Damage to temporo-parietal cortex decreases incidental activation of thematic relations during spoken word comprehension.

Both taxonomic and thematic semantic relations have been studied extensively in behavioral studies and there is an emerging consensus that the anterior temporal lobe plays a particularly important role in the representation and processing of taxonomic relations, but the neural basis of thematic semantics is less clear. We used eye tracking to examine incidental activation of taxonomic and thematic relations during spoken word comprehension in participants with aphasia. Three groups of participants were tested: neurologically intact control participants (N=14), individuals with aphasia resulting from lesions in left hemisphere BA 39 and surrounding temporo-parietal cortex regions (N=7), and individuals with the same degree of aphasia severity and semantic impairment and anterior left hemisphere lesions (primarily inferior frontal gyrus and anterior temporal lobe) that spared BA 39 (N=6). The posterior lesion group showed reduced and delayed activation of thematic relations, but not taxonomic relations. In contrast, the anterior lesion group exhibited longer-lasting activation of taxonomic relations and did not differ from control participants in terms of activation of thematic relations. These results suggest that taxonomic and thematic semantic knowledge are functionally and neuroanatomically distinct, with the temporo-parietal cortex playing a particularly important role in thematic semantics.