Academic journal article Cognitive, Affective and Behavioral Neuroscience

Brain Regions Activated by Endogenous Preparatory Set Shifting as Revealed by fMRI

Academic journal article Cognitive, Affective and Behavioral Neuroscience

Brain Regions Activated by Endogenous Preparatory Set Shifting as Revealed by fMRI

Article excerpt

An ongoing controversy concerns whether executive control mechanisms can actively reconfigure the cognitive system in preparation for switching to a new task set. To address this question, we recorded brain activity from 14 healthy participants, using event-related functional magnetic resonance imaging, while they performed a cued attention task. Critically, in any particular trial, the cued task set was either the same as that in the previous trial or switched. As was hypothesized, cue-related, switch-specific preparatory activity was observed in a network of dorsal frontal and parietal brain areas that are typically associated with cognitive control processes. Moreover, the magnitude of switch-specific preparatory activity varied with the number of possible task sets that could be presented in a given trial block. These findings provide compelling support for the existence of top-down, preparatory control processes that enable set switching. Furthermore, they demonstrate that global task structure is a critical determinant of whether switch-specific preparatory activity is observed.

Models of cognitive control posit that the ability to flexibly adjust behavior in response to changing environmental conditions is fundamental to the achievement of behavioral goals (Baddeley, 1986; Norman & Shallice, 1986). This requires changes in task set, the organization of mental resources necessary to accomplish a specific task (e.g., Monsell, 2003). A long-standing controversy involves the question of whether the cognitive system can be actively reconfigured in preparation for performing a new task (Altmann, 2003; Monsell, 2003). In line with this view, several behavioral studies have demonstrated that increasing the time between an instructional task cue and a subsequent target stimulus minimizes performance decrements (i.e., switch costs) for trials requiring a switch in task set (switch trials), in comparison with trials in which no switch in task set is required (repeat trials; Meiran, 1996; Rogers & Monsell, 1995). However, recent behavioral studies have suggested that the effects of preparation on switch costs are due largely to the additional time needed to encode a new instructional cue, regardless of whether a switch in task set occurs (Altmann, 2004; Logan & Bundesen, 2003). Thus, it is still unclear whether control processes can actively prepare the system in advance to switch to performing a new task.

To resolve this issue, we used event-related functional magnetic resonance imaging (fMRI) to directly measure cue-triggered, switch-specific preparatory processes whose existence in behavioral paradigms is typically inferred only by the indirect measure of performance on target stimuli. Although set switching has been associated with greater activity in a network of frontal and parietal regions thought to implement cognitive control processes, prior fMRI studies have not resolved the issue of whether it is possible to prepare in advance for a set switch (Braver, Reynolds, & Donaldson, 2003; Dreher, Koechlin, AH, & Grafman, 2002; Forstmann, Brass, Koch, & von Cramon, 2005; Kimberg, Aguirre, & D'Esposito, 2000; Rushworth, Paus, & Sipila, 2001; Shulman, d'Avossa, Tansy, & Corbetta, 2002; Smith, Taylor, Brammer, & Rubia, 2004; Sohn, Ursu, Anderson, Stenger, & Carter, 2000; Yantis et al., 2002). For example, in several studies, switch and repeat trials were presented in separate blocks, thereby confounding any possible preparatory switch-related activity with nonspecific effects, such as task difficulty, arousal, or strategy (e.g., Shulman et al., 2002; Sohn et al., 2000). In other studies, in which switch and repeat trials occurred randomly within the same blocks, the designs did not allow for the isolation of cue-related, switch-specific activity (e.g., Brass & von Cramon, 2004; Forstmann et al., 2005; Rushworth et al., 2001; Smith et al., 2004; Yantis et al., 2002). For example, in the study by Brass and von Cramon (2004), a double-cue design was used in which the second cue could indicate a task that was the same as or different from that indicated by the first cue, and two cues were assigned per task. …

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