Nancy Lundin
Department of Psychiatry and Behavioral Health
The Ohio State University
Thought disorder is a cardinal feature of psychotic disorders, described as disorganized, tangential, illogical, and/or impoverished thought observed through speech. Higher levels of thought disorder relate to poorer functioning and long-term outcomes among individuals with psychotic disorders, yet the cognitive and neural underpinnings of this set of symptoms remain poorly understood. “Semantic foraging” is a new theoretical framework for examining potential processes underlying thought disorder with bases in behavioral ecology and cognitive science. Just as non-human animals search for food and mates by exploiting local patches of the environment and leaving to explore new patches when resources are depleted, humans may search for related concepts in memory using similar explore-exploit trade-offs. This has been studied using the verbal fluency test, in which individuals name items from a particular category or beginning with a particular letter in a limited time and often “cluster” (exploit) and “switch” (explore) between related groupings of items to optimize performance. In this seminar, I will discuss research examining search strategies during verbal fluency word retrieval tasks among individuals with psychotic disorders indicating preliminary evidence of alterations in semantic foraging, such as lower semantic similarity and longer interitem response times during search for related items than comparison groups. I will also discuss findings of neural signatures of semantic foraging processes from a study in which participants without a psychiatric diagnosis performed verbal fluency tests during functional magnetic resonance imaging (fMRI). We found that switching to new patches of related items was associated with activation in the hippocampus or posterior cerebellum depending on the way switching was operationalized (i.e., switches designated post hoc by participants versus computational metrics of similarity). Moreover, these regions exhibited activity which linearly increased during within-cluster search and re-set once a participant switched to a new patch, suggesting potential cognitive monitoring processes guiding the search. I will close with discussion of several future directions of this work. These include the need for replication of findings and consolidation of methodologies, with a particular focus on addressing the challenges to defining patch boundaries for when someone has stopped exploiting and started exploring, given the multifaceted ways in which concepts are related. Additional future directions include investigating the neural correlates of altered semantic foraging patterns among individuals with psychotic disorders and, most importantly, testing whether these explore-exploit patterns serve as a reliable marker of the production of cohesive speech to identify treatment targets for thought disorder.
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