An influential study addressing the effects of PD and frontal lesions on task switching conducted by Rogers et al. (1998) was based on a paradigm originally devised for healthy volunteers, where subjects were presented with two targets, a letter, and a number, only one of which was the task-relevant stimulus on any given trial, depending on the task at hand. The task alternated between judging the letter as a vowel
or consonant, and judging the number as odd or even (Rogers & Monsell, 1995) and vice versa. This original switching paradigm employed abstract rules that map several stimuli to a categorical response (e.g., 2, 4, 6, 8 map to ‘even’) and engendered a reconfiguration RAD001 cell line which impacted on both stimulus as well as response set as subjects switched between categorization rules: a grammatical rule applied to letters and a parity rule applied to numbers. This paradigm was tailored
for use with the clinical population by simplifying the tasks to letter and number naming, selleck chemicals which, however, employed a concrete, naming rule assigning unique vocal responses to stimuli mapped directly to stimulus identity (2 maps to ‘two’). Thus, a task switch in the adapted paradigm only required a reconfiguration in stimulus sets, as patients switched attention between numbers and letters, and simply vocalized their target: the rule that determined the response to the stimulus remained the same across switch trials from one task to the next. Switching between such rules was since employed in many studies demonstrating a form of the parkinsonian deficit which is present under conditions of interference from task-irrelevant targets (distracters, referred to as cross-talk) in the display which encumber attentional selection (Cools, Barker, Sahakian, & Robbins, 2001a,b, 2003; Rebamipide Pollux, 2004; Witt et al., 2006). This type of switching
has been argued to load on dorsal frontostriatal loops which are dopamine (DA) depleted in PD, since the deficit can be ameliorated by dopaminergic medication (Cools et al., 2001a; Cools et al., 2003). A complementary interpretation suggested here is that this type of switch, particularly when it pertains to selecting the appropriate stimulus in a display, may also involve the inferior temporal cortex, given its central role in object-based attention (Desimone & Duncan, 1995) and its projections to the dorsal (associative) striatum. In contrast, when task switching paradigms engender reconfiguration in both stimulus and response sets as a result of a switch between abstract categorization rules, along the lines discussed previously, PD patients do not demonstrate robust switching impairments (Fales, Vanek, & Knowlton, 2006; Kehagia, Cools, Barker, & Robbins, 2009; Woodward, Bub, & Hunter, 2002).