Author Page for Sam McDougle

To Sleep, Perchance To Eat

Why do organisms sleep?

“Methought I heard a voice cry, “Sleep no more!
Macbeth does murder sleep!” the innocent sleep,
Sleep that knits up the ravelled sleave of care,
The death of each day’s life, sore labor’s bath,
Balm of hurt minds, great nature’s second course,
Chief nourisher in life’s feast.”

Macbeth spoke these words to his lady with strained desperation as he brooded over his murderous deed.  Sleep is a curious contradiction – slumber is both vulnerable and comforting.  However, assuming you’re not wrapped up in any malicious political assassination plots, it’s more often the latter.

The “how” of sleep has been widely researched – from the progression of the stages of “slow-wave” sleep and the details of deep slumber (REM), to the heavy physical and cognitive impairments resulting from sleep deprivation.

The “why” of sleep is more of a mystery.  There are countless theories about the purpose of sleep. It has been implicated in the secretion of vital hormones, neurogenesis (the creation of new neurons), memory consolidation, and immune system optimization.  However, in a recent article in Nature’s special review issue celebrating Darwin’s 200^th birthday, Jerome Siegel of UCLA argues that these effects of sleep don’t explain the considerable variation in sleep patterns across the animal kingdom.

Mammals range from less than 3 hours of REM sleep a day to more than 8 hours.  Some hibernate (brown bears, ground squirrels), while others seldom doze (giraffes, walruses).  Dolphins enter an intriguing REM imitation called “ultra slow-wave sleep,” where they alternate between brief bouts of lazy floating and slow swimming (though they remain very responsive to environmental stimuli).  When fur seals slumber deeply they turn off one hemisphere of their brain at a time, with one flipper keeping balance while the other remains motionless.

Non-mammals show similar levels of variation.  White-crowned sparrows sleep very little, and sometimes not at all when they’re migrating.  Hummingbirds enter a hibernation-like state called “torpor,” which is marked by a relatively short period of extremely low metabolism (think of it as a shorter but more “turned-off” hibernation).  Reptiles have not been definitively shown to enter REM sleep, and their sleeping habits are often dependent on temperature.  Even non-animals exhibit sleep-like behaviors – many deciduous trees are dormant in certain seasons, parasites often enter suspended cystoid phases during their life cycle, and one species of yeast was brought back from a 45 million year slumber and brewed into a beer.

Siegel’s argument is that the variation mentioned above (which is a small sample of the data he cites) makes it unlikely that sleep has some widely-applicable neurological function, which is a common belief.  Bears have unexceptional immune systems, but go into wildly long periods of deep hibernation. Lizards can learn and have memories, but show no REM sleep at all.  Dolphins don’t have growth hormone deficiencies, but are moving around their entire life.  Trees certainly don’t have neurogenesis (or any neurons at all) but enter states of seasonal sleep-like dormancy.

***

There are certain obvious functions of sleep that work across species and explain variation.  When sleeping, animals remain in one spot, thus decreasing the chance of running into a hungry predator and this defense mechanism is especially practical when the animal sleeps in a protected cave or nest (perhaps King Duncan should have taken a cue from these animals).  Furthermore, one aspect of sleep is absolutely universal across all living things – it saves energy.  Siegel likens sleep to “turning off the lights” when you leave a room – animals only want to spend the energy they need to spend to carry out vital behaviors (eating, mating, rearing children, etc).  The more energy the animal burns, the more it needs to be out and about foraging for food, at risk for both predation and starvation.  This idea is supported by the variation of sleep patterns in the animal kingdom, and these patterns are dependent on environmental factors – brown bats sleep 20 hours a day to avoid bird predation and they forage vigorously for the other 4, Giraffes sleep very little as they need to keep moving to avoid open-plain predation and eat plenty of low-nutrition flora, and lions sleep most of the day to conserve vigor for the demanding hunt.

Sleep is an energy saving mechanism, or as Siegel puts it, “adaptive inactivity.”  It may be a rather simple answer to the “why we sleep” question, but it covers the bases and makes convincing adaptive sense:

“Why would some species need so much more of the mysterious restorative process that has been proposed to determine sleep duration than other species?…Sleep is best understood as a variant of dormant states seen throughout the plant and animal kingdoms and that is itself highly adaptive because it optimizes the timing and duration of behavior.”

That is not to say the other proposed functions of sleep aren’t significant, but they are less likely to be the reason sleep evolved in the first place.  Simple energy conservation and risk avoidance tell a compelling story – sleep is, above all, the “Chief nourisher in life’s feast.”

I look forward to the unearthing of Dr. Shakespeare’s methodical research on the correlation of foraging patterns, food intake, and REM duration in soon-to-be assassinated medieval Scottish kings.

Beauty Isn’t Meninges Deep

Beauty Isn’t Meninges Deep

Neuroscientists on the looks of the brain and its parts

“Soft.”

“Squishy.”

“A convoluted mass of gray and white matter.”

