Modulating neural network dynamics of speech comprehension: The role of the angular gyrus

Speech and language are key elementary mental capabilities that humans use to communicate. Using neuroimaging techniques, an extended speech comprehension network involving the expected fronto-temporal brain areas but notably also the angular gyrus, situated in inferior parietal cortex, has been unequivocally identified. Furthermore, using virtual lesions, the applicants recently showed that the left angular gyrus causally benefits speech comprehension in challenging listening situations. However, this speech comprehension network does not operate in isolation: When acute or chronic challenges such as a brain lesion arise, the relative involvement of other, more domain-general networks (parieto-frontal; cingulo-opercular) is also increased. To foster future ecologically valid models of speech comprehension and any translation of such models into therapeutic interventions using non-invasive brain stimulation, it is of importance to, first, scrutinize the effective connectivity of angular gyrus (as a key node of the speech comprehension network) to other, domain-general networks. This will be achieved using both, functional magnetic resonance imaging (fMRI), in younger but also healthily aging participants (WP1), and repetitive transcranial magnetic stimulation (rTMS). Second (WP2), we will test specific hypotheses about adaptive, compensatory short-term plasticity within this array of networks to maintain successful speech comprehension: How do these network nodes modulate their activity in response to focal perturbations induced by virtual lesions to the angular gyrus? And how does their effective connectivity change according to measures of dynamic causal modeling (DCM)? Answers to this second question constitute the main part of this proposal and will involve an online combined fMRI experiment preceded by offline rTMS conditioning. Third and last (WP3), we will put results of WP1 and 2 to a direct test in an fMRI-based investigation of the reorganized network, in a group of patients with lesion overlap in angular gyrus, in the chronic phase after stroke.In sum, the proposed multimodal research approach combines an established behavioural paradigm (i.e., degraded speech comprehension) with plasticity-inducing rTMS protocols and functional neuroimaging in healthy as well as chronically challenged participants. In this synergistically rich collaboration of an auditory fMRI specialist and a language-networks brain stimulation expert, the two principal investigators will train and exchange young scientists across two laboratory sites. Our results will first and foremost further advance current thinking in the neuroscience of speech and language, but moreover help developing an optimal framework to investigate and employ rapid reorganization and adaptive plasticity on the network level.