Exploring the Link Between Heart Rate Variability and the Brain

Ever felt a sudden wave of emotion roll over you after an unsettling thought pops into your head? Or that overwhelming feeling when in a high-pressure sporting situation? If you've experienced either of these, you'll know how your heart reacts. It beats faster and harder until the wave of stress eventually disappears, and your heart returns to its steady, familiar rhythm. It therefore makes sense to believe that heart rate may be a great measure of stress or when someone is ready to perform. But interestingly, the difference in time (variability) between each beat of the heart appears to be a much more reliable index of what's going on.

This is known as heart rate variability (HRV) - the variation in interval between heartbeats. An abundance of research has shown that HRV is a reliable index of anxiety, PTSD, depression, risk of disease, mortality, degree of physical performance, recovery, and much more. Many athletes currently use HRV as an indicator of when to perform and when to rest, however, few have investigated the link between HRV and the brain...

In order to understand how the brain is connected to HRV, it is important to first understand a bit about the mechanics of HRV. Don’t worry, I’ll keep it brief. HRV is influenced by the automatic nervous system (ANS). The ANS has two branches: (1) sympathetic, associated with 'fight or flight' responses, and (2) parasympathetic, associated with 'rest and digest' responses. These two systems feed directly to the heart; parasympathetic regulation lowers heart rate thus permitting a rise in variability, whereas the reverse is true for sympathetic regulation.

Imagine a house with a light outside shining either green or red. When red, the mood in the house is bad. When green, the mood inside is good. HRV resembles the light; it reflects the state of the house (body) but we do not know what is contributing to this. When the people inside are laughing, someone - the light-switcher – flicks the green-light switch on. When people are arguing and shouting, the light-switcher turns on the red switch. The people inside the house resemble the brain, continually acting and reacting to whether the situation is sweet or sour. The light-switcher represents the ANS, feeding information about the people (the brain) to the light outside (reflecting HRV).

So daily stressors trigger the sympathetic and inhibit the parasympathetic system, thereby increasing heart rate and lowering HRV. All of which, as you know, creates detrimental effects for sporting performance.

But what if we could reduce sympathetic activation and in turn improve HRV? Research has shown that people with anxiety, PTSD and specific phobias have elevated amygdala activity and reduced medial prefrontal cortex (mPFC) activation. The amygdala brain region is associated with threat detection and the mPFC region is association with emotion regulation. This finding clearly demonstrates that the brain regions associated with perceived threat and its appraisal are believed to be structurally and functionally connected to HRV.

Could neuro-stimulation to the brains threat and threat appraisal regions therefore improve HRV, and so improve someone's health and wellbeing? In theory, yes. Transcranial direct current stimulation is a technique that causes the resting membrane potential of particular neurons to depolarise. This means that the excitability of neurons increases, allowing for more spontaneous cell firing. To this end, stimulating the mPFC whilst someone is performing emotion regulation may initiate synaptic plasticity of a particularly strong effect. The effects of this would be huge, sharpening one’s ability to quickly control their ANS responses.

If such an idea is true, the performer could then reap all the consequent benefits of higher HRV from this simple method.

The insights of HRV are clear. It is one of the best indexes of general health and well-being. Here at Adeki, we are dipping our feet into the untouched waters of HRV. We are growing our knowledge on the brain-HRV relationship, investigating unexplored avenues such as: oscillatory synchrony, binaural beats, emotion regulation and various forms of neural stimulation. Picture a quick and easy method, a neural bio-hack if you will, that renews your HRV to the ideal conditions for performance. Anytime, anywhere…

Now who wouldn’t want to give that a go?

Written by Head of Neuroscience, Max Wiggins