Q:Read the following article and select the best answer. Article: For grown-ups,an afternoon snooze is often easier said than done.But many of us have probably experienced just how simple it can be to catch some sleep in a gently rocking hammock .By examining brain waves in sleeping adults,researchers reported in the June 21issue of Current Biology,a Cell Press publication,that they now have evidence to explain why that is. "It is a common belief that rocking causes sleep:we fall asleep in a rocking chair soon and,since ancient times,we cradle our babies to sleep,"said Sophie Schwartz of the University of Geneva."Yet,how this works had remained a mystery.The goal of our study was made up of two parts:to test whether rocking does indeed improve sleep,and to understand how this might work at the brain level." Schwartz,Michel Muhlethaler,and their colleagues Laurence Bayer and Irina Constantinescu asked twelve adult volunteers to nap on a custom-made bed or"experimental hammock"that could either remain still or rock gently.All participants were good sleepers who didn't typically nap and did not suffer from excessive sleepiness during the day.Each participant took two 45-minute afternoon naps,one with the bed still and one with the bed in motion,while their brain activity was monitored. "We observed a faster transition to sleep in each and every subject in the swinging condition,"Muhlethaler said."Surprisingly,we also observed a dramatic boosting of certain types of sleep-related brain waves." More specifically,rocking increased the length of stage N2sleep,a form of non-rapid eye movement sleep that normally occupies about half of a good night's sleep.The rocking bed also had a lasting effect on brain activity,increasing slow brain waves and bursts of activity known as sleep spindles . Schwartz and Muhlethaler say the next step is to find out whether rocking can improve longer periods of sleep and to find out whether it may be useful for the treatment of sleep disorders,such as insomnia . Question: What can we learn about the study? - The participants were divided into two groups. - The participants had some problems in falling asleep. - Twelve adults and children were invited to take part in it. - The participants'brain waves were examined during their nap.
A:
The participants'brain waves were examined during their nap.