Scientists are investigating what happens in the brain when people sleep and how they can enjoy the restorative effects of better deep sleep.
Everyone suffers from restless nights from time to time. Ruminating on failures or worries at the end of the day undermines rest, especially deep sleep. “A restless mind makes a restless pillow,” wrote author Charlotte Brontë.
A good night’s sleep serves as a tonic. Additionally, shuteye has long been recognized to boost learning and memory. More recently, scientists revealed that the initial phase of slow-wave deep sleep is particularly important.
“When you learn something in the evening, this information is reactivated during sleep,” said Dr. Bjoern Rasch, who participated in the MemoSleep project and is a professor at the University of Freiburg.
The Swiss researcher added that “Ruminations and negative thoughts increase our arousals during sleep, make us wake up earlier than we want and make us sleep less deeply.”
But there is also good news. Positive thoughts can also reactivate brain circuits and, in the process, improve sleep, according to Dr. Rasch. He organized an experiment around the whole idea.
His test was a small help for students at his university who received 50 Swiss francs (52 euros) for each night they spent sleeping in a comfortable four-bed laboratory.
The students were connected to an electroencephalogram that monitored their brain waves. They also monitored their muscles to record when they fell asleep and what state of sleep they were in.
Some relaxation strategies help people fall asleep faster, but don’t change the quality of sleep afterward, Dr. Rasch says. He played hypnotic tapes with images such as a fish swimming in deep water, and with words suggesting safety and relaxation, for the students.
“Subjects spent more time in the deeper slow-wave sleep stage after listening to the hypnotic tape,” Dr. Rasch said. “We would explain this by a greater reactivation of relaxing and reassuring thoughts during sleep, previously heard during the hypnosis tape.”
In future studies, Dr. Rasch hopes to help patients who suffer from insomnia.
“Not only could it help them fall asleep, but it could make their sleep more restful,” he said. In addition, this could help people with psychological illnesses, such as post-traumatic stress disorder, who sleep poorly.
Seahorses and learning
The seahorse-shaped part of the brain called the hippocampus (from the Greek word for seahorse) is especially important for learning and memory. Scientists often use rodents to investigate their hippocampus during learning and sleep.
Rats, for example, are masters at remembering paths through mazes to find food. The hippocampus is key to this memory.
Dr. Juan Ramírez-Villegas uses rodents to investigate how mammalian brains store memories, work that could eventually contribute to fighting human diseases such as Alzheimer’s.
As part of the DREAM project, he discovered that another part of the brain, the brainstem, plays a crucial role along with the hippocampus and is activated earlier.
“It appears that the brainstem is setting the stage for the hippocampus to reactivate memories at different stages of sleep,” said Dr. Ramírez-Villegas, who is a postdoctoral fellow at the Austrian Institute of Science and Technology.
He has attached electrodes to record activity in the rats’ brains as they navigate a maze and then while they sleep. Sleep allows the brain to replay the day’s events and record them as long-term memories.
“It’s very striking that the cells fire in the same order during sleep as they did during learning, but during sleep they are more compressed in time,” said Dr. Ramírez-Villegas.
As we remember
The discovery was surprising because it suggests that the brainstem has an overlooked function in stimulating and changing memory formation. This appears to be true for both rodents and primates, and as a result is likely to be a basic mechanism of the mammalian brain, including humans.
The research, while crucial to understanding the basic workings of the brain, could also have clinical benefits. “We are unraveling the basic principles of memory processes, but we can also use them to ameliorate the effects of memory-related diseases,” said Dr Ramírez-Villegas.
About this research news about sleep, learning and memory
Author: Anthony King
Contact: Anthony King – Horizons
Image: Image credited to Kinga Cichewicz