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Study finds lack of sleeps impairs memory, exam performance

After being trained in a motor task, subjects showed improved performance after resting

Though pulling an all-nighter often seems a necessary pre-exam ritual, new research indicates that lack of sleep can hurt students’ ability to retain information and perform well on exams.

After measuring subjects’ abilities to perform certain tasks after getting four hours of sleep, Masako Tamaki, a postodoctoral research associate, found increased activity in the supplementary motor area of the brain’s cortex. This phenomenon, which happens during sleep, correlated with improved performance on a motor task. The findings were part of a study published Aug. 21 in the Journal of Neuroscience.

Previous studies suggest sleep plays a significant role in memory consolidation, or enhancement, Tamaki said. But researchers have had difficulty pinpointing which brain regions are involved in that process.

Participants in the study learned a finger-tapping motor task and were then allowed to sleep. The researchers measured brain activity during sleep to determine if increased neural oscillations in specific regions correlated with better performance on the task when the subjects awoke.

“Our study is kind of first to apply this detailed technique, the combination of MRI and MEG,” said Yuka Sasaki, an associate professor of research who worked on the study. Through the technology, the researchers were able to identify where neural changes occurred during sleep.

Oscillations indicate activity within or between neurons and are differentiated according to their frequency. Delta and sigma bands, two forms of neural oscillations, often characterize brain activity while sleeping. If subjects slept after being trained in the finger-tapping task, many experienced a significant increase in delta and sigma band oscillations in the supplementary motor area on the side of the brain opposite to the hand used during the task.

The bands “may have different roles in consolidating memory,” Tamaki said. Giulio Tononi, a neuroscientist and psychiatrist with the University of Wisconsin, hypothesized delta oscillations may be related to reducing the number of synapses, or connections between neurons, during sleep.

“If your synapses are growing too much, then you have no more space. So you have to make some kind of down-scaling or normalization so that you would have a space for newer learning,” Sasaki said.

Another theory suggests “there is an active process, a central process to learning, which is one of the main sleep functions,” Sasaki said. Sigma oscillations are hypothesized to play a role in this process. Because the correlation between sigma wave activity and performance was stronger in her study, she said the sigma theory pointing to a central process of learning during sleep may be more viable, or that the two processes could be working together.

The study found a significant correlation between increased activity during slow-wave, or non-REM, sleep and performance on a motor task. But Sasaki said memory consolidation may occur during REM sleep as well, though further research is needed to confirm this suggestion. Sasaki pointed to the extensive REM sleep during infancy, when people are learning a significant amount, as possible evidence for this phenomenon.

Tamaki’s research contributes to a growing body of evidence that points to the relationship between sleep and learning.

“People with low sleep quality, their learning abilities are a little bit lower … such as schizophrenic patients and maybe depressed people,” she said. A higher count and frequency of spindles — such as delta and sigma oscillations — may also point to greater learning ability, she said.

Tamaki’s finger-tapping task involves sequential learning .  But she said she is interested in the role sleep plays in other forms of learning and is currently studying the relationship between visual perceptual learning and sleep.

“Probably, we can use this knowledge to enhance your memory while you’re sleeping. We can’t do it right now,” Sasaki said.

But with this new knowledge, the future of productive sleep looks bright.

“Maybe we can invent a pillow that … would stimulate your SMA while you’re sleeping, and you would have better performance in piano playing,” Sasaki said.



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