A Study Of Transcranial Direct Current Stimulation Intervention On Sleep-dependent Memory Consolidation

Sleep is one of the most important activities in human life. Exploring the mechanisms of sleep is beneficial for human life. Sleep is restorative, and it plays an important role in high-order cognition. Memory initializes in the activities during the day, but the consolidation of memory happens in sleep. Previous studies have suggested that the Non-rapid eye movement(NREM) sleep is associated with the consolidation of memory, and different types of memory is consolidated by different waveforms in sleep Electroencephalograph(EEG). The declarative memory has been shown to be associated with Slow wave sleep(SWS) sleep. The reason that sleep can help the consolidation of memory is the existence of slow oscillations activity, which is a decisive factor in the memory consolidation of sleep.Transcranial direct current stimulation(TDCS) is a new technology which can alter the excitability of the neuron. For its non-invasive and safety, it is used in the research of cognitive function. Slow oscillations activities in sleep can consolidate the memory which is initialized in the daytime, therefore, transcranial slow oscillations current stimulation may promote sleep-dependent memory consolidation. The time and stimulus parameter of slow oscillations current stimulation must be determined properly for that sleep is easily disturbed. Both Satage2 of non-rapid eye movement(N2) and SWS sleep have slow oscillations activity.in this research, the 0.75 Hz slow oscillations stimulation is applied in the N2 sleep. It turns out that less subjects wake when stimulation is applied in the N2 sleep. It is suggested that the intervention of sleep by slow oscillations stimulation is feasible.In the present research, we designed a declarative memory task, after the task was fulfilled, subjects were instructed to sleep with EEG data collected simultaneously. The slow oscillations current stimulation was implemented in the N2 sleep, which is expected to promote sleep-dependent memory consolidation. Our results indicated that the improvement of memory after slow oscillations current stimulation is greater than the sham stimulation. This suggests that slow oscillations current stimulation promotes sleep-dependent memory consolidation. With respect to EEG power,we found that the sleep power after slow oscillation stimulation was significantly enhanced.These results suggested that the slow oscillation can improve sleep memory consolidation effect asmore slow oscillation occur in the sleep. Howver, not all the slow oscillation stimulation during sleep were successful, and the aborted stimulation reduced memory consolidation. Correlation analysis inidated that the deeper the sleep after stimulus, the better memory consolidation. We suggested that the role of transcranial electrical stimulation affecting sleep is two-way, successful intervention produced more slow oscillation activities and can improve memory consolidation of sleep, however, the unsuccessful intervention will not reduce memory consolidation as it destroyed the original structure of sleep. Therefore, more reseach about the sleep mechanism are needed to determine the better time when slow oscillation stimulation intervention can be intervened.