Sleep, Hippo, Sleep...

   The past few nights have been rather fitful, our partially-paralyzed dog growing restless and keeping us (mostly me) awake until the early morning hours.  Feeling is beginng to return as her legs twitch during strolls, and the front part of her paws ever so gradually begin to uncurl on their own.  It is doubtful that she will become a full-on walker again, but she is beginning to feel something and the result for my wife and me is a mixture of happiness and exhaustion as we average 4-5 hours of broken sleep each night.  In our younger days, this would almost be called a binge, a purposeful few nights of staying up late to study or be with friends or to sneak in the maximum amount of play before work.  But in our later years, this is just called exhaustion.  Grabbing a nap sounds like a great plan, but it rarely happens as there is simply too much to do.  The morning begins, the sun heating the air quickly (our temps have beaten the monthly record by a full seven degrees, our hottest July in nearly 150 years) so both dogs and duties have to be started and finished quickly.  Soon it is afternoon and errands and trips to the moms or library or doc or something, then it is three and time to wind down except that it isn't.  The train has again forgotten to stop and we can only stare at the surprised faces of those waiting at the station; sorry, we shrug, didn't know that this was an express train either (as one grows older, it almost seems as if the only thing available are express trains).

   So none of this would have really concerned me, for one makes do with what one is presented.  As the ancient proverb goes, this, too, shall pass.  But here comes a review by Gavin Francis on the book The Mystery of Sleep by sleep professor Meir Kryger, a review which appeared in the London Review of Books.  In his review which he titled "cerebral hygiene," he wrote: Some cetaceans, seals and birds sleep with one half of their brain at a time, which is taken as evidence that sleep has a vital role in maintaining cerebral hygiene.  Sleep is thought to remove waste material produced by brain cells, restore aspects of the body’s function and repair injured tissues.  One of the reasons children sleep so much is that it’s during sleep that growth hormone is generated by the body.  The longer we’re awake the more a chemical called adenosine accumulates in the fluid around brain cells.  Adenosine is crucial for cellular energy metabolism, but too much of it makes us feel terrible: sleep returns it to its normal levels.  And sleep was a topic I discussed in a post at the beginning of the year (there's that train again...that was January and here summer is almost over??).  But now comes a few different thoughts, that of dreaming even if not in a REM (Rapid Eye Movement) stage (...From the 1950s until the 1990s it was widely assumed that to be in REM sleep was to be dreaming, but more recently that’s been shown to be wrong.  If you wake someone during slow-wave sleep, there’s a 10 per cent chance they will report a dream, though the dreams tend to be more conceptual and less vivid than dreams reported during REM.  If you’re prevented from drifting into deep sleep (through exposure to sounds in a sleep lab for instance) your chances of reporting a dream when awoken from non-REM sleep rise above 70 per cent.  No one can agree on the purpose or meaning of dreaming, but it looks as if Freud’s theory – that dreams are the guardians of sleep – is at least partly right: they convert external stimuli such as lights or sounds into dreams rather than waking awareness...Newborn babies spend about half their sleep time in REM sleep, and adults about a quarter.  The deepest phases of slow-wave sleep diminish as we age – some elderly people don’t engage in slow-wave sleep at all.) and the effects of light and regulating "triggers" that likely engages other plants and animals as well (‘Early to bed, early to rise’ isn’t a marker of moral probity, but a genetic inheritance: some people are naturally ‘larks’, others are ‘owls’, according to the ‘clock genes’ they inherit...Light suppresses the secretion of the hormone melatonin from the pineal gland, which is how the brain tells the body there’s a shape to the day.  In humans the gland is buried deep between the two cerebral hemispheres {Descartes thought it was the seat of the soul}.  It receives its information about ambient light via nerve fibres in the retina that respond specifically to blue light.  In some lower-order animals, the pineal gland is exposed near the surface of the brain, and responds directly to ambient light filtering through the skull.  Melatonin pills can enable blind people to establish a diurnal rhythm, and help with jetlag.  It was discovered that the best way to keep the Antarctic base running to a 24-hour clock was to set up bright lights around the base and at every workstation, and to make sure everyone had enough exposure to them in the ‘morning’.  Light isn’t the only means of synchronising the body clock: scheduled meals and the timing of exercise are important too.  

