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

Abstract

Abstract■ Aphasic patients with multimodal semantic impairment following pFC or temporo-parietal (TP) cortex damage (semantic aphasia [SA]) have deficits characterized by poor control of semantic activation/retrieval, as opposed to loss of semantic knowledge per se. In line with this, SA patients show "refractory effects"; that is, declining accuracy in cyclical word-picture matching tasks when semantically related sets are presented rapidly and repeatedly. This is argued to follow a build-up of competition between targets and distractors. However, the link between poor semantic control and refractory effects is still controversial for two reasons.(1) Some theories propose that refractory effects are specific to verbal or auditory tasks, yet SA patients show poor control over semantic processing in both word and picture semantic tasks. (2) SA can result from lesions to either the left pFC or TP cortex, yet previous work suggests that refractory effects are specifically linked to the left inferior frontal cortex. For the first time, verbal, visual, and nonverbal auditory refractory effects were explored in nine SA patients who had pFC (pFC+) or TP cortex (TP-only) lesions. In all modalities, patient accuracy declined significantly over repetitions. This refractory effect at the group level was driven by pFC+ patients and was not shown by individuals with TP-only lesions. These findings support the theory that SA patients have reduced control over multimodal semantic retrieval and, additionally, suggest there may be functional specialization within the posterior versus pFC elements of the semantic control network. ■

Distinct loci of lexical and semantic access deficits in aphasia: Evidence from voxel-based lesion-symptom mapping and diffusion tensor imaging

“…That the VLSM did not identify the LIFG as associated with increasing relatedness effects in the blocked-cyclic tasks is inconsistent with previous findings (Campanella et al, 2013;Gardner et al, 2012;Jefferies et al, 2007;Schnur et al, 2009). However, only nine patients in M A N U S C R I P T…”

“…In contrast, theories of language comprehension assume that semantic interference occurs when accessing the semantic system (Forde & Humphreys, 1995Warrington & Cipolotti, 1996) due to co-activation of shared semantic features that makes distinguishing the target amongst related non-target representations more difficult. Evidence for a semantic locus of interference in comprehension comes from studies demonstrating that the effect does not depend on the stimulus input modality (e.g., spoken word, written word, associatively matching picture, and/or environmental sound; Gardner et al, 2012), that the effect transfers both across input modalities (e.g., auditory word-written word matching and auditory word-picture matching; Forde & Humphreys, 1997, Experiment 11) and languages (i.e., English to French and vice versa; Ferrand & Humphreys, 1996), and that interference does not occur when accessing presemantic visual representations (i.e., unusual views matching; Forde & Humphreys, 1997, Experiment 5). Thus, repeatedly accessing semantic and lexical representations belonging to the same semantic category creates semantic interference by increasing competition amongst a target and co-activated categorically related representations, but most accounts assume a lexical locus in production and a semantic locus in comprehension.…”

“…A number of neuropsychological studies demonstrate that patients with aphasia show exaggerated semantic interference when naming (Biegler et al, 2008;McCarthy & Kartsounis, 2000;Schnur, Schwartz, Brecher, & Hodgson, 2006;Schnur et al, 2009;Wilshire & McCarthy, 2002) and comprehending semantically related stimuli (Campanella, Crescentini, Mussoni, & Skrap, 2013;Forde & Humphreys, 1995Gardner et al, 2012;Jefferies et al, 2007; M A N U S C R I P T…”

“…comprehension (Campanella, Mondani, Skrap, & Shallice, 2009;Gardner et al, 2012) in the absence of increasing relatedness effects. However, these studies (Schnur et al, 2005;Campanella et al, 2009;Gardner et al, 2012) examined production or comprehension separately making it unclear whether damage to the same or different temporal lobe regions was associated with impaired performance across tasks.…”

“…However, these studies (Schnur et al, 2005;Campanella et al, 2009;Gardner et al, 2012) examined production or comprehension separately making it unclear whether damage to the same or different temporal lobe regions was associated with impaired performance across tasks. In a meta-analysis of neuroimaging studies on word production, Indefrey and Levelt (2004;see also Indefrey, 2011) identified the mid-to posterior middle temporal gyrus (MTG) as important for semantically driven lexical retrieval, suggesting a posterior temporal lobe (including the mid-posterior MTG) neural locus of the relatedness effect in naming.…”