It’s easy to view the brain as a soggy, somewhat repellent heap of warm biological pudding.  But when you really get inside the supple pink mass, layers of neurons (or “butterflies of the soul” as their discoverer Ramón y Cajal called them), gleaming axons, branching dendrites, and countless complex sub-structures reveal the brain’s undeniably exquisite (and ancient) architecture.

Studying the brain is somewhat like studying astrophysics;  Investigators are burdened with the task of picking apart a complex universe of myriad micro and macro forms about which they know relatively little.  The gaps in knowledge start with the very small (i.e. does neuron X interact with neuron Y through electrical coupling or a chemical synapse?  Is it inhibitory or excitatory? etc…) and inflate as the lens gets wider (What is going on in Alzheimer’s disease? What is sleep for?  How are reflexes timed?).  There is no Einsteinian figure that has provided a binding theoretical foundation that illuminates the functioning of the brain, and, like quantum physics, some fields leave remarkably much to be desired (what the hell is “Consciousness?”).

Neuroscientists are often forced to decide which area of the brain to study early in their careers.  While they aren’t destined to choose one spot and stick to it, they often find themselves consumed by a single region of choice, lightheartedly pointing out its superlative qualities at dinner parties and lab meetings.  Many factors go into the decision.  Some areas, like the neocortex, offer appealing theoretical conundrums about “higher order” cognitive processing, thinking, and identity.  Others have been implicated in debilitating, unhealthy behavioral patterns (i.e. the insula and addiction) and may thus appeal to the more righteous of the brainoids – those who tirelessly look for cures and neurological therapies.  Those interested in sexual behavior have a handful of choices as well (the caudate nucleus, the amygdala, anterior cingulate cortex, etc).

Nevertheless, it often seems as though researchers are drawn to certain aesthetic aspects of brain regions, even if the functional aspects are of primary interest.

***

• At a recent lecture I attended at the University of Pennsylvania, the gifted neuroscientist Rachel Wilson commented on the remarkable “order” of vertebrate chemosensory neurons before she spoke about her research on sensory processing in the fruit fly olfactory system. The neurons that line the fruit fly’s antennal lobe are positioned in a tight, repeated pattern.  Wilson often publishes gorgeously stained photos of the chemosensory neurons of the fruit fly antenna, such as the one seen here to the right– and she’s clearly drawn to their visual splendor.

• “Order,” it seems, is an attractive attribute.  Javier Medina (the neuroscientist I work for) of The University of Pennsylvania often champions the coral-like, tightly-folded cerebellum for its functional worth as well as its graceful, structured beauty.

“Confocal micrograph from a cerebellum expressing green-fluorescent protein in Purkinje cells”: The bright green circles are the cell bodies and the middle area shows their parallel axons.

Medina recently disclosed to me one reason why he studies the cerebellum instead of the ever-popular cortex:  ” [in the cortex] More than anything, you find silent cells…cells that don’t like to talk much, fire an electrical impulse here or there, but for the most part, keep quiet. For all the hoopla about it, the cortex is a sort of boring place… but if you dig your electrodes deeper, you’ll discover a neurophysiologist’s wonderland.  The cerebellum is never silent.”  The cerebellum is an exciting place indeed, with its “star-like stellate cells,” illuminating chandelier cells, and “gazillions of little granule cells, packed together like sardines.”  Furthermore, Dr. Medina is from Spain, and cites Cajal, his compatriot, as a “hero” and a “genius.” Cajal tackled the cerebellum – below is his skillfully detailed sketch of the cerebellum’s Purkinje cells, with their characteristic labyrinthine trellis of interlaced dendrites:

• The unique appearance of certain brain regions has sometimes played a role in their naming. The hippocampus was given its distinctive moniker because of a physical resemblance to the sea horse, which itself shares a name with the half-horse, half-serpent creature of Greek Mythology.

Cajal’s Hippocampus

• The structure of the enigmatic organ as a whole can actually be quite appealing as well.

The brain at the top is a common shrew's, the bottom a dolphin's. Note the "back bends" and the major differences in appearance.

Cognitive scientist and author Mark Changizi, of the Rensselaer Polytechnic Institute, alludes to the beauty found in the diversity of brains across species, writing, “brains differing by several orders of magnitude in size look so different that a visiting alien would have no idea they’re the same organ at all.”  His new research looks at the meandering twists and turns (“back bends”) that brain tissue must take in order to accommodate parallel increases in body and brain size across evolutionary time.  Those bends can be seen in the dolphin brain below, which he’s quick to describe as “gorgeous.”

***

From the iconic pop culture image of a brain in jar, to it’s oft-satirized role as zombie food, the brain is not usually known for its beauty.  But when we synthesize our knowledge of the organ’s extraordinary abilities with glances into its intricate inner architecture, the brain is revealed as a truly unequaled natural wonder.

Beauty Isn't Meninges Deep

Beauty Isn’t Meninges Deep

Neuroscientists on the looks of the brain and its parts

“Soft.”

