new study has revealed an important way in which sleep helps the brain
process emotions for the next day, and while the findings were
discovered in mice, they could also help us solve some of the mysteries
of human sleep.
The role of sleep in brain function is still very much an enigma, but there is overwhelming evidence that rapid eye movement (REM) sleep helps humans consolidate their emotional memories.
But how that actually plays out in the brain is something scientists are still investigating.
prefrontal cortex is a part of the brain that is heavily involved in
emotional processing, and yet during REM sleep, some of its neurons,
known as pyramidal neurons, are strangely quiet.
might sound paradoxical at first. After all, how is this part of the
brain helping us control our emotions during sleep if it's not being
active when we're actually getting some shut-eye?
it turns out, silence is also a powerful tool. Research on sleeping and
awake mice suggests the quieting of the prefrontal cortex during REM
sleep helps the whole system reset.
The findings are consistent with other recent studies that suggest sleep keeps neuronal activity under control.
proper REM sleep, networks in the brain can become 'oversaturated' with
emotional messages, like fear, making it harder to determine important
signals from background noise. When awake, this can lead a mouse to act
overly fearful or not fearful enough.
active and awake, neurons in the brain receive messages from their
'arms' (aka their dendrites). These messages are then conveyed to the
body of the neuron (aka the soma), which is responsible for propagating
messages to other neurons.
REM sleep, however, neurons in the prefrontal cortex of mice appear to
behave differently. The dendrites show increased activity, but the soma
shows decreased activity.
"This means a decoupling of the two cellular compartments, in other words soma wide asleep and dendrites wide awake," explains neurologist Antoine Adamantidis from the University of Bern in Switzerland.
simple terms, this decoupling means that neurons are processing
information they have already received, but not sending messages on.
the body of the neuron no longer sending off as many messages, the arms
of the neuron have time to consolidate the information they have
already received, essentially 'learning' which incoming messages should
be sent off and which should not.
allows the brain to better respond to environmental changes the next
day, allowing animals to discriminate between danger and safety with
the activity of dendrites were inhibited during REM sleep, mice in the
study lost their ability to discriminate between audio cues associated
with danger and safety.
Meanwhile, when the soma was not effectively silenced during REM sleep, mice became more attuned to danger signals overall.
may result in overconsolidation of emotional memories observed in
post-traumatic stress disorders and other affective psychiatric and mood
disorders often associated with REM sleep disturbances," the authors suggest.
mechanism has not yet been observed in human neurons, but the findings
could help scientists better understand why conditions like post
traumatic stress disorder and sleep disturbance are so closely linked.
The study was published in Science.