Mind the Body

In which we embody the mind (and add some microbes)

My body and I, we don’t always get along. It’s too scrawny, weak, fragile, and it doesn’t always do what I want it to.

Wait. That’s weird. Who is the ‘I’ in that sentence?

French philosopher René Descartes is known for, among other things, his mind-body dualism. There is a res cogitans, or thinking stuff, and a res extensa, or material stuff. That intuitive mind-body dualism is hard to shake. It certainly feels as if there’s some kind of thinking thing looking out of our eyes, caught in this body we’re stuck with. (Honestly, religions that posit a soul still cling to this notion.)

We now know that this is wrong. Root around in the brain and ‘you’ change. Phineas Gage is the paradigm example. While preparing an explosion to clear a roadbed somewhere in Vermont, something went wrong, and Phineas’ head was pierced by a tamping iron - a 6kg metal rod with a 3.2cm diameter - that turned his left frontal lobe into mush.

Game over, you’d think.

Only Phineas survived for twelve more years. During those years, though, he was a different person entirely. One of the few direct sources we have describing the accident, an 1868 case report (Gage passed away in 1860) with the killer title ‘Recovery from the passage of an iron bar through the head’ by physician John Harlow, states it like this:

He is fitful, irreverent, indulging at times in the grossest profanity (which was not pre­vi­ous­ly his custom), manifesting but little deference for his fellows, impatient of restraint or advice when it conflicts with his desires,… Previous to his injury, although untrained in the schools, he possessed a well-balanced mind, and was looked upon by those who knew him as a shrewd, smart business man, very energetic and persistent in executing all his plans of operation. In this regard his mind was radically changed, so decidedly that his friends and acquaint­ances said he was "no longer Gage."

Whatever the thinking thing was behind Phineas’ eyes, the metal rod in his brain definitely changed it. The res cogitans has a material base. (Neuroscientist António Damásio also uses Gage as an anchoring example in his book with the telling title ‘Descartes’ Error’.)

Let’s take it a step further. The thinking thing need not be contained by our skulls; it is - to some extent? - spread throughout the body. That’s the general idea behind embodied cognition, which comes in a few different flavors that make stronger or weaker claims. This family of theories is sometimes referred to as ‘the four E’s’ - embodied, embedded, extended, and enactive cognition, although embodied cognition can also be used as an umbrella term to cover all four of these.

(I’ve explored this in the context of AI here. Still one of the most interesting posts I’ve written so far if you ask me…)

But today it’s not about AI; it’s about mental health. If our thoughts, emotions, and so on are (partially?) embodied then we can’t truly separate physical and mental health. This is not necessarily new, but a recent intriguing study suggests that the extent to which our mental and physical health overlap is greater than our intuitive experience of the mind-body separation suggests.

tl;dr:

• Over 85,000 people with diagnosed mental health issues and over 87,000 controls.

• Brain imaging data, physiological measures, as well as blood- and urine-based biomarkers that reflect the relative health of various organs and bodily systems.

Run the analysis, crunch the numbers, and…

… neuropsychiatric disorders shared a substantial and largely overlapping imprint of poor body health.

In other words, mental health issues are not merely ‘visible’ in the brain but throughout the body. Especially problems with metabolic, liver, and immune health correlate with depression, bipolar disorder, anxiety, and schizophrenia. Looking at the data even makes the researchers conclude that:

Poor physical health was a more pronounced manifestation of neuropsychiatric illness than brain health.

Of course, this doesn’t tell us anything about how the causal arrow might run. Do the bodily problems cause the mental health problems? Vice versa? Hold up, mind and body are not separate entities, so does the question even make sense? The answer is probably ‘all of the above’ wrapped in a bunch of feedback loops. Sounds complicated, but if there’s one thing that I’ve learned as a biologist/philosopher it is that living systems get real complex real quick. That’s life for you.

We could end it there, but then we would ignore another big player. Or rather, a bunch of tiny players. After all, you probably have roughly as many microbial cells in your body as you do human cells. Your gut houses a teeming ecosystem of bacteria, viruses, and fungi - collectively, the gut microbiome.

Our microbial residents are thought to affect how we metabolize food and how hungry we get, but also our risk for certain diseases, such as Alzheimer’s, and perhaps our personality traits. Heck, gut viruses might even be linked to your IQ.

Of course, for all that, we need to be careful not to extrapolate too wildly. As far as the human data is concerned, we’re talking mostly about correlations, not bacterium X causes thing Y. And yet, we know that our gut bacteria produce many compounds that can travel to our brains and do funky things there. Let’s consider a recent study in humans. In very short: experiencing positive or negative emotions, as well as emotional regulation, appears to correlate with specific bacteria in the gut. Firmicutes bacterium CAG 94 and Ruminococcaceae bacterium D16 are correlated with feelings of happiness if you’re interested.

Again, the caveat is that correlation is not causation. I have to be careful not to oversell the gut microbiome. Recent work suggests that the causal effect of our gut microbes on our health is smaller than what we read in the media headlines.

Anyway, you are mind and body and microbe, all rolled into one. You are a complex network of overlapping processes.

As if life isn’t complicated enough already.

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! Of course, all of the above sets aside all the external influences of the social, cultural, and natural environment, which also have their (big) say in all of this.

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Hey, thanks so much for spending your virtual time with me. Much appreciated!

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