Closed-loop auditory stimulation time-locked to the down-phase of sleep slow waves provides a tool to locally interfere with brain activity during deep sleep

Fattinger, S and Volk, C and de Beukelaar, T and Ruddy, K and Herbst, J and Hahnloser, R and Wenderoth, N and Huber, R
Slow waves (SW) during deep NREM sleep consist of an active on (up-phase of SW) and a quiet off-state (down-phase of SW) and are locally regulated. The silent off-state has been suggested to be vulnerable to incoming stimulation, resulting in a cessation of the off-state. Thus, the off-states might represent a time window to locally interfere with the ongoing slow oscillation during deep sleep. During counterbalanced nights, high-density sleep EEG was recorded in subjects. During one night, automatic closed-loop auditory stimulation was performed. SWs of one specic electrode were detected in real-time and tones (~ 50 dB) were played, time-locked to the down-phase of SWs. During the second night no tones were applied and a similar SW detection was performed ofine. Acoustic stimulation reduced slow wave activity by 9.2 3.2% (P = 0.001) in a local cluster of 8 electrodes close to the stimulation electrode. Moreover, stimulation induced immediate effects by steepening the slope of the up-phase (P = 0.01) and shortening the duration of the manipulated SW (P = 0.01). These ndings might indicate a faster recruitment of cortical neurons from the susceptible silent down-phase into the next up-phase due to incoming auditory stimulation. Furthermore, the stimulation also caused after-effects in the subsequent SWs. The average down-slope of SW was less steep (P = 0.04) and the probability for high-amplitude SW was smaller in the STIM than the NOSTIM night (P < 0.001). Thus, acoustic stimulation seems to reduce the level of synchronization within local cortical networks necessary for the generation of large amplitude SWs. 
Disclosure: Nothing to disclose.