Functional interplay between stimulus-oriented and stimulus-independent attending during a prospective memory task

Recent studies have suggested that medial (medBA10) and lateral (latBA10) portions of the Brodmann area 10 subserve respectively stimulus-oriented (SO) and stimulus-independent (SI) attending during prospective memory (PM) tasks. We investigated this dissociation by manipulating the saliency (SO) and the memory load (SI) of PM cues. Sixteen healthy subjects participated to a functional imaging protocol with a 2×2×2 experimental design, including the factors: task (ongoing target vs. PM cue), Saliency (high vs. low; with targets/cues either embedded or standing out from distracters), and memory load (high vs. low; with 1 or 4 possible PM targets). We localized the medBA10 and latBA10 by means of a localizer task. In medBA10 we found a significant main effects of high Saliency and low memory load; whereas in the left latBA10, we found a significant task×load interaction, with maximal activation for PM cues presented in the high load condition. These results are in agreement with the gateway hypothesis: during a PM task medBA10 biases attention toward external salient stimuli, SO attending, while latBA10 biases attention toward internal mnemonic representations, SI attending. Additional whole-brain analyses highlighted activation of other areas besides BA10, consistent with recent proposals that emphasise the role of distributed networks during PM performance.