Regions of neural dysfunction associated with impaired naming of actions and objects in acute stroke

The proposal that there are distinct neural regions devoted to the representation or processing of names of objects versus actions has received support from a variety of sources. However, there have been conflicting results regarding the localisation of the postulated mechanisms that are more crucial for one category or the other. There is also controversy as to whether the separation of mechanisms devoted to object versus action naming arises at the level of lexical-semantics or at the level of accessing lexical representations for output. We addressed these issues by testing oral naming and word comprehension of object and action names in 33 right-handed patients with acute left-hemisphere stroke, and by obtaining magnetic resonance (MR) perfusion-weighted and diffusion-weighted imaging of each patient at the same time. We identified regions of abnormal blood flow or infarction associated with impaired naming (with and without impaired word comprehension) of objects, of actions, or of both, using Fisher Exact tests. We found both neural regions shared by networks underlying naming of actions and networks underlying naming of objects, and other neural regions that were crucial to only one network or the other. One of the shared components (in the left superior temporal gyrus) was also essential to comprehension of action and object names (as tested by word/picture verification). These results converge with evidence from chronic lesion studies and functional imaging studies, indicating that some components of the neural networks for accessing lexical representations for output are more important for object names (e.g., left temporal cortex) and others more important for action names (e.g., left posterior frontal cortex).