[Sequence] Affective Neuroscience

Visceral Neuroanatomy

Specific Emotions

Core Sequence

Old Material

Evolutionary Game Theory

Part Of: Game Theory sequence
Content Summary: 1300 words, 13 min read

Prisoner’s Dilemma Review

The classical Prisoner’s Dilemma has following setup:

Two prisoners A and B are interrogated, and separated asked about one another.

  • If both prisoners betray the other, each of them serves 2 years in prison
  • If A betrays B but B remains silent, A will be set free and B will serve 3 years (and vice versa)
  • If both prisoners remain silent, they will only serve 1 year in prison.

We can express the decision structure graphically:

IPD- Prisoner's Dilemma Overview

We can also represent the penalty structure. In what follows, arrows represent preference. CC → DC is true because, given that B cooperates, A would prefer the DC outcome (0 years in prison) more than CC (1 year).

IPD- Prisoner's Dilemma Regret

Our takeaways from our exploration of the Prisoner’s Dilemma:

  • An outcome is strategic dominance happens when one choice outperforms other choices, irrespective of competitor behavior. Here, DD is strategically dominant.
  • Pareto improvement is a way to improving at least one person’s outcome without harming any other player. Here, DD → CC represents such an improvement.
  • Pareto optimal outcomes are those outcomes which cannot be Pareto-improved.

The Prisoner’s Dilemma shows us that strategically-dominant outcomes need not be Pareto optimal.  Although each arrow points towards the origin for that color, the sum of all arrows points away from the origin.

It packages together the tragedy of the commons, a profound and uncomfortable fact of social living. A person can be incentivized towards an outcome that she, and everybody else, dislikes.

Towards Iterated Prisoner’s Dilemma (IPD)

In the one-off game, mutual defection is the only (economically) rational move. If a person chooses to defect, they will likely receive a bad result.

But consider morwhat happens in a more social setting, where players compete for resources multiple times. An Iterated Prisoner’s Dilemma (IPD) has the following structure:


What strategy is best? Let’s consider two kinds of strategies we might adopt. We can imagine some vindictive prisoners always defecting (AD). Other prisoner’s might be more generous, adopting a Tit-for-Tat (TfT) strategy. This has them initially cooperating, and mirroring their opponent’s previous move.

Let’s imagine that there are 200 “prisoners” playing this game, with each strategy adopted by half of the population. Which strategy should you adopt, in such a scenario?

The games look as follows:

  • AD vs AD: { DD, DD, DD,  … }. After 10 rounds: A has 20 years, B has 20 years.
  • AD vs TfT: { CD, DD, DD,  … }. After 10 rounds: A has 18 years, B has 21 years.
  • TfT vs TfT: { CC, CC, CC, … }. After 10 rounds: A has 10 years, B has 10 years.

These computations can be generalized to n rounds:

IPD- Always Defect vs TfT

The tit-for-tat (TfT) strategy wins because TfT-TfT games are collaborative, but these players also aren’t effectively exploited by players who Always Defect (AD).

Which Kinds of Strategies Are Best?

There is an very large number of possible IPD strategies. Strategy design might include considerations such as:

  • Deterministic vs Mixed. Should we follow logical rules, or employ randomness?
  • Impersonal vs Personal. Do we remember the behavior of each opponent? Do we change strategies given what we know of other players?
  • Fixed vs Adaptive. Should we use our experiences to change the above on-the-fly?

Given this behavioral diversity, which kinds of strategy are most successful?

To answer this question, in 1980 Robert Axelrod conducted a famous experiment. He invited hundreds of scholars to enter an IPD tournament, submitting their agent’s decision algorithm digitally. In a computer simulation, every agent played every other agent 200 times. The agent with highest cumulative utility was declared the winner.

Many agent strategies employed quite complex, using hundreds of lines of code. The surprising result was that simple strategies, including Tit-for-Tat, often proved to be superior. Axelrod described three properties shared among successful strategies:

IPD- Characteristics of Winning Strategy

We can call such strategies instances of reciprocal altruism.

Moral and Emotional Implications

The theory of evolution has shown us that biological systems are the product of an optimization process known as natural selection. Only genes that improve reproductive success win over evolutionary time.

From this context, it has long seemed unclear how human beings (and other animals) came to express altruistic behavior.  W.D Hamilton’s notion of inclusive fitness explains why we behave generously to relatives. As J.B.S Haldane famously joked,

I would willingly die for two brothers or eight cousins.

Game theory explains our behavior towards non-relatives. Specifically,

IPD provides insight into moral cognition. It shows how our selfish genes might, purely for selfish reasons, come to promote behaviors that are (reciprocally) altruistic.

IPD similarly explains certain emotional processes. For example, I have posited elsewhere the existence of social intuition generators like Fairness. We can now explain why natural selection generated such “socially intelligent” mental modules.

Application: Vampire Bats

Instead of jail time, we can modify our outcome structure to be more relevant to biology.

IPD- Ecological Prisoner's Dilemma (1)

Thus, we can use game theory to interpret animals competing for resources. Consider, for example, behavior of the vampire bats.

Vampire bats feed on the blood of other mammals. Their energy budget is such that they can tolerate 2 days of food deprivation before starving to death.

On a given night, 8% of adult vampire bats will fail to find food on a given night. But when they do find food, it is often more than they need.

Of course, these animals have a genetic incentive to share blood within family. But you can also observe bats sharing their food with strangers.

How can selfish genes reward altruistic behavior? Because vampire bats are playing IPD:

  • CC (Reward). I get blood on my unlucky nights. I have to give blood on my lucky nights, which doesn’t cost me too much.
  • DC (Temptation). You save my life on my poor night. But I also don’t have to feed you on my good night.
  • CD (Sucker): I pay the cost of saving your life on my good night. But on my bad night I still may starve.
  • DD (Punishment) I don’t have to feed you on my good nights. But I run a real risk of starving on my poor nights.

Towards Evolutionary Game Theory

To show why altruistic bats are more successful? Yes; we need only invent evolutionary game theory (EGT). Recall how natural selection works:

Individuals with more biological fitness tend to leave more copies of their genes.

EGT simply adds this replicator logic to the Iterated Prisoner’s Dilemma (IPD). Players with higher final scores (most resources) leave more descendants in subsequent populations (image credit):


We saw previously that