Fractionating the neural substrates of incidental recognition memory.

Familiar stimuli are typically accompanied by decreases in neural response relative to the presentation of novel items, but these studies often include explicit instructions to discriminate old and new items; this creates difficulties in partialling out the contribution of top-down intentional orientation to the items based on recognition goals. Here, we used an incidental recognition functional MRI paradigm to compare response to repetition of novel and familiar stimuli in the absence of any ongoing memory task demand. The inferior frontal gyrus and hippocampus both displayed enhanced response to novelty and suppressed response to familiar stimuli, notably, under conditions which did not encourage intentional orientation to recognize novel or old items. Functional connectivity analyses additionally suggested that familiarity processing is associated with a network incorporating the hippocampus and prefrontal cortex. We conclude that recognition memory substrates can be fractionated even in the absence of memory goals.