Simon Friderichs, first-year, drifts through the murky universe of sleep physiology.
The scene is set. It’s Thursday afternoon after a marathon of a morning filled with lectures on cranial osteology and acute neuralgia. Revision is required. Paper out, pen gripped, poised to tackle Parkin’s “shopping lists” of anatomy from the night before until a familiar wave of exhaustion piles on. Like any other diligent medical student this has no immediate consequence. However as time carries on, your notes begin to become less legible and symptoms of fatigue take hold. Resonating yawns, tearing eyes, and an overall lack of gumption become common symptoms. There is no time for a tempting nap as the entire weeks lectures stare up from the desk simply begging for attention. Such is the dilemma a medical student often faces… to nap or not to nap… that is the question.
Dr. Maria Korman and Prof. Karni of the Center for Brain and Behavior Research at the University of Haifa conducted a study into daytime sleep and its effects on memory consolidation . Dr. Korman proposed that there are two main types of memory: declarative memory referring to “what”, for example what you learned yesterday, and what you had for dinner last night, and non-declarative memory referring to movements of the body, for example how to play the piano, or ride a bike. In this study two groups of volunteers were taught repeated motor activity with their fingers – touching thumb to each digit in a specified sequence – examining the procedural type of memory. One group was allowed to nap for 90 minutes prior to testing and post teaching while the other stayed awake the entire time. Upon examination, the group that slept during the afternoon showed a distinct improvement in motor memory and function compared to the group that stayed awake which did not show any improvement. Dr. Korman concluded, “a daytime nap has been shown to speed up performance improvement in the brain”.
A second experiment by Dr. Korman and Prof. Karni was then conducted to show another type of memory concept: memory interference. Memory interference refers to an instance where one learns to perform a second task different to the first. As a result the brain struggles to successfully remember the first task, hence termed interference. In this second study, a third group of participants were taught the first sequence of digit movements, then were introduced to a second sequence two hours later. Upon examination, the second task disturbed the memory consolidating process and no improvement in skill was achieved. In contrast, the fourth group demonstrated a significant increase in performance when taught the same second sequence and allowed a 90 minute nap between sequences. This study suggests that daytime sleep can improve memory interference and consolidation.
It has been shown that optimal sleeping time per night should range between six to eight hours . Recent studies compiled by researches in the UK and Italy have found a link between sleeping less then six hours a night and premature death. There was a 12% increase in premature death of those who slept for less then six hours a night as compared to those who consistently had six to eight hours sleep per night. This study also concluded that those who consistently had more than nine hours of sleep a night had a greater risk of premature death. Professor Capuccio, who led the study stated, “while short sleep can represent ill health, long sleep is more of an indicator of ill health.” This study also noted previous research had linked lack of sleep to an as- sociation with heart disease, high BP, obesity, and diabetes. So for those late nights when studying is crucial and sleeping comes second to none, what does one do?
Sleep is cumulative in nature and the effects of sleep loss will surely be experienced the next day. This “sleep deficit” can impair motor function, vision, and most importantly motivation . Many people experience a natural drowsiness occurring in the after- noon around 8 hours after waking. Research shows that a nap can increase alertness, and cognitive function, while reducing stress and panic ; factors needed to survive medical school. Researchers suggest a fifteen to thirty minute nap improves cognitive function, but also isn’t long enough to fall into the deeper stages of sleep. However, EEG analysis conducted by Dr. Hayishi has also shown a one- hour nap to have an increased level of restoration compared to a thirty-minute nap .
In 2005, Dr. Dinges of the University of Pennsylvania School of Medicine led an experiment funded by NASA to help astronauts nap and to measure how effective these naps were in terms of memory, alertness, response time, and other cognitive skills . In the study, 91 volunteers spent 10 days on one of 18 different sleep schedules in a laboratory. These schedules involved normal night sleep combined with a variety of 0 to 2.5 hour naps. To measure the effectiveness, scientists then gave the participants a wide range of cognitive tests. In general, results concluded that the longer the nap the better but that “working memory” benefited most exponentially from these naps. “Working memory,” Dr. Dinges explains, “involves focusing attention on one task while holding other tasks in memory and is a fundamental ability critical to performing complex work.” Other studies at NASA on sleepy military pilots and astronauts found that a 40-minute nap improves performance by 34% and alertness by 100% .
Unfortunately, naps can sometimes backfire, leaving one on a more groggy and less energetic feeling. This phenomenon is known as Sleep Inertia. Little is known about the mechanisms for Sleep Inertia, but a theory proposed by Dr. Peters,  posits that sleep inertia results from a build up of adenosine neurotransmitters in the brain during non-REM (rapid eye movement) sleep causing a feeling of tired- ness. This may be resolved by inhalation of fresh air, experiencing a fluctuation of temperature as in taking a cold shower, or by exposure to light.
Many studies have been conducted to demonstrate that napping improves cognitive function and decreases the chances of memory interference. Despite all this the main stigma of napping still remains that napping is only for children, the sick, and the elderly. “That’s a foolish notion held by people who have no imaginations” to quote Winston Churchill. Sir Winston and myself are in strong agreement on this point. Many of the public is not aware of the benefits of an afternoon “ziz” (as I call them), and the advantages they offer. One must always keep in mind however that the best way to battle fatigue and increase brain output is ensuring that you consistently get up to 8 hours of sleep a night. But, when these nights are unrealistic and fatigue starts to set in the next day, a quick nap will do wonders for your mental and physical stamina .
If nothing else, it proves an effective excuse to “shut your eyes and consolidate your memories while repairing your cognitive functions.” Besides, you will be in good company, as Winston Churchill, Napoleon, Albert Einstein, and Thomas Edison were all known to have valued an afternoon nap.