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| Dreaming brain rhythms lock in memories | Dreaming brain rhythms lock in memories |
| (about 3 hours later) | |
| Disrupting brain activity in sleeping mice, specifically during the rapid eye movement (REM) phase, can stop the animals remembering things they learned that day, a study suggests. | |
| It is the clearest evidence to date that REM sleep is critical for memory. | It is the clearest evidence to date that REM sleep is critical for memory. |
| By switching off certain brain cells, the researchers silenced a particular, rhythmic type of brain function - without waking the mice. | By switching off certain brain cells, the researchers silenced a particular, rhythmic type of brain function - without waking the mice. |
| If they did this during REM sleep, the mice failed subsequent memory tests. | If they did this during REM sleep, the mice failed subsequent memory tests. |
| The research is reported in the journal Science. | The research is reported in the journal Science. |
| REM sleep is the phase during which, at least in humans, dreams take place - but the question of whether it is important for settling new memories has been difficult to answer. | REM sleep is the phase during which, at least in humans, dreams take place - but the question of whether it is important for settling new memories has been difficult to answer. |
| Recent studies have tended to focus on deep, non-REM sleep instead, during which brain cells fire in various patterns that reflect memory consolidation and "re-play" of the day's experiences. | Recent studies have tended to focus on deep, non-REM sleep instead, during which brain cells fire in various patterns that reflect memory consolidation and "re-play" of the day's experiences. |
| During REM sleep, while our eyes flicker and our muscles relax, exactly what the brain is doing is something of a mystery. But it is a type of sleep seen across the animal kingdom, in mammals and birds and even lizards. | During REM sleep, while our eyes flicker and our muscles relax, exactly what the brain is doing is something of a mystery. But it is a type of sleep seen across the animal kingdom, in mammals and birds and even lizards. |
| Especially in animals, REM phases can be quite fleeting. This and other complications have made it difficult to test what effect such sleep has. | Especially in animals, REM phases can be quite fleeting. This and other complications have made it difficult to test what effect such sleep has. |
| Simply waking up humans or animals when they enter the REM phase, for example, causes stress and other problems that can confound any memory tests. | Simply waking up humans or animals when they enter the REM phase, for example, causes stress and other problems that can confound any memory tests. |
| So Dr Sylvain Williams, from McGill University in Canada, working with colleagues at the University of Bern, Switzerland, decided to meddle directly with the sleeping brain. | So Dr Sylvain Williams, from McGill University in Canada, working with colleagues at the University of Bern, Switzerland, decided to meddle directly with the sleeping brain. |
| "What we did was we used a technique, in mice, to solely disrupt REM sleep activity," Dr Williams told BBC News. | "What we did was we used a technique, in mice, to solely disrupt REM sleep activity," Dr Williams told BBC News. |
| Using the system known as "optogenetics", he and his colleagues were able to control a particular population of brain cells in the mice, just by shining light through a tiny, implanted optical fibre. | Using the system known as "optogenetics", he and his colleagues were able to control a particular population of brain cells in the mice, just by shining light through a tiny, implanted optical fibre. |
| Whenever they switched on the light, they drastically reduced a particular rhythm in the brain, called "theta oscillations". | Whenever they switched on the light, they drastically reduced a particular rhythm in the brain, called "theta oscillations". |
| And if that disruption was delivered during a mouse's REM sleep, there were consequences. | And if that disruption was delivered during a mouse's REM sleep, there were consequences. |
| "Disrupting the activity only during REM sleep, and not other sleep, basically obliterates consolidation and memory formation," Dr Williams said. | "Disrupting the activity only during REM sleep, and not other sleep, basically obliterates consolidation and memory formation," Dr Williams said. |
| For example, if it was shown one brand new object and one that it had seen the day before, the mouse would thoroughly investigate both, instead of concentrating - like a normal mouse would - on the unfamiliar one. | For example, if it was shown one brand new object and one that it had seen the day before, the mouse would thoroughly investigate both, instead of concentrating - like a normal mouse would - on the unfamiliar one. |
| Optogenetics: switches for brain circuits | Optogenetics: switches for brain circuits |
| So it seems that REM sleep is crucial, in some cases, for laying down new memories. Dr Williams said this arguably poses more questions than it answers. | So it seems that REM sleep is crucial, in some cases, for laying down new memories. Dr Williams said this arguably poses more questions than it answers. |
| For one thing, the other, deeper phase of sleep is already known to be involved in memory consolidation. So what are their distinct jobs? | For one thing, the other, deeper phase of sleep is already known to be involved in memory consolidation. So what are their distinct jobs? |
| "I think at the moment we don't know the difference between the two phases," he said. | "I think at the moment we don't know the difference between the two phases," he said. |
| "It's an eye-opener to say that REM sleep has this very central role." | "It's an eye-opener to say that REM sleep has this very central role." |
| Whatever that role is, the new findings suggest it involves the oscillations that the scientists disrupted - in which brain cells synchronise their activity, leading to a widespread and measurable rhythm with, in this case, about seven beats per second. | Whatever that role is, the new findings suggest it involves the oscillations that the scientists disrupted - in which brain cells synchronise their activity, leading to a widespread and measurable rhythm with, in this case, about seven beats per second. |
| That signature could be something to study in patients with dementia or other memory problems, Dr Williams said. | That signature could be something to study in patients with dementia or other memory problems, Dr Williams said. |
| "It'd be interesting to see, for example, how this normal activity... might be affected, specifically, in Alzheimer's patients. To see if that contributes to memory impairments." | "It'd be interesting to see, for example, how this normal activity... might be affected, specifically, in Alzheimer's patients. To see if that contributes to memory impairments." |
| Dr Daniel Bendor, a neuroscientist at University College London who also studies memory formation in rodents, said the study was "a big step forward" in understanding REM sleep. | Dr Daniel Bendor, a neuroscientist at University College London who also studies memory formation in rodents, said the study was "a big step forward" in understanding REM sleep. |
| "After decades of work that's been inconclusive, they're showing that something important is happening," he said. | "After decades of work that's been inconclusive, they're showing that something important is happening," he said. |
| The Swiss-Canadian team had found a neat way of specifically disrupting REM sleep, Dr Bendor added. | The Swiss-Canadian team had found a neat way of specifically disrupting REM sleep, Dr Bendor added. |
| "These are difficult experiments to do. It's a really impressive demonstration of a potential role of theta oscillations during REM sleep." | "These are difficult experiments to do. It's a really impressive demonstration of a potential role of theta oscillations during REM sleep." |
| Follow Jonathan on Twitter | Follow Jonathan on Twitter |