Attention to Retrieval: Prestimulus Alpha Power Signals Ready-to-Retrieve Mode

The human brain is in distinct processing modes at different times. Specifically, a distinction can be made between encoding and retrieval modes, which refer to the brain's state when it is storing new information or searching for old information, respectively. Recent research has proposed the idea of a "ready-to-encode" mode, which describes a prestimulus effect in brain activity that predicts subsequent memory performance. Whether there is also a corresponding "ready-to-retrieve" mode in human brain activity is currently unclear. Here we demonstrate that prestimulus alpha power decrease can be linked to such ready-to-retrieve mode. We found that cuing participants to prepare for retrieval in comparison to restudy led to a significant decrease of prestimulus alpha power before the onset of stimuli. Beamformer analysis localized this effect in the right secondary visual cortex (Brodmann area 18), which is located in parts of the lingual gyrus. Correlation analysis showed that the prestimulus alpha power effect is positively related to stimulus-related alpha/beta power, which in turn predicts participants’ memory performance. Complementing recent evidence for the ready-to-encode mode, the results provide evidence for the existence of a ready-to-retrieve mode in brain oscillatory activity. Specifically, prestimulus attention to retrieval is suggested to “ramp up” visual imagery and the processing of conceptual features, which promotes the reconstruction and long-term consolidation of episodic memories. Future research on brain-computer interfaces may find these results interesting regarding the potential of using online measures of spontaneous fluctuating alpha oscillations to trigger the presentation and sequencing of restudy and retrieval trials.