Task-independent semantic activation for numbers and animals.

UNLABELLED: Semantic processing of numbers and animals was contrasted with PET in two different tasks (comparison and classification) to test the hypothesis that knowledge about numbers is associated with increased activation in the parietal cortices, regardless of the semantic task (i.e. CLASSIFICATION: is seven odd? Comparison: is seven larger than 5?). By contrast, processing animal names was expected to produce activation in inferior temporal areas. Task-independent activation was observed in the left and right intraparietal sulci for number names, whereas task-independent activation of the left inferior temporal gyrus was found for animal names. No significant interaction between the category (numbers or animals) and the semantic task (comparison or classification) was observed. Accordingly, the IPS activation classically observed during numerical processing appears to be related to category-specific semantic knowledge about numbers. Likewise, the activation of the inferior temporal gyrus associated with the processing of animal names is probably related to category-specific knowledge about animals. The results strongly support the hypothesis that different brain regions are important for storing conceptual knowledge about different semantic categories.