The Differential Contributions of pFC and Temporo-parietal Cortex to Multimodal Semantic Control: Exploring Refractory Effects in Semantic Aphasia

摘要

Aphasic patients with multimodal semantic impairment followingnpFC or temporo-parietal (TP) cortex damage (semanticnaphasia [SA]) have deficits characterized by poor control of semanticnactivation/retrieval, as opposed to loss of semantic knowledgenper se. In line with this, SA patients show “refractory effects”;nthat is, declining accuracy in cyclical word–picture matching tasksnwhen semantically related sets are presented rapidly and repeatedly.nThis is argued to follow a build-up of competition betweenntargets and distractors. However, the link between poor semanticncontrol and refractory effects is still controversial for two reasons.n(1) Some theories propose that refractory effects are specificnto verbal or auditory tasks, yet SA patients show poor controlnover semantic processing in both word and picture semanticntasks. (2) SA can result from lesions to either the left pFC or TPncortex, yet previous work suggests that refractory effects are specificallynlinked to the left inferior frontal cortex. For the first time,nverbal, visual, and nonverbal auditory refractory effects werenexplored in nine SA patients who had pFC (pFC+) or TP cortexn(TP-only) lesions. In all modalities, patient accuracy declined significantlynover repetitions. This refractory effect at the group levelnwas driven by pFC+ patients and was not shown by individualsnwith TP-only lesions. These findings support the theory that SAnpatients have reduced control over multimodal semantic retrievalnand, additionally, suggest there may be functional specializationnwithin the posterior versus pFC elements of the semanticncontrol network.