Interdependence of Nonoverlapping Cortical Systems in Dual Cognitive Tasks

Abstract

One of the classic questions about human thinking concerns the limited ability to perform two cognitive tasks concurrently, such as a novice driver's difficulty in simultaneously driving and conversing. Limitations on the concurrent performance of two unrelated tasks challenge the tacitly assumed independence of two brain systems that seemingly have little overlap. The current study used fMRI (functional magnetic resonance imaging) to measure cortical activation during the concurrent performance of two high-level cognitive tasks that involve different sensory modalities and activate largely nonoverlapping areas of sensory and association cortex. One task was auditory sentence comprehension, and the other was the mental rotation of visually depicted 3-D objects. If the neural systems underlying the two tasks functioned independently, then in the dual task the brain activation in the main areas supporting the cognitive processing should be approximately the conjunction of the activation for each of the two tasks performed alone. We found instead that in the dual task, the activation in association areas (primarily temporal and parietal areas of cortex) was substantially less than the sum of the activation when the two tasks were performed alone, suggesting some mutual constraint among association areas. A similar result was obtained for sensory areas as well.

A decrease in brain activation associated with driving when listening to someone speak

“…For example, although one might have thought that multitasking would make special demands on executive processes that coordinate the performance of two tasks simultaneously, there was in fact no increase in activation from the single-to dual-task in the prefrontal areas commonly associated with executive function. This replicates a previous result that was obtained when the comprehension task used here was combined with a mental rotation task (Just et al, 2001;Newman et al, 2007). Other imaging studies have also failed to find additional frontal areas specifically involved in dual-task performance (Adcock et al, 2000;Bunge et al, 2000;Goldberg et al, 1998;Klingberg, 1998), although there is also ample evidence that for some combinations of tasks, prefrontal activation does increase in the dual-task situation (D'Esposito et al, 1995;Szameitat et al, 2002;Dreher and Grafman, 2003;Loose et al, 2003).…”

“…The new fMRI results here suggest that although the oculomotor activity may remain similar when a concurrent task is added to driving, preserving the visual input to primary sensory areas, the processing carried out in secondary visual areas is diminished. We note, however, that other studies of divided attention between visual and auditory tasks have shown decreased primary visual activation in the divided attention condition (Loose et al, 2003) and our earlier study combining mental rotation with listening comprehension also found a decrease in activation in primary visual areas for the dual-task condition relative to performing the mental rotation task alone (Just et al, 2001). The effect of a concurrent auditory task on primary visual areas may depend on the automaticity of the visual task, with there being less impact on a more automatic task, such as driving, and more impact on a strategically controlled task, such as mental rotation.…”

“…The new findings clearly establish the striking result that the addition of a sentence listening task decreases the brain activation associated with performing a driving task, despite the fact that the two tasks draw on largely non-overlapping cortical areas (Just et al, 2001;Newman et al, 2007). Activation decreased when the listening comprehension task was added to the driving task in bilateral parietal and superior extrastriate secondary visual areas.…”

“…In a study of mental rotation and sentence comprehension tasks that were performed in isolation or concurrently, the activation volume in these non-overlapping regions associated with each task was substantially less when the tasks were performed together than the sum of the activation volumes when the two tasks were performed separately (Just et al, 2001). In other words, each component task evoked much less cortical activity when it was performed concurrently with another task than when performed alone, even though the two tasks drew on different regions.…”

Brain imaging of the central executive component of working memory

“…The question of interference between apparently dissociable neural systems was directly explored by Just et al [62]. In their fMRI study, participants performed an auditory sentence comprehension task alone (judging general-knowledge sentences), a visual mental rotation task alone (judging similarity of rotated abstract 3-D figures), or both tasks simultaneously.…”