This week, we resumed our biweekly journal club in sleep and circadian rhythms for the year. I presented a paper published last week in the journal Sleep. It was more of a methods papers, but still important because non-invasive tools for measuring sleep have become best-sellers: FitBit, Zeo, and other Nike/iPod-based physical activity software. This new technology that I talked about in journal club is reserved only for rodents although the researchers state that it could eventually transform the human sleep laboratory. The system, known as the piezoelectric system, has been around for about a decade, but has really only been used by selective groups. However, now that the system is commercially available (Signal Solutions), there may be more papers using it to record sleep. Hopefully, these researchers are cautiously doing so as I will explain why.

ResearchBlogging.orgThe hardware of the piezo system is fairly straightforward. There is a polymer “mattress” placed under a light layer of bedding on which the animals move around, groom, sleep, eat, drink, etc on. This polymer is connected to a box that encases the animals’ cages. The box also contains many tiers of infrared beams to measure general locomotion. Basically, the amount of mechanical pressure generated from movement and breathing is proportional to the amount of electric signal generated. These two variable–mechanical pressure and electrical signals–are assigned a score that is above or below a “wake” threshold shown here. The lower the positive score, the deeper the stage of sleep and the higher the negative score, the more intense the stage of wake.

Basically, these researchers found that the temporal distribution of sleep and wake across multiple days is largely in agreement between this system and the traditional EEG/EMG system that also requires someone to score each individual epoch of recording, a process that can take hours to days.

Decision Statistic determining sleep or wake

There were some concerns about over-reporting sleep during the light or rest phase of rodents as well as the system being a poor measure of particular EEG waveforms characteristic of each state of sleep and wake.

Temporal distribution of sleep and wake with EEG and this new non-invasive piezo system

But for the most part, I do think this is an ideal system for high-throughput research requiring quick sleep-wake analysis in hundreds of mice. It also removes human error of scoring sleep records out of the equation. Obviously, there are some limitations as to what types of studies should rely on the piezo system alone. Personally, I think it is ideal for high-throughput studies of drug screens. If you are interested in gross changes in sleep from baseline levels, then sure. But if you are trying to identify a new model of sleep dysfunction then this system may not be sufficient enough to accurately identify brief awakenings as sleep or wake. Regardless, I do hope to see more studies using this type of recording technology soon.

Mang GM, Nicod J, Emmenegger Y, Donohue KD, O’Hara BF, & Franken P (2014). Evaluation of a piezoelectric system as an alternative to electroencephalogram/ electromyogram recordings in mouse sleep studies. Sleep, 37 (8), 1383-92 PMID: 25083019