| The transformation of perceptual experience into episodic memory requires the participation of neural assemblies in the medial temporal lobes (MTL) and the prefrontal cortex (PFC), as well as neocortical zones sensitive to the material under study. Here, we test a new hypothesis concerning how these regions work together to form new memories, drawing upon recent research suggesting that 'top-down' selection (or 'cognitive control') is a domain-general function of the prefrontal cortex. We argue that perceptual experiences are selected for encoding by control mechanisms originating in the PFC, which arbitrate among perceptual codes competing for inclusion in a new episodic memory. In support of this view, we report that functional coupling between PFC and the posterior neocortex is a robust predictor of encoding success, and offer evidence that neuronal synchronisation in the theta (4-8Hz) and gamma (25-55Hz) bands may be a carrier signal for this long-range cooperativity (study 1). Further evidence for the contribution of PFC-based control processes to episodic memory formation is offered in study 2, where a novel encoding paradigm (in which the predictability of the encoding stimuli is manipulated) is used to tease apart the neural correlates of 'bottom-up' and 'top-down' mechanisms during encoding. In a third study, using fMRI, we return to the question of fronto-posterior connectivity, revealing that posterior cortical regions sensitive to the contents of the material under study ('face' and 'place' sensitive regions) exhibit coupling with left dorsolateral PFC, the extent of which predicts later encoding success. Together, these studies offer new evidence for a role for 'top-down' control mechanisms in episodic encoding, in line with an emerging view that cognitive control is an important function of the prefrontal cortex. |
