Migratory bats are sensitive to magnetic inclination changes during the compass calibration period.

The Earth's magnetic field is used as a navigational cue by many animals. For mammals, however, there are few data to show that navigation ability relies on sensing the natural magnetic field. In night-time migrating bats, experiments demonstrating a role for the solar azimuth at sunset in the calibration of the orientation system suggest that the magnetic field is a candidate for their compass. Here, we investigated how an altered magnetic field at sunset changes the nocturnal orientation of the bat Pipistrellus pygmaeus. We exposed bats to either the natural magnetic field, a horizontally shifted field (120°), or the same shifted field combined with a reversal of the natural value of inclination (70° to -70°). We later released the bats and found that the take-off orientation differed among all treatments. Bats that were exposed to the 120° shift were unimodally oriented northwards in contrast to controls which exhibited a bimodal north-south distribution. Surprisingly, the orientation of bats exposed to both a 120° shift and reverse inclination was indistinguishable from a uniform distribution. These results suggest that these migratory bats calibrate the magnetic field at sunset, and for the first time, they show that bats are sensitive to the angle of magnetic inclination.

Abnormally abrupt transitions from sleep-to-wake in Huntington's disease sheep (Ovis aries) are revealed by automated analysis of sleep/wake transition dynamics.

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 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.