We spend one third of our lives sleeping, but we still do not know exactly why we sleep. Recent research shows that that the brain does its housekeeping while we sleep, and clears away its waste. According to another hypothesis, sleep plays the vital role of restoring the right balance of brain synapses to enhance learning, and two studies published in today’s issue of Science now provide the most direct evidence yet for this idea.
How the brain encodes and stores memories is one of the enduring mysteries of neuroscience. Memories are thought to be encoded by the strengthening of synaptic connections, and many researchers believe that they are retained by proteins at the synapses. And yet, while memories can persist over our entire lifetimes, these synaptic proteins are continuously being destroyed and replaced, over a time-frame of hours or days.
Several years ago, neuroscientist Roger Tsien of the University of California, San Diego, proposed that long-term memories are stored in patterns of holes created within a lattice-like structure called the perineuronal net. Sakina Palida, a graduate student in Tsien’s lab, presented evidence for such a ‘punch-card’ mechanism at the annual meeting of the Society for Neuroscience in Chicago earlier this month.