Sleepsmart, learn easy
it is a fix. Students are told that they would not do well in exams if they do not get a good night's sleep, while several immensely creative people hardly sleep at all. How important is sleep to the functioning of our brain? A recent study claims to have discovered a new link between sleep and memory, seriously challenging the wisdom of skipping on time spent sleeping.
Experiments show that when people learn a new skill, their performance does not improve until after they have had more than six, preferably eight hours of sleep. Researchers say skills and even new factual information may not get properly encoded into the brain's memory circuits if they have not been rested. Moreover, a person's intelligence may be less important than a good night's sleep in forming many kinds of memories. The experiments point to a new hypothesis for memory formation, involving the interaction between two stages of sleep: one that occurs at the beginning of the night and one that occurs early in the morning. It has been found that during both periods, the brain undergoes physical and chemical changes that help strengthen memory traces ( Journal of Cognitive Neurosciences , Vol 12, No 2).
Robert Stickgold of the Harvard Medical School and his team at the Laboratory of Neurophysiology at the Massachusetts Mental Health Centre in Boston, usa , have conducted the study. It is the first to show that humans have a sleep window for learning and memory. The researchers trained Harvard undergraduates to spot visual targets on a computer screen and to press a button as soon as they were certain they had seen one. At first, it might take 400 milliseconds for a target to reach the students' conscious awareness. But with an hour or so of practice they could reliably see the targets much faster. For example, at the end of training a student might accurately press a button in 75 milliseconds. According to Stickgold, students who are trained to do this task showed absolutely no improvement in speed beyond their best time at the end of training when they were tested 3-12 hours later on the same day. Students who slept six hours or less after training also showed no improvement when they perform the same task the next day.
Only those who slept six hours or more seemed to improve. For example, someone whose best time was 75 milliseconds at the end of training might, after a good night's sleep, reliably perform the task in 62 milliseconds. This improvement in speed and accuracy is somehow consolidated during sleep, Stickgold says.
But it is not just any kind of sleep that matters. The students who improved the most slept for eight hours, during which they got solid bouts of two kinds of sleep as measured in a sleep laboratory. The first two hours of the night were spent in deep, slow-wave sleep. The last two hours were spent in rapid eye movement ( rem ) sleep, when vivid dreams occur. People needed both kinds of sleep to do better on what they had learned the day before. Moreover, the good night's sleep continued to pay dividends. Well-rested students tested two days to a week after training could do the visual task even faster.
Experts are enthusiastic. Carlyle Smith, a sleep study expert and professor of psychology at Trent University in Peterborough, Ontario, says: "It means that people who cut their sleep short for the last couple of hours each night generally won't do as well as those who get a full night's sleep.' The research has important implications for institutions like universities, medical schools and the military, which often train people amid long bouts of sleep deprivation.
Stickgold says that during the first two hours of slow-wave sleep, certain brain chemicals plummet and information flows out of a memory region called the hippocampus and into the cortex. During the next four hours, he theorises, the brain engages in a kind of internal dialogue that distributes this new information into the appropriate networks and categories. A slow process of protein synthesis begins to strengthen connections between nerve cells that have newly acquired information. "It is as if you have to wait for the dough to rise,' Stickgold says. In the last two hours of sleep, brain chemistry and activity again change drastically as the cortex goes into an active dreaming state. The hippocampus is shut off from the cortex as the brain literally re-enacts the training and solidifies the new connections throughout its memory banks.
In the experience of the Harvard team, the six-hour cutoff really scares students as many college students suffer from a kind of sleep bulimia in which they binge and purge sleep time. They get by on three to five hours a night during the week and binge on weekends, thinking that they will be fine. But much of the information learned during a sleep-deprived week is not well-integrated into memory circuits. After a few days, facts memorised during an "all nighter' tend to fade away, say the researchers. It seems that rem sleep is important for integrating all kinds of information into the brain over the long haul and how well they slept the previous night decides their performance. More importantly, Strickgold says that it would work for any kind of learning.