If a magician gave you a list of words to memorize, and was then able to predict precisely which words you would be able to recall, you would no doubt be impressed. Reporting in the Journal of Neuroscience, Sederberg and colleagues show that this feat can be achieved without resorting to magic or 'mind-control' tricks. Using intracranial recordings from the cortex, they identified specific patterns of rhythmic neuronal activity that correlated with successful memory formation.

Sederberg et al. used a group of 10 patients, aged from 8–17, each of whom had up to 128 electrodes implanted into their brains to monitor epilepsy. The patients were asked to memorize a list of 20 common nouns while the authors recorded their cortical and subcortical brain activity. The patients were then asked to recall as many words as possible, after being distracted briefly with an arithmetical task to reduce bias towards the most recently presented words.

The authors observed increases in both low-frequency theta oscillations (4–8 Hz) and high-frequency gamma oscillations (28–64 Hz) during the presentation of words that were subsequently recalled successfully. The theta oscillations were detected largely in the right temporal and frontal cortex, whereas the gamma oscillations were more widespread.

What is the importance of gamma and theta power for memory formation? Both types of activity have been implicated in processes that are crucial to memory encoding — gamma oscillations in attention, and theta oscillations in long-term potentiation. Approaches such as that of Sederberg et al. should help us to understand how different cortical regions are recruited to these processes as new memories are laid down, and to clarify the precise role of this rhythmic activity in memory formation.