A new study has integrated neuroscience and psychological research to reveal how sleep is more complex than previously imagined. The Scripps Research Institute (TSRI) research shows in animal models that sleep suppresses the activity of certain nerve cells that promote forgetting, insuring that at least some memories will last. Senior author Ron Davis said that many scientists have tried to figure out how we learn and how our memories become stabilized, but far less attention has been paid to forgetting, which is a fundamental function for the brain and potentially has profound consequences for the development of memory therapeutics. He noted that the current study merges the neuroscience of forgetting, that is, the brain mechanisms that lead to forgetting, and the psychology of forgetting into an integrated picture. The new study in experimental animals reveals the biological underpinnings of the earlier psychology studies, pointing to the activity of the neurotransmitter dopamine. Dopaminergic activity is known to regulate various types of "plasticity," the ability of the brain to change in direct response to learning and memory formation. That ability includes forgetting as well. The study shows that increasing sleep, with either a sleep-promoting drug or by genetic stimulation of the neural sleep circuit, decreases signaling activity by dopamine, while at the same time enhancing memory retention. Conversely, increasing arousal stimulates dopamine signaling and accelerates forgetting. Davis noted that this signal activity isn't constant but is tied directly to the animal's arousal level, adding that sleep reduces the forgetting signal in the brain, thereby keeping memories intact. As sleep progresses to deeper levels, dopamine neurons become less reactive to stimuli and this leads to more stable memories. The study is published online ahead of print by the journal Cell.