physiology


David Barker is one of those intuitive scientists, a latterday Alexander Fleming who is able to follow up on a chance observation to develop a theory of fundamental importance.  He knows his stuff, he has a prepared mind and the imagination to see the possibilities of a chance observation.

Barker is an epidemiologist.  He became interested in the geographical variation of mortality from so called life style diseases, bronchitis, ischaemic heart disease, stroke, diabetes in various parts of the country and observed that this was related to poverty, impaired nutrition and high infant mortality.   Although nutrition had improved over the years, it  did not seem to prevent death from these diseases.  Barker wondered whether infant mortality and death from life style diseases were somehow connected.  In Hertfordshire, they had kept meticulous records of birth weight from early in the last century.  Barker found that those individuals born underweight and who remained  underweight at one year of age, were much more likely to die of  cardiovascular disease later in life.  These early observations were confirmed in Preston, Burnley, Wakefield and other areas of the UK and also in children born during the Dutch famine of 1944-5.  So was there something about the early intrauterine environment that programmed the infant along a track to life threatening disease?  Subsequent observations showed that low birth weight was often associated with big placentas, but what did that imply?   Did the placenta adapt in some way to try to extract nutrients from the mother or did it hypertrophy to produce growth factors?  Was it the placenta that programmed the infant to conserve nutrients? 

If Barker’s hypothesis has any relevance, it must be in regions like India, Arabia or the Southern Seas, where there is a veritable epidemic of premature diabetes and heart disease.  In India, scientists have found that even in areas where people had a very healthy life style with low fat high vegetable diets and lots of exercise, people still died early of diabetes and heart disease.  Birth weight was low but as they developed children remained thin but had a very high percentage of body fat and early signs of a tendency to diabetes – the thin-fat infants. They had concluded that this tendency was related to micronutrient deficiency and are doing a study in which they are supplementing the diets of pregnant women and comparing their infants with un-supplemented mothers.    

 The foetus is not just inert and passive.  It reacts to stimuli.  Scientists have shown that shaking a rattle by the mother’s abdomen, even through the mother is listening to something else through headphones, produces an alarm response in the some foetuses.  And some mothers will testify how their baby will be calmed by music or even beat time to the rhythm.  There is also evidence that maternal stress may produce a nervous baby and this tendency will continue throughout life. 

‘A day or two old and they’ve already got a personality; this one lies there as stiff as a mummy – a regular banker, the next one is throwing himself all over the place happy as a young horse, the next is Miss Dreary, already worried about her hemline.’    

                                                                     Margaret, scene 10, Broken Glass by Arthur Miller.

Show me the baby and I will show you the man or the woman. 

There is even data to show that male babies born to mothers who survived the bombing and shelling of Berlin, were more likely to become gay. 

The data suggest that neonatal stress can rest the hypothalamo-pituitary-adrenal axis and render the rats more sensitive to stress and therefore more susceptible to stress related but otherwise unexplained illness.  The conditions of one pregnancy may be different from another.  Anxious and busy mothers may beget twitchy babies.

This doesn’t deny the influence of genetics nor the subsequent effects of life events and life style.  Genetics provides the potential to respond to a particular environment in a particular way.  Early life experience will enhance or reduce that tendency and the environment later in life will either realise that life script or suppress it.  So malnutrition early in life will cause a person to over-consume nutrients and store them as fat, increasing the risk of cardiovascular disease and diabetes.  In the same way, emotional deprivation may cause a person to be wary and needy, so that they have less tolerance of solitude and more emotional tension and illness.   Psychotherapy is there to help those people afflicted whose developmental limitations have left vulnerable to the viscissitudes of life.  

So Barker’s hypothesis exhibits the truism that whatever happens to us makes us the person we are and life is like a tree,  the things that influence us early in our existence affect how we grow and develop much more that the events that occur later in life.   

