Delivering a non-invasive brain stimulation when a person is sleeping can improve their memory, a study has found.
The transfer of memories from the hippocampus to the neocortex for long-term storage is thought to be enabled by synchronisation of these parts of the brain during sleep.
Researchers from the University of New Mexico in the US sought to enhance this natural process of overnight reactivation or neural replay to improve memory with a closed-loop transcranial alternating current stimulation system matching the phase and frequency of ongoing slow-wave oscillations during sleep.
Participants were trained and tested on a realistic visual discrimination task in which they had to detect potentially threatening hidden objects and people such as explosive devices and enemy snipers.
The researchers found that when participants received stimulation during overnight visits to their sleep laboratory, they showed improved performance in detecting targets in similar but novel situations the next day compared to when they did not receive the stimulation, suggesting an integration of recent experience into a more robust and general memory.
Overnight memory changes correlated with stimulation-induced neural changes, which could be used to optimise stimulation in future applications.
The findings provide a method for enhancing memory consolidation without disturbing sleep.