Fragmented sleep 'harms memory'

25 July 2011 Last updated at 21:20 GMT Continuous sleep is important for memory formation Broken sleep affects the ability to build memories, a study of mice suggests.

The Proceedings of the National Academy of Science findings could help explain memory problems linked to conditions including Alzheimer's and sleep apnoea.

The Stanford University research found disrupting sleep made it harder for the animals to recognise familiar objects.

A UK sleep expert said the brain used deep sleep to evaluate the day's events and decide what to keep.

This study looked at sleep that was fragmented, but not shorter or less intense than normal for the mice.

It used a technique called optogenetics, where specific cells are genetically engineered so they can be controlled by light.

They targeted a type of brain cell that plays a key role in switching between the states of being asleep and being awake.

Mouse memory test

The researchers then sent light pulses directly into the brains of mice while they slept.

This meant they could disrupt their sleep without affecting total sleep time or the quality or composition of sleep.

The animals were then placed in a box with two objects, one of which they had encountered before.

Mice would naturally spend more time examining the newer object, and those who had been allowed uninterrupted sleep did just that.

But those whose sleep had been disrupted were equally interested in both objects, suggesting their memories had been affected.

Writing in the journal, the researchers, led by Dr Luis de Lecea, said: "Sleep continuity is one of the main factors affected in various pathological conditions that impact memory, including Alzheimer's and other age-related cognitive deficits."

Broken sleep also affects people addicted to alcohol, and those with sleep apnoea - a condition in which the throat repeatedly narrows or closes during sleep, restricting oxygen and causing the patient to wake up.

The researchers add there is no evidence of a causal link between sleep disruption and any of these conditions.

But they added: "We conclude that regardless of the total amount of sleep or sleep intensity, a minimal unit of uninterrupted sleep is crucial for memory consolidation."

Independent sleep expert Dr Neil Stanley, a former chairman of the British Sleep Society, said: "During the day, we accumulate all these memories.

"At some point we have to sort through what's happened during the day.

"There are some things that we need to 'lock down' as a permanent hard memory.

"That process occurs in deep sleep. So anything that affects sleep will have an effect on that process to a greater or a lesser extent."

Dr Stanley said there was particularly striking evidence that people with sleep apnoea had particular problems "locking down" memories.

And he added that people with Alzheimer's often had trouble sleeping, but said: "There is something there. But whether it's the degeneration of the brain that causes poor sleep, or poor sleep that aids the degeneration of the brain has not been determined."

Miranda Watson, director of communications at the British Lung Foundation, said: "For patients with the dangerous sleep disorder, obstructive sleep apnoea, this study will come as no surprise.

"Patients regularly stop breathing during the night when their airways become blocked depriving them of a full night's rest.

"This interrupted sleep can cause extreme day time tiredness and memory loss."

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Internet is 'changing our memory'

16 July 2011 Last updated at 15:37 GMT By Jason Palmer Science and technology reporter, BBC News The collective memory of the internet may make us simply remember less Computers and the internet are changing the nature of our memory, research in the journal Science suggests.

Psychology experiments showed that people presented with difficult questions began to think of computers.

When participants knew that facts would be available on a computer later, they had poor recall of answers but enhanced recall of where they were stored.

The researchers say the internet acts as a "transactive memory" that we depend upon to remember for us.

Lead author Betsy Sparrow of Columbia University said that transactive memory "is an idea that there are external memory sources - really storage places that exist in other people".

"There are people who are experts in certain things and we allow them to be, [to] make them responsible for certain kinds of information," she explained to BBC News.

Co-author of the paper Daniel Wegner, now at Harvard University, first proposed the transactive memory concept in a book chapter titled Cognitive Interdependence in Close Relationships, finding that long-term couples relied on each other to act as one another's memory banks.

"I really think the internet has become a form of this transactive memory, and I wanted to test it," said Dr Sparrow.

Where, not what

The first part of the team's research was to test whether subjects were "primed" to think about computers and the internet when presented with difficult questions. To do that, the team used what is known as a modified Stroop test.

The standard Stroop test measures how long it takes a participant to read a colour word when the word itself is a different colour - for example, the word "green" written in blue.

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I don't think Google is making us stupid - we're just changing the way that we're remembering things…”

End Quote Dr Betsy Sparrow Columbia University Reaction times increase when, instead of colour words, participants are asked to read words about topics they may already be thinking about.

In this way the team showed that, after presenting subjects with tough true/false questions, reaction times to internet-related terms were markedly longer, suggesting that when participants did not know the answer, they were already considering the idea of obtaining it using a computer.

A more telling experiment provided a stream of facts to participants, with half told to file them away in a number of "folders" on a computer, and half told that the facts would be erased.

When asked to remember the facts, those who knew the information would not be available later performed significantly better than those who filed the information away.

But those who expected the information would be available were remarkably good at remembering in which folder they had stored the information.

"This suggests that for the things we can find online, we tend keep it online as far as memory is concerned - we keep it externally stored," Dr Sparrow said.

She explained that the propensity of participants to remember the location of the information, rather than the information itself, is a sign that people are not becoming less able to remember things, but simply organising vast amounts of available information in a more accessible way.

"I don't think Google is making us stupid - we're just changing the way that we're remembering things... If you can find stuff online even while you're walking down the street these days, then the skill to have, the thing to remember, is where to go to find the information. It's just like it would be with people - the skill to have is to remember who to go see about [particular topics]."

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