Japanese scientists have shown that a new class of sleeping pill that preserves the ability to wake in response to a threat, unlike the commonly prescribed drugs that muffles a sleeping brain's "intruder alert".

Even during sleep the brain continuously processes sensory information, waking us if it detects a threat. But the most widely prescribed class of sleeping pills, known as benzodiazepines, makes us less likely to rouse in response to sensory input.

The findings showed that millions prescribed on these sleeping pills would sleep through a fire alarm as someone vacuuming next to their bed. However, the new class of drugs called dual orexin receptor antagonists (DORAs) more selectively targeted the brain's sleep or wake pathways, which gives them safety advantages over benzodiazepines, said researchers from the Kagoshima University. 

These include a reduced "hangover effect", with DORAs less likely to affect driving ability the day after use. "Benzodiazepines stimulate the widespread brain receptor GABA-A, which makes us sleepy but also suppresses off-target brain areas - including the 'gatekeeper' that decides which sensory inputs to process," explained author Tomoyuki Kuwaki, Professor at the varsity.

In the study, published in Frontiers in Behavioral Neuroscience journal, mice that were given the new experimental hypnotic drug DORA-22 wake as quickly when threatened as drug-free sleepers -- and then fall back asleep as quickly as ones given standard sleeping pills, once the threat is gone.

While DORA-22 allows mice to wake to a threat, it still helps them sleep. Thus, the selectivity of DORAs could make them a safer alternative during sleep as well -- by allowing the brain's sensory gatekeeper to stay vigilant to threats, the researchers said.

However, more studies on humans are needed to confirm DORA safety and efficacy, they noted. "Although it remains to be seen whether DORAs have the same properties when used in humans, our study provides important and promising insight into the safety of these hypnotics," Kuwaki said.