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Stephen J. Heinen, Jess Rowland, Anca Velisar, Alex R. Wade; Cortical evaluation of a rule-based trajectory revealed by fMRI. Journal of Vision 2005;5(8):845. doi: 10.1167/5.8.845.
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Kim and Heinen (2001) introduced a novel paradigm for investigating rule-based eye movements in awake, behaving monkeys. The rule in their “baseball” task was to follow a target with eye movements if it crossed a visible “strike zone”, and withhold eye movements if it did not. Neurons were recorded in the supplementary eye fields (SEF) that signaled early whether the target would cross the strike zone or not. Here, using fMRI, we show neural correlates of trajectory evaluation in humans. Three observers signaled with a key press whether or not a target's trajectory would cross a strike zone. Subjects were scanned on a 3T GE Signa system with 23 functional slices covering the entire head at a resolution of 3×3×5mm and a TR of 3s. Spiral k-space acquisition was used to reduce susceptibility artifacts in anterior cortical regions. Regions whose activity covaried with the psychophysically-determined difficulty of the baseball task were identified based on a signal coherence analysis. Three areas showed significant, consistent activity during the task. One, the inferior parietal sulcus (IPS), is a region implicated in spatial processing and attention, and in integrating motion signals. Two frontal areas were also active: right dorsolateral prefrontal cortex (DLPFC), and bilateral inferior frontal gyrus close to or within ventrolateral prefrontal cortex (VLPFC). Right hemisphere DLPFC has been previously implicated in spatial working memory and rule evaluation. The VLPFC has been suggested to play a role in short-term storage of visual images. Our results suggest that these areas are involved in interpreting the trajectory of a moving stimulus, and using this information to guide behavior in the context of a rule. These regions may in turn send this information to the SEF if eye movements are required. This study represents a first step in humans of elucidating the network involved in interpreting the trajectory of a moving target within the context of a rule.
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