Researchers delving into the relationship between sleep and memory found that when we doze our brain prunes out unimportant memories but enhances those that need to be retrieved and are relevant to complete a task in the future.

Though, the human brain encodes and stores daily experiences in the form of memory, this information is quickly erased.

Lead author of the study, Dr. Jan Born of the University of Lubeck in Germany stated, "Our results show that memory consolidation during sleep indeed involves a basic selection process that determines which of the many pieces of the day's information is sent to long-term storage.

"Our findings also indicate that information relevant for future demands is selected foremost for storage."

Study details
In a bid to determine how the brain decides which memories to retain and which to forget, the researchers conducted study.

For the purpose of the study, they recruited 191 volunteers for a couple of experiments to test their memory retrieval.

The study subjects were split into two groups. The first was asked to memorize 40 pairs of words while the second group had to match photos of animals and objects.

Half of participants in both groups were told they would be re-tested within 10 hours on the material they had learned while the remaining were told to expect another task later.

During the 10-hour interval some members of both the groups were allowed to sleep.

Findings of the study
The researchers found that people who slept performed better when re-tested. However, the volunteers who went to sleep anticipating a test post the nap exhibited a better memory recall.

They remembered 12 percent more words as opposed to those who were not expecting a test.

The brain waves of the volunteers were also monitored by electroencephalograms (EEG) while they slept.

The study found that the participants who were aware that they would be tested displayed an increase in brain activity during deep or "slow wave" sleep that is known to be linked to memory consolidation.

Dr Gilles Einstein, an expert in memory at Furman University stated, "These results suggest that sleep is critical to this memory enhancement.

"This benefit extends to both declarative memories (memory for a road detour) and procedural memories (memory for a new dance step)."

The findings were reported in the 'Journal of Neuroscience.'