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Hormonal Signaling and Behavior

Related concepts: receptor, function, causality, subject. Related mechanism: electrical signaling in the nervous system.

Purpose of This Document

This document describes hormonal signaling as a biological mechanism. Acknowledging the mechanism does not require accepting in advance the stronger ontological thesis that hormones produce the subject or exhaustively determine the subject’s decisions.

It is necessary to distinguish:

a biological mechanism exists
≠
the mechanism unambiguously determines an action

What Hormonal Signaling Is

Hormonal signaling is a form of chemical interaction in which a released molecule affects cells capable of binding it through the corresponding receptors.

A simplified sequence:

synthesis of a signaling molecule
→ release
→ transport through the blood or diffusion through tissue
→ binding to a receptor
→ intracellular changes
→ changes in the state of a cell, tissue, or organ

Depending on the substance, receptor, and target cell, the following may change:

  • cellular excitability;
  • secretion of other substances;
  • metabolism;
  • gene activity;
  • sensitivity to subsequent signals;
  • the probability of a particular physiological or behavioral response.

A hormone does not act on “behavior in general” but on cells with appropriate receptors within an already existing state of the organism.

Why a Hormone Is Not a Ready-Made Command

The same signaling molecule does not carry within itself an unambiguous instruction for an action.

Its effect depends on:

  • receptor distribution and density;
  • the types of cells carrying those receptors;
  • signal concentration and timing;
  • the current state of cells and tissues;
  • other molecules acting simultaneously;
  • the organism’s previous experience;
  • external and social context;
  • the level at which the outcome is measured.

Therefore, the formula

hormone X → action Y

usually compresses the actual chain excessively:

hormonal signal
→ receptor-dependent changes
→ changes in the operation of cells and networks
→ changes in the conditions and probabilities of a response
→ behavior in a specific situation

The Example of Oxytocin

Oxytocin simultaneously demonstrates the reality of biological influence and the danger of reduction.

In mouse experiments, disruption of oxytocin signaling impaired social recognition, while administration of oxytocin into a particular brain region restored it. This provides strong causal evidence that oxytocin participates in a specific mechanism of social recognition in that experimental model.

In prairie vole experiments, the formation of partner preference depended not on oxytocin in isolation, but on the joint availability of oxytocin and dopamine D2 receptors in the nucleus accumbens.

Later experiments in voles showed that the way oxytocin affected synaptic transmission changed after social experience. Consequently, the effect of the signal depended on the history of interactions and the state of the neural network.

In human experiments, intranasal oxytocin also did not behave as a simple “bonding hormone”: in one placebo-controlled study, it increased envy and schadenfreude in situations of social comparison.

These findings imply:

Oxytocin participates in the regulation of certain social processes, but it does not contain a single behavioral algorithm for “creating attachment.”

Statistical Dependence and Causal Inference

The statement

when a signal is absent or disrupted, behavior Y is observed less frequently

is not identical to the statement

signal X fully determines the subject’s decision to perform Y.

Even if an experiment shows that a particular component is necessary for an effect under specified conditions, it does not follow that this component is sufficient for the effect or constitutes its complete cause.

The following distinctions must be maintained:

correlation
→ states X and Y are statistically associated

causal involvement
→ changing X changes the probability or parameters of Y

necessary condition within a model
→ without X, effect Y does not occur under the specified conditions

sufficient condition
→ X by itself ensures Y under the specified conditions

complete determination of an action
→ a specific action by the subject follows unambiguously from X

Moving from the first four levels to the last requires separate justification.

Hormonal Signaling Is Not Separate from Neural Signaling

Hormonal and neural mechanisms cannot be presented as two independent contenders for control over a human being.

  • Neural activity can trigger the release of hormones and neuropeptides.
  • Hormones and neuropeptides can alter neuronal excitability and synaptic transmission.
  • A single behavioral episode can involve sensory signals, electrical activity of neurons, neurotransmitter release, and hormonal regulation.

Oxytocin particularly clearly breaks down a rigid separation: it is synthesized by neurons, can be released from their terminals, and can modify the operation of neural circuits.

Therefore, the formula

hormones = emotional decision
nerve impulses = rational decision

does not describe two biologically isolated channels.

What the Mechanism Allows Us to Assert

It is justified to assert that:

  • hormonal signals causally participate in regulating physiological states;
  • changes in hormonal signaling can alter the probability and character of behavior;
  • for certain experimental effects, a particular hormonal pathway may prove necessary;
  • hormonal signaling interacts with neural circuits, experience, and context.

By itself, this mechanism does not prove:

  • that an unambiguous hormonal algorithm of action exists;
  • that a statistically more frequent response is inevitable;
  • that a hormone independently chooses an action;
  • that the subject is identical to the totality of hormonal processes;
  • that describing the mechanism resolves the question of the ontological source of subjectivity.

Levels of Assertion

Observation:
a change in hormonal signaling is associated with a change in a measurable state or behavior.

Causal experiment:
intervention in a specific signaling pathway changes the outcome under specified conditions.

Biological model:
hormonal signaling is one of the mechanisms regulating behavior.

Additional ontological hypothesis:
hormonal and other biological processes exhaustively produce the decision and the subject.

The earlier levels do not automatically become the last.

Final Formula

Hormonal signaling is receptor-dependent chemical action that changes the state of cells and thereby changes the conditions and probabilities of subsequent physiological and behavioral processes.

In brief:

A hormone influences the space of possible responses, but the existence of an influence does not by itself prove that an action is unambiguously determined.

Studies

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