Abstract
Learning novel skills involves reorganization and optimization of cognitive processing involving a broad network of brain regions. Previous work has shown asymmetric costs of switching to a well-trained task vs. a poorly-trained task, but the neural basis of these differential switch costs is unclear. The current study examined the neural signature of task switching in the context of acquisition of new skill. Human participants alternated randomly between a novel visual task (mirror-reversed word reading) and a highly practiced one (plain word reading), allowing the isolation of task switching and skill set maintenance. Two scan sessions were separated by 2 weeks, with behavioral training on the mirror reading task in between the two sessions. Broad cortical regions, including bilateral prefrontal, parietal, and extrastriate cortices, showed decreased activity associated with learning of the mirror reading skill. In contrast, learning to switch to the novel skill was associated with decreased activity in a focal subcortical region in the dorsal striatum. Switching to the highly practiced task was associated with a non-overlapping set of regions, suggesting substantial differences in the neural substrates of switching as a function of task skill. Searchlight multivariate pattern analysis also revealed that learning was associated with decreased pattern information for mirror vs. plain reading tasks in fronto-parietal regions. Inferior frontal junction and posterior parietal cortex showed a joint effect of univariate activation and pattern information. These results suggest distinct learning mechanisms task performance and executive control as a function of learning.
Highlights
One of the hallmarks of skill acquisition is that a task that initially requires substantial executive resources can come to be performed in a manner that seems effortless (James, 1890)
Switching from mirrorreading to plain reading showed increased activations in inferior frontal junctions and posterior and superior parietal cortices (Figure 3C and Table 1), regions commonly reported in previous literature of task switching (e.g., Dove et al, 2000; Kimberg et al, 2000; MacDonald et al, 2000; Braver et al, 2003; Koechlin et al, 2003; Sakai and Passingham, 2003, 2006; Brass and von Cramon, 2004; Crone et al, 2006; Jimura and Braver, 2009; Kim et al, 2011, 2012)
There was a widespread decrease in both activation and pattern information from pre-training to post-training for mirror-reversed compared to plain text items; no significant increases were observed
Summary
One of the hallmarks of skill acquisition is that a task that initially requires substantial executive resources can come to be performed in a manner that seems effortless (James, 1890). Any skill consists of a series of cognitive processes governed via executive control systems (Smith and Jonides, 1999; Miller and Cohen, 2001), which are decreasingly necessary as expertise is acquired (Milham et al, 2003; Kelley et al, 2006) It is unclear how executive control interacts with the acquisition of a novel skill. Flexibility of behavior is a fundamental function of frontostriatal pathways (Milner, 1963; Jones and Mishkin, 1972; Frank and Claus, 2006; Stelzel et al, 2010) This function has been examined in task-switching paradigms where different tasks are alternated (Jersild, 1927; Allport et al, 1994; Rogers and Monsell, 1995), in which response times are generally slower when switching tasks as opposed to repeatedly performing the same task The degree to which these asymmetric switch costs are associated with different neural mechanisms is currently unknown
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