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From Negative to Positive : Harnessing the Ventral Parietal Attention System to Promote Rather than Detract from Episodic Encoding

Efforts to characterize the neural mechanisms of episodic encoding have primarily focused on the medial temporal lobe (MTL) and prefrontal cortex (PFC), however neuroimaging studies often reveal effects in posterior parietal cortex (PPC) alongside those in MTL and PFC. Indeed, a recent meta-analysis (Uncapher & Wagner, in prep) demonstrated that PPC is consistently implicated in successful encoding, such that the extent to which PPC mechanisms are engaged during an experience is predictive of subsequent memory for the experience. Dual-attention theories of lateral PPC function posit that dorsal (superior parietal lobule and intraparietal sulcus) and ventral (inferior parietal lobule and temporo-parietal junction) PPC subregions support ‘top-down’, goal-directed attentional allocation and ‘bottom-up’ capture of attention by unexpected or salient stimuli, respectively. When viewed through the lens of attention, the dorsal PPC correlates of encoding can be interpreted to signify that dorsal attention mechanisms facilitate episodic encoding. By contrast, ventral PPC activation has been shown to correlate negatively with subsequent memory. The present functional MRI study sought to determine whether ventral PPC mechanisms can facilitate rather than detract from encoding, specifically when event information is captured in a bottom-up manner. Participants were scanned while incidentally encoding stimuli in a variant of the Posner cueing paradigm. On each trial, participants were cued (leftward or rightward pointing arrow) to expect a stimulus in one of two spatial locations (left or right of central fixation). Stimuli—line drawings of real and nonsense objects––appeared in the cued location (‘valid’ trials) with .82 probability and in the non-cued location (‘invalid’ trials) with .18 probability. Participants judged whether the stimulus was a real or a nonsense object. Approximately 10 min post-scanning, recognition memory for the real objects was assessed. Behavioral results indicated that participants allocated goal-directed attention to the cued location, as revealed by longer reaction times during invalid vs. valid trials. Additionally, subsequent memory for both validlyand invalidly-cued objects was well above chance. The fMRI data revealed enhanced activity in dorsal PPC regions during the cue period (suggestive of top-down attentional allocation), and in ventral PPC regions for invalidlyvs. validly-cued objects (suggesting bottom-up attentional capture). Activation in ventral PPC correlated with the later mnemonic fate of the object, being greater during trials for which the object would be later recognized vs. forgotten. Critically, the magnitude of this subsequent memory effect was larger for objects that appeared in the unexpected vs. expected location. These findings indicate that, when recruited, bottom-up attention mechanisms subserved by ventral parietal cortex can enhance the capture of event information in episodic memory.