Stress: Linking Mind and Body

Ross Harper
Oct 4, 2018 · 5 min read

It’s a Wednesday afternoon and you’re sitting around a conference room table with twelve stern faces staring you down. The company partners are all waiting to hear you talk. But you can’t. Your heart is racing, your mouth is dry, and your hands are shaking. All eyes are on you.

Relax, it’s not you in the headlights (… this time). You’re safe and sound reading this blog post. However, stress is likely an all too familiar feeling. As the CEO of Limbic — where we make software to measure stress — I receive a lot of questions from clients. What is stress? Why is stress? Where is stress? This blog post is long overdue.

Let’s Start with the ‘What’

Stress is the body’s response to a perceived threat. It describes a reaction to a situation, rather than the situation itself. That means if you’re a confident public speaker, the scenario described above won’t phase you. (Perhaps the thought of a big hairy spider crawling up your back would do it?)

Now for the ‘Why’

A philosophical question. Allow me to narrow the scope.

Stress is a behaviour that evolved in our species, and many others. The laws of natural selection therefore imply it gives us some selective advantage. This is true. Stress keep us alive.

When you perceive danger — real or imagined — your body’s defence mechanisms kick in. Imagine it’s 300,000 years ago and you’re an ancient Homo sapiens wandering the African plains. You hear a rustling noise behind you, and turn to discover a tiger. What do you do?

Well, you either summon the courage to attack the ferocious beast (fight), run for your life (flight), or stand very very VERY still and hope not to arouse interest (freeze). This is your stress response, and it’s there to keep you alive.

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Sure, why not!

And Finally, the ‘Where’

To answer this question, we’ll need to dive into the neuroscience a bit.

The Central and Peripheral Nervous System

Our nervous system is divided into two major parts — the central and peripheral nervous system (CNS and PNS) respectively. The CNS, which can be considered the body’s control centre, comprises the brain and the spinal cord. The PNS covers the rest of the nervous system, relaying information from around the body to and from the CNS¹.

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The Autonomic (Involuntary) Nervous System

The PNS can be further subdivided into somatic (voluntary) and autonomic (involuntary) pathways. The somatic nervous system allows us to perform controlled movement and sense the world around us. It’s very important, however our hunt for the ‘where’ of stress involves the autonomic nervous system (ANS).

The ANS innervates smooth muscle (e.g. heart tissue) and glands (e.g. those that produce adrenaline). It influences the function of internal organs and is responsible for many of the things we do automatically: heart rate, digestion, respiratory rate, pupillary response, urination, and sexual arousal, to name a few¹.

The Sympathetic and Parasympathetic Nervous System

The ANS has two components: the sympathetic pathway and the parasympathetic pathway. These can broadly be thought of as stimulating or inhibiting target organs, and the two pathways have opposite effects. The stress response is delivered by the sympathetic pathway; relaxation and recovery is mediated by the parasympathetic pathway.

The stress response is delivered by the sympathetic pathway

For example, activity in the sympathetic pathway acts to increase heart rate, decrease heart rate variability, and increase respiration rate. These are all physiological changes associated with fight, flight or freeze. Conversely, activity in the parasympathetic pathway decreases heart rate, increases heart rate variability, and decreases respiration rate².

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Putting it all Together

So you’ve just turned around to find a tiger staring into your soul. Given that you’re not an even larger tiger, you consider this a threat. Your body reflexively begins a variety of processes designed to combat the threat — a.k.a. your stress response (the ‘what’). The sympathetic pathway of your autonomic nervous system kicks into action, sending signals to target organs all over the body (the ‘where’). Your breathing rate increases (so you have more oxygen in your blood), your heart begins to race (so your muscles get more blood and therefore energy), and your pupils dilate (so you can see your impending doom more clearly). You either fight, flight, or freeze, and hopefully live to do all three another day (the ‘why’).

It’s worth noting that while evolutionarily useful, stress is not always good for us. Too much stress, or stressful reactions to harmless events, can be very damaging to our health. (I’ll explore this further in the next blog post of this series).

Wearables are a Game Changer

Stress is realised in physiological changes around the body. Wearable devices are growing in popularity, creating an opportunity to collect this data. Apple Watch, Samsung Galaxy Watch, and FitBit all include an optical heart monitor (while other wearables can measure skin conductance and even brain waves).

Personal computing is moving from the pocket to the body. The result is that stress is now quantifiable and therefore usable. Imagine the clinical implications for treating anxiety or PTSD. Imagine if your iPhone only sent you the most important message alerts when it recognised you were stressed 🤯.

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And stress is just the beginning. At Limbic, we’re building algorithms that can measure six different emotional states. We’re decoding biology to understand emotion. Linking body and mind.

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  1. S.E. Borst, S. Goswami, D.T. Lowenthal, and D. Newell. Autonomic nervous system. In James E. Birren, editor, Encyclopedia of Gerontology (Second Edition), pages 129–135. Elsevier, New York, second edition edition, 2007.
  2. Filippos Triposkiadis, George Karayannis, Grigorios Giamouzis, John Skoularigis, George Louridas, and Javed Butler. The sympathetic nervous system in heart failure. Journal of the American College of Cardiology, 54(19):1747–1762, 2009.

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