Presentation
Search Abstracts | Symposia | Slide Sessions | Poster Sessions | Poster Slams
Disentangling semantic and domain-general control networks: the role of stimuli versus task process
Poster B29 in Poster Session B and Reception, Thursday, October 6, 6:30 - 8:30 pm EDT, Millennium Hall
Also presenting in Poster Slam B, Thursday, October 6, 6:15 - 6:30 pm EDT, Regency Ballroom
Victoria Hodgson1, Matthew Lambon Ralph1, Rebecca Jackson1; 1University of Cambridge
The semantic control network (SCN) is primarily focused on left inferior frontal and posterior temporal cortices, and is believed to be critical for the effortful, goal-oriented manipulation of meaningful stimuli. It has typically been studied in isolation from the multiple demand network (MDN), where the core regions implicated are bilateral frontal and parietal areas. Whilst both networks are specialised for the performance of executively demanding tasks, they differ in their reported domain-specificity. The MDN is thought to be domain-general and, therefore, to be activated across a range of challenging cognitive operations regardless of modality or specific cognitive process. In contrast, the SCN is defined on the basis of control processing in the semantic domain alone, regardless of the role of these regions in any other domain. The key regions implicated in each network differ (e.g., implicating dorsal vs. ventral prefrontal cortices, parietal vs. posterior middle temporal areas), yet these two networks appear to overlap in some regions, for instance in the dorsomedial prefrontal cortex and posterior inferior temporal cortex. It remains unclear how best to characterise these overlapping regions, what underlying neural processes they may be supporting, or what it is about the difficult, task-oriented use of semantic knowledge in particular that could prompt a switch to a dedicated semantic control network. This is because these networks are typically compared across, rather than within, studies, and when studies are designed to delineate these networks by comparing semantic and non-semantic stimuli, they may also differ in the types of tasks they utilise, confounding the effect of stimulus by tapping into distinct cognitive processes. We have addressed this by systematically assessing the impact of both the nature of the stimuli and the processing required with fMRI in a factorial design. Stimulus (semantic words vs. meaningless shapes) and task (n-back working memory vs. an “odd-one-out” task, adapted from the Cattell Culture Fair battery) were varied orthogonally within the same study, to create four distinct task-stimulus conditions. Each condition was delivered at two levels of difficulty, so that the regions implicated in demanding control processes could be isolated from domain-specific representation areas, and subsequently compared across the four conditions. This allowed us to assess the independent and interacting effects of task process and stimulus modality on the pattern of activation, within a sample of 32 neurotypical participants. Results indicate that both task and stimulus modality impact activation for difficult tasks, but most importantly, that these two factors interact. The semantic and nonverbal variants of the n-back task revealed little difference in activity. However, when the task involves selection, inhibition and rule-switching, as in the odd-one-out task, there is a much greater effect of modality, with the semantic odd-one-out task more closely resembling the typical SCN regions. This indicates that neither task process nor stimulus are sufficient alone to maximally recruit the SCN; instead, both impact the control regions engaged. These findings clarify the conditions which dictate SCN and MDN recruitment, bringing us closer to understanding the specific cognitive operations that different control areas perform.
Topic Areas: Control, Selection, and Executive Processes, Meaning: Lexical Semantics