Human beings don’t just adapt to their environment, they create and control it.  Ever since the early hominids developed an opposable thumb that enabled them to grasp and manipulate objects, they could make things happen.   The ability to throw missiles is a metaphor for how we could influence events at a distance, not only in space but also in time.  The use of tools to make shelters, to control external sources of energy allowed us to escape the urgent prerogatives of survival and find time to think.   Within the space of a few generations, humanoids endowed with the magic of manipulation,  could create the future by intention .   

Evolution does not happen by the gradual accretion of advantage,  it is jerked forwards by a change in environment.  That is what is thought to happen with our ancient ancestors.  A change in climate in eastern Africa constricted the forest, concentrating the apes that lived there and creating a niche on the edge, where the tall grassland encroaches, a space where only those apes with upright postures and opposable thumbs could hunt in.  Within the space of few generations,  certain humanoids have developed a specialised way of life; they became upright savannah apes that hunted in packs with spears and missiles.    

One advance creates the space of opportunity for other adaptations to occur. Using tools and  throwing missiles required a big, strategic brain to imagine, plan, predict and create.   Up to a point these abilities could be learnt by the small chimpanzee-like brain of our early ancestors, but those who had bigger and more clever brains were quicker and better at it, would survive at the expense of the others.   No longer did the strongest and fiercest inherit the earth by fear, the ability to create the future at a distance allowed the development of a meritocracy based on intelligence.  All that was required was the ability to project, not just physically, but literally throw one’s mind forward,  to imagine the way things might be, how others might think, to create a world out of our own mind.  Discovery always favours a mind, prepared by imagination and necessity.    And with imagination comes  strategy, planning, forecast, insight, hope, anticipation, and meaning; all the tools needed  to build a civilisation.

Survival on the savannah needed teamwork, the ability to work together as a group.  The maverick and loner would just starve.   Teamwork requires empathy and identification, the ability to project our wishes and desires onto others, to inspire them and create a group identity, based on meaning.  If people share the same meaning, then they will stay together and help each other.  So tribes stayed together and developed into larger communities not just because of a practical need, but because the tribe could preserve  the word, the identity that held them together.  Having an imaginative brain allowed human beings to derive meaning from things to make sense of their environment, to interpret, tell stories, invent Gods.

We begin to see the enormous advance the upright posture and opposable thumb, how these features allowed humans to project their minds into an infinity of intellectual space, rich in possibility.   

Godlike, we have produced a world in our own image and become adapted to that world.  We have determined our own evolution;  narcissism on an universal  scale.   No longer the tough stone age survivors, fighting to stay alive, dependant on the exigencies of the external environment, constantly on the move to where it is warmer and there is food,  we have tamed the wilderness and created a society, in which we can produce all we need, shelter, energy, food, water, entertainment. 

But in order to do this, we have had to forge ever more complex collaborations.  We have outgrown the narrow self centred confines of the tribe to develop much larger societies with different values, different priorities.   The ever increasing size of our communities from tribes to villages, to towns, cities, countries and finally a global community linked electronically, not only required a major logistic exercise in providing basic human utilities to everybody, but also created the need for civilisation, laws, morals and manners to keep such large in control.  Only those whose behaviour is compatible with the customs of society, will be allowed the freedom to live and breed in that society. Those who are more assertive and aggressive have been weeded out, killed, locked up, exiled. 

So we have we inbred domestication and passivity by our civilisation and laws.  We have selected out dangerous characteristics such as aggression,  ruthlessness,  physical strength and activity, and bred in other characteristics like laziness, passivity, dependency and overeating.  We have tamed ourselves.  And since aggression and physical strength are male prerogatives,  the new man has become more feminine. Civilisation means that men no longer seize their women by force, the power of selection is in the arms of the women, who arguably have a greater grasp of human nature.  And women are more likely to seek out sensitive, caring men to breed with.  They in turn will rear more sensitive children.     

