Relaxed and Contented: Activating the Parasympathetic Wing of Your Nervous System

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Relaxed and Contented

Relaxed and Contented: Activating the Parasympathetic Wing of Your Nervous System, © Rick Hanson, PhD, 2007


It’s remarkable but true: part of your nervous system exists to you feel peaceful and alright. Its formal title is: “the parasympathetic wing of the autonomic nervous

system” or PNS, for short.

You can trigger the PNS at will, which immediately lowers your sense of stress, brings health benefits like reducing blood pressure and strengthening the immune system,

and lifts your mood. This gives you more control over your inner landscape – a nice thing at times when the outer world seems driven by forces that are beyond your

influence, from local traffic jams to global warming.

In this article, you’ll get a crash course in your own nervous system and how the PNS fits into it, mixed with lots of ways you can use to activate your own PNS. These

everyday techniques include: intentional relaxation, balancing heart rate variability, mindfulness of the body, yawning (really!), and increasing positive emotion.

If you want a clear picture of what is happening inside you every single time you are hassled, pulled in too many directions, irritated, worried, threatened, injured, or upset,

then you might want to read carefully the descriptions of your bodily processes when your SNS flips its switches. On the other hand, that might be more detail than you

really want, and if so, you could skim through it and focus on the methods themselves, which are numbered as exercises.


The Autonomic Nervous System

If you like, take a moment to observe your breathing as it is, right now. Next, relax and let your breathing slow down. Then, for another moment, deliberately breathe faster.

Doing this shows the workings of what is called the “autonomic nervous system” (ANS). This system regulates many automatic bodily processes, and it usually

operates outside of your awareness. But actually, you can exercise conscious influence over the ANS – and that remarkable fact puts you in the driver’s seat for the core

machinery of emotional well-being in your body.

Overview of the Nervous System in General 

To operate that machinery, it helps to have some background information about your own nervous system:

  • Individual neurons act to inhibit or excite, to put on the brakes or hit the gas, red light or green light.
  • Those functions of individual cells get writ large in assemblies of thousands, even millions, of neurons.
  • The nervous system (NS) is divided into the Central NS and the Peripheral NS.
  • In turn, the Peripheral NS is divided into the Somatic NS and the Autonomic NS.
  • The Autonomic NS (ANS) contains the sensory and motor neurons that “innervate” – that are woven into and guide – the internal organs and the digestive tract.

Then, the ANS is divided into the sympathetic, parasympathetic, and enteric nervous systems. This article focuses on the first two of these, but as a parting bow to the enteric system, I’ll mention that it pervades your digestive tract and has enough autonomy that some scientists call it a “second brain.”

The ANS Itself

The ANS is responsible for maintaining the equilibrium of our vital functions, including breathing, the heartbeat, glandular secretions, salivation, and perspiration.

On autopilot, it’s directed by the brain stem and spinal cord. That’s why someone with a massive head injury can still keep breathing in a vegetative state for years.

It carries out its responsibilities through three kinds of nerve assemblies:

  • Sensory – These bring information in, and are called “afferent.”
  • Decision-makers – These process sensory information and decide what to do.
  • Motor – These carry out the plan of the decision-makers by sending instructions throughout your body; they’re called “efferent.”

Breathing: Exercise #1

As noted, you have control over certain ANS functions. For example, land animals like humans use breathing for more than oxygen and so they need to be able to turn off the autopilot and take the wheel themselves for things like sniffing the air for smells and making sounds such as speech.

It’s interesting that most spiritual traditions have contemplative practices that work with the breath. Perhaps one reason for this is that the breath is a point where conscious intention meets primal nature – with its poignant reminders of disease, old age, and death.

If you want, you could take a moment to activate the parasympathetic wing of the ANS by exploring our first major method – deep, full breaths:

  • When you inhale, fill your lungs fully, hold for a second or so, and then exhale in a relaxed way.
  • Try breathing in this way for 60 seconds.

It’s striking that such a simple and brief method is so powerful for most people. It works because deep, long inhalations expand your bronchioles: the passageways in your lungs to the tiny alveoli where oxygen enters the blood and carbon dioxide leaves it. The PNS is in charge of constricting the bronchioles, so by making them swell up with a big breath, you trigger the PNS to bring them back to their “resting” size.

Parasympathetic and Sympathetic Systems: Structure and Functions

Getting A Sense of Each System

If you tried the deep breathing exercise just above, you got a sense of what lighting up the parasympathetic system feels like. For the sympathetic system, imagine something

stressful, like being put on the spot by your boss, or a car cutting in front of you in traffic, or getting upset with a family member. Try to get into the experience, and then

notice what it feels like in your body and mind. When you want, take a couple full breaths to get back to center.

