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Common and Contrasting Areas of Activation for Abstract and Concrete Concepts: An H₂¹⁵O PET Study

¹ Lady Davis Institute and McGill University, ² Institut Universitaire de Gériatrie de Montréal, ³ Hôpital L'Enfant Jésus and Université Laval

Lesion studies indicate that the lateral and inferior temporal cortex is a critical area of semantic memory storage, but little is known about the cortical organization of semantics within this area. One proposition has been that dominant physical characteristics of objects (structure, motility) are determining factors. A positron emission tomography experiment using the H₂¹⁵O bolus method was performed to test this hypothesis by contrasting activation for concrete and abstract concepts. Unlike previous studies that considered this question, the task required explicit word meaning judgments, and blocks of trials were designed to be of equal difficulty for the two word classes. The task required elderly participants to read aloud the pair of words that was closer in meaning (e.g., spade–shovel vs. spade–carpet). Subtraction analyses that compared the semantic judgment tasks with a baseline condition indicated that both abstract and concrete concepts activated the left lateral temporal cortex. A direct comparison of abstract versus concrete scans indicated differences in the lateralization of fusiform activation. We conclude that although concreteness might be a critical factor in the fusiform cortex, it is not dominant in the lateral temporal cortex. A multistudy overview suggests that tasks that focus on one concept per trial activate areas posterior to y = –40, whereas those that invoke several concepts, as in the present study, activate areas anterior to this. Increased processing complexity may proceed in a posterior–anterior direction in the lateral temporal cortex.