Different Levels of Activity in the Left Intraparietal Sulcus Triggered by Lasting and Unlasting Cues in the Posner Task

In experimental paradigms, voluntary orienting of visual-spatial attention is conventionally achieved through the Posner task in which predictive central cues remain present until target offset (lasting cue) or disappear prior to target onset (unlasting cue). Previous studies have implied that lasting and unlasting cues elicit different levels of activity in the intraparietal sulcus (IPS). However, no study to date has directly compared the neural correlates of visual-spatial attention under unlasting versus lasting cue conditions. We investigated the neural mechanisms involved in the processing of both types of cues using functional magnetic resonance imaging (fMRI). Behaviorally, subjects exhibited no difference in the two cue type conditions. However, neuroimaging data revealed increased activation of the left IPS in the unlasting cue condition. We propose that in the unlasting cue condition, the time interval between the onsets of cue and target requires subjects to maintain a location in spatial working memory. This hypothesis suggests that the difference in activity in the left IPS between lasing and unlasting cue conditions is the neural correlate of spatial working memory.