That back and forth – calm from breathing deeply, then aroused by stress, and then calm again – illustrates how the parasympathetic and sympathetic systems work in

balance with each other, much like the brakes and the gas pedal of a car. By learning how to control them more skillfully, you can increase your positive experiences,

reducing negative ones, and – if you like – develop the steadiness of mind and equanimity that are vital for contemplative depth and realization.


The PNS conserves energy in your body and is responsible for ongoing, mellow,

steady-state activity. The feeling of it is relaxation, often with a sense of contentment.

(And signals for it originate in the Nucleus Ambiguus – love the term – in the brain


The parasympathetic nervous system:

Opens (dilates) blood vessels leading to the GI tract, aiding digestion.

Stimulates salivary gland secretion and accelerates peristalsis, helping the

absorption of nutrients.

• Engorges the male and female genitals

• Constricts the bronchioles of the lungs.

• Dampens the sympathetic nervous system.

The primary hormone/neurotransmitter of the PNS is acetylcholine. For example,

levels of this rise when we are sleeping, helping to slow the heart and decrease the

force of its contraction.

Relaxation: Exercise #2

Relaxation is at the heart of most stress management trainings. Since you use the PNS

in order to relax, relaxing engages its circuitry and thus activates the PNS.

Relaxing also has a significant indirect activation of the PNS: relaxed muscles send

messages to the alarm centers in the brain that nothing is alerting the body to a threat.

Many people have their own key methods, and here are a few of the most common

“quickies” for relaxing without going to yoga camp:

Relax your tongue

Relax your eyes

Relax the diaphragm area

Imagine being in a very comfortable setting

Feel everything draining out of you and sinking deep into the earth

You might like to try one or more of these right now, maybe one you’re not so familiar

with, and see how it feels.


The SNS deals with immediate, rapid responses to changing environmental conditions.

It lights up when an organism – a mouse in the field and the cat hunting it, or you and

me – has to do something actively to preserve its equilibrium.

Much SNS activity is not particularly dramatic. For example, standing up would cause

a big drop in your blood pressure if the SNS did not compensate by momentarily

increasing it. Similarly, just before you wake up, sympathetic activity increases,

getting your body ready to be active.

The sympathetic system deals with “fight or flight” reactions, but it’s more versatile

than that. Even in high-drama survival situations, such as a rabbit seeing a snake, the

SNS may trigger not fighting nor fleeing . . . but freezing. (This latter response can

become increasingly habitual in victims of inescapable trauma, such as mistreated

prisoners or children in an abusive home.) In some fish, the SNS can cause a swift

change in color. Your SNS activates whenever you’re upset – like irritated at a co-

worker, saddened by an unexpected loss, or worried about how to pay the bills

On a happier note, SNS activation in women can be accompanied by a release of the

soothing hormone oxytocin and increased “tend-and-befriend” behaviors. Partial or

mild SNS activations may lead to negotiation among social animals, or even a kind of

play, such as kittens – or preschool boys – tussling with each other.

Working Together

Broadly, the SNS deals with:

tight engagement with the external environment

• high levels of energy

• mainly exteroceptive (external) sensory information

On the other hand, the PNS handles:

disengagement from the external environment

• low levels of energy

• mainly proprioceptive (internal) information

• recovery from stressful experiences

• return to homeostasis

In short, the SNS prepares the organism to act upon its environment, while the PNS

prepares the organism to act upon itself. Put more dramatically, if the SNS is for “fight

and flight,” the PNS helps you “rest and digest.” Both systems evolved to keep

animals, including humans, alive in very harsh and potentially lethal environments,

and we need them both.

Nonetheless, we live in a culture that prizes the excitement, aggressiveness, high-

stress worklife, pace, and general intensity that is fueled by the SNS. Further, unlike

most other developed nations, it is a simple fact that our society has chosen not to take

steps such as universal health care, family friendly laws, and an economic safety net

that would lower much of the SNS-activating anxiety that gnaws at many people.

Yet if anything, the PNS is more fundamental to life. If your sympathetic system were

surgically disconnected – as it was in years past as a last-resort treatment for hyper-

tension – you would remain alive and pretty much yourself – though unable to cope

well with commuter traffic, root for the home team, or have an orgasm. But if your

PNS were disconnected, you would die quickly. PNS activation is the resting state of

the body-mind: in other words, relaxed contentment is your fundamental home base,

your bottom line. Pretty sweet!

Most of us live in a chronic state of SNS over-activation. Conscious attention to the

parasympathetic system brings the pendulum back to center.

Increasing and Balancing “Heart Rate Variability”: Exercise #3

The HeartMath Institute has pioneered a number of research-based techniques for

influencing the heart rate in ways that improve physical and mental health. Most if not

all of their methods engage the parasympathetic nervous system.

