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Posts Tagged ‘science’

11 APRIL, 2014

The Science of Mood in Animals: Can Pets Be Depressed?

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The science behind what every pet-parent knows.

“What were the secrets of the animal’s likeness with, and unlikeness from man?” John Berger pondered in his influential meditation on our relationship with animals. “The secrets whose existence man recognized as soon as he intercepted an animal’s look.” And yet for all the progress we’ve made, for all the advances afforded us by pioneering animal scientists like Jane Goodall, we still struggle to understand — or, in some cases, even acknowledge — the inner lives and emotional realities of our fellow non-human beings. Despite what every pet-parent sees with absolute clarity in watching, say, her dog whimper with agonizing anxiety or greet a friend with exquisite elation, the question of animal emotionality is still, perplexingly, something of a taboo.

In The Depths: The Evolutionary Origins of the Depression Epidemic (public library) — his fascinating exploration of how mood science illuminates “the unaddressed business of filling our souls” — psychologist Jonathan Rottenberg addresses this paradox:

Depression in animals has long been a hard sell. In the wake of René Descartes, an enormous gulf opened between humans and other species, and Cartesian thinkers ever since have argued that other animals are mere automata, furry robots. Skepticism about complex inner states in other species has endured even into the twenty-first century. The torch has been passed from behaviorists, who wanted to banish all notions of motivation from scientific purview, to contemporary neuroscientists, who accepted basic motivational drives but not anything as elusive as animal feelings, and finally to cultural psychologists, who have no place for animal depression, but for different reasons. For them, depression is a shared understanding, a historical artifact defined by human words and deeds.

Mood science seeks to refute these views… Our fellow mammals, be they rats, cats, or bats, provide the most compelling and dramatic evidence for depression in the animal kingdom. High and low moods equip these animals to track opportunities and resources in their environments; the capacity for mood is essential for guiding behavior in a changing world.

Illustration by Wendy MacNaughton based on Gay Talese. Click image for more.

Much like the human version, Rottenberg argues that depression in animals spans the full spectrum of severity, from brief and shallow periods of low mood to long and intense stretches of depression. Animals also experience the same hormonal changes that depressed humans do, including higher secretion of steroid hormones and dampened immune system function. Perhaps most interestingly and indicatively, the body clocks of depressed animals — their circadian rhythms, which we already know are of tremendous importance to human well-being — are so disrupted that they produce the same irregularities in body temperature and sleep-wake cycle seen in depressed humans. Rottenberg adds:

Beyond the official symptoms of human depression, dogs and cats manifest numerous unofficial signs that are characteristic of depressed humans. Those who live with them know that reduced exploratory behavior, long hours hiding under the bed, and reduced interest in self-care and personal hygiene, reflected in less grooming or use of a litter box, are all signs that something is amiss.

In a heartbreaking illustration of my longtime lament that there is no nuance in news today, Rottenberg points out a particularly ungenerous and gratuitously one-note instance of how the popular media tends to treat what’s clearly a complex subject:

Psychiatric problems in small animals are often trivialized, so it is easy for pet depression to fly under the radar. Fortune Magazine mocked Eli Lilly’s decision to pursue FDA approval of a chewable Prozac for pets as the second dumbest moment in business of 2007, writing, “Thank God. We’ve been so worried since Lucky dyed his hair jet black and started listening to the Smiths.”

Photograph by Tim Flach from his series 'More Than Human.' Click image for more.

Understanding non-human depression, Rottenberg reminds us, isn’t just a matter of compassion but might also hold important keys to better understanding, and treating, human depression, which is what he explores further in the altogether fantastic The Depths. Sample it further here.

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10 APRIL, 2014

The Science of Smell: How the Most Direct of Our Senses Works

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Why the 23,040 breaths we take each day are the most powerful yet perplexing route to our emotional memory.

