Sleep/wake transitions in sheep

Sleep disturbance is a common and disruptive symptom of neurodegenerative
diseases such as Alzheimer’s and Huntington’s disease (HD). In HD
patients, sleep fragmentation appears at an early stage of disease,
although features of the earliest sleep abnormalities in presymptomatic HD
are not fully established. Here we used novel automated analysis of
quantitative electroencephalography to study transitions between wake and
non-rapid eye movement sleep in a sheep model of presymptomatic HD. We
found that while the number of transitions between sleep and wake were
similar in normal and HD sheep, the dynamics of transitions from
sleep-to-wake differed markedly between genotypes. Rather than the gradual
changes in EEG power that occurs during transitioning from sleep-to-wake
in normal sheep, transition into wake was abrupt in HD sheep. Furthermore,
transitions to wake in normal sheep were preceded by a significant
reduction in slow wave power, whereas in HD sheep this prior reduction in
slow wave power was far less pronounced. This suggests an impaired ability
to prepare for waking in HD sheep. The abruptness of awakenings may also
have the potential to disrupt sleep-dependent processes if they are
interrupted in an untimely and disjointed manner. We propose that not only
could these abnormal dynamics of sleep transitions be useful as an early
biomarker of HD, but also that our novel methodology would be useful for
studying transition dynamics in other sleep disorders.