Alpha/beta oscillations track orienting attention towards long-term memory representations

Many studies have investigated the orienting of internal attention towards information maintained in short-term memory (STM). However, how internal attention can be oriented towards information stored in long-term memory (LTM) remains unclear. Here, we investigated whether orienting attention to selective contents of LTM representations modulated oscillatory activity in the alpha (8-14 Hz) and beta bands (15-30 Hz) in an analogous fashion to internal attention orienting in STM. Twenty-nine participants learned a series of spatial-contextual associations between images of scenes and everyday objects over two days. On the third day, we recorded EEG from the participants while they performed delayed-response tasks with LTM or STM information. Spatial retro-cues after the initial scene array indicated the location of the object that would be probed at the end of the trial, or neutral retro-cues provided no spatial information. At the end of the trial, a probe object appeared, and participants decided whether it was associated with that scene. In the LTM task, participants viewed empty scenes they had previously studied and oriented their attention to previously associated objects. In the STM task, participants encoded new scenes containing two new objects and oriented their attention to scene objects maintained in STM. Our behavioural data showed a significant cueing benefit for valid cues over neutral cues for both tasks. When comparing the alpha and beta power between valid cues versus neutral cues, we found a similar pattern of alpha/beta power attenuation between STM and LTM tasks, with a stronger alpha power attenuation for the LTM task than the STM task. Finally, we showed a similar alpha-power lateralization for both tasks, with more decreased power contralateral than the power ipsilateral to the cued hemifield. Our results showed that alpha/beta oscillations track internal attention not only in STM but also when information is reactivated in LTM.