Functional neuroanatomy of executive processes involved in dual-task performance

Abstract

The subjective experience of allocating one's attentional resources among competing tasks is nearly universal, and most current models of cognition include a mechanism that performs this allocation; examples include the central executive system and the supervisory attentional system. Yet, the exact form that an executive system might take and even its necessity for cognition are controversial. Dual-task paradigms have commonly been used to investigate executive function. The few neuroimaging studies of these paradigms have yielded contradictory findings. Using functional MRI, we imaged brain function during two dual-task paradigms, each with a common auditory component task (NOUN task) but varying with respect to a visual component task (SPACE or FACE tasks). In each of the two dual-task paradigms, the results showed that the activated areas varied with the component tasks, that all of the areas activated during dual task performance were also activated during the component tasks, and that surplus activation within activated areas during DUAL conditions was parsimoniously accounted for by the addition of the second task. These findings suggest that executive processes may be mediated by interactions between anatomically and functionally distinct systems engaged in performance of component tasks, as opposed to an area or areas dedicated to a generic executive system.

Figure 1

Behavioral tasks. Block-design paradigms were used, with blocks alternating between isolated (SINGLE) and concurrent (DUAL) performance of the component tasks. (A) Graphic representation of the experimental task runs. Task 1 is performed continuously whereas Task 2 is performed only in alternate blocks. Tasks 1 and 2 were counterbalanced for component task (auditory or visual) and for starting block (SINGLE or DUAL) for each paradigm. (B) Component tasks and sample stimuli for each paradigm. The NOUN task used new categories and word lists for each run of data acquisition.

Figure 2

Activation map overlays for composite data, showing anatomical relationship of dual-task activations (yellow outline masks) to component tasks (solid colors: red, NOUN; blue, SPACE; green, FACE). For clarity of display, maps are cluster-filtered at three contiguous voxels; however, the logical analysis used to identify activations attributable to CES function did not use a cluster filter. Changing thresholds changes size and scatter of activations but does not affect ratio of SINGLE/DUAL overlap of activations.

Figure 3

Activation map overlays for Subject 3. Color conventions are as in Fig. 2. (a) SPACE, NOUN, and SPACE + NOUN. (b) FACE, NOUN, and FACE + NOUN. Note absence of (MFG) activations across DUAL and SINGLE conditions in this subject. All activations above t = 1.96 (for two-run averages P < 0.00125 one-tailed, P < 0.0025 two-tailed, uncorrected for multiple comparisons) are represented for each task. Here too, maps for DUAL conditions are predictable from their SINGLE component task maps. Just as for individual data, changing map thresholds changes spread of activations but does not change the amount of overlap between DUAL and SINGLE conditions.