Two groups of researchers have shown the health benefits of a daily siesta or afternoon nap of up to 90 minutes.

A 90-minute nap in the afternoon helps speed up the process of long term memory consolidation, researchers at the Center for Brain and Behavior Research at the University of Haifa have found.

The study, conducted by Professor Avi Karni and Dr Maria Korman at the University of Haifa in cooperation with the Sleep Laboratory at the Sheba Medical Center,and researchers from the Department of Psychology at the University of Montreal, was published in the January issue of the journal Nature Neuroscience.

The ‘what’ and ‘how to’ of longterm memory

Longterm memory is defined as a permanent memory that doesn't disappear or that disappears after many years. There are two types – memories of ‘what’ (what happened yesterday, what one remembers from an article read recently) and memories of ‘how to’ (how to read, how to drive, or play the piano).

Two groups of participants were given a simple activity sequence to perform and were examined on how well they remembered the ‘how to’ of performing it. One group was allowed an afternoon nap of 90 minutes after learning the task, while the other group stayed awake.

The group that slept in the afternoon showed a distinct improvement in their task performance by that evening, as opposed to the group that stayed awake, which showed no improvement.

"We still don't know the exact mechanism of the memory process that occurs during sleep, but the results of this research suggest the possibility that it is possible to speed up memory consolidation, and in the future, we may be able to do it artificially," said Professor Karni.

Cardiovascular benefits of napping

In Britain, researchers have also being looking at the health benefits of napping.

Researchers at the John Moores University in Liverpool, looked at the cardiovascular benefits from an afternoon snooze, and concluded that the actual time of falling asleep was where beneficial cardiovascular changes take place.

The study, Acute Changes in Cardiovascular Function During the Onset Period of Daytime Sleep: Comparison to Lying Awake and Standing, by Dr Mohammad Zaregarizi and his team, was published in the online edition of the Journal of Applied Physiology.

The study tested nine healthy volunteers (eight men, one woman) who did not routinely take afternoon naps. The volunteers attended the university laboratory on three separate afternoons after sleeping four hours the night before. They wore equipment that checked blood pressure, heart rate, and forearm cutaneous vascular conductance (which determines dilation of blood vessels).

During their first session, each volunteer spent an hour resting, lying face-up in bed. In the next session, they spent an hour relaxed, but standing up. And in third session, they were allowed an hour to sleep, lying face-up.

Blood pressure drops just before falling asleep

A significant drop in blood pressure was recorded for all volunteers during the sleep periods, but not during the resting or standing trials. This drop in blood pressure occurred mostly just before the volunteers fell asleep.

This reduction in blood pressure may be one explanation for the lower rates of cardiovascular mortality that some studies have found among people who habitually take siestas, Dr Zaregarizi said in the abstract of the study.

So, while the ‘hard science’ isn’t in yet, it seems a cat nap in the afternoon can do more than just refresh you. It can help you remember what you need to learn while lowering your blood pressure.

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