In brief, here’s a simple, three-part method:

Breathe in such a way that your inhalation and exhalation are the same duration;

for example, count 1-2-3-4 in your mind while inhaling and 1-2-3-4 while exhaling.

At the same time, imagine or sense that you’re breathing in and out through the

area of your heart.

Meanwhile, bring to mind a heartfelt emotion like gratitude or love.

Try this for a minute or two, and you will probably be struck by the results.

Technically, you are both increasing and harmonizing the natural, tiny changes in the

interval between heart beats: what’s called “heartrate variability.” Fairly large changes

in that interval, and changes that vary smoothly from one beat to the next, link to

cardiovascular health, improved immune system function, and elevated mood.

How the Sympathetic System Gets Triggered


Since PNS activation is the baseline of your body, with SNS activation being a change

in that baseline in order to cope with something “perturbing,” it’s really useful to

understand the answers to these questions:

What triggers the SNS?

What happens then?

Activation Signals

As noted, much of the routine activation of the SNS is quiet and in the background

(like maintaining blood pressure when you stand up). As usual, it’s the fireworks that

get noticed! Still, it is those fireworks that cause us the most trouble – in our

experience of living, in our health, and in our relationships – so we’re going to focus

here on them.

Here’s a survey of the different sorts of things that signal the SNS to WAKE UP AND


Imagine an extreme situation, such as you’re driving along and suddenly a tire

blows and your car starts to spin into oncoming traffic. Or you get a call from school

and your child has had a terrible fall and is being rushed in an ambulance to the

hospital. Or you’re walking down a dark street and suddenly you feel someone

grabbing you and trying to take your wallet or purse. These are mortal threats to

yourself or people you love.

Imagine less extreme situations, such as stubbing your toe (pain) or getting into

an argument with your partner (emotional upsets).

Imagine just having low blood sugar: you had a donut and a diet Coke for

breakfast, it’s 11:00 o’clock, and you’re stuck in a boring meeting at work.

Imagine something really exciting, in a wonderful way: you get the envelope

saying you’re accepted into the college of your choice, or your beloved asks you to

marry him, or the Red Sox finally win the World Series (that one sure pumped me up).

Imagine being trapped in stop-and-go traffic. Or having to write a difficult report

under a tight deadline. Or being blasted with a bright light or a loud noise. Or having

to do a lot of multi-tasking, or getting constantly interrupted (a description of raising

young children . . . ). Or anything else that’s significantly stressful.

Danger, pain, upsetting feelings, low blood sugar, excitement – and stress in general – all

activate the sympathetic nervous system.

And so does the anticipation of something bad (or really wonderful) . . . even if that

anticipation is exaggerated or flat wrong.

Or even simply seeing the name of someone who we’re upset with on an email.

Exacerbating Factors

This last effect of an internal, psychological variable – such as antici - - - - - - - pation –

points to the powerful role of psychological factors in modulating the impact of


For example, if we expected a job interview to be serious and demanding, then when it

is, it’s (probably) not that stressful. But if we expected a mere formality, a cakewalk,

but it’s actually serious and demanding, then that could be quite stressful. The

violation of an expectation activates the SNS, which deals with novelty; the violation of

a positive expectation is especially stressful.

Additionally, studies have shown that the impact of events is increased when we:

Do not have emotional outlets

Feel like we’ve got little or no control

Are not supported by others

Lack hope that there’s a light at the end of the tunnel

As Robert Sapolsky, PhD wrote in Scientific American (8/10/03):

“. . . a rat will be less likely to develop an ulcer in response to a series of electric shocks if it can

gnaw on a bar of wood throughout, because it has an outlet for frustration. A baboon will

secrete fewer stress hormones in response to frequent fighting if the aggression results in a rise,

rather than a fall, in the dominance hierarchy; he has a perception that life is improving. A

person will become less hypertensive when exposed to painfully loud noise if she believes she

can press a button at any time to lower the volume; she has a sense of control.”

So, with or without one of these of these exacerbating factors, let’s say something has

disturb your equilibrium. What happens then? (And we’ll focus here on reactions to

negative stimuli, since that’s where most of the action is.) As we go through this

discussion step by step, try to get a sense of this process actually happening in your

own body. It’s also a vivid way to learn about your nervous system.

Initial Arousal

First, within a fraction of a second, your brain orients to the novelty of whatever has

occurred: “Oh, something new, something different, compared to my prior


Then, there is a deepening attentiveness to the stimulus. The nerve circuitry involved

in processing a particular sort of information – let’s say a troubling noise in the night,

or the avalanche of thoughts about the audit notice you just got from the IRS –

becomes physically more sensitive and active when attention is paid to that kind of


Feeling and Perception

Next, the stimulus gets flagged by the hippocampus and amygdala as “pleasant,

unpleasant, or neutral.” This is the “feeling tone” in Buddhism, the second of the Five

Aggregates of existence. And with that feeling tone comes the related behavioral

inclination: approach, avoid, move on.

