A team of researchers in Germany has found that a certain type of memory improves when a person's brain is stimulated with a mild electric current during a particular phase of the sleep cycle.
Neuroscientist Jan Born, of the University of Lubeck, has been studying the role of sleep in human memory for the past decade. In recent years, there's been evidence to suggest that REM sleep and non-REM sleep serve to strengthen neuron connections for different kinds of memories. While the scientific community is split on just how these phases influence memory, Born and his colleagues have recently focused on non-REM sleep, specifically the initial, drowsy, slow-wave phase. They're interested in its role in strengthening declarative memories, otherwise known as fact-based memories, as opposed to other types of memory such as motor-skill, or procedural learning.
"You remember the things consolidated during sleep better than not during sleep," says Born. "Our research is finding out which stages are more important for memories."
In previous studies, scientists have found that different phases of sleep are characterized by different patterns of brain activity. The most well-known is that of REM sleep, a period of heightened activity within the cortex when dreaming usually occurs. During a full night's rest, REM sleep occupies 20 percent of a person's sleep.