A new study suggests more sleep decreases dopamine's signaling activity, improving memory retention.
The new study, led by researchers at The Scripps Research Institute (TSRI) in Florida, is published in the journal Cell.
The American Physiological Society has previously noted that the ability to form memories is crucial for an organism to adapt strategically to a changing environment. And from the beginning of experimental memory research, scientists have observed that sleep benefits memory.
Ron Davis, senior author of the latest study, says scientists have previously tried to determine how we learn and how our memories are secured.
"But far less attention has been paid to forgetting," he says, "which is a fundamental function for the brain and potentially has profound consequences for the development of memory therapeutics."
This latest study, however, pulls from both the neuroscience and the psychology of forgetting to create a unified view.
Davis and his team note that early psychology studies have suggested that sleep supports memory retention by quieting mental and behavioral activity. Meanwhile, neuroscience has suggested sleep enhances memory stability - also called consolidation.
More sleep, less dopamine, better memory retention
In their latest study, the researchers investigated animal models to look at the biological basis of previous psychology studies, which indicated that the neurotransmitter dopamine played a role.
Dopamine regulates different types of plasticity, which is the brain's ability to change in response to both learning and memory formation. But this ability also includes forgetting, say the researchers.
Through their study, the team was able to demonstrate that increasing sleep - with either drugs or by genetically stimulating the neural sleep circuit - decreases dopamine's signaling activity while improving memory retention. They also found that increasing arousal speeds up forgetting by stimulating dopamine signaling.
These findings support earlier psychological studies as well as recent findings in the field of neuroscience. Davis says their results "add compelling evidence to support the model that sleep reduces the forgetting signal in the brain, thereby keeping memories intact."
"As sleep progresses to deeper levels," he adds, "dopamine neurons become less reactive to stimuli and this leads to more stable memories."
Though it is widely known that sleeping helps memories, first author Jacob A. Berry says they have uncovered a crucial aspect of how this works. He explains:
"Importantly, we have revealed that one of the ways sleep protects a new memory is by quieting dopamine neuron activity that causes forgetting. Since laboratory animals and humans share a need for sleep, as well as many genetic and circuit mechanisms underlying learning and memory, our findings may shed light on the mechanisms underlying the interaction between sleep and memory in humans."
Medical News Today recently reported on a study that suggested extra sleep could improve memory for people with Alzheimer's. Researchers from Washington University School of Medicine in St. Louis, MO, found that extra sleep restored the ability of fruit flies - whose brains regulate sleep much like humans' do - to make new memories.