All Competition Is Not Alike: Neural Mechanisms for Resolving Underdetermined and Prepotent Competition

Abstract

People must constantly select among potential thoughts and actions in the face of competition from (a) multiple task-relevant options (underdetermined competition) and (b) strongly dominant options that are not appropriate in the current context (prepotent competition). These types of competition are ubiquitous during language production. In this work, we investigate the neural mechanisms that allow individuals to effectively manage these cognitive control demands and to quickly choose words with few errors. Using fMRI, we directly contrast underdetermined and prepotent competition within the same task (verb generation) for the first time, allowing localization of the neural substrates supporting the resolution of these two types of competition. Using a neural network model, we investigate the possible mechanisms by which these brain regions support selection. Together, our findings demonstrate that all competition is not alike: resolving prepotent competition and resolving underdetermined competition rely on partly dissociable neural substrates and mechanisms. Specifically, activation of left ventrolateral prefrontal cortex is specific to resolving underdetermined competition between multiple appropriate responses, most likely via competitive lateral inhibition. In contrast, activation of left dorsolateral prefrontal cortex is sensitive to both underdetermined competition and prepotent competition from response options that are inappropriate in the current context. This region likely provides top-down support for task-relevant responses, which enables them to out-compete prepotent responses in the selection process that occurs in left ventrolateral prefrontal cortex.

The ventrolateral prefrontal cortex facilitates processing of sentential context to locate referents

“…Similarly, Martin and Cheng (2006) showed that patients with VLPFC damage were not impaired in generating a verb in response to a noun probe as long as the two were highly associated, even if multiple possible answers were possible. For example, both “apple” → eat, and “door” → close/open were easier for VLPFC patients compared to “rug” → roll, lay, walk, etc., even though “apple” was strongly associated with only one verb, and “door” with more than one (see also Snyder, Banich, & Munakata, 2014). The authors argued that these results pointed to VLPFC’s role in strengthening associations, as opposed to selection among alternatives.…”

“…This is compatible with VLPFC activity affecting the drift rate by boosting the associations between the bottom-up cues and the target. It is noteworthy that variations in the drift rate may also reflect “top-down attention” (e.g., Bogacz et al, 2006; p.731), but implementation of top-down attention seems to be more aligned with the role of dorsolateral PFC (e.g., Snyder, et al, 2014). …”

“…It is important to note that while this computational framework provides a unified account of integration and conflict resolution in case of indeterminacy (i.e., when several responses are associated with the probe with equal strength), additional mechanisms are required for resolution of conflict in favor of the less potent response when in competition with a response that is more strongly associated with the probe (e.g., naming the ink color in Stroop). A recent study shows that resolution of conflict in the face of prepotent responses might be critically dependent on DLPFC, a region that is hypothesized to selectively support the task relevant responses (Snyder et al, 2014). Regardless of whether VLPFC has a role in boosting associations in cases where overriding a prepotent response is required (e.g., January et al, 2009; Novick et al, 2005, 2009; Thompson-Schill et al, 1997; Thothathiri et al, 2012) or not (Snyder et al, 2014), contribution of a region that links task goals to the to-be-selected representations seems necessary in those conditions.…”

“…A recent study shows that resolution of conflict in the face of prepotent responses might be critically dependent on DLPFC, a region that is hypothesized to selectively support the task relevant responses (Snyder et al, 2014). Regardless of whether VLPFC has a role in boosting associations in cases where overriding a prepotent response is required (e.g., January et al, 2009; Novick et al, 2005, 2009; Thompson-Schill et al, 1997; Thothathiri et al, 2012) or not (Snyder et al, 2014), contribution of a region that links task goals to the to-be-selected representations seems necessary in those conditions.…”

The ins and outs of meaning: Behavioral and neuroanatomical dissociation of semantically-driven word retrieval and multimodal semantic recognition in aphasia

“…First, if the critical semantic control hub were in the IFG/VLPFC grey matter, then multimodal semantic deficits should have been most strongly associated with damage to that region rather than to the underlying white matter as we observed. In fact, stroke damage to the left IFG/VLPFC has been associated with a more specific deficit of lexical selection in the context of semantic competition (e.g., Mirman & Graziano, 2013; Schnur et al, 2006, 2009; for related fMRI evidence see also Snyder, Banich, & Munakata, 2014). Second, although some of the tests that loaded strongly on the Semantic Recognition factor have substantial semantic control demands (e.g., Camel & Cactus Test), others do not (e.g., Semantic Category Discrimination is a simple AX semantic discrimination task), so it is not simple to argue that the Semantic Recognition factor was rather a Semantic Control factor.…”