René Descartes, French polymath and founder of entire academic disciplines, also spent years seeking the physical location of the soul — and thought he’d found it.
It’s understandable in context: Descartes wanted to understand sensory perception, cognition and the mind; he equated the latter two things with souls, but recognized that cognition must also have a physical seat. Though his hunt picked the wrong candidate, the structure he focused on was much more important than his contemporaries realized. Moreover, its functioning had a major effect on Descartes’ own life.
In his hunt, Descartes focused on unpaired, unique structures within the brain, reasoning that ultimately all perception has to land in one place, for cognition to be performed on it. The pineal gland (a.k.a. the conarium), largely overlooked at the time, met those criteria.  Though the pineal gland does perform a kind of sensory processing via its connection to the eye, its role is indirect and subsidiary, despite its central location. Again, given the information available to Descartes, this still represents major progress. Even with a modern biological understanding, the true answer is somewhat counter-intuitive—human cognition is in fact asymmetrical. 
So what does the pineal gland do, then? This: the pineal gland decides when you can sleep. Broadly speaking, it bases this on how much light your eye takes in. But it doesn’t do so directly. Instead, it uses a godawful mess of a system called the circadian clock. This “complex loop” involves at least four anatomical structures  and six gene families. The loop is controlled by a repurposed antioxidant (the familiar melatonin) which never stopped serving its original function, potentially disrupting the loop’s timing; the clock is affected by non-light-related external stimuli, too. 
Somehow, this bricolage of nonsense seems to work acceptably for most people. But things can, and do, go funny along the way.
I have an innate condition called “primary DSP.”  My circadian loop doesn’t work the same way your typical one does. Current science can’t peek in to see exactly what goes wrong; it can only observe DSP patients’ melatonin levels. Still, those readings are suggestive. In primary DSP, a uselessly small amount of melatonin might fire from the pineal gland around sundown; but the brunt of it doesn’t come until very late into the night.
The end result is that, if left alone, the DSP patient will get a healthy amount of sleep, at a consistent time. That time just isn’t what other people would expect.
However, if an attempt is made to force the DSP patient to sleep and wake up at the same time as everyone else on any sort of regular basis, they simply… won’t. No amount of yelling, guilt, desire, or self-discipline will change the circadian loop. No drug on the market normalizes it (supplemental melatonin included), which isn’t surprising because no one understands the problem in the first place. The inevitable results — even of ineffective attempts — are withering and unyielding sleep deprivation, and, at times, physical ill health. (Sleep deprivation can suppress one’s immune system.) 
Thus, “treating” DSP is about as effective as trying to make a tortoise faster by kicking it repeatedly down a racetrack — and similarly harmful.
It is a historical fact that René Descartes almost always woke up around lunchtime and went to bed around midnight.
It is also a historical fact that, when Descartes was finally compelled to wake up early in the morning, he lasted only weeks on this schedule before succumbing to a minor illness and dying. 
I didn’t unearth this historical parallel just to validate that DSP exists. I already know it exists, because I have it: over a decade of exhausting, occasionally torturous experiments have proven that to my satisfaction. If no trace of it were found in history, I wouldn’t have it any less.
I unearthed this to highlight Descartes’ response. He lacked models to draw from; he didn’t have his future self to consult, nor all those who came after. All he knew is that if he was made to wake up early — as he was in childhood, and again near the end of his life — he failed to adjust to the new schedule, and on top of that got very terribly sick. Out of stark necessity, Descartes pushed for what accommodations he could get in group environments, most notably in schooling, and mostly got them. When he lived on his own, he simply slept when he needed to, and by that time never thought it a burden. 
Four centuries later, Descartes shines like a star in the pages of history. Few care that he made mistakes and pursued some bizarre theories; those are overshadowed by the words and ideas he propounded that still endure today. But even in the stranger weeds of Descartes’ writings, there’s often still a glimmer of truth.
Current economic systems force many people to trade adequate sleep for dollars. The well-off, many of whom have contributed themselves to this problem, very seriously tell masses (who already know) that sleep deprivation is bad, and profit richly from their hectoring. Descartes even knew four centuries ago.  That’s not a lesson we need in 2016.
Descartes, if born into this generation, wouldn’t produce the same things he produced in the 1640s. Most of that ground’s been covered by now, and most of his mistakes then are due to knowledge gaps that have since been filled in. By following his own instincts and his own body, he’d find some truth — and he’d almost certainly make an entirely new set of mistakes to go with it.
But those mistakes, I think, would still be fascinating.
 “Descartes and His Peculiar Sleep Pattern,” Damjanovic et al., Journal of the History of the Neurosciences, 00:1–12, 2015, page 2. Much of this post is commentary on Damjanovic’s paper.
 Damjanovic, 3.
 “Human: The Science Behind What Makes Us Unique,” Gazzaniga, 1st ed., 2008, 13; 33. The whole right side of the brain can be disconnected from the left, with relatively few ill effects; but similar, originally redundant structures the left and right hemispheres have been repurposed, to some extent, for specialized functions. Oddly, though this is not the case for most mammals, it is for birds.
 The pineal gland, the retina, the superchiasmatic nucleus (part of the hypothalamus), and the superior cervical ganglion.
 Damjanovic, 7.
 DSP means “delayed sleep phase”; I’m not expanding its acronym because of my distaste for the general connotations of the word “delayed” here. I was born with this condition; it’s no temporary anomaly, and I’m not going to be back on the air at a more convenient time next week. Using only the acronym allows me to focus on the thing itself, not its name.
Damjanovic et al. also discuss a “secondary” DSP. The basic idea is that adolescents somehow screw up their own sleep schedules on purpose; it presents like DSP except that it’s allgedly fixable through the patient’s own effort. Diagnosing someone with secondary DSP when they really have primary DSP is potentially lucrative for the therapist, but often very painful for the patient.
 Damjanovic, 6. “Since sleep in patients with DSP is essentially normal, albeit pushed into later hours, when left to choose the sleep schedule that feels natural to them, their sleep complaints typically dissipate. For many patients […] following their natural sleep timing could be the only viable outcome.”
 Damjanovic, 8-9.
 Damjanovic, 6.
 Damjanovic, 5. Descartes vividly described wakefulness as a process by which “the substance of the brain is dried up and its pores enraged”; sleep, he said very accurately, is “nourishment for the brain.”