With neuroimaging and electrophysiological techniques, researchers have been able to gain many new insights into dreaming. Scientists have found that neurological activity in the brain while people are awake can be similar to brain activity while dreaming, though some parts of the brain seem to be more active while people dream. It's long been thought that our emotional concerns follow us from our waking state into the dream world, and rapid eye movement (REM), which often coincides with dreaming, has been linked to the processing of emotional memories. Dreams that occur during REM sleep tend to have intense emotional aspects, though little is known about how those emotions are triggered. Now researchers have learned more about neurological activity in the brain during REM sleep.
Our brains can deal with emotions as we dream; the brain consolidates positive emotions and reduces the consolidation of negative emotions. While we're awake, the prefrontal cortex helps to integrate emotions. But as we sleep, the activity in the prefrontal cortex quiets down. REM sleep has now been connected to a process called 'somatodendritic decoupling' in the pyramidal neurons that sit in the prefrontal cortex of the brain. This new work, which was reported in Science, has revealed one reason why sleep is so important to mental health.
"Our goal was to understand the underlying mechanism and the functions of such a surprising phenomenon," said Professor Antoine Adamantidis of the University Hospital of Bern.
Emotions like fear have to be controlled in all animals so they can survive. When people experience intense or prolonged negative emotions, conditions like post-traumatic stress disorder can arise. Understanding how the brain deals with negative emotions, and how they might be reinforced, could lead to treatments for disorders like PTSD or anxiety.
This study used a mouse model in which the animals were conditioned to associate certain sounds with danger, an aversive stimulus. Brain activity was recorded as the mice slept and woke. With this data, the researchers learned how emotional memories change during REM sleep. The cell bodies of neurons or soma stayed inactive, while the extensions of neurons, called dendrites, became active; the two parts of the cell were decoupled.
"This means a decoupling of the two cellular compartments, in other words soma wide asleep and dendrites wide awake," explained Adamantidis.
The researchers suggested that decoupling helps dendrites encode danger and safety emotions, as the inhibited soma stops output from the cell, and overreactions, as we sleep. "This bidirectional mechanism is essential to optimize the discrimination between dangerous and safe signals," explained first study author Mattia Aime of the University of Bern.
When the brain isn't good and differentiating between those signals, anxiety disorders may arise. In PTSD, trauma can be over consolidated during sleep. "We hope that our findings will not only be of interest to the patients, but also to the broad public," said Adamantidis. They will have to be confirmed in humans first, but this study is a major step forward.
Sources: University of Bern, Science
