes limiting the imaging tasks and analysis to one component of the language system and using a powerful design, such as a crossover with two therapeutic conditions.

This study therefore aims to use systematic methodology to add information to the diminutive body of literature concerning chronic aphasia rehabilitation by exploring a specific component of the language network, inner speech, and its potential influence on speech production (neurophysiologically and neuropsychologically).

A previous study has shown that inner speech involves networks and areas dissociable from those implicated in speech production, such as the left inferior frontal gyrus, especially the pars opercularis and the supramarginal gyrus. Further, behavioural analysis has shown an interesting interaction of inner and overt speech in a small chronic aphasic population, whereas some chronic stroke patients showed poor inner speech coupled with good overt speech, while others showed good inner speech coupled with poor overt speech. This finding implies an unexplored relationship between the two networks: conceivably, that improvement in speech production during rehabilitation might be facilitated by an intact inner speech network.