Abstracts

RATIONALE:The mechanisms behind sleep activation of epileptic activity are unknown. We are studying the relationships between phasic neurophysiologic REM sleep features, including sawtooth waves (STWs), rapid eye movements (REMs), and muscle tone reduction (MTR). We previously reported quantitative, predictable relationships between MTR, STWs, and REMs at stage REM onset. This study utilizes an ultradian rhythm model to predict the cyclicity of STW activity throughout REM sleep. METHODS:Sawtooth wave activity was scored throughout 79 REM cycles in 20 PSGs of 11 normal adult subjects. STW density measurements were subjected to a mixed effects analysis to test the significance of periodicity and amplitude estimates. RESULTS:Mean STW density measurements were 0.97 bursts/min REM [95% CI: 0.85, 1.09] and 6.85 secs/min REM [5.95, 7.76]. There was a statistically significant difference (p<0.001) in STW density between cycles. The intra-subject variability over REM cycles was higher than the inter-subject variability, with an increase in STW density after the first cycle. The ultradian rhythm model allows us to obtain estimates for the periodicity and amplitude of the data. This model allows us to test the significance of these parameter estimates and partition the variability of STW activity into many segments. CONCLUSIONS:The increase in STW activity after the first REM cycle is analogous to the overnight lengthening of REM cycles, and has implications for the sources of REM sleep. The ultradian rhythm model allows us to examine more precise measures across time for each subject, and determine the periodicity of STWs. We can next compare these models with ones generated from a population with epilepsy.