(A) study on the cognitive load-dependent cortical responses during semantic and visual working memory tasks

Abstract

Cognitive load is considered in cognitive load theory (CLT) as the amount of information that working memory can hold at one time. Previous studies have suggested that the change in cognitive load affects attention levels and neural responses of the involved cortical regions during working memory tasks. Moreover, prior working memory research suggests that the engagement of cortical regions during working memory depends on the property of maintained information according to task goals. However, it remains unclear how goal-dependent different properties of maintained information in working memory affect cognitive load-dependent cortical responses. To address this, the present study performed a functional magnetic resonance imaging (fMRI) experiment based on the semantic and visual working memory tasks with two cognitive load levels. Whole-brain mapping revealed that greater cognitive load increased neural response levels in the dorsolateral prefrontal cortex (DLPFC) and parietal cortex during both semantic and visual working memory tasks, indicating a common effect of cognitive load between tasks. In contrast, in the posterior cingulate cortex (PCC) and dorsal medial prefrontal cortex (DMPFC), there was a decrease in neural response levels with a concomitant increase in cognitive load during both working memory tasks. However, a markedly different tendency was found in the response levels of the visual cortex between tasks. While a cognitive load-dependent decrease in neural response levels was found during visual working memory, little effect of cognitive load on neural response levels was observed during semantic working memory in the visual cortex. Taken together, these results demonstrate that different properties of maintained information during working memory affect cognitive load-dependent responses prominently in low-level cortical regions such as the visual cortex, rather than in high-level areas.