“Get a life in which you notice the smell of salt water pushing itself on a breeze over the dunes,” Anna Quindlen advised in her indispensable Short Guide to a Happy Life. Susan Sontag listed “linen” and “the smell of newly mown grass” among her favorite things. “A man may have lived all of his life in the gray,” John Steinbeck wrote in his beautiful meditation on the meaning of life, “and then — the glory — so that a cricket song sweetens his ears, the smell of the earth rises chanting to his nose.” Why is it that smell lends itself to such poetic metaphors, sings to us so sweetly, captures us so powerfully?

That’s precisely what science historian Diane Ackerman explores in A Natural History of the Senses (public library), her 1990 prequel to the equally fantastic A Natural History of Love. Ackerman, who also happens to be a spectacular poet and the author of the gorgeous cosmic verses that Carl Sagan mailed to Timothy Leary in prison, paints the backdrop of this perplexing and unique sensory experience:

Our sense of smell can be extraordinarily precise, yet it’s almost impossible to describe how something smells to someone who hasn’t smelled it… We see only where there is light enough, taste only when we put things into our mouths, touch only when we make contact with someone or something, hear only sounds that are loud enough to hear. But we smell always and with every breath. Cover your eyes and you will stop seeing, cover your ears and you will stop hearing, but if you cover your nose and stop smelling, you will die.

Illustration by Wendy MacNaughton from 'The Essential Scratch and Sniff Guide to Becoming a Wine Expert.' Click image for more.

In fact, every breath we take in order to live is saturated with an extraordinary amount of olfactory information — a fact largely a matter of scale:

Each day, we breathe about 23,040 times and move around 438 cubic feet of air. It takes us about five seconds to breathe — two seconds to inhale and three seconds to exhale — and, in that time, molecules of odor flood through our systems. Inhaling and exhaling, we smell odors. Smells coat us, swirl around us, enter our bodies, emanate from us. We live in a constant wash of them. Still, when we try to describe a smell, words fail us like the fabrications they are…

The charm of language is that, though it is human-made, it can on rare occasions capture emotions and sensations that aren’t. But the physiological links between the smell and language centers of the brain are pitifully weak. Not so the links between the smell and the memory centers, a route that carries us nimbly across time and distance.

Indeed, that route is a greater shortcut to our cognition and psychoemotional circuitry than any of our other senses can offer. Ackerman outlines the singular qualities of our smell-sensation that set it apart from all other bodily functions:

Smell is the most direct of all our senses. When I hold a violet to my nose and inhale, odor molecules float back into the nasal cavity behind the bridge of the nose, where they are absorbed by the mucosa containing receptor cells bearing microscopic hairs called cilia. Five million of these cells fire impulses to the brain’s olfactory bulb or smell center. Such cells are unique to the nose. If you destroy a neuron in the brain, it’s finished forever; it won’t regrow. If you damage neurons in your eyes or ears, both organs will be irreparably damaged. But the neurons in the nose are replaced about every thirty days and, unlike any other neurons in the body, they stick right out and wave in the air current like anemones on a coral reef.

Illustration by Tomi Ungerer from 'The Cat-Hater's Handbook.' Click image for more.

That’s also what makes perfumes so powerful — if you’ve ever walked into a crowded room and instantly experienced a pang of emotion as you thought you smelled your ex, or your mother, or your third-grade teacher, you’ve had a first-hand testimony to the potency of smell as a trigger of emotional memory. Ackerman explains:

A smell can be overwhelmingly nostalgic because it triggers powerful images and emotions before we have time to edit them… When we give perfume to someone, we give them liquid memory. Kipling was right: “Smells are surer than sights and sounds to make your heart-strings crack.”

