Rocking to a Good Night's Sleep

Katrina -   This week has seen breakthroughs into the mysteries of sleep, helping us understand the ancient tradition of rocking babies to sleep, and why we need our shut-eye at all.

Researchers from France and Switzerland have discovered that the rocking motion found in cradles and hammocks not only lulls people to sleep more quickly than lying still, but also encourages deeper sleep.

They asked volunteers to have a 45 minute nap in their 'experimental hammock', which was either still or gently rocking, while an electroencephalogram, or EEG, was used to monitor the waves of activity in their brains.

The study, published this week in Current Biology, found that the rocking motion helped volunteers fall asleep more quickly, with a shorter period of stage 1, or light, sleep. The rocking caused more stage 2 sleep, and increased the number of sleep spindles. These are important patterns of brain activity that seem to be needed to refresh our ability to learn after our sleep.

So rocking helps send us to sleep, and helps deepen our sleep in an afternoon nap. The next step will be to see if the same thing applies for a full night's sleep, and to see if the sleep changes caused by rocking help with learning and memory consolidation. Perhaps rocking beds will soon be standard options in all furniture shops!

But why we need to fall asleep at all? Also in the news this week, fruit flies have taught us more about the role of sleep in refreshing our minds so that they can lay down new memories.

Researchers publishing in the journal Science used fruit flies that were genetically modified to fall asleep if the temperature rises above 31 degrees centigrade. Armed with this ability to induce sleep on demand, they wanted to investigate the 'synaptic homeostasis model', the idea that new connections between nerves are continuously formed when an animal is awake, and these are downscaled during sleep to prevent an overload of circuits.

They showed that flies in a socially enriched environment, with exposure to 90 other flies, formed lots of new connections between nerves. This meant that they were unable to lay down long term memories when researchers tried to train them to suppress their mating rituals. Flies that had been socially isolated, on the other hand, formed fewer new connections between their nerves, and later performed well on the long term memory task.

But can sleep 'refresh' the brain, and abolish the effect of the social enrichment? The researchers used temperature to allow the flies 4 hours of sleep after their social enrichment. This did indeed restore the ability of the flies to form new long term memories, supporting the idea that a period of

sleep simplifies neural connections and leaves the flies better able to learn.

Ben -   Is there a bit of a risk with this sort of experiment, similar to that we see with bending animal behaviour experiments that we're actually imposing our own judgment in what they're doing, and it's very, very hard to say exactly why a baby does something, just like it would be hard to say why a bird does something or why a monkey does something?

Katrina -   There certainly is that risk, yes and all you can really tell from this study is that there was definitely a significant difference in the decisions that the babies made according to how the experiment has reacted and what toys they were given.

Ben -   It would be very interesting and I'm sure there are lots of new parents around who would love to know exactly what their babies are thinking.