Sleep spindle incidence dynamics: a pilot study based on a Markovian analysis

Results are reported, based on 5 healthy subjects, concerning patterns in the dynamics of the sequential arrangement of spindles in human stage 2 sleep. Specifically, the conditional probability of incidence of successive spindle lengths and successive inter-spindle intervals is investigated. The results show that successive spindle lengths may be statistically independent. However, their distribution (histogram) may be similar for two different stage 2 periods, one in the first third and another in the second third of the night sleep record. In contrast to the finding about spindle lengths, results show that successive inter-spindle intervals may not be statistically independent. Furthermore, the overall dynamics of the sequential arrangement of inter-spindle intervals may be similar for the two sleep periods. These findings are discussed in the context of the "sleep maintenance" role of spindles.