The Construction of Body Status

Part Of: Neuroeconomics sequence
Content Summary: 800 words, 8 min read

Connection To Philosophy of Well-being

What is well-being?

Philosophers have put forward three theories.

• Hedonic Theory. Well-being is experiencing pleasure.
• Desire Fulfillment Theory. Well-being is achieving your goals.
• Objective List Theory. Well-being is living an objectively good life.

In this post, we ask “does the brain have any incentive to compute biological measures of well-being? If so, what would this data structure be used for?”

Well-being is Body Status

Everyone agrees that the following are true about well-being:

1. Well-being is sensitive to variables of body status. Instantaneous well-being is less if an animal is in pain, other things being equal.
2. Well-being responds to many divergent factors (e.g., both pain and hunger reduce instantaneous well-being).

But there is only one biological apparatus that satisfies these properties:

Proposition 1. Well-being is body status, constructed by regulatory processes.

In 1925, Walter Cannon formulated homeostasis, which posits the body striving to maintain internal variables essential for life. For example, the body measures its own body temperature. If it is too hot or cold, a negative feedback process will initiate actions to bring the variable back into its optimal value.

The body tracks many more variables besides body temperature. These variables together constitute a representation I will call body status:

Body status representations play a key role in the biological construction of personal identity and subjectivity. We will return to this topic at another time.

Desire from Body Status

Markov Decision Process (MDPs) are a lens through which we can interpret behavior. An MDP contains states, actions, and a reward signal. The organism selects a policy $\pi$ such that the states encountered maximize the reward signal.

Within the brain, the basal ganglia implements two data structures which together generate motivation:

• A policy 𝝅 which maps states to actions, S → A.
• A value function V(s) which represents expected reward.

Reinforcement learning theory is silent on the biological substrate of the reward signal. But to us, the solution is clear:

Proposition 2.  Reward is derived from the body status representation.

This is one mechanism by which low body temperature is corrected. Body status deviations elicit a reward signal that prompt “cold” motor desires (e.g., shivering). In contrast, notice that “hot” visceral desires (e.g., blood vessel constriction) are constructed directly, not implemented by the basal ganglia.

Hedonics from Body Status

There are two liking systems in the brain:

1. Hedonics is a global measure of pleasure and pain. It summarizes body state information.
2. Valence is an object-specific judgment of value. Valence usually correlates with desire: we approach things that are pleasant, and avoid things that are unpleasant.

Yet drug addicts often reach the point where drug consumption is unpleasant, yet they pursue a fix regardless. Wanting and liking are dissociable. Why? Because they are implemented by different neurochemical systems (phasic dopamine and opioids, respectively).

Body status is not only used to behaviorally motivate. In my view, it also tags perceptual data with information about its visceral relevance.  This includes the two primary affective dimensions:

• Object salience (“does this merit attention, further computation”)
• Object valence (“is this safe to approach”)

So we have arrived at our next thesis:

Proposition 3. Hedonics and valence are derived from body status representation.

Philosophers debate whether well-being is best attributed to pleasure/pain or desire. But body status is used to construct both of these phenomena. This gives us reason to believe that the philosophical theories of hedonism and desire fulfillment can be unified.

The Socialification of Body Status

Across the course of natural history, certain animals have become increasingly social, able to interact more meaningfully with their conspecifics.

• In mammals, social status. Animals track their standing in the group.
• In primates, social inclusion. Group living made possible by e.g., exchange of favors.
• In hominids, social reputation. An prosocial alternative to power, independent of the dominance hierarchy.

How might a biological organism introduce these new behavioral repertoires? A simple way to do it might be to extend body status to incorporate social variables of interest:

Proposition 4. Body status was extended to support novel social behaviors.

This proposition lends a biological perspective why social ostracization is so painful, and elicits physiological distress directly comparable to e.g., evading predation.

This socialification hypothesis is more speculative than my other three propositions. How might we go about evaluating whether it is true?

Recall that body status is represented by an overlapping set of neurochemical networks, whose main connecting hub is the hypothalamus. If Proposition 4 is true, we would expect to find new chemical systems uniquely responsive to these proposed dimensions.

I suspect these connections will be established rather quickly. We already possess several extremely suggestive lines of evidence. See, for example, Hennessy et al (2014). Sociality and sickness: have cytokines evolved to serve social functions beyond times of pathogen exposure?

Takeaways

Today, I presented the following ideas:

• Proposition 1. Well-being is body status, constructed by regulatory processes.
• Proposition 2. Desire is derived from body status representation.
• Proposition 3. Hedonics and valence are derived from body status representation.
• Proposition 4. Body status was extended to support novel social behaviors.

Until next time.