We are interested in semantic cognition – i.e., our store of conceptual information, and the processes in the brain that allow us to access and use this information. We study how these processes may be disrupted by brain injury (e.g., stroke). Items that we know about (such as the dog in the picture) have multiple meanings attached to them – in sound, image, movement and smell. We often only need to retrieve some aspects of our knowledge at any one time, depending on the context.
For example, you might throw a stick into a river for your dog to fetch on a hot sunny day. For this action, you need to know that your dog can swim, that she is loyal and will come back, that the stick is not an unrealistic size for your dog grab in its mouth and that sticks float. Information about the fact that your dog chews bones and has smelly breath is not relevant for this context.
It is thought that information relating to an item is stored separately from areas which retrieve the appropriate bits of information for a context. Our research has shown that people who’ve had a stroke are often unable to retrieve the relevant bits of information, even though they may retain most or all of this information. We know this because participants who’ve had a stroke can show very good retrieval of semantic information, so long as the questions are put across in a straightforward way and the tasks tap more ‘automatic’ aspects of retrieval.
As many stroke survivors do not have damage to the areas of the brain associated with storing conceptual knowledge, but instead to the ‘access’ mechanisms that allow retrieval, we are exploring the hypothesis that tDCS can be used to help people find information about items which are still stored in the brain. It’s a bit like a library full of books but without a catalogue to help select the appropriate title. As a result, the only books you can find on a particular topic are those with bright yellow covers – and you may select those brightly coloured books, even if the information within them isn’t exactly what you wanted to find. tDCS and task training may help people to retrieve their knowledge in a more flexible way.