What’s perhaps most extraordinary is that scent lodges itself largely in the long-term memory system of the brain. And yet, we remain inept at mapping those links and associative chains when it comes to describing smells and their emotional echoes. To shed light on how perfumery plays into this paradox, Ackerman offers a taxonomy of the basic types of natural smells and how they became synthetically replicated, unleashing an intimate dance of art, science, and commerce:

All smells fall into a few basic categories, almost like primary colors: minty (peppermint), floral (roses), ethereal (pears), musky (musk), resinous (camphor), foul (rotten eggs), and acrid (vinegar). This is why perfume manufacturers have had such success in concocting floral bouquets or just the right threshold of muskiness or fruitiness. Natural substances are no longer required; perfumes can be made on the molecular level in laboratories. One of the first perfumes based on a completely synthetic smell (an aldehyde) was Chanel No. 5, which was created in 1922 and has remained a classic of sensual femininity. It has led to classic comments, too. When Marilyn Monroe was asked by a reporter what she wore to bed, she answered coyly, “Chanel No. 5.” Its top note — the one you smell first — is the aldehyde, then your nose detects the middle note of jasmine, rose, lily of the valley, orris, and ylang-ylang, and finally the base note, which carries the perfume and makes it linger: vetiver, sandalwood, cedar, vanilla, amber, civet, and musk. Base notes are almost always of animal origin, ancient emissaries of smell that transport us across woodlands and savannas.

And so we get to the actual science of smell — what actually makes us have an olfactory experience, and why we often confuse those with taste:

We need only eight molecules of a substance to trigger an impulse in a nerve ending, but forty nerve endings must be aroused before we smell something. Not everything has a smell: only substances volatile enough to spray microscopic particles into the air. Many things we encounter each day — including stone, glass, steel, and ivory — don’t evaporate when they stand at room temperature, so we don’t smell them. If you heat cabbage, it becomes more volatile (some of its particles evaporate into the air) and it suddenly smells stronger. Weightlessness makes astronauts lose taste and smell in space. In the absence of gravity, molecules cannot be volatile, so few of them get into our noses deeply enough to register as odors. This is a problem for nutritionists designing space food. Much of the taste of food depends on its smell; some chemists have gone so far as to claim that wine is simply a tasteless liquid that is deeply fragrant. Drink wine with a head cold, and you’ll taste water, they say. Before something can be tasted, it has to be dissolved in liquid (for example hard candy has to melt in saliva); and before something can be smelled, it has to be airborne. We taste only four flavors: sweet, sour, salt, and bitter. That means that everything else we call “flavor” is really “odor.” And many of the foods we think we can smell we can only taste. Sugar isn’t volatile, so we don’t smell it, even though we taste it intensely. If we have a mouthful of something delicious, which we want to savor and contemplate, we exhale; this drives the air in our mouths across our olfactory receptors, so we can smell it better.

Illustration by Wendy MacNaughton from 'The Essential Scratch and Sniff Guide to Becoming a Wine Expert.' Click image for more.

The rest of A Natural History of the Senses is just as fascinating a read, diving deeper into the mysteries and miracles of smell and our other sensory faculties. Complement it with Ackerman’s A Natural History of Love and her impossibly wonderful love letter to the Solar System, The Planets: A Cosmic Pastoral.

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08 APRIL, 2014

The Science of How Memory Works

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What the four “slave” systems of the mind have to do with riding a bicycle.

“Whatever becomes of [old memories], in the long intervals of consciousness?” Henry James wistfully pondered upon turning fifty. “They are like the lines of a letter written in sympathetic ink; hold the letter to the fire for a while and the grateful warmth brings out the invisible words.” James was not alone in seeking to understand the seemingly mysterious workings of human memory — something all the more urgently fascinating in our age of information overload, where we’re evolving a new kind of “transactive memory.” But like other scientific mysteries of how the brain works — including what actually happens while we sleep and why some people are left-handed — memory continues to give scientists more questions than answers.

In The Guardian of All Things: The Epic Story of Human Memory (public library) technology writer Michael S. Malone takes a 10,000-year journey into humanity’s understanding of our great cognitive record-keeper, exploring both its power and its ongoing perplexity.

Illustration from 'Neurocomic,' a graphic novel about how the brain works. Click image for more.

