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The right hemisphere supports but does not replace left hemisphere auditory function in patients with persisting aphasia

Lookup NU author(s): Sundeep Teki, Professor Tim GriffithsORCiD

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Abstract

In this study, we used magnetoencephalography and a mismatch paradigm to investigate speech processing in stroke patients with auditory comprehension deficits and age-matched control subjects. We probed connectivity within and between the two temporal lobes in response to phonemic (different word) and acoustic (same word) oddballs using dynamic causal modelling. We found stronger modulation of self-connections as a function of phonemic differences for control subjects versus aphasics in left primary auditory cortex and bilateral superior temporal gyrus. The patients showed stronger modulation of connections from right primary auditory cortex to right superior temporal gyrus (feed-forward) and from left primary auditory cortex to right primary auditory cortex (interhemispheric). This differential connectivity can be explained on the basis of a predictive coding theory which suggests increased prediction error and decreased sensitivity to phonemic boundaries in the aphasics' speech network in both hemispheres. Within the aphasics, we also found behavioural correlates with connection strengths: a negative correlation between phonemic perception and an inter-hemispheric connection (left superior temporal gyrus to right superior temporal gyrus), and positive correlation between semantic performance and a feedback connection (right superior temporal gyrus to right primary auditory cortex). Our results suggest that aphasics with impaired speech comprehension have less veridical speech representations in both temporal lobes, and rely more on the right hemisphere auditory regions, particularly right superior temporal gyrus, for processing speech. Despite this presumed compensatory shift in network connectivity, the patients remain significantly impaired.

Publication metadata

Author(s): Teki S, Barnes GR, Penny WD, Iverson P, Woodhead ZVJ, Griffiths TD, Leff AP

Publication type: Article

Publication status: Published

Journal: Brain

Year: 2013

Volume: 136

Issue: 6

Pages: 1901-1912

Print publication date: 01/06/2013

Online publication date: 28/05/2013

Acceptance date: 17/02/2013

ISSN (print): 0006-8950

ISSN (electronic): 1460-2156

Publisher: Oxford University Press

URL: http://dx.doi.org/10.1093/brain/awt087

DOI: 10.1093/brain/awt087

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