The tiny city of Kent (Ohio) borders a major, busy railroad. At least 12 times a day, you hear the multiple blarring “BAHHHHHHHs” of the commercial trains crossing intersections late at night or you are constantly stuck at one of these major intersections waiting for a 40-car train to pass. When I first moved here, I would be woken up every night around 3 AM by one of these stereotypically Midwestern forms of transportation. But now I don’t. Initially, I assumed that this was due to Pavlovian habituation–that is, hearing a repeated noise decreases responsiveness to the point that you (or a rodent) fully ignore it. This week, however, I learned that my habituation to “BAHHHHS” while asleep, which prevents me from awakening, is due to increased sleep spindles. Sleep spindles are a defining characteristic of stage 2 sleep. Similar to K-complexes, they can be invoked by noise. If someone shuts (not slams) a door or lightly claps their hands while your in stage 2 sleep, your brain will begin to “spindle.” Obviously, this can’t be tested at home unless your a sleep nerd and have this equipment freely available. Sleep spindles are also indicative of improved memory consolidation. Daytime naps that are saturated with Stage 2 sleep and spindle activity improve retention of emotionally-salient information and performance on a motor task.
To focus on this particular study, Harvardian researchers have uncovered that sleep spindles protect people in noisy sleeping environments. To support this, they did baseline sleep recordings in individuals and found either a high or low density of sleep spindles. Following three days of exposure to a quiet (the country) or to a noisy (the city) environment induced, of course, by a sound machine, they found that those individuals who slept more soundly across the night in the noisy environment, as electrophysiologically determined through less nighttime arousals, had much greater densities of sleep spindles!
I immediately thought of sleep machines. I always assumed that sleep machines producing the sounds of the rainforest and beach were consumer lunacy, but perhaps this is the best way, after all, to ensure a good night’s sleep, though through an entirely different mechanism; your training your brain to spindle more and not training your stress systems to be soothed by the mating calls of tree frogs and crashing of waves.
Dang-Vu TT, McKinney SM, Buxton OM, Solet JM, & Ellenbogen JM (2010). Spontaneous brain rhythms predict sleep stability in the face of noise. Current biology : CB, 20 (15) PMID: 20692606