2 The European Brain
“Owl,” said Rabbit shortly, “you and I have brains. The others have fluff. If there is any thinking to be done in this Forest—and when I say thinking I mean thinking—you and I must do it.”
—A. A. Milne (1882–1956), The House at Pooh Corner
Rabbit, the intellectual of the Forest, holds that the brain is for thinking. There is rather little evidence for this, though it may be true. The brain is, however, important for other things for which there is strong evidence, although we tend to neglect them as less important, or less mysterious, or less human than thinking. This scale of values is naturally to be endorsed by intellectuals, but I’m not sure that an inevitable logic underlies it.
When I was a child, one of my small pleasures was to eat fish and chips soaked in vinegar and salt. The fish and chips were wrapped in newspaper. My favorite was the News of the World, a newspaper that fed on scandal until it closed in 2011 in the wake of a scandal of its own, its journalists embroiled in allegations of greed, bribery, corruption, and sleaze.
The paper’s motto was “All human life is there.” The News of the World and its sister paper the Sun told the story of human life through stories of the extraordinary lives of ordinary people and the ordinary lives of extraordinary people. “The world’s tallest man lives in Neasden” was a headline I remember, and I remember the woman who ate only crisps and the centenarian who smoked a pack of cigarettes every day. There were stories of fat people and thin people, large families and single mothers, gamblers, alcoholics, drug addicts and sex addicts. There was lots of sex: footballers romping in hotel rooms, three in a bed, secret love children and jealous wives, and lots of violence—the petty tantrums of the famous and nasty tantrums of the not-so-famous—road rage, the revenge of lovers scorned, the despoilation of gardens, the theft of garden gnomes and the kidnapping of pets. The greed of the rich, the sloth of the poor, the fecklessness of the young, the frauds and con-artists were celebrated alongside heroes and heroines who qualified for inclusion mainly by being unlikely.
What makes us human, by this accounting, is not our symphonies but our soap operas; not our ability to love, but our ability to seduce; not our poetry but our smooth tongues and spite; not our curiosity about the cosmos but our curiosity about our neighbors. Our absurdities and stupidities, hypocrisies and delusions, fallibilities and imperfections, not our reason, intelligence, and apprehension.
Despite claims that men think with their gonads, this is only approximately true. What is true is that our brains are very much concerned with sex. When we talk about The Brain we are sometimes thinking of the convoluted floppy bits that form the cerebral cortex. These are so much more extensive in humans than in other mammals that we are inclined to suspect that the explanation of our humanity and our intelligence lies in them. Perhaps they do explain our intelligence, but our humanity is entwined with our emotionality: our capacities for love and empathy, anxiety and disappointment; our experiences of fear, anger, and stress; our wayward passions and diverse appetites. How many of the decisions we make depend on our rationality? Behavioral economists know that even when we address problems eminently amenable to reason, such as where we should invest or how to spend our money, or when to gamble and when to hold, our decisions are subverted by a multitude of cognitive biases. Our human decisions—the big ones like whom to choose as a life partner, the sometimes big ones like when to fight and when to flee, and the smaller ones like what and when to eat and drink—these we might think about, but often only to wonder why we made the choices we did.
We might begin by asking where in the brain these decisions are made. Neuroscientists use maps of the brain, charting the anatomy, marking the paths that connect different regions, and they use these maps, with evidence from many sources, to attribute functions to particular parts. In the atlas of the human brain, the cerebral cortex is a bit like all the oceans of the world together, and about as featureless. By contrast, the hypothalamus is small, old, and gnarled, and what it does ranges from the mundane to the sublime. When we are dehydrated, it makes us thirsty and tells our kidneys not to waste water but to concentrate our urine. When we are ill, it raises our body temperature, generating a fever that kills off infections. When our blood sugar is low, it tells us to eat, and when our stomach is full, to stop. It determines the shape of our bodies, how tall we will grow, how fat we will be, and where our fat and muscle will grow. When we are frightened or anxious or stressed it determines whether we will set our teeth, stiffen our sinews, freeze, or fight—or flee. The rhythms of days and of seasons are beaten by its drums, and we grow and attain puberty under its tutelage. And, led by the hypothalamus, we preen and woo, and the sap rises in our loins; a man produces sperm, and in a woman the ovarian cycle turns; we court and mate and bond. A woman conceives, and her body changes to the needs of the child within, and she gives birth and produces milk, and she loves and nurtures her children.
A map of Europe is filled with small countries with aggressively different identities, their stupidities, absurdities, fallibilities and imperfections, grime and squalor jostling among pinnacles of art and beauty. The hypothalamus is the Europe of the brain, where different regions control gluttony, anger, sloth, obesity, drinking, addiction, stress, love and hate, and sex. All human life is there.