“Squishy.”

“A convoluted mass of gray and white matter.”

It’s easy to view the brain as a soggy, somewhat repellent heap of warm biological pudding.  But when you really get inside the supple pink mass, layers of neurons (or “butterflies of the soul” as their discoverer Ramón y Cajal called them), gleaming axons, branching dendrites, and countless complex sub-structures reveal the brain’s undeniably exquisite (and ancient) architecture.

Studying the brain is somewhat like studying astrophysics;  Investigators are burdened with the task of picking apart a complex universe of myriad micro and macro forms about which they know relatively little.  The gaps in knowledge start with the very small (i.e. does neuron X interact with neuron Y through electrical coupling or a chemical synapse?  Is it inhibitory or excitatory? etc…) and inflate as the lens gets wider (What is going on in Alzheimer’s disease? What is sleep for?  How are reflexes timed?).  There is no Einsteinian figure that has provided a binding theoretical foundation that illuminates the functioning of the brain, and, like quantum physics, some fields leave remarkably much to be desired (what the hell is “Consciousness?”).

Neuroscientists are often forced to decide which area of the brain to study early in their careers.  While they aren’t destined to choose one spot and stick to it, they often find themselves consumed by a single region of choice, lightheartedly pointing out its superlative qualities at dinner parties and lab meetings.  Many factors go into the decision.  Some areas, like the neocortex, offer appealing theoretical conundrums about “higher order” cognitive processing, thinking, and identity.  Others have been implicated in debilitating, unhealthy behavioral patterns (i.e. the insula and addiction) and may thus appeal to the more righteous of the brainoids – those who tirelessly look for cures and neurological therapies.  Those interested in sexual behavior have a handful of choices as well (the caudate nucleus, the amygdala, anterior cingulate cortex, etc).

Nevertheless, it often seems as though researchers are drawn to certain aesthetic aspects of brain regions, even if the functional aspects are of primary interest.

***

• At a recent lecture I attended at the University of Pennsylvania, the gifted neuroscientist Rachel Wilson commented on the remarkable “order” of vertebrate chemosensory neurons before she spoke about her research on sensory processing in the fruit fly olfactory system. The neurons that line the fruit fly’s antennal lobe are positioned in a tight, repeated pattern.  Wilson often publishes gorgeously stained photos of the chemosensory neurons of the fruit fly antenna, such as the one seen here to the right– and she’s clearly drawn to their visual splendor.

• “Order,” it seems, is an attractive attribute.  Javier Medina (the neuroscientist I work for) of The University of Pennsylvania often champions the coral-like, tightly-folded cerebellum for its functional worth as well as its graceful, structured beauty.

“Confocal micrograph from a cerebellum expressing green-fluorescent protein in Purkinje cells”: The bright green circles are the cell bodies and the middle area shows their parallel axons.

Medina recently disclosed to me one reason why he studies the cerebellum instead of the ever-popular cortex:  ” [in the cortex] More than anything, you find silent cells…cells that don’t like to talk much, fire an electrical impulse here or there, but for the most part, keep quiet. For all the hoopla about it, the cortex is a sort of boring place… but if you dig your electrodes deeper, you’ll discover a neurophysiologist’s wonderland.  The cerebellum is never silent.”  The cerebellum is an exciting place indeed, with its “star-like stellate cells,” illuminating chandelier cells, and “gazillions of little granule cells, packed together like sardines.”  Furthermore, Dr. Medina is from Spain, and cites Cajal, his compatriot, as a “hero” and a “genius.” Cajal tackled the cerebellum – below is his skillfully detailed sketch of the cerebellum’s Purkinje cells, with their characteristic labyrinthine trellis of interlaced dendrites:

• The unique appearance of certain brain regions has sometimes played a role in their naming. The hippocampus was given its distinctive moniker because of a physical resemblance to the sea horse, which itself shares a name with the half-horse, half-serpent creature of Greek Mythology.

Cajal’s Hippocampus

• The structure of the enigmatic organ as a whole can actually be quite appealing as well.

The brain at the top is a common shrew's, the bottom a dolphin's. Note the "back bends" and the major differences in appearance.

Cognitive scientist and author Mark Changizi, of the Rensselaer Polytechnic Institute, alludes to the beauty found in the diversity of brains across species, writing, “brains differing by several orders of magnitude in size look so different that a visiting alien would have no idea they’re the same organ at all.”  His new research looks at the meandering twists and turns (“back bends”) that brain tissue must take in order to accommodate parallel increases in body and brain size across evolutionary time.  Those bends can be seen in the dolphin brain below, which he’s quick to describe as “gorgeous.”

***

From the iconic pop culture image of a brain in jar, to it’s oft-satirized role as zombie food, the brain is not usually known for its beauty.  But when we synthesize our knowledge of the organ’s extraordinary abilities with glances into its intricate inner architecture, the brain is revealed as a truly unequaled natural wonder.