So far, typically less than a second has elapsed. Jump first. Ask questions later.

Notwithstanding the sometimes problematic effects today, this hard-wiring in the

brain helped our great- great- great-grandparents survive in the wild.

Coming quickly on the heels of the feeling tone, there is a labeling – often culminating

in a verbal tag – of what the stimulus is, and this is known as “perception” in

Buddhism, the Third Aggregate.

Bringing up the rear, but hopefully gathering in influence as the seconds tick by,

comes the analysis and commentary of the frontal lobes. This enriches, shapes, and

edits the initial take by the hippocampus and amygdala. In Buddhism, this wave of

activity is known as the “mental {or volitional] formations,” the Fourth Aggregate. (To

round out the picture, the First Aggregate is all of physical reality and the bare

sensation of it, and the Fifth Aggregate is consciousness.)

Primary Reactive Cascade

As soon as the amygdala and hippocampus register that something significantly

unpleasant is happening – or threatened (including anticipated) – they trigger a

primary cascade of changes throughout your body. All often in less than a second,

sometimes much less.

Note that the follow-on waves of perception and mental formations that come seconds

and minutes – or hours and days – afterwards can also influence the primary reactive

cascade, but they are playing catch up, trying to slow down or redirect primal currents

of neuronal information and hormonal/neurotransmitter discharges after the

floodgates have already opened.

This primary cascade works both through the sympathetic nervous system, and

through what is called the hypothalamus-pituitary-adrenal (HPA) axis of your

endocrine (hormone) system. While the SNS and HPA are anatomically distinct, they

are so intertwined that they’ll be described together.

So here we go:

The thalamus – the major relay station smack in the middle of your head – sends

a “Wake Up!!” signal to the locus ceruleus, a cluster of just a few hundred neurons in

your brain stem that plays a central role in arousal and alertness.

The norepinephrine-releasing neurons of the locus ceruleus spread throughout your

brain, and when the LC lights up, those neurons disperse this activating

neurotransmitter/hormone far and wide.

Amygdala neurons extend (“project”) down into the midbrain and brain stem,

and they activate the control centers of the sympathetic nervous system – whose major

trunk lines run down your spine and send wiring into every major organ and muscle

group of your body – and that makes the SNS light up.

Meanwhile, within the HPA axis, the amygdala has also released a

neurotransmitter called “corticotropin releasing hormone” (CRH). This, and other

signals from that axis and the sympathetic nervous system, cause surges of the major

“stress hormones”: Epinephrine and, to some extent, norepinephrine (adrenaline and

noradrenaline), plus glucocorticoid hormones, particularly cortisol.

Interestingly, both physical stress and social stress activate the HPA axis, though

through different pathways. But this gives a neurological explanation for why getting

rejected or shamed can feel as stressful as a root canal.

And you can see the central role of the amygdala, since it triggers both the SNS and

the hormones of stress.

In all, there are multiple, redundant pathways to get the organism ready to “do

or die.” (That’s why it’s complicated to describe – and understand.) It’s that important

to survival.

Secondary Reactive Cascade

OK, so now your brain is on red alert, your sympathetic nervous system circuitry is lit

up like a Christmas tree, and tidal surges of stress hormones are washing through

your blood. Great! Now what happens?

Epinephrine makes your heart beat faster and stronger, makes your pupils dilate

to gather more light, improves your visual acuity a bit, and makes you sweat to cool

the body.

Norepinephrine constricts the blood vessels in the skin, which makes the skin a

little cooler.

Triggered by the locus ceruleus, norepinephrine also excites – in the neurological

sense – your brain as a whole, making it more susceptible to stimulation and priming

it for activation. By the way, this could be one of the primary sources of the experience

of slowing your perceptual time clock in an emergency (e.g., car crashes, falls in rock

climbing): since your brain speeds up, the world seems to slow down.

Epinephrine and norepinephrine – called “adrenal hormones” – act quickly,

while the glucocorticoids have slower effects. They suppress the immune system,

perhaps to reduce inflammation from wounds.

Glucocorticoids also add to the activation of the locus ceruleus, making it release more

norepinephrine into the brain. In a circular feedback loop, the locus ceruleus sends

projections back to the amygdala, which tell it to release more CRH, which leads to

more glucocorticoids, which activate the locus ceruleus further, and so on.

Unfortunately, glucocorticoids in pregnant women can cross the placenta to reach

their young, and very high levels of these stress hormones can permanently alter the

hippocampus of the fetus, with effects discernible in adulthood. (But please know that

this refers to really, really high levels of stress hormones, not the normal fears and

hassles that accompany many pregnancies.)

