Comparison of neural responses between exogenous and endogenous rule shifting in cued switching task; an ERPs study

Comparison of Neural Responses between Exogenous and Endogenous Rule Shifting in Cued Switching Task; an ERPs study Maki Miyajima (miyajima.med@gmail.com) Atsuhito Toyomaki Ichiro Kusumi Tsukasa Koyama Department of Psychiatry, Hokkaido University Graduate School of Medicine North15, West 7, Kita-ku, Sapporo, Japan Abstract Task switching is a well-known cognitive paradigm to explore task-set reconﬁguration processes such as rule shifting. In particular, endogenous task switching is thought to differ qualitatively from stimulus-triggered exogenous task switching. However, no previous study has examined the neural substrate of endogenous task switching. The purpose of the present study is to explore the differences between event- related potential responses to exogenous and endogenous rule switching at cue stimulus. We modified two patterns of cued switching tasks: exogenous (bottom-up) rule switching and endogenous (top-down) rule switching. In each task cue stimulus was configured in order to induce switching or maintaining rule. In Exogenous switching tasks, late positive deflection was larger in the switch rule condition than in the maintain rule condition. However, in endogenous switching tasks late positive deflection was unexpectedly lager in the maintain rule condition than in the switch rule condition. These results indicate that exogenous rule switching is explicit stimulus-driven processes whereas endogenous rule switching is implicitly parallel processes independent of external stimulus. Keywords: Switching task; Event related potentials; rule shifting Introduction Executive function is thought to be one of most important cognitive functions, and it is conceptualized as having four components: volition, planning, purposive action, and effective performance (Lezak, 1995). There are several neuropsychological tests that assess executive function, such as the Wisconsin Card Sorting Test (WCST), the Trail Making Test, and the Tower of London task. In WCST, the subject suppresses a no-longer-relevant task-set and replaces it with an appropriate new task-set; this process is called set shifting (Anderson, Damasio, Jones, & Tranel, 1991; Gold, Carpenter, Randolph, Goldberg, & Weinberger, 1997; Goldberg & Weinberger, 1994; Milner, 1963). The task switching paradigm is a well-known and sophisticated paradigm that engages these cognitive processes and requires predictable or random alternation between two response selection tasks (Jersild, 1927; Rogers & Monsell, 1995). For example, participants have previously been instructed to switch between a letter classification task (Task A) and a digit classification task (Task B) in a predictable sequence (e.g., AABB) or in a random sequence. Many studies using the task switching paradigm have observed that reaction time (RT) was reliably greater in switching trials than in maintain trials (no-switching trials) (Rogers & Monsell, 1995). Switch cost is estimated by subtracting the RTs in trials requiring no switch from those in trials requiring a switch; switch cost is thought to be an index of the extra difficulty associated with reconfiguring the active task-set. Previous Event-related potential (ERP) and fMRI studies have identified the neural substrates of task switching processes. Some previous studies have implicated the lateral prefrontal cortex and the parietal cortex as being centrally involved in preparatory processing during task switching (Johnston, Levin, Koval, & Everling, 2007; Kamigaki, Fukushima, & Miyashita, 2009; Rowe J, 2008; Ruge, 2007). Savine and Braver (Adam C. Savine, 2010) reported that using incentives to modulate cognitive control specifically enhanced task-cue-related activation of the left dorsolateral prefrontal cortex. In an ERP study, Karayanidis et al. (Karayanidis, Coltheart, Michie, & Murphy, 2003) indicated that switch-related positivity and switch-related negativity were elicited by a target stimulus in switching trials. These ERP data reflected that switch-related positivity was unaffected by irrelevant task-cueing, whereas the amplitude and latency of switch-related negativity were modulated by the response-stimulus interval. Many studies have used task switching, in which stimulus- triggered, bottom-up processes to shift between rules operate via external stimuli such as contextual stimuli, but few studies have focused directly on endogenous, voluntary rule shifting. Rogers and Monsell (Rogers & Monsell, 1995) used an endogenous task switching paradigm that required task-set alternation between trials; this paradigm places high demands on working memory. Participants were told to switch between “Task A” and “Task B” in a predictable sequence (AABB). Target stimuli were presented in one of four boxes continuously displayed on a computer screen, and stimulus position was rotated in a clockwise direction. Thus, on a given trial, the active task was cued by the position of the displayed stimulus. This paradigm seems to require a certain form of endogenous rule switching, because participants change tasks in a predictable sequence.