All of this has created a different strain of human being, passive, a civilised, comfort seeking, intelligent and inventive creature.  Experiments conducted in Novobirsk, Eastern Siberia has shown that selective breeding over 50 generations has succeeded in domesticating Silver Foxes.  They become tame like dogs. The strange thing is that in breeding out aggression, other characteristics change too, like the colour of their coats and the shape of their heads, their ears and their tails.  In fact, they become like puppies.  Selective breeding for domesticity favours juvenile characteristics.

Has the same thing happened in human societies?  Has sexual selection succeeded in breeding out aggressive characteristics?   Are we all just big babies?   Have we bred domesticity in ourselves and in doing so become passive, lazy, needy and child-like?   And like the domesticated foxes,  have these social characteristics of being tamed, altered our appearance and the diseases we are predisposed to?    Has it, for example, caused us to become fatty and less hairy.  Has the combination of neediness and passivity predisposed to a plethora of diseases of civilisation; obesity, diabetes, heart attacks as well illnesses related to depression, such as Fibromyalgia and Irritable Bowel Syndrome?

Obesity and depression are the two most common illnesses of western society, affecting more than half the population.  Obesity is a disease of passive overconsumption and insufficient exercise.   We are consuming more than we need and we no longer need to work to get it.  There is an abundance of high energy food in infinite variety in our supermarkets.  Most of it is ready prepared and cooked and just requires reheating.  And without the basic requirements to hunt and fight, there is little need to exercise.  We travel to work in our cars and trains, we get our entertainment from the television, we do not even need to go out to work; we can work from our homes.  We don’t even need to get out of bed. 

In fact, we can exist without ever having to meet other people.  With personal computers, many people have their office at home.  No wonder we become quite isolated and depressed.    

If we remove the need to hunt, to build our own houses, to fight and compete, then we remove personal initiative.   And without human contact and something to strive for, life has little meaning.   We just exist, eating, drinking and sitting in front of the television,  rendered inert by the trappings of our own civilisation. Chronically bored, eating becomes less a necessity, more a displacement activity.  Many obese people are depressed.          

A few years ago,  I walked out from Malleleuca along Tasmania’s South Coast Track, carrying all the food I needed for 9 days on my back.  Meals were rationed; just enough for sustenance and no extra. I walked continuously from dawn to dusk across traversing precipitous mountain ridges interrupted by boggy valleys.  I felt more alive than I had for years and lost over nearly a stone in weight.

Our world and everything in it including ourselves has been shaped by water.  Yet how much do we understand it?

Left to itself, water approximates to a sphere, circular currents bounded by surface tension,  but when subjected to gravity, then the circular forces in the water turn the flow into a spiral form (or two spirals in one), bending it from side to side and creating meanders in rivers as silt is taken from the outside off the curve and deposited on the inside of the next bend. The same spiral arrangement also exists where water from different sources come together – the warm waters of the gulf stream spiral around the colder currents, the clear Rio Negro and the muddy Amazonas spiral adjacent to each other for scores of miles after they merge above Manaus.    

Add an external force like dropping a pebble in a bowl and water will adopt a natural frequency of vibration depending on the configuration of the container.  Vibration may also be imposed by wind or obstructions to flow, creating ripples, that can be recorded on sand and rocks.  The gravitational effect of the moon exaggerates natural rhythm of water around the globe.  

Waves in open water are created by the wind on the surface or a rising sea bed close to the shore. Although the wave moves, the water in it just circulates. Rays and other fish swim like a wave through the static circulating water.  The wave ‘breaks’  when wind accelerates the top and causes it to overbalance or when the rising shore line slows down the base.   This creates a horizontal air/water vortex that churns and oxygenates the water. 

In contrast, the standing wave generated by the fall of water in a weir is static and water flows through it.   So the wave is a feature of water, but does not necessarily relate to its flow.  

An obstruction in a river or the flow of a stream of water into a static pool,  creates vertical vortices; paired boundary areas where fluids of different pressures coalesce and mix.  

