Training-related changes of brain activation for speech production in healthy speakers – a longitudinal fMRI study to mimic aphasia therapy

ABSTRACT

Background: Re-learning of lexical entries is fundamental to rehabilitation of the common word finding deficits in language disorders after brain damage. Previous studies examined and compared neural correlates of speech production and word learning in aphasic and healthy speakers, but longitudinal control studies were rarely set out to mimic the lexical confusion and therapeutic remediation in aphasia.

Aims: Thus, we aimed to examine functional brain organisation before (familiar word naming), during (learning phase) and after (consolidation phase) standardised training of speech production modulated by aphasia therapy.

Methods & Procedures: During the first functional magnetic resonance imaging (fMRI) measurement, participants were asked to name pictures using familiar words; during learning and in the consolidation phase, they were asked to name pictures using newly acquired pseudowords. To examine differential involvement of brain areas dependent on learning and consolidation success, we followed up activations for finally correctly learned (CoL) items between fMRI measurements, and compared activation during naming of CoL versus finally not learned (NoL) items at each measurement.

Outcomes & Results: Naming accuracy of participants improved significantly. Although performance increase until the second fMRI measurement was minor, brain activation was present for CoL in comparison to NoL items in right hemisphere homologues of fronto-temporal language-related areas in this phase. Comparing learning with consolidation phases for pseudowords, naming CoL items was accompanied by activation in areas related to monitoring and selection between multiple lexical competitors, and in the right posterior middle temporal gyrus. Conversely, activation specific to the consolidation phase, and also to CoL items in that phase, consisted of a widely distributed network involving areas associated with motor, language and consolidation processes. Activation in right supramarginal and left superior temporal gyrus was related to individual learning success.

Conclusions: We were able to demonstrate phase- and performance-dependent activation differences in various areas of the speech production network, which were in part correlated with learning success. The observed similarities to therapy-induced activation changes in aphasia reveal that the novel paradigm is useful in mimicking therapy and may uncover compensatory mechanisms specific to aphasia.

KEYWORDS:

• Speech production
• naming
• fMRI
• verbal learning
• pseudowords

Acknowledgements

We thank all participants and our colleagues from the Brain Imaging Facility “Functional Imaging” at the International Center for Clinical Research-Aachen (http://www.izkf-aachen.de/) for technical support and assistance during scanning. We also thank our student assistant Lena Reising for her help during data analysis and the two reviewers for their helpful comments.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplemental Data

The supplemental data for this article can be accessed here.

Additional information

Funding

This work was supported by the START program of the Medical Faculty RWTH Aachen University [Abel, START 28/11].