Lots of changes occur in the cardiovascular system. For example, blood gets

shunted from the interior of the body to the major muscles, dilating the blood vessels

there for maximum strength. In fact, in the skeletal muscles in the core of your body,

blood flow can increase by as much as 1200%.

Interestingly, the emotion of fear tends to increase blood flows to the legs, while the

emotion of anger tends to increase them to the arms . . . the one to run away, the other

to turn and fight.

The bronchioles of the lungs get dilated, for more gas exchange . . . . enabling you

to run farther and hit harder. We also tend to hold our breath when we are anxious, to

extract as much oxygen from it as possible.

Blood sugar rises, to get more fuel to cells that need to burn hot.

Sometimes you get goose bumps – the fancy term for this is “piloerection” –

raising the hairs on your skin, a vestige of an ancient reaction that made our animal

ancestors look bigger when they felt threatened.

Reproduction is sidelined. The production of reproductive hormones in women

decreases, and erections in males are suppressed. No time for sex when a lion is

charging! And the effects of chronic stress on libido are apparent even without a

mortal threat at hand; just ask those caring all day long for young children.

By the way, male arousal involves a delicate minuet between the SNS and PNS,

charmingly explained by Robert Sapolsky in his marvelous book, Why Zebras Don’t Get

Ulcers. In brief, men need some SNS activation to get sexually excited in the first place,

but then the SNS needs to take a back seat for awhile to the PNS, which dilates (opens)

blood vessels in the sex organs (though the SNS is responsible for dilating them in

much of the rest of the body). Then, as orgasm approaches, the SNS is responsible for

ejaculation. This complexity is one of the reasons why erectile dysfunction is not

uncommon, and why stress and anxiety can have such an effect on sexual


Digestion is suppressed. Salivation is reduced, the reason for a dry mouth when

you’re afraid. Peristalsis (the rippling of the intestines that moves food along) slows

down, which is why stress leads to constipation.

Related emotions intensify – like fear, disgust, and anger – which sensitize your

sensory circuits to threatening information, so they will pick it out more quickly. From

an evolutionary perspective, emotion is a very effective development.

But emotional reactivity also has its drawbacks. It makes you prone to over-estimate

threats and not see positive resources. Also, circular and snowballing processes often

reinforce any initially distorted perspectives. For example, if your original appraisal of

the other person’s action was that it was a “5” on the Badness Scale (but actually it was

really just a “2”), then you’re likely to get extra huffy . . . which in turn could irritate

the other person, who’s probably thinking: “Hey, that was barely a ‘1’!” And that

irritation could reactivate him or her further, seeming to confirm your original – but

actually exaggerated – appraisal.

Mindfulness of the Body: Exercise #4

Since you’ve been reading about the body, maybe you’ve been bringing your attention

to it a little – a good segue to mentioning another method for PNS relaxation:

mindfulness of the body.

Since the PNS deals mainly with internally directed activities, bringing attention

inwardly – especially when not related to something alarming, like worrying if you

have an ulcer – activates PNS networks. Plus mindfulness is generally relaxing, which

also activates the PNS (as we discussed above).

Probably you’ve already had some formal practice with mindfulness of the body (e.g.,

while meditating, doing yoga, in a stress management class). It’s simple: just be

attentive to physical sensations. And you can focus, if you like, on some sensations in

particular, such as the breath in general or even localized to the area around the outer

nostrils and upper lip.

Long-term Effects of Chronic SNS Activation

In a nutshell, the SNS shunts resources away from long term projects – like building a

strong immune system, or digesting food, or making babies – in favor of short term

crises, like getting away from an attacking lion a million years ago. Crises that were

usually resolved quickly. One way or another.

But long after the lion has pounced on someone else and left you alone, you’re still

shaking like a leaf! That’s because the effects of the SNS diminish gradually, while the

effects of the PNS diminish abruptly. For example, in a frightening situation (= SNS

arousal), it takes your heartbeat awhile to go back to normal even after the danger is

over. But when you wake up – and are no longer so regulated by the PNS – your

heartbeat increases briskly.

One reason for this is that, unlike many other hormones, the dominant SNS hormones

– epinephrine (adrenaline), norepinephrine, and catecholamines (which include

dopamine) – do not exert any negative feedback to reduce their own synthesis.

Bottom-line, lighting up your SNS is not just a fleeting experience, but something that

has a real stickiness to it, a lasting impact.

For example, chronic activation of the SNS burdens five major systems of your body:

gastrointestinal, immune, cardiovascular, endocrine, and nervous. Let’s look at the

lingering effects of that wear and tear for each system, with an emphasis on the

nervous system, since that’s where it feels like we live as conscious beings.


