Summary: Monitoring sleep spindles in sheep may one day translate to sleep based diagnosis of neurodegenerative diseases in humans.
People may count sheep when they cannot sleep, but when they do finally drift off their brains generate the same type of brain wave as their ovine counterparts, according to new research published in eNeuro. Monitoring how a sheep’s sleep changes during the progression of a brain disease may one day translate to sleep-based diagnosis in humans.
Sleep is essential for consolidating memories and maintaining brain health. During sleep, a specific brain wave occurs – the sleep spindle. They are associated with converting short-term memories into long-term memories. Spindles may also predict brain health.
Schneider et al. recorded the brain activity in sheep over one day and two nights using electroencephalography. The sheep generated sleep spindles falling within the frequency range typical of human sleep spindles. Like humans, each sheep maintained their own pattern of spindles that stayed consistent during both nights of sleep. During sleep, spindles occur all over the brain. However, a unique type of sleep spindle appeared in specific brain areas while the sheep were awake. These spindles may be connected to thinking and remembering during the day. Because they possess similar brain structure, sleep patterns, and even brain disorders, sheep are an excellent model for studying human sleep and brain disorders.
Calli McMurray – SfN
The image is credited to Schneider et al., eNeuro 2020.
Characterising Sleep Spindles in Sheep
Sleep spindles are distinctive transient patterns of brain activity that typically occur during non-rapid eye movement (NREM) sleep in humans and other mammals. Thought to be important for the consolidation of learning, they may also be useful for indicating the progression of aging and neurodegenerative diseases. The aim of this study was to characterise sleep spindles in sheep (Ovis aries). We recorded electroencephalographs (EEG) wirelessly from 6 sheep over a continuous period containing two nights and a day. We detected and characterised spindles using an automated algorithm. We found that sheep sleep spindles fell within the classical range seen in humans (10- 16 Hz), but we did not see a further separation into fast and slow bands. Spindles were detected predominantly during NREM sleep. Spindle characteristics (frequency, duration, density, topography) varied between individuals, but were similar within individuals between nights. Spindles that occurred during NREM sleep in daytime were indistinguishable from those found during NREM sleep at night. Surprisingly, we also detected numerous spindle-like events during unequivocal periods of wake during the day. These events were mainly local (detected at single sites) and their characteristics differed from spindles detected during sleep. These ‘wake spindles’ are likely to be events that are commonly categorised as ‘spontaneous alpha activity’ during wake. We speculate that wake and sleep spindles are generated via different mechanisms, and that wake spindles play a role in cognitive processes that occur during the daytime.
Statement of Significance
Sleep spindles provide an indication of brain health and function. In this study we characterise sleep spindles in sheep (Ovis aries) for the first time. We found that sleep spindles in sheep are similar to those found in humans in many respects (such as density, duration and frequency) and occurred mainly during NREM sleep. Interestingly however, we also saw spindles during wake in the day. Spindles detected during wake were characteristically distinct from those occurring during sleep. We suggest that wake and sleep spindles are generated via different mechanisms and may have different functional roles. Wake spindles may be a component of cognitive processes that occur during the daytime, such as memory retrieval and attention.