Neural correlates of spontaneous language production in two patients with right hemispheric language dominance

Abstract

ABSTRACT Background It is not conclusively explored what kind of reorganisation processes are set off after a stroke with resulting aphasia. Since the development of functional Magnetic Resonance Imaging (fMRI), linguistic processes and their neural representation have been researched, especially in aphasic patients after left hemispheric insult. The situation differs in aphasic patients with crossed aphasia or aphasia after a right hemispheric lesion, for which only few studies have been carried out. In order to close this gap, the present study deals with the localisation of language functions in the brain of patients with crossed aphasia and right hemispheric language dominance. Aim The objective of the current study was to provide insights into the neural correlates of continuous aphasic language production of patients with right hemispheric language dominance. Based on the current state of research, a mirror image representation was expected. Methods & Procedures Two patients with fluent aphasia due to right hemisphere lesions, one presenting with crossed aphasia, described complex pictures. The continuous language output was transcribed and categorised into events. Lexical search (i.e. the difference between unimpaired speaking and word-finding difficulties) was analysed using fMRI. The neural activation clusters were compared with the corresponding areas of a control group consisting of 12 patients with left hemispheric aphasia. Outcomes & Results The analysis of the behavioural data revealed word-finding difficulties as one of the most limiting factors in the spontaneous language output of the patients. The neural correlates of lexical search (unimpaired minus impaired) were observed in four activation clusters both patients had in common. Each cluster was predominantly localised in the contra-lesional hemisphere. Compared to the corresponding areas of the control group, in general, a mirrored image representation could be confirmed. Conclusions The combination of detailed linguistic analysis and fMRI confirmed the assumption of mirrored language organisation for anomia in continuous language production. Moreover, the study might add to a more general understanding of the contribution of the contra-lesional hemisphere to language recovery in aphasia after left or right hemisphere damage.