Sleep researchers have, for the first time, observed the human mind consolidating and storing memories in incredible detail, in real time, reinforcing existing ideas about the function and importance of sleep to human cognition.
For decades, there has been a strong but poorly understood connection between sleep and the formation and solidification of memory in the human brain.
In a recent study, the team of international researchers conducted two experiments on some 20 volunteers who they asked to remember specific links between given words and scenes, or specific words and objects, before taking a nap.
The two kinds of word-scene or word-object associations trigger different parts of the brain, allowing researchers greater insight into which memories were being reactivated over the course of the experiment and how strongly.
They then monitored the participants’ brains using electroencephalogram (EEG) scans as they slept for at least 30 minutes but up to 120 minutes. The volunteers were then tested about what they remembered when they woke up.
The sleep scientists wanted to examine the interaction between two types of brain activity: slow oscillations (SOs) of brain waves that normally take place throughout human sleep cycles and sleep spindle bursts of activity, which typically occur during dreamless slumber outside of Rapid Eye Movement (REM) sleep.
Through the course of their research, the team was able to draw a connection between the SO-Spindle connection and better, more detailed recall of past memories.
The combination of SO and spindle patterns of brain activity has now been observed and documented, and appears to indicate exactly how the brain ‘locks’ certain experiences into long-term memory.
The stronger these two brain activity patterns combine and align in the first instance, the more likely we are to remember the events, and in greater detail.
“Our main means of strengthening memories while we sleep is the reactivation of previously learnt information, which allows us to solidify memories in neocortical long-term stores,” says neuropsychologist Bernhard Staresina from the University of Birmingham in the UK.
“We have discovered an intricate interplay of brain activity – slow oscillations and sleep spindles – which create windows of opportunity enabling this reactivation.”
The experiments only involved a maximum of two hours’ sleep, so now the researchers want to explore brain activity over the course of a full night’s sleep while also examining activity in other parts of the brain such as the hippocampus, to better home in on the exact mechanism used to store long-term memories and access them later in life.
According to neuropsychologist Thomas Schreiner, the findings emphasize the “importance of orchestrated sleep rhythms in strengthening our powers of recall and orchestrating the creation of memories.”
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