If you find it hard to get a good night’s sleep, your bedmate might be part of the issue, according to recent research from the University of Michigan.

The study, focusing on the sleep behavior of mice in a social setting, observed that these small rodents actively seek physical contact before starting their sleep and continue to cuddle while sleeping. The researchers discovered that this cuddling behavior during sleep is motivated by a deep-seated desire for prolonged physical contact, a phenomenon they termed “somatolonging.”

This research emphasizes the significant need for social contact in species beyond just humans.

“The lack of this kind of contact was evident during the COVID-19 pandemic, during which people experienced somatolonging,” the researchers explain.

Intimacy penalty

Cuddling during sleep may have its drawbacks, as observed in mice where it often leads to disruptions in each other’s sleep. Similar challenges can be seen in humans, where co-sleeping doesn’t always result in positive outcomes and can even lead to the transmission of insomnia between bed partners. The reason why both humans and animals willingly choose situations that might compromise their sleep remains unknown to researchers.

However, on a positive note, individuals who co-sleep exhibit synchronization in various neurophysiological measures, including the timing of sleep/wake onset and REM sleep. The study employed advanced wireless devices and video recordings to simultaneously monitor multiple mice within a group for 24 hours.

Interestingly, the mice were willing to sacrifice their preferred sleep locations to enjoy social contact. This suggests that the desire for prolonged physical contact motivates their huddling behavior. The researchers also observed coordination in multiple neurophysiological features among co-sleeping individuals, including the timing of falling asleep and waking up, as well as sleep intensity.

Notably, the synchronization of rapid eye movement (REM) sleep timing was observed among co-sleeping male siblings but not among co-sleeping female siblings or unfamiliar mice. This implies that an individual’s internal state, such as feeling safe, influences the degree of synchronization.