Multiple sources, sinks and currents combine to create more complex fluid structures that has been compared to a symphony in which different instruments have their own entries and rests and are brought together by an invisible conductor.  Flow must be turbulent for exchange to  occur.  If it is channelled through a straight pipe, or settles at the bottom of a deep pool, it cannot form vortices, transfer of material cannot occur and water stagnates .

Water is a complex, sensitive medium that can respond to the environment to create a multiplicity of forms.  Living creatures start their live as suspensions of cells in water.  They must therefore be  influenced by flow patterns of the medium of suspension and develop out of these patterns   So simple multi cellular organisms living in water often adopt spiral forms.  Snails have a spiral shell.  The muscle fibres of the heart adopt a spiral arrangement with compartments forming at the junction of different flows (oxygenated blood from the lungs and deoxygenated blood from the rest of the body).  Movements of fluid are incredibly sensitive; they respond to minor change.   Nerve cells seem to line up at the boundary zones where the effects of those changes have most effect. 

Now if we imagine that the world and everything in it was initially composed of fluids initially, then we can see how solid forms in nature conform to a vortex configuration.  Vortices are consolidated in rocks when they cool.  Jellyfish are 96% water and resemble complex vortices.  When their mantle contracts, they produce mirror images of themselves in the vortices they leave behind.  And look at other vortex forms, the cochlea of the ear, the semicircular canals, which in the lamprey are still fluid vortices, the turbinate bones of the deer, the intestine of the lungfish is spiral in form, the intestine of the cow circular. Even the embryo starts off as a complex vortex of cells, whirling boundaries where things occur, cells are laid down, nervous connections are created.   We might even envisage organs being created out of paired vortices).     

Water cannot just be understood by its chemical properties.  It is the stuff of life, the circulation that runs through all living things.  Sensitive Chaos; creation of flowing forms in water and air was written by Theodore Schwenk (1910- 1986), anthroposophist, engineer and director of The Institute of Water Research and Flow Science in the Black Forest.  It is a remarkable, thought provoking book that escapes the stagnation of research protocols and methodology and allows the imagination to flow unimpeded; the sort of book that makes us reflect on what might be so.  That, surely, is the  essence of science.    

 

 

It lurks tucked up behind the stomach, a soft black leather purse moulded to the contours of adjacent organs like a dark shadow, the sort of organ you’d ignore, a remnant, a vestige, a redundancy.  No wonder surgeons removed the spleen with impunity if they were operating on the stomach.  But this ain’t no vestige.  Remove it at your patients peril.  People without a spleen have six times the risk of getting pneumonia and other infections and a fifty percent increase in heart attacks.  Be it ever so ‘umble,  the spleen is none the less important.  

Cut into its surface.   A red black pulp like raspberry jelly oozes out and between the pulp islands of white tissue so called Malpighian tubercles. 

The red pulp is composed of large blood spaces or sinuses lined with columns of cells.  The blood passes slowly though the sinuses and the cells filter it, destroying  bacteria, viruses, protozoa .  Similar arrangements of fixed macrophages exist in the sinuses of the liver (Kupffer Cells) and in the lymph nodes.  Together they comprise what is known as the body’s ‘reticulo-endothelial system’.  But the spleen also destroys tired red blood cells, worn out and dysfunctional after their 120 day journey round the vascular system,  recycling the haemoglobin to bile pigments and iron stores.   

The white nodules contain lymphoid follicles rich in B lymphocytes, which produce antibodies and sheaths of T lymphocytes, responsible for ‘hand to hand’ cellular conflict.  They are also major producers of monocytes, which are despatched to sites of injury where they transform into dendritic cells and macrophages and assist wound healing.  So both white and red components of the spleen are important parts of the immune system.  The same functions can be carried out in other parts of the body, but without a spleen, immunity is seriously compromised.      

