From decapitation to positive psychology: how one nerve connects body, brain and mind

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The relationship between mind, brain and body has kept philosophers and scientists busy for centuries. Some of the first interesting – albeit gruesome – experiments on the role of the body in human consciousness considered life after decapitation.

In 1905, French physician Dr Gabriel Beaurieux believed he had communicated with prisoner Henri Languille after his head had been severed from his body. Writing of the experience, Beaurieux said:

I called in a strong, sharp voice: “Languille!” I saw the eyelids slowly lift up, without any spasmodic contractions – I insist advisedly on this peculiarity – but with an even movement, quite distinct and normal, such as happens in everyday life, with people awakened or torn from their thoughts.

Almost two decades later, Soviet scientist Sergei Brukhonenko reportedly kept a dog’s severed head alive for nearly six months using a primitive heart-lung machine. Video footage allegedly shows the head responding to light, sound and citric acid stimuli. But while Brukhonenko’s research may have been an important in the development of cardiac surgery – it is more often regarded as faked Soviet-era propaganda.

Consciousness and non-physical properties

Investigations into the human consciousness have moved on since these intial observations – though we haven’t got away from decapitation just yet. More recently, however, neuroscientists have questioned just how it is that physical matter comes together to make the mind.

In 1995, Dr Francis Crick proposed the “astonishing hypothesis”, that we are nothing more than an “immensely complex collection of neurons”. This theory is a form of reductive physicalism, a philosophical position – to which modern neuroscience typically subscribes – that everything in existence is no more than its physical properties.

Again using animal decapitation, though this time with rats, neuroscientists have explored the question of how long brain activity is observed after death – a step forward from just consciousness.

In a 2011 experiment, it was reported that decapitated rats’ time to unconsciousness – defined by a decrease in cognitive activity of 50% – was four seconds. The researchers also observed a very large and much later slow wave in brain activity. This was interpreted as what they called a “wave of death” – when all the brain’s neurons died at the same time – and perhaps, the ultimate border between life and death.

But some believe that the mind is more than just the sum of its physical brain cells. A contrasting position to physicalism is the dualist assumption that physical and mental “substances” are fundamentally different.

Furthermore, some philosophers and scientists have suggested that “information” may be the key to consciousness. Consistent with this idea is “integrated information theory”, which accepts the existence of consciousness. Though a controversial implication of this is that anything at all may be conscious, even a smartphone, if it possesses “phi”. That is a measure of information integrated in a system which cannot be reduced to that which is specified by its parts.

From psychological moments to mortality

While I have left out many important details in this fascinating discussion, better understanding the link between mind, brain and body has been the focus of my own research. And in recent years, I have looking at how the vagus nerve functions to investigate these connections.

The vagus nerve, part of the parasympathetic nervous system.

Higher vagus nerve function (measured and indexed by heart rate variability) supports a person’s capacity for emotion regulation, social engagement and cognitive function. By contrast, impairment in vagal function – lower HRV – may play a role in the onset of depression.

But the vagus nerve doesn’t just affect the mind. Higher levels of vagal function may lead to improved glucose regulation, reduced inflammation and reduced risk for disease morbidity and all-cause mortality.

Vagal function is also known to play an important role in brain cognition. It helps to suppress irrelevant and interfering stimuli. Studies have also suggested that the vagus nerve might play an important regulatory role over inflammatory processes, contributing to diabetes, obesity and cardiovascular disease – all of which also impact on cognitive function.

However, little research has been done which looks at how the vagus nerve affects body and mind together. That’s why I teamed up with colleagues to question whether previously reported relationships between vagal function and cognitive performance could be explained through a single neurological/psychological/physiological pathway.

Supporting this possibility, we observed that impairment in vagal function appears to increase insulin resistance contributing to a thickening of the carotid arteries, which then adversely impacts on cognitive function. This means that low vagal function provides a “spark” that initiates a cascade of adverse downstream effects which subsequently lead to cognitive impairment.

While simple health behaviours – weight loss and exercise for example – may “short circuit” adverse effects on brain function, more research into the causal pathways involved is still needed to discover just how the vagus nerve connects the body, brain and mind.

Our research is a first step into uncovering how the health of the body and mind can be affected by this one nerve. But it is one on a path that we hope will develop with our own research into “positive psychology” for people living with neurological disorders.