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The Dopamine Dial

Watch one ant's brain chemistry
shape its foraging behaviour.
Friedman et al. (2018) iScience

Biogenic Amines

Dopamine 47pg
hesitantbold forager
Policy precision — confidence in what to do
Serotonin 20pg
recklesscautious
Prior precision — homeostatic caution
Octopamine 36pg
sluggisharoused
Motor precision — arousal & readiness
Tyramine 14pg
low gainhigh gain
Baseline neural gain

Environment

Humidity 60%
aridhumid

Precision Channels

Πpolicy1.00
Πprior1.00
Πmotor1.00

Foraging State

DA:5-HT2.35
Water risk0.20
Free energy1.00
DecisionFORAGE
Seeds found0
The Dopamine Dial
Neuromodulation as Precision Control

What You Are Seeing

A single red harvester ant in its desert environment. The brain inset (bottom-right) shows its four neurotransmitter channels as a live neural network. Change the sliders and watch the ant's behaviour change in real time — the same animal, the same algorithm, but different precision settings.

"The increases in forager brain dopamine seemed to increase individual ant foraging."— Daniel Friedman, Stanford University (2018)

Try This

1. Set DA low (~15) and humidity low (~20%). The ant huddles near the nest — low policy precision means no confident action plan.

2. Click "Administer dopamine". Watch the ant surge outward — the precision spike gives it confidence to forage.

3. Set DA high (~90) and click the button again. The effect is much smaller — diminishing returns, exactly as Friedman et al. observed.

4. Raise serotonin — the ant becomes cautious, retreating in dry conditions. 5-HT weights homeostatic priors.

5. Drop octopamine to minimum. The ant knows what to do but can't initiate movement — motor precision too low.

"Precision and attention are synonyms."— Parr, Pezzulo & Friston (2022), Ch.5 p.95
Core Concepts
From Molecules to Decisions

Neurotransmitters as Precision

Π = 1/σ² — Precision = Inverse Variance
Higher precision → sharper predictions → more influence on behaviour

Dopamine → Πpolicy — confidence in what to do.

Serotonin → Πprior — confidence in homeostatic preferences.

Octopamine → Πmotor — confidence in state transitions (motor readiness).

Tyramine → Πgain — baseline neural excitability.

"The dopaminergic system signals confidence in what to do."— Parr, Pezzulo & Friston (2022), Ch.5 p.97

The DA:5-HT Ratio

DA:5-HT ↑ → Explore (forage despite risk)
DA:5-HT ↓ → Exploit safety (stay home)

This ratio maps directly to the explore-exploit balance — epistemic value (DA) vs pragmatic value (5-HT) in expected free energy decomposition.

Why Low-DA Colonies Respond More

Low baseline DA means low policy precision — the ant is uncertain what to do. Adding exogenous DA produces a large precision shift because the system was far from saturation. High baseline DA means the ant is already confident — additional DA produces diminishing returns. This is a natural consequence of precision being a nonlinear function of neuromodulator concentration.

ΔΠ ∝ 1/DA² — marginal gain decreases with baseline
Friedman et al. (2018): low-DA colonies responded MORE to exogenous DA
Glossary
Molecules to behaviour
Precision (Π)
Inverse variance. In neural terms: synaptic gain. Neuromodulators implement precision by controlling how strongly prediction errors influence belief updates. (Ch.4-5)
Biogenic Amines
Dopamine, serotonin, octopamine, tyramine. Small-molecule neurotransmitters that control precision across different inference channels. Daniel measured all four in single ant brains. (Shin et al. 2020)
DA:5-HT Ratio
The ratio between policy precision and prior precision. Controls explore-exploit balance. High ratio = explore. Low ratio = stay safe. Varies between colonies. (Friedman et al. 2020)
Sensory Attenuation
Downweighting sensory errors to initiate movement. Without it, the belief "I am moving" is immediately corrected. OA (motor precision) enables this. (Ch.5, Ch.8 Box 8.1)
Expected Free Energy (G)
Evaluates future policies. Decomposes into epistemic value (DA-weighted) and pragmatic value (5-HT-weighted). The ant picks the policy minimising G. (Ch.7)
References
Primary sources

Parr, T., Pezzulo, G., & Friston, K. J. (2022). Active Inference. MIT Press.

Friedman, D. A. et al. (2018). The Role of Dopamine in the Collective Regulation of Foraging in Harvester Ants. iScience, 8, 283–294.

Friedman, D. A. et al. (2020). Gene expression variation in the brains of harvester ant foragers. Comms Biology, 3, 100.

Shin, M. et al. (2020). Neurotransmitter tissue content in red harvester ant brains. Anal. Chem., 92(7).

Developed by Alexander Sabine · temporalgrammar.ai
Alexander@activeinference.institute

Neural State▼
Daniel Friedman · Active Inference Institute