Attentional selection for short-term memory: Gaze-direction predicts retrieval activity in fronto-parietal cortex

In everyday life short-term memory involves processing of complex and unrepeated environments, which is in striking contrast with standard experimental paradigms typically utilizing highly stereotyped, simple and repeated stimuli. Remembering of complex visual stimuli demands a tight interplay between memory functions and attentional selection. Here, we examined this interplay during free-viewing of complex and dynamic visual scenes (8 videos, approx. 5 min each). Each video was characterized by 8 different actors/actresses who entered twice into the scene, at unpredictable times: the first appearance corresponded to the memory “encoding” phase, while the second presentation represented the memory “retrieval” phase. Participants were asked to watch the videos without any specific task-requirement. During fMRI scanning, we monitored gaze-direction and we used the tendency of the subjects to look towards each actor/actress as an index of attentional selection. Accordingly, we categorised each actors/actresses as: “high probability of selection/encoding”, when subjects fixated the actor more during the first than the second presentation; versus “low probability of selection/encoding”, when subjects fixated the actor more during the second than the first presentation. The fMRI analyses considered the second presentation of the actors/actresses (i.e. the memory retrieval phase) and compared activity for actors with “high versus low” indexes of selection. This revealed activation of fronto-parietal regions, including the inferior frontal gyrus and the intra-parietal sulcus, plus the middle temporal complex (MT+). We conclude that differential patterns of eye-movements can predict retrieval-related activation in fronto-parietal regions during passive viewing of complex and dynamic visual environments.