This book is about the hypothalamus and all the related parts of what we might call the heart of the brain. It tells stories of things that matter to all of us, but not because they matter. It tells these stories to build an argument.
The conventional view of the brain is as a sophisticated and massively complex computational machine. Each of 100 billion neurons communicates with 10,000 others up to 200 times per second, constantly changing those connections in the face of changing demands and experience. This vision sees neurons as essentially all reliable and all alike, differing mainly in whether the signals that they generate are inhibitory or excitatory. The connections between neurons create a web so complex that, even if we may never be able to understand exactly what is happening, its capacity for doing wonderful things needs no further explanation. It is a vision that seeks to understand the brain from its connectome—the precise organization of anatomical connections. The years have embellished this vision but the core has remained unchanged; in the brain, information is the cacophony of electrical signals in billions of axons triggering hundreds of billions of tiny chemical signals, from neuron to neuron in networks within networks within networks, and by some miracle explainable only by the incomprehensibility of this complexity, information is processed to yield coherent and sensible outcomes.
Neurons of the hypothalamus are not all alike; far from it. They comprise many subpopulations—tribes, if you like. Living as I do in Scotland, I’d rather think of clans.1 Members of a clan are all different from each other, but are more like each other than like members of other clans. Each clan has its characteristic phenotype, dictated by the “tartan” of genes that it wears. Different genes make some neurons sensitive to glucose, temperature, or osmotic pressure, or to particular hormonal signals from the periphery. Others determine the signals that neurons of a clan generate. Different clans can be defined by the signals they use to communicate and the signals to which they can respond: different clans use different combinations of peptides as chemical signals along with “classical” neurotransmitters. These combinations come from more than a hundred known neuropeptides, and to these we should add yet more signaling molecules—prostaglandins, neurosteroids (steroids synthesized in the brain itself), endocannabinoids (endogenous, cannabis-like molecules), and gases like nitric oxide and carbon monoxide. Yet other genes determine where the clan is in the hypothalamus, and the shapes and connectivity of its members.
Some clans regulate the autonomic nervous system, which controls blood pressure, heart rate, digestion, respiration, urination, and sexual arousal. Some others are neuroendocrine neurons: these regulate the secretion of hormones from the pituitary gland—many of which control the secretion of other hormones, including those from the ovary and testes, the adrenal and thyroid glands—and also hormones from the liver, kidneys, gut, and heart. They control not only the functions of organs in our body, but also our behavior, by their actions on other parts of the brain. The hypothalamus of a male is not the same as that of a female—it is a sexually dimorphic structure. It is also plastic—its structure and functions are malleable, and alter according to physiological needs: after puberty, in pregnancy and lactation, in cold and hunger.
Behaviors important to who we are—love and hate, how much we eat and what we eat, how we respond to threat and to stress—are governed by the hypothalamus, and not by the map of how the neurons are connected, but by where the receptors for these peptide signals are found. Neurotransmitter signals are ephemeral and confined by anatomical connectivity, but the peptide signals that hypothalamic neurons generate are potent, wide-reaching, and long-lasting, and they affect not just neuronal signaling but also the genes that neurons express. Remarkably, different peptides when injected into the brain induce coherent, meaningful behaviors—some, for example, trigger eating, others induce a longing for salt or initiate maternal behavior or aggression or sleep.
As we began to recognize the complexity of the hypothalamus, the diversity of its systems and the scope of their effects, and the interactions between hormonal systems and behavior, the emerging “hypothalamocentric” vision began to look different from the conventional view of the brain. This vision embraces the heterogeneity of neurons—the differences between neurons that do not merely or mainly reflect differences in how they are connected to other neurons. It also confronts the uncomfortable recognition that delivering a drug into the brain with no anatomical precision and no sophisticated pattern of delivery can elicit coherent behavioral outcomes. I find it hard to express just how shocking this is: it’s as though you can take a sonnet of Shakespeare, cut out the words, and scatter them in the wind, only to find them gathered together faultlessly.
Individually, neurons are not perfect: they are erratic, messy, quarrelsome, and unreliable. But each clan organizes itself, and can do things that the individuals in it can’t. The clans make light work of some apparently difficult tasks but struggle with other tasks that are apparently trivial: our intuitions are a poor guide. Clans talk to clans, and do so in many different ways with many types of signals on different spatial and temporal scales; they use not one language but many. Understanding those clans and their languages lets us see how patterns can emerge from apparent chaos, robustness from noise, decisions from quarrels, purposeful behavior from heterogeneity and confusion. Perhaps one day Europe will do as well.
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