Semantic control for understanding concepts

Objects can be identified at different hierarchical levels. For example, a dog may be called a dog, but we can also use a more general name like animal or mammal, or a more specific name such as collie or Lassie. We found that understanding superordinate concepts (mammal), relative to basic-level concepts (dog), engaged the left lateral prefrontal cortex. Importantly, such activation was modulated by the proportion of features shared by the members of the concept. This interaction between concept level and feature sharedness in the PFC suggests that understanding superordinate concepts requires extra semantic control to retrieve less shared information in a goal-directed manner.




Semantic strategies during episodic memory retrieval

Sometimes knowledge comes to mind automatically (e.g. remembering our mother's name) but often we must search memory strategically in a goal-directed manner. My research revolves around the mechanisms that allow us to recover past experiences depending upon our goals and needs. We found that a specific region of the prefrontal cortex - the left ventrolateral portion - is critical for the self-initiation of semantic strategies during episodic recovery. Importantly, activation of this region predicted individual differences in performance, such that increased activation facilitated recollection. This study constitutes a first step towards a broader set of experiments looking at how individuals use semantic information as a strategy for episodic retrieval.




Integration of semantic information in social decision making

In the layered setting of social decision making, semantic knowledge plays a critical role, not just in understanding our own mental states, but also in understanding others and in establishing relations between oneself and others. In an fMRI study we looked at the contributions of the frontopolar cortex to semantic decisions about self, others, and relations. Results showed a functional dissociation between medial and lateral frontopolar cortex. Medial regions were activated during semantic decisions about self and others, consistent with a role in mentalizing, whereas lateral frontopolar was recruited during relational judgments that required the integration of semantic information. This research adds to a growing body of results on the contribution of the frontopolar cortex to higher-order cognition.



Semantic disambiguation in spoken language

A crucial component of semantic memory is the knowledge about words and its meanings. I used the phenomenon of semantic ambiguity (words that have more than one meaning) to explore how the meaning of concepts is integrated in contextually appropriate sentences. In a set of fMRI studies, we found that action words in literal sentences (e.g. kick the ball) activated regions along the motor cortex responsible for movement execution. However, such activation did not occur for the same words in idiomatic sentences, where the context emphasized non-action features (e.g. kick the bucket). These findings lend support to cognitive theories of semantic flexibility, by showing that semantic context determines the degree to which relevant features are processed when a word is heard.