The Effect Of TENS On Sleep-dependent Memory Consolidation

Human sleep is primarily involved in memory consolidation. Sleep spindle, a characteristic wave of non-rapid eye movement sleep(NREM), is associated with memory process. Spindle, slow oscillation and hippocampal sharp waves work together to mediate the short-term hippocampal memory to long-term storage sites where they become integrated into preexisting long-term neocortical memories. Studies show that different interventions can change sleep architecture and various parameters of sleep spindles, thus indirectly affect memory consolidation during sleep. Transcutaneous electrical nerve stimulation(TENS) is a non-invasive means of treating pain. Because of its inexpensive and painless advantage, TENS is widely used to treat cancer pain, joint pain, migraines, etc. Shenmen is a sedative acupuncture point and regulate Chinese qi of the heart. It can help people fall asleep. Whether TENS stimulation in Shenmen can affect sleep architecture and improve sleep efficiency, thus contributing to memory consolidation or not is unknown. There is no related research findings so far.Visual detection of sleep spindle is the golden standard all along. However, due to the large amount of sleep data, this method is very time-consuming. A variety of time-frequency methods are used to detect spindles. Because of the non-stationary property and big inter-individual differences of spindles, matching pursuit(MP) is an ideal method for automatic detection. Yet, whether the efficiency and accuracy of this algorithm are good or not compared with visual detection, there is little relevant research.To this end, we applied Electroencephalography(EEG) to record human sleep data and used both visual detection and MP to detect spindles. Visual evaluation of these data was done by two experienced electroencephalographer, which resulted in a maximum of14% false positive classification per subject and a maximum of 7% false negative classification per subject. Thus, 88% of all epochs were classified correctly. In the study of TENS intervention on sleep-dependent memory consolidation, We used MP to detect sleep spindle and chose paired words(declarative memory) memory task to study if there are differences of the healthy male’s memory consolidation in TENS and control night sleep. We compared sleep structure and spindle parameters in different nights.After preliminary screening, a total of 18 subjects completed the experiment. Results showed that the percentage of the first stage of non-rapid eye movement sleep(N1) inTENS night was significantly lower than the control night, and the percentage of rapid eye movement(REM) sleep was higher than the control night, but didn’t reach significance level. Furthermore, sleep efficiency was also no significant difference in two nights. However, spindle number was significantly lower in TENS night than the control night and spindle wave power spectral density was higher than control night. In the behavioral task, memory performance had marked difference before and after sleep in both nights, After sleep, the score of paired words was dramatically increased than that before sleep. This indicated that sleep indeed facilitate memory consolidation. To our surprise, the extent of the consolidation had no remarkable difference in different nights. It demonstrated that spindle number was positively related to memory performance both in TENS and sham nights. The degree of the correlation between them in sham night was higher than that in TENS night. Also, spindle density was positively correlated with memory performance only in sham night. Besides, spindle power spectral density and activity were associated with memory performance in TENS night while this correlation in sham night didn’t achieve significance level.Our conclusions showed that MP was an effective method for detecting spindles, thus saved human resources. The impact of TENS on memory consolidation was small. N1 decreased in TENS night, indicating TENS help subjects easier to fall asleep. In addition, sleep efficiency didn’t differ significantly in both nights. The reduction of spindle number in TENS night may related to the learning task before sleep. Consistent with previous findings, we found the correlation between spindle parameters and memory consolidation. However, we need to do more to improve the accuracy and detection speed of MP. We made a preliminary exploration of TENS intervention on sleep research. Although we tried hard to control unrelated experimental variables, due to limitations of the experimental conditions, interviewer human factors, sleep environment, the disturbance of EEG cap on subjects normal sleep and lack of enough amount of subjects, we couldn’t do more finer TENS research. Yet, with the continuous improvement of the technological means, there may be more advanced TENS research on sleep and may do more scientific explanation for the mechanisms of TENS intervention on human sleep in the future.