Have you ever heard someone say they were a bad napper?
I have not and can remember my undergraduate days when one of my first thoughts after turning my alarm off was, “when can I take a nap today?” I wasn’t necessarily staying up too late or pulling all night cram sessions – although that did happen. However, I can look back now and see that I wasn’t practicing behaviors of good sleep hygiene. The Mayo Clinic.org (1) has a lot of good advice for getting a good night’s sleep. You’ve heard of some of them I’m sure:
- Create a restful setting.
- Use your bed for sleep and not work or T.V.
- Go to bed and wake up on a schedule.
- Sleep for about 7 hours.
A common sleep recommendation is to limit naps! Wait, what?
Anyone who has struggled to get children to nap should be laughing so hard now they might be crying. As a parent of two young boys, I cherish times when they both settle down for an afternoon nap. Certainly, children should be getting more sleep than adults, but how tempted am I to nap with them? Mayo Clinic.org (2) explains that adults who nap should pay attention to the length of their nap. They suggest that going past 90 minutes in a nap is a deal breaker. After 90 minutes you typically progress into deeper sleep. Spending too much time or not enough in deep stages can cause you to feel terrible after you wake.
I have been teaching my students about the role of sleep in forming memory for a while now. Psychologists Georg Muller and Alfons Pilzecker were among the first to suggest that what we learn changes overtime, and sleep can account for some of this change by improving long-term memory (3). They found that participants learning short sets of “non-sense” syllables (e.g., FOV) would recall syllables randomly, over time, even when these syllables were no longer being tested. They called the ability to remember without intention, “perseveration.” Consider not being able to stop thinking about an embarrassing event, long after you were embarrassed; this is perseveration. Muller and Pilzecker called this process of consistently remembering consolidation. This word makes me think of taking all the leftovers in my fridge and planning to eat what is still good and throw out what is too far gone each week. Consolidation is an important process to remembering.
When we make new memories, the hippocampus is heavily relied upon. Overtime, memories begin to rely predominately on the cortex and in turn, less on the hippocampus. It is not that the knowledge “moves” from one place to the other. It is that as time passes, we tend to use and connect long-term memory with other memories. (4) This image from research by Gordon and Diekelmann depicts how information at learning relies on activation of the hippocampus, but, after sleep and retrieval, activation shifts to the cortex.
In the two sets of diagrams labeled “Cortex” and “Hippocampus”, the dark shaded “neural connections” in the hippocampus at first wakefulness are solid colored but become clear circles during sleep. In turn, during sleep, the neural connections in the Cortex become a darker shade and their dotted lines link together. The bottom line is that memories are dependent on sleep AND consistent retrieval to facilitate learning.
Back to napping. Taking a nap longer than 90 minutes can leave you feeling unrested and may keep you from falling to sleep later that night. But are there benefits to taking naps for learning? Researchers have been making the case that naps, no longer than 90 minutes may help. Work from Axel Mecklinger’s and colleagues (5), describes benefits in declarative memory after naps. Declarative memories are those you are aware of learning. For example, I can teach you facts about glaciers in a lecture, show you pictures of glacial melt, and ask you questions about your learning. You are consciously aware of your learning and you intend to remember this new information about glaciers.
What happens during napping less than 90 minutes that seems to help with memory? Mecklinger’s work focuses on sleep activity, spindles specifically. Consider holding a spool of twine. As you firmly grip on the spool with one hand, you use the other to find the twine’s end. You pull. With a quick jerk of the twine, you release a long piece high into the air. You pull gently, and the twine comes slowly out of your fingers. A sleep spindle looks like pulling twine off a spool. As we sleep our brain produces ups and downs of energy called oscillations. These are shorter and slower or higher and faster (like different pulls on the twine) as we sleep. Mecklinger has found that spindles occurring when we are not in Rapid Eye Movement Sleep (REM) produce vibrations crucial for memory consolidation.
There is much more we need to understand about sleep and memory but for now, take a nap! Keep it shorter than 90 minutes though. This might be all you need to improve things you just learned and keep you feeling rested and ready for new learning!
- Mayoclinic.org: https://www.mayoclinic.org/healthy-lifestyle/adult-health/in-depth/sleep-the-foundation-for-healthy-habits/art-20270117
- Mayoclinic.org: https://www.mayoclinic.org/healthy-lifestyle/adult-health/in-depth/napping/art-20048319
- Lechner, H.A., Squire, L. R. & Byrne, J. H. (1999). 100 years of consolidation – Remembering Muller and Pilzecker. CSH Press, Learning & Memory. Retrieved online: (http://learnmem.cshlp.org/content/6/2/77.full
- Gordon, B. & Diekelmann, S. (2014). Sleep smart—optimizing sleep for declarative learning and memory. Frontiers in Psychology, 6. Retrieved from: https://www.frontiersin.org/article/10.3389/fpsyg.2015.00622
- Studte, S., Bridger, E. & Mecklinger, A. (2017). Sleep spindles during a nap correlate with post sleep memory performance for highly rewarded word-pairs. Brain and Languages, 167, 28-35.