Semantic memory brings meaning to our world - it allows us to recognise visual images and to understand words. It also allows us to produce meaningful behaviours and thoughts. Semantic cognition reflects an interplay of long-term memory representations and control processes that allow us to focus on aspects of knowledge that are relevant to our current goals or the context we are in. For example, the relationship between cat and milk is obvious, but more control is needed to flexibly associate more weakly related items such as cat and tin to make a meaningful connection. Our research is examining the brain basis of this multi-faceted flexibility in semantic cognition.
We use different methods to understand flexible semantic cognition. We use functional magnetic resonance imaging (MRI) and magnetoencephalography (MEG) to characterise the brain's response to tasks manipulating semantic retrieval over space and time, with a focus on brain connectivity. These methods also allow us to study differences between people in the way that different networks in the brain interact, and relate these individual differences to cognitive strengths and weaknesses. Informed by this research, we use brain stimulation methods such as transcranial magnetic stimulation to test the causal role of particular brain areas in these network interactions. We also study patients who have aphasia after left hemisphere stroke, who have difficulties in regulating the retrieval of semantic information, and investigate ways in which these problems can be ameliorated.
Professor Jefferies' areas of expertise include the cognitive and neural organisation of semantic memory and learning.