Chronic stress and other sources of SNS activation increase your risk for to ulcers,

colitis, irritable bowel syndrome, diarrhea, and constipation.


Routine SNS arousal weakens your body’s defenses in numerous ways. This finding is

well-documented in numerous studies, and we’ve all had the personal experience of

catching a cold when we’re run-down.


Hardening of the arteries and heart attacks are all more likely if you experience

chronic stress – especially when combined with a steady dose of hostility.


A steady diet of SNS increases risks for Type II diabetes, especially when combined

with lots of sugary and refined carbohydrate foods. In the erotic department, it leads

to impotence in men and low desire for both sexes.

And it’s probably not very good for your longevity, either. The body makes cortisol

(one of the stress hormones) and DHEA from the same raw materials. DHEA is

sometimes called the “anti-aging hormone” due to its beneficial effects. But under

stress, production is shifted toward cortisol, so there’s less DHEA.


The amygdala. Repeated experiences of fear (and perhaps other negative emotions

such as disgust or anger) increase what’s called the Long-Term Potentiation (LTP) of

neurons in the amygdala; in other words, the synaptic connections there are

strengthened. Further, repeated stressful experiences lead amygdala neurons to grow

more connections with each other. As a result, in a vicious cycle, repeated experiences

of fear and stress make the amygdala more sensitive to and more reactive to fear- and

stress-related information.

Now, the amygdala plays a central role in the formation of implicit memories: the

registration of lived experience (especially the emotional and sensate parts) beneath

conscious awareness. When the amygdala has become sensitized and energized in a

fearful and negative direction, then it shifts implicit memory that way. Over time, this

“dark shading” can lead you to feel a free-floating anxiety, depressed mood, and


Your implicit memories and negative emotions also create the conceptual lenses

through which you see the world. These perspectives seem self-evident – of course

most relationships are disappointing, of course you’ll get in hot water if you say what

you really feel, etc. – and are thus typically unquestioned, which is what makes them

most problematic; like the proverbial fish, we swim in the waters of our belief systems

without realizing we’re soaked in assumptions.

When you peer at the world through subtly shadowed glasses, it looks more daunting

and less friendly, which naturally makes you too cautious or too aggressive . . .

sometimes with serious consequences. And in a feedback loop, any “tinted”

information coming through your lenses increases the negative sensitization of the

amygdala, which in turn darkens your worldview, leading to incoming information

that’s even more shaded.

The hippocampus. Compared to the amygdala, stress hormones – notably cortisol –

have an opposite effect on the hippocampus, a part of the brain that is vital for

forming explicit memories of events: a clear record of what actually happened. In

other words, stress hormones reduce long-term potentiation (LTP) in the hippocampus.

In the extreme, intense and longstanding stress or trauma can literally shrink the


Further, recent evidence has shown that at least some portions of the brain actually do

grow brand-new neurons (contrary to long-held belief), including the olfactory bulb

(for smell) . . . and the hippocampus. But glucocorticoids due to stress prevent the birth

of new neurons in the hippocampus, impairing its ability to produce new memories.

The effects of all this can be quite extreme. For example, in people who have a history

of severe depression – which could be regarded as both a result and a cause of stress

and painful feelings – the hippocampus can shrink by as much as 10 – 20%. This

shrinkage could be one of the reasons for the poor memory associated with

depression. Unfortunately, hippocampus atrophy persists after depression resolves; it

appears to be a permanent consequence of intensely painful experiences.

The amygdala-hippocampus one-two punch. When the amygdala is over-sensitized

and the hippocampus is compromised, it’s a horrible combination: painful experiences

can get recorded in implicit memory – with all the distortions and turbo-charging of

an amygdala on over-drive – without an accurate explicit memory of them! Then it

may feel like: “Something happened, I’m not sure what, but I’m really upset.”

This could be a reason why victims of trauma sometimes feel dissociated from the

actual events surrounding their trauma, yet are very reactive to any trigger that

reminds them unconsciously of what once happened.

Depression. Routine activation of the sympathetic nervous system is closely

linked to depression, for three kinds of reasons. First, an underlying source of SNS

arousal – such as getting fired or needing to care for a demented parent – could also be

depressing in its own right; in this case, the two effects, SNS arousal and depression,

are associated simply because they share a common cause. Second, the experience of

chronic stress has psychological consequences – e.g., no chance to let down, feeling

irritable, sense of hopelessness – which can wear down your mood over time.

Third, the physical effects of sympathetic activation undermine the biochemical basis

of an even-keeled, let alone cheerful, disposition:

Glucocorticoids slowly deplete the norepinephrine released throughout your

brain by the neurons of the locus ceruleus. Norepinephrine makes you feel alert,

attentive, and mentally energetic, so when stores of it run down, you tend to feel a

certain dullness, flatness of emotion, weakening of concentration, even apathy – which

are hallmark symptoms of depression. (This could a reason why taking glucocorticoid

hormones for arthritis can lead to depression as an unwanted side effect.)

