Brain Rhythms: Enhancing Memories

A new study shows that different processes are responsible for maintaining relevant and suppressing irrelevant information. By promoting the suppression of irrelevant information, memories may be enhanced. Everyday we are bombarded with information from the media, colleagues, spouses and friends. Some of this information is relevant and important, but other information is irrelevant and should have no influence on our behaviour. When listening to the weather forecast, only the weather predicted for our region is relevant to our behaviour. Adapting our behaviour to the predicted conditions — for example, driving rather than walking into work when severe rain is forecast — may depend upon us encoding the forecast in our region and ignoring the weather conditions in other regions. Distinct neural processes, as reported by Sauseng et al. [1] in this issue of Current Biology, are responsible for encoding relevant, whilst suppressing irrelevant, information. The successful retention of relevant information depends upon the synchronization of specific brain rhythms — a coupling between theta and gamma rhythms — whereas the suppression of irrelevant information depends upon a single, distinct rhythm, the alpha rhythm. The evidence for this double dissociation comes not just from correlations: a functional link has been established between these brain rhythms and memory processing. In their work, Sauseng et al. [1] found that promoting the alpha rhythm increased suppression of irrelevant information and so enhanced memory performance. Thus, a simple model of memory formation in which relevant information is maintained and irrelevant information is suppressed has been shown through correlative and causative work to have a biological basis. In the new study [1], participants were asked to learn an array of coloured squares appearing on one half of the screen, while suppressing the irrelevant coloured squares, appearing on the other half of the screen. Later, following a retention interval, participants viewed a set of 'probe' stimuli and were asked to decide whether those stimuli matched the relevant stimuli. The use of this probe tested whether learning of the relevant coloured stimuli had occurred. During the retention interval, the brain rhythms associated with learning the relevant and suppressing the irrelevant stimuli were identified by recording electrical brain activity (with an electroencephalogram). The retention of relevant information was related to the synchronization between theta and gamma oscillations. Prior work has implicated theta oscillations and their interaction with gamma oscillations in the neuroplastic processes that underlie memory formation [2,3]. Promoting theta …