One of the most astounding facts Malone points out is that memory — that is, the creation of memories — is the result of a biochemical reaction that takes place inside neurons, one particularly common among neurons responsible for our senses. Scientists have recently discovered that our short-term memory — also known as “working memory,” the kind responsible for the “chunking” mechanism that powers our pattern-recognition and creativity — is localized to a few specific areas of the brain. The left hemisphere, for instance, is mostly in charge of verbal and object-oriented tasks. Even so, however, scientists remain mystified by the specific distribution, retrieval, and management of memory. Malone writes:

One popular theory holds that short-term memory consists of four “slave” systems. The first is phonological, for sound and language that (when its contents begin to fade) buys extra time through a second slave system. This second operation is a continuous rehearsal system — as you repeat a phone number you’ve just heard as you run to the other room for your phone. The third system is a visuo-spatial sketch pad that, as the name suggests, stores visual information and mental maps. Finally, the fourth (and most recently discovered) slave is an episodic buffer that gathers all of the diverse information in from the other slaves, and maybe other information from elsewhere, and integrates them together into what might be described as a multimedia memory.

It’s worth noting that memory and creativity have a great deal in common — the combinatorial process of memory-making that Malone describes is remarkably similar to how creativity works: we gather ideas and information just by being alive and awake to the world, record some of those impressions in our mental sketch pad, then integrate the various bits into new combinations that we call our “own” ideas, a kind of “multimedia” assemblage of existing bits.

Malone goes on to explore the inner workings of long-term memory — a substantially different beast, designed to keep our permanent mental record:

Chemically, we have a pretty good idea how memories are encoded and retained in brain neurons. As with short-term memory, the storage of information is made possible by the synthesis of certain proteins in the cell. What differentiates long-term memory in neurons is that frequent repetition of signals causes magnesium to be released — which opens the door for the attachment of calcium, which in turn makes the record stable and permanent. But as we all know from experience, memory can still fade over time. For that, the brain has a chemical process called long-term potentiation that regularly enhances the strength of the connections (synapses) between the neurons and creates an enzyme protein that also strengthens the signal — in other words, the memory — inside the neuron.

From the functional, Malone moves on to the structural organization of memory, where another dichotomy emerges:

Architecturally, the organization of memory in the brain is a lot more slippery to get one’s hands around (so to speak); different perspectives all seem to deliver useful insights. For example, one popular way to look at brain memory is to see it as taking two forms: explicit and implicit. Explicit, or “declarative,” memory is all the information in our brains that we can consciously bring to the surface. Curiously, despite its huge importance in making us human, we don’t really know where this memory is located. Scientists have, however, divided explicit memory into two forms: episodic, or memories that occurred at a specific point in time; and semantic, or understandings (via science, technology, experience, and so on) of how the world works.

Implicit, or “procedural” memory, on the other hand, stores skills and memories of how to physically function in the natural world. Holding a fork, driving a car, getting dressed — and, most famously, riding a bicycle — are all nuanced activities that modern humans do without really giving them much thought; and they are skills, in all their complexity, that we can call up and perform decades after last using them.

One of the most confounding pieces of the cognitive puzzle, however, is a form of memory known as emotional memory — a specialized system for cataloging our memories based on the emotions they evoke. It’s unclear whether it belongs to the explicit or implicit domain, or to both, and scientists are still seeking to understand whether it serves as a special “search function” for the brain. (What we do now know, however, is that sharpening “emotional recall” might be the secret to better memory.)

From all this perplexity emerges Malone’s bigger point, a somewhat assuring testament to the idea that science, at its best, is always driven by “thoroughly conscious ignorance”:

What we do know is that — a quarter-million years after mankind inherited this remarkable organ called the brain — even with all of the tools available to modern science, human memory remains a stunning enigma.

The Guardian of All Things is a fascinating read in its entirety. Complement it with Joshua Foer’s quest to hack memory to superhuman levels and Henry James on aging and memory.

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