Stress reduces the amount of serotonin – the neurotransmitter that is relaxing,

regulates sleep, and buttresses your mood – in your brain. Additionally, it reduces the

number of serotonin receptors in the frontal lobes, so they are less responsive to the

dwindling stocks of serotonin that do arrive.

Serotonin also encourages the locus ceruleus (LC) to release norepinephrine. When

serotonin levels drop due to stress, that leads to even less norepinephrine from the

locus ceruleus, which has already reduced its norepinephrine flows due to increased

glucocorticoid stress hormones (which we discussed in the bullet just above).

In short, less serotonin means more tension, worse sleep, more vulnerability to a blue

mood, and less alert interest in the world.

Moderate and brief stresses – in other words, manageable doses – lead to a

release of the neurotransmitter, dopamine, in the pleasure circuitry of the brain. That’s

one source of the “high” in some stressful activities like race car driving, difficult

skiing, rock climbing, etc.

But – prolonged exposure to glucocorticoids flattens dopamine production. Then, as

the classic criterion for depression says, there is a loss of enjoyment in activities once

found pleasurable.


We evolved to handle short bursts of intense stress, and live to tell the tale. But the

modern lifestyle of fairly steady levels of moderate stress is completely unnatural, and

it has many bad consequences for your physical and mental health. That’s perhaps the

most fundamental reason for increasing the activation of your parasympathetic

nervous system.

Yawning: Exercise #5

So now, as another method for activating the PNS – and one that could be happening

on its own as you try to assimilate all the material we just plowed through – try


Yawning activates the PNS on inhalation and the SNS on exhalation. Taken as a

whole, it sure feels like a net PNS intervention.

Strategic Perspectives

Even though you’ve just had a fairly nightmarish tour through the potential collateral

damage of the sympathetic nervous system, we still need that system, and it’s got to

work well, whether it’s to get through a minor crisis at work or rise to meet the

challenge of a late-night call from a teenager who needs a ride home from a party-


Nonetheless, we really do live in a time of SNS gone amok, and we would really

benefit from reducing its over-reactions. How to do that?

For sure, it makes sense to deal with your environment. That could mean looking for a

job with a less insane commute, parenting a spirited child in ways that help him learn

more self-control, or simply fixing the leaky faucet that’s driving you crazy at night.

You could also take medications. For example, tranquilizers like the benzodiazepines

work by relaxing muscles and by inhibiting the locus ceruleus excitation of the

amygdala, reducing its reactivity. Another class of drugs called beta blockers fit into

some of the neuronal receptors for epinephrine and block its effects – like a bandaid

covering a lock so the key can’t get in. (Interestingly, beta blockers reduce the

formation of memories of upsetting events, and are being explored in the treatment of


That said, there are a lot of limits on working with the external world, and lots of

benefits in working with the inner world (see the article, Why Inner Skills, at And there are well-known problems with

prescription medications; for example, the benzodiazepines are sedating and


Therefore, I believe that both research and personal experience tell us that it is the

inner skills – not environmental fixes or medical treatments – which make the greatest

difference to our resilience, well-being, and long-term health.

In terms of bringing a better balance to your autonomic nervous system, you can be

skillful inside your own body/mind in three kinds of ways:

In the moment, dampen the immediate SNS response. For example, focus on

moderating factors like social support, the sense of what you can do, and hope for the

future. Or distract yourself, or remind yourself not to sweat the small stuff.

Over the long-term, soothe SNS reactivity. For example, really emphasize

positive emotions in your life and practice taking in the good to help those good

experiences register deeply in implicit memory, both of which should reduce

amygdala reactivity over time.

Activate the parasympathetic nervous system. As we’ve discussed, PNS arousal

has inherent benefits, plus it puts a blanket on the SNS. Inner skills for triggering the

PNS have been the focus of Parts One and Two of this article.

Further Methods for Parasympathetic Activation


By the way, you may have already noticed that many techniques of PNS activation

work together. For example, relaxing is itself usually a pleasant experience, thus

triggering mildly positive emotions.

To review, we have already covered:



Lowering heart rate

Mindfulness of the Body


Now we’ll explore three more methods.

Meditation: Exercise #6

Meditation activates the PNS for many reasons, including pulling attention away from

stressful subjects and activities, sitting quietly, relaxing, and bringing awareness into

the body.

An interesting, possible additional reason has to do with a common method of

meditation: paying attention to the sensations of the breath around the nostrils and

upper lip. In your brain, the olfactory bulb – which receives sensory signals from the

nostrils – sends neuronal projections directly to the amygdala, probably due to the

evolutionary importance of detecting disgusting, frightening – and sometimes,

pleasant – aromas. When you bring your attention to the breath around the nostrils,

you activate the sensory networks in that area, including the olfactory system.

