Damage to temporoparietal cortex is sufficient for impaired semantic control

Hannah Elizabeth Thompson, Krist A. Noonan, Ajay Halai, Paul Hoffman, Sara Stampacchia, Glyn Paul Hallam, Grace E Rice, Blanca De Dios Perez, Matthew A. Lambon Ralph, Beth Jefferies

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Semantic control allows us to focus semantic activation on currently relevant aspects of knowledge, even in the face of competition or when the required information is weakly encoded. Diverse cortical regions, including left prefrontal and posterior temporal cortex, are implicated in semantic control, however; the relative contribution of these regions is unclear. For the first time, we compared semantic aphasia (SA) patients with damage restricted to temporoparietal cortex (TPC; N=8) to patients with infarcts encompassing prefrontal cortex (PF+; N=22), to determine if prefrontal lesions are necessary for semantic control deficits. These SA groups were also compared with semantic dementia (SD; N=10), characterised by degraded semantic representations. We asked whether TPC cases with semantic impairment show controlled retrieval deficits equivalent to PF+ cases or conceptual degradation similar to patients with SD. Independent of lesion location, the SA subgroups showed similarities, whereas SD patients showed a qualitatively distinct semantic impairment. Relative to SD, both TPC and PF+ SA subgroups: (1) showed few correlations in performance across tasks with differing control demands, but a strong relationship between tasks of similar difficulty; (2) exhibited attenuated effects of lexical frequency and concept familiarity, (3) showed evidence of poor semantic regulation in their verbal output – performance on picture naming was substantially improved when provided with a phonological cue, and (4) showed effects of control demands, such as retrieval difficulty, which were equivalent in severity across TPC and PF+ groups. These findings show that semantic impairment in SA is underpinned by damage to a distributed semantic control network, instantiated across anterior and posterior cortical areas.
Original languageEnglish
Pages (from-to)71-85
Number of pages15
JournalCortex; a journal devoted to the study of the nervous system and behavior
Early online date29 Sept 2022
Publication statusPublished - 1 Nov 2022

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