Cognition is supported by networks of brain regions working in concert. For example, semantic cognition involves interactions between at least three types of brain regions that support (i) modality-specific features of concepts (i.e. visual features and sounds) (ii) heteromodal conceptual representations that integrate these features and (iii) control processes that shape retrieval to focus on currently relevant features and associations. Inhibitory TMS combined with functional magnetic resonance imaging (fMRI) can be used to investigate compensatory changes and interdependencies between these networks.
We use TMS to explore functional dissociations between sites that make distinct contributions to semantic cognition and language and also stimulate different sites within the same network to provide evidence for functional similarity. TMS combined with fMRI shows how the response across a broader network changes as a consequence of inhibition of one site. In recent studies, we have used these approaches to provide evidence for a 'semantic control network:' inhibitory stimulation of different sites within this network elicits similar cognitive disruption and inhibition of one site is associated with increased activation of other distant sites within the same network. We have also used TMS to examine how language regions contribute in dissociable ways to verbal short-term memory.
Professor Jefferies' areas of expertise include the cognitive and neural organisation of semantic memory and learning.