Guest Talk of Dr. Katharina Saß

Guest Talk of Dr. Katharina Saß

from the Department of Psychiatry and Psychotherapy, RWTH Aachen

Date: 14.12.2010 (colloquium of the Experimental Neuropsychology Unit)

Topic: Is the banana or the gorilla more important to the monkey: Neural correlates of different semantic relations.  

Abstract: One principle of knowledge organization is the connection between concepts in the semantic network. Most current models of knowledge organization are based on taxonomic categories (e.g., vehicles, animals) but there recent studies showed that another important organizational pattern is thematic categorization, i.e. categories held together by an external and functional relationship (e.g., car – garage). But how these types of relations are represented, stored or created in the brain is still an open question. In a series of experiments, we used fMRI to investigate the processing of both relations by means of semantic priming.

The results revealed differential activation patterns (thematic: left temporal; taxonomic: right frontal) but also an interaction in the left temporal sulcus with thematic categories inducing response enhancement and taxonomic categories response suppression. The examination of semantic distance revealed an effect within the right precuneus and the left middle temporal gyrus for thematic categories. Additionally, a current investigation of thematic influence on language production revealed activation cluster within right temporo-parietal and left frontal regions.

Semantic priming was associated with activation clusters corresponding to a large bilateral fronto-temporo-parietal network. The interaction between thematic (enhancement) and taxonomic (suppression) categories in left temporal regions reflects the influence of specific memory contents. The variation of semantic distance between thematic relations showed that the differential activation of the right precuneus and the left middle temporal gyrus underline the role of these regions during semantic priming and association processing as well as the involvement of specific episodic memory contents. Moreover, we examined the impact of thematic categories beyond the single word level using a modified version of the picture-word interference task. Results suggest that related concepts are active during sentence production and can be competitors to the target. These results provide new insights in the models of lexical access in speech production, leading to the conclusion that contextual factors like the complexity of noun phrases have an important influence on sentence planning. Overall, thematic categories are an important component for the understanding of knowledge representation in the brain. In comparison to taxonomic categories, thematic relations seem to play a different, complementary role in concept formation that is particularly linked to episodic memory contents represented by left temporal regions.