In other mammals, the spleen is also an important reservoir of blood.  In the horse, 30% of the blood is stored in the spleen; in the dog 15%. Operate on a dog and you can see the spleen shrink before your eyes.  The spleen used to produce new red blood cells but loses that ability just before birth when that function is taken over by the bone marrow.   

Doctors have known about the spleen since ancient times.   It was, they thought, the origin of black humours, the source of melancholy (literally black bile) and hypochondria (below the ribs).   In the eighteenth century, women were often diagnosed as suffering from The Spleen when they were sad, bad tempered and out of sorts in mind, body and spirit.  Alternatively they might be said to be suffering from the Vapours (of the Spleen).   The term splenetic indicated that somebody was in a foul mood, though the same term in French meant sad and melancholic. 

So don’t ignore the spleen or provoke it, for if it ever gets ‘vented’, take cover immediately!

The little bastards that that bloody insect injected into me have swollen my spleen from 11cm to 15cm.  The insurance company seem to think it will explode in the low pressure environment of the aircraft cabin. It’s a solid organ, I insist!  Physics doesn’t work like that!  It’s enough to give anybody The Spleen!          

I can’t stomach not knowing,  I can’t just take it in. It gives me a lump in my throat and makes me so up tight, but if the firm really went bust, then I know I’d never get off the toilet for a week.  

So many everyday expressions are based on parts of the gut.  How many can you think of?   I can’t stomach it?  I can’t swallow it?  Butterflies in the stomach?  Lily livered?   

When I was very young, my grandmother used to ask me;  ‘What’s the difference between a rotten egg, a grand piano and your face?’  I’d smile expectantly. ‘Well’, she’d say, her eyes glinting,   ‘a rotten egg makes you sick, a grand piano makes mu-sick and your face  – yes, you’ve got it,- makes me sick. 

And there’s ‘up tight’ and  ‘Gutted’.  One of my patients developed IBS for the first time after his girl friend dumped him.  And how did you feel, I asked.  ‘I were gutted’, was his response.  Exactly! 

Of course this isn’t at all surprising.  It’s nothing new!  Think of the some of the old words for emotion; melancholic, choleric, splenetic, phlegmatic.  There is no better barometer of our emotions than the way we ‘feel’.  That’s why we use the term feelings interchangeably with emotion.  And the gut has often been considered ‘the root of our feelings’. 

Indeed when we were very, very young before we could express emotion and we just had bodily feelings, so much was expressed through the gut.  Mothers knew only too well that when their baby was uncomfortable, frustrated, hungry, cold or just lonely, because then they wouldn’t eat, th’d choke, bring their feed up, their bowels were runny or they didn’t go at all or they had colic.  Such gut feelings and gut reactions are mediated by the sympathetic and parasympathetic nervous systems, which bring about actual alternations in gut function.   It’s only as we get older and begin to think, that we can bring our feelings to mind and deal with them.  Then the symptoms quickly go.

Of course, it may not always work like that.  If something happens that we cannot deal with, something that we feel so ashamed of we can’t admit it to anybody, then the tension and the feelings stay, wrenching the gut out of kilter and making our lives a complete misery. 

So listen to your gut.  It has a hot line to the mind.  It will often tell you that things don’t feel right even before you know it yourself.  Trust your gut feelings.  Understand your gut reactions. Learn to deal with the situations and events that cause them.  This will make you stronger, more resilient, give you the guts to cope with anything in life.  But in order to preserve that vital early warning system, look after your gut, treat it well, eat sensibly, don’t overload it, have enough off- time. You are the proud owner of a fine instrument, strung with the most delicate gut, tune it well and learn to trust it!

‘A dog is a man’s best friend’, so they say.  They are our companions. They are, like us,  social carnivores that hunt in the daylight. We were made to collaborate. How much more effective we would have been as hunters with dogs to detect and chase our prey.  And dogs would have played a crucial role in the development of civilization by protecting our crops and home and herding our animals. 

