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Abstract
Converging evidence supports the existence of functionally and neuroanatomically distinct
taxonomic (similarity-based; e.g., hammer-screwdriver) and thematic (event-based;
e.g., hammer-nail) semantic systems. Processing of thematic relations between objects
has been shown to selectively recruit the left posterior temporoparietal cortex. Similar
posterior regions have also been shown to be critical for knowledge of relationships
between actions and manipulable human-made objects (artifacts). Based on the hypothesis
that thematic relationships for artifacts rely, at least in part, on action relationships,
we assessed the prediction that the same regions of the left posterior temporoparietal
cortex would be critical for conceptual processing of artifact-related actions and
thematic relations for artifacts. To test this hypothesis, we evaluated processing
of taxonomic and thematic relations for artifacts and natural objects as well as artifact
action knowledge (gesture recognition) abilities in a large sample of 48 stroke patients
with a range of lesion foci in the left hemisphere. Like control participants, patients
identified thematic relations faster than taxonomic relations for artifacts, whereas
they identified taxonomic relations faster than thematic relations for natural objects.
Moreover, response times (RTs) for identifying thematic relations for artifacts selectively
predicted performance in gesture recognition. Whole brain Voxel-based Lesion-Symptom
Mapping (VLSM) analyses and Region of Interest (ROI) regression analyses further demonstrated
that lesions to the left posterior temporal cortex, overlapping with LTO and visual
motion area hMT+, were associated both with relatively slower RTs in identifying thematic
relations for artifacts and poorer artifact action knowledge in patients. These findings
provide novel insights into the functional role of left posterior temporal cortex
in thematic knowledge, and suggest that the close association between thematic relations
for artifacts and action representations may reflect their common dependence on visual
motion and manipulation information.