Investigation of sleep dynamics through multi-auditory stimuli

Objective: The aim of the present study is to investigate the brain responsiveness during different stages of sleep, which are scored according to classical sleep scoring and BIS systems, via auditory stimulations and ?Evoked Potentials?.Materials and Methods: In the study sleep recordings of 18 volunteer subjects were analyzed (18-32 year old, mean age: 24.4 ± 3.6; 5 females). During sleep recordings, auditory stimuli were applied into the ear channel (etymotic). Sleep stages were scored according to conventional sleep scoring systems and BIS system and in each of these stages Auditory Evoked Potentials (AEP) were analyzed. The alterations of N100, P200, N300, P450, N550 and P900 waveforms were investigated in different sleep stages.Results: A very high correlation factor was obtained between BIS system and classical NREM sleep stages. Sleep recordings were scored into more levels according to BIS system than conventional scoring systems. Deepening of sleep were followed by the decrease of N100 component amplitude, whereas N300 and P900 components? were found to be increased. Also, it has been found that, there was a very high correlation between AEPs which were scored according to classical methods and BIS system. Furthermore, it has been shown that, there was prominent differences in the first and second halves of sleep AEPs. In the second half of the sleep, N100 amplitude was higher in the light sleep and the amplitudes of P200 and P900 were higher in deep sleep stages.Conclusion: The present research is the first in studying BIS and AEPs together in sleep. The results showed that, BIS system may serve as a fruitful method in studying sleep dynamics. Furthermore, with the usage of BIS system, sleep could be analyzed in more stages which will in turn be useful studying the underlying processes of AEPs. In the present study, it was not the intention to claim that BIS system can replace classical staging methods, rather it is recommended as an accompanying method to sleep staging.Understanding the processes underlying the sleep AEPs needs further comprehensive researches. Future studies with dynamic AEPs and BIS system might also be beneficial in clarifying the pathological processes underlying sleep disorders.Key words: Sleep, Electrophysiology, Auditory Evoked Potentials, N100, P200, N300, P450, N550, P900