Long distance functional coupling associated with EEG state changes: The examination of phase and amplitude synchrony of neural assemblies across hemispheres during REM and non -REM sleep onset

Purpose. The innovation and importance of this study is that it assesses the functional relationship between hemispheric synchrony (phase and amplitude) and sleep onset. Our preliminary analysis of the pilot data demonstrates that there is an increase in inter-hemispheric phase synchrony and a decrease in amplitude synchrony during non-REM sleep onset (von Gizycki et al, 2007). The phase synchrony increase during sleep onset supports previous findings in hemispheric coherence research, however, the amplitude synchrony decreases does not. This can be explained by the fact that previous studies that examined hemispheric synchrony used such measures as cross correlation and coherence, and these widely used measures only provide a joint measure of amplitude and phase synchrony, therefore, the unique contribution of hemispheric amplitude at sleep onset could not be detected. We also will examine this effect during sleep onset REM periods in narcoleptic patients where we expect the results to be different than that of non-REM sleep onset. Additionally, prior to the analysis of this human data, I used data from an animal seizure synchrony model (von Gizycki et al, 2006) where hyper-synchrony (elicited epileptic events) is manipulated in order to test and validate phase and amplitude synchrony measures. Therefore, we will further develop and test our findings that demonstrate that sleep onset produced changes in synchrony of neural assemblies across hemispheres does not just happen in the phase realm but also in the amplitude realm.;Methods. Phase synchrony methods that were employed will be the following, phase synchrony index, synchrony entropy index, and our proprietary method instantaneous phase synchrony distribution. The amplitude synchrony measures were the amplitude synchrony index, and the entropy amplitude index.;Results and conclusions. Study 1, validated the synchrony methods with animal data because it was with synchrony methods it was possible to differentiate between two conditions baseline, and pre-seizure. Study 2, demonstrated that during the time course of sleep, there are linear changes and time locked changes in phase synchrony. In addition study 3, demonstrated that for narcoleptics there are synchrony changes that are only observable prior to a sleep onset REM nap during the waking state.