But there’s more to it than that.  Dogs offer us their devotion.  To them we  are the pack leaders – to be appeased and served. Dogs are attuned to us, they obey our commands, respond appropriately when we point; they can be trained. Chimpanzees, although they have 99% of  our genetic code, tend to do their own thing, albeit intelligently. There is even a dog who has learnt 300 words and can fetch an object from another room, having only just seen a picture of it.  And think of how working dogs can be trained to herd sheep, to retrieve an animal that been shot, to sniff out drugs or explosives.   

Dogs make a deep emotional bond with us.  Studies have shown that when dogs look at images of humans, they are drawn to the left side of the face which expresses emotion more eloquently and has a direct connection with the emotional right side of the brain.  They tune into our emotions and can respond to our feelings.  They know when we are upset or angry. They feel it. And dogs are good for us.  We are more likely to survive a myocardial infarction if we have a dog and less likely to have another heart attack.  

Dogs have evolved an elaborate vocal repertoire to communicate with us.  Most dog owners can recognize at least six types of bark.  These are emotional signals; excitement, anger, aggression, hurt, fear, playfulness.  Brains scans have shown that the same area of orbito-frontal cortex lights up and we release the bonding hormone, oxytocin, when we look at pictures of dogs as when we look at images of children.  Our need to nurture runs deep. Dogs induce the nurturing behaviour in us they need for survival, and they also release oxytocin when they look at their owners and are fondled.  Dogs not only give but they induce unconditional love. 

DNA data has established that our domestic dog is descended from the grey wolf and came into existence about 100,000 years.  But wolves or wild dogs do not acclimatize to humans naturally. They cannot read our emotions and they don’t have the same vocal repertoire.  When wolf puppies are brought up with humans, they revert to wolves at about 8 weeks and become dangerous.  It takes many generations of selective breeding to get an animal that behaves like a dog.  Long term experiments conducted on Silver Foxes in Eastern Siberia has shown that domesticity can only be induced after 50 generations.  Only then do they behave like dogs. The strange thing is that in breeding out aggression, other characteristics change too, like the colour of their coats and the shape of their heads, their ears and their tails.  In fact, they become like puppies.  Selective breeding for domesticity favours juvenile characteristics.

This makes me wonder whether sexual selection in human societies over the many generations since civilization began has also succeeded in breeding out aggressive characteristics?   Are we just all big babies?   Have we bred domesticity in ourselves and with this passivity, laziness, neediness and a predisposition to obesity, heart attacks and diseases related to anxiety, such as Fibromyalgia and Irritable Bowel Syndrome?    

Contrast our open faced, needy population with the hard bitten images of tribal chieftains, warlords who seize and impregnate their women by force.  Such brutal sexual acquisition might perpetuate a much more ruthless typology until such time as civilization suppresses the behaviour that has induced it?  The aggressive no longer rule the earth,  at least outside the strongholds of Afghanistan, but have we become too tame, like the dogs?

This article was inspired by this month’s BBC Horizon programme.

Frozen grapes are delicious served with chocolate truffles and cream.  If you let them warm up a bit, you can bite through them and feel the cold juice squirt around your mouth.  But Roz found this difficult.   

‘I can’t eat these. I have sensitive teeth.’

‘Well just try swallowing them and feel the cold go all the way down,’ I suggested. ‘Look it’s easy.’  And with that I popped one into my mouth, let it roll down back into my pharanx and swallowed, then waited for the wave to slide it down.   

The grape was as hard as a marble and cold as a lump of ice.  It got so far and stopped just behind the sternal notch, generating a dull ache that spread like a band around my chest.   I swallowed again. It still wouldn’t budge.  In fact I could feel it coming back up again and the pain intensified.  I swallowed a third time.  Nothing.  I could feel my face turning red and a wave of nausea rising up from my stomach. 

I stood there, my neck sunk into my chest, eyes bulging, not sure what to do. Simon was laughing, tears rolling down his face. ‘You’re such a  daft bugger!’