Hippocampus image from Wikipedia

     Okay, there's that, with sleep entering and affecting different parts of our brain, much as the simplified chart on drugs displayed...but concurrently I was finishing Dr. Thad A. Polk's series on our "aging" brain* and what kept popping up was the hippocampi (the word "hippocampus," of which we have one on each side of our brain, actually translates from the Greek definition of "seahorse" due to its similarity in appearance).  Turns out that it shrinks as we age and when it does, it takes with it our "episodic" memory and our neurons needed for that type of long-term memory (another type of long-term memory is termed semantic memory).  Here's how Dr. Polk briefly described episodic memory: Episodic memories are tied to a specific time and place and are remembered from a first-person perspective. Unlike working memories, which are short-term memories, episodic memories can last for a long time and are therefore considered to be long-term memories.  For example, you may still have episodic memories from your childhood.  But episodic memories can also be from just a few minutes ago.  Some memories such as muscle and procedural and semantic (related to remembering facts) are not as affected by aging perhaps because they are not relegated by the hippocampi.  And studies show that our brain adapts to some of these changes by shifting duties, moving more of the work to the back portion of the brain (as compared to younger age groups), a key element in what is called memory suppression -- take a handful of visual or auditory information and discard what isn't necessary when presented with another batch of such information; the older brain seems to have trouble discarding such "extra" information.  Adds Dr. Polk: Roberto Cabeza, Patricia Reuter-Lorenz, and a number of other researchers have repeatedly found that cognitive tasks that evoke activity in a single brain hemisphere in young adults often evoke activity in both hemispheres in older adults.  

    White matter, gray matter, what's it matter?  Turns out that exercise --active exercise as in exercise that causes you to breathe harder for 20 minutes or so-- has been shown to slow and in some cases stop the decline and shrinkage of the hippocampi, as have lab studies showing the receiving of "young" blood vs. receiving blood from an older person (human studies are only now being started on such possible blood differentiations); but conversely, such a factor as stress can accelerate the shrinkage of our hippocampi: Chronic stress and abnormally high glucocorticoid levels have also been found to impair brain function.  As we age, we tend to lose neurons in the hippocampus, which is the key brain structure involved in long-term memory.  Rats also experience neuron loss in the hippocampus as they get older.  But if you remove their adrenal glands and prevent the production of glucocorticoids, then you don’t see the normal age-related loss of hippocampal neurons.  Conversely, repeatedly injecting rats with glucocorticoids speeds up the loss of these neurons...glucocorticoids are hormones typically released during a panicked fight-or-flight situation as well as other stressful times. 

    Ours brains, aging or not, are just a part of our rather selfless, silent, and cooperative bodies, working diligently with each passing moment whether we understand it or not.  It is life, allowing us the freedom to enjoy the seasons and savor the flavors of all that surrounds us.  For some, this is ideal and relaxing and for others, the unexpected arrives.**  For my wife and I, we are happy to just have our pup, panting or not; we wish she could travel beyond her vocal-eyes and actually tell us what is going on and how she feels.  But limited sleep or not, my wife and I realize how fortunate we are.  It may be due to our shrinking hippocampi, our memories of all of this perhaps passing almost as quickly as the days seem to do.  But the memories staying with us are well worth the price...not the grogginess and bags under our eyes, but the love and joy that we get to experience for yet another day with our friends, our mums, and our pups.  And there is no shrinking that...


*This is a lecture course offered (and often on sale) by The Great Courses...click on the "full description" link for a more detailed description. Says the literature about Dr. Polk: Professor Thad A. Polk is an Arthur F. Thurnau Professor in the Department of Psychology and the Department of Electrical Engineering and Computer Science at the University of Michigan.  He received a B.A. in Mathematics from the University of Virginia and an interdisciplinary Ph.D. in Computer Science and Psychology from Carnegie Mellon University.  He also received postdoctoral training in cognitive neuroscience at the University of Pennsylvania. 

**I use the term unexpected because our hearts go out to those caught in the needless, cowardly, and selfish violence that has happened in Barcelona and Charlottesville...even with such a complex structure as our brain, it is difficult to understand why and how such behaviors are made justifiable (even in our state governments, the act of running a vehicle into a group of protesters is now considered legal and being defended).  Perhaps our brains are incapable of understanding a few things after all...