As a result, you are flooding the amygdala with information that has a neutral quality

to it (that quality is called “feeling” – distinct from emotion – in Buddhism), or a

positive quality if you meditate with incense. That would tend to crowd out

unpleasant information within the amygdala. It could also sensitize the amygdala

increasingly over time to neutral information, leading its processing to be increasingly

dedicated to neutral information compared to negative information.

This is not the place to give instructions about meditation, which you’ve probably

been exposed to already. And you can get good information from the books of

Christina Feldman, Jack Kornfield, Jon Kabat-Zinn and many others.

Here, I would simply like to encourage you to meditate regularly. Even for just one

minute a day. But every day.

And consider joining a regular sitting group in your area. There are an amazing

number of meditation groups sprouting up around the country.

Positive Emotion: Exercise #7

Positive feelings activate the PNS directly by lowering cardiovascular reactivity. They

also do so indirectly by priming a person to experience life in more optimistic and

pleasant ways, and the effects of that include reducing the sensitization of the

amygdala to negative events. Anything that gives you a positive feeling – especially of

a more relaxed sort, like contentment, gratitude, lovingkindness, or tranquility – will

usually arouse your PNS.

Yes, sometimes it is hard to have positive emotions. And that difficulty alone can

cause some negative emotion! But just do what you can. There are two great wings to

psychological growth and spiritual practice: being with and working your inner and

outer worlds. While being with is primary, there is still a great role for working with,

including the cultivation of positive feelings. (For more on this point, please see the

Two Wings article in Bulletin #2, at

If you like, experiment with cultivating positive emotion for a few moments, and

whatever you experience is really fine.

Perhaps focus on what you feel grateful for. Or feelings of lovingkindness, perhaps

for yourself or some people you are close to.

And to really reap the rewards of experiencing positive emotions, help yourself by

taking them in 

Fiddling the Upper Lip: Exercise #8

Last, here’s a cool but kind of goofy method: fiddling with the upper lip, including

producing that “blub blub blub” noise kids love to make. The evidence for it is

anecdotal – mainly from people who work with horses or with troubled children who

bite – but interesting.

This method could work by:

Stimulating the PNS nerve fibers that innervate the lips, and thus send activating

reverberations throughout the whole PNS.

Triggering positive emotions associated with nursing, feeding in general, thumb-

sucking, etc. Note that children and even adults can comfort themselves through

touching their lips.

• Stimulating salivation, which is controlled largely by the PNS.

• Simply distracting yourself from stressful stimuli through its sheer absurdity.

Concluding Perspectives

Over the Long Haul

Many of us balance a driven and routinely stressful way of life with vacations or the

occasional day off. This is a kind of “binge and purge” approach to stress

management, but it is not at all effective. You cannot undo the accumulating effects of

chronic stress with intermittent respites, even in Tahiti.

There is no way around it: each of us needs to have minimal chronic stress combined

with a steady state of relaxed, alert, contented coping that emphasizes PNS activation

with just enough SNS arousal to get the job done – whatever it is. In a single sentence,

that’s your best-odds prescription for a long, productive, and happy life.

Foreground and Background

Consider puffy white clouds against a blue sky: the element that’s least present – the

clouds – pops to the foreground and dominates the picture. And if you’ve ever tossed

three coins to produce the six lines of the hexagram used in the I Ching, the ancient

Chinese system of divination, you’ve encountered a similar phenomenon, this time

from a great wisdom tradition: if heads represent yang (the light and active principle)

and tails represent yin (the dark and receptive principle), then one head and two tails

would be a yang line, since it is the yang element – in the minority – which stands out.

Or consider TV shows or movies which spotlight conflict and lack of communication .

. . but against a backdrop of routine daily cooperation in human societies. Cooperation

is so ubiquitous that it becomes the “sky” against which the clouds of conflict stand

out – and capture and dominate our attention.

Recall the point made in Part One: if your SNS were shut down, you would continue

to live and function (though maybe be sluggish in an emergency). But if your PNS

were deactivated, you would quickly die. Your parasympathetic nervous system is

absolutely fundamental to life.

The PNS is wallpaper, sky, taken for granted, undramatic, in the background. Human

culture, and definitely the modern media of television and movies, are largely about

the SNS. Action, conflict, sex, million dollar moments, death, crisis, fairy-tale endings,

etc. are different and dramatic. It’s therefore easy to start thinking that chronic stress

and living awash in the SNS are what’s really natural, the bedrock of existence.

But in reality, cooperation, relaxation, and equilibrium are the hub of the great wheel

of life.