At that I started laughing too and then stopped.  There was a real risk of asphyxiation and while it might be a good way to go, I wasn’t ready for that yet. I needed to stay calm. I breathed gently in and out and when I felt in control, swallowed some water and felt the grape move painfully down.   

I turned to Judy, who was a scientist.  ‘Why don’t you write this up as an experiment  – the induction of reverse peristalsis by an ice cold bolus?  But first we need to test its reproducibility.’  Emboldened by experience,  I took another grape and swallowed.  The  obstruction behind my breastbone was exquisitely painful this time and it was so hard not to laugh when others were swaying about with general mirth.  But another glass of water did the trick.  Eureka! 

‘Now, Judy, we need to try this on somebody else. What about Roz?  And we need a genetic control.  Simon would do. And then you must do a series.  You could put a capillary tube down and measure pressures or you could fill the grape with contrast medium before freezing and then X-ray your volunteers.  Reverse oesophageal peristalsis is controversial in humans, but this could be the proof.  You could be famous, Judy.  It could be known as the Donnelly Provocation Test.  You could patent it.’ 

Ah well,  you can lead a scientist to water, but ………  Judy was not impressed.  Another opportunity missed! 

All of this reminded me of a demonstration forty five years ago in Cambridge. Dr Giles Brindley, then a young lecturer in physiology, stood on his head on the class bench and swallowed water through a rubber tube from a large Winchester bottle, just to prove that swallowing does not occur by gravity but by persistalsis.  The next issue of the Med. Soc. magazine demonstrated the trick.  Beneath the bench was the laboratory assistant who was opening a stop cock to drain the bottle. 

Who said science wasn’t theatre?

A Health and Safety Warning.  These experiments are risky. Please don’t be tempted to try them at home.

The weather was a bit grim this morning; just off freezing and pouring in rain. I slipped on the mud and was soaked through in seconds, losing any insulation afforded by my leggings.  My hands soon felt like blocks of ice, but my back, which was covered with a winter running top and a light waterproof , remained dry and warm and I didn’t feel chilled.  I wasn’t even shivering, but this got me thinking exactley where we feel cold.  

I think we feel it at the back of our necks, across the shoulders and a few inches down the centre of our backs. I call it the shiver spot.  It’s where shivering seems to start.  Say you have washed in the open air or been for a swim in a cold river, and your teeth are chattering, if you pour hot water onto the shiver spot, or better still get somebody else to do it, then the chattering and shivering stops immediately.  The effect is still there if you pour warm water over your shoulders though less intense. 

But why is that?  What is special about that spot?  Well in animals it is the major subcutaneous site of brown fat, that particular type of metabolically active fat that generates heat in animals that live in temperate or cold zones. Brown adipose tissue (BAT for short) is well supplied with sympathetic nerves, which are activated by cold;  a   fall of temperature of the skin of the shiver spot of just a few degrees is enough to trigger an anticipatory thermogenic response that will prevent a drop in core temperature. This area has, as it were, a hot line to the brain. A drop in the temperature of the hands and the feet is not enough to cause a thermogenic response probably because this induces a local vasoconstriction that shunts blood away from the skin and returns it to the trunk via counter current heat exchange between the major arteries and veins in the centre of the limb. 

A fall in the temperature of the skin at the back of the neck is a much more immediate indicator of an imminent fall in core temperature because the back is more exposed – think of the way all mammals curl up in the cold.  Also that area at the back of the neck is close to blood vessels supplying that part of the brain stem that houses the life support systems of the body, so the temperature of this area must be maintained as a matter of necessity. 

But what about a rise in temperature? Does this area also stimulate heat loss?  I don’t think it does.  But if not, is there any sweat spot.  Might it be the mouth?  Foods that produce a sensation of heat in the mouth stimulate sweating immediately.  Does gustatory sweating have any role in temperature regulation?  Or is there another area?  Does anybody know?