Mental Leaps Cued by Memory’s Ripples

Over the past few decades, researchers have worked to uncover the details of how the brain organizes memories. Much remains a mystery, but scientists have identified a key event: the formation of an intense brain wave called a “sharp-wave ripple” (SWR). This process is the brain’s version of an instant replay — a sped-up version of the neural activity that occurred during a recent experience. These ripples are a strikingly synchronous neural symphony, the product of tens of thousands of cells firing over just 100 milliseconds. Any more activity than that could trigger a seizure.Now researchers have begun to realize that SWRs may be involved in much more than memory formation. Recently, a slew of high-profile rodent studies have suggested that the brain uses SWRs to anticipate future events. A recent experiment, for example, finds that SWRs connect to activity in the prefrontal cortex, a region at the front of the brain that is involved in planning for the future.Studies such as this one have begun to illuminate the complex relationship between memory and the decision-making process. Until a few years ago, most studies on SWRs focused only on their role in creating and consolidating memories, said Loren Frank, a neuroscientist at the University of California, San Francisco. “None of them really dealt with this issue of: How does the animal actually pull [the memory] back up again? How does it actually use this to figure out what to do?”The new results are also prompting a broad shift in our understanding of the hippocampus, a C-shaped nub of brain tissue behind each ear. Since the late 1950s, when the region was famously tied to memory loss in the patient known as H.M., researchers have focused on its role in creating and storing memories. But newer studies have shown that the hippocampus is active when people imagine performing a task in the future. Similarly, people who have damaged hippocampi cannot imagine new experiences. The hippocampus doesn’t just allow instant replays — a kind of mental time travel into the past — it also helps us mentally leap forward.In fact, complex planning may be the true benefit of the hippocampus. “That’s the point of having a memory, right?” Frank said. “To go back to the experiences you’ve had, extract general principles from them, and then use those principles to figure out what to do next.”Read more at...Quanta, October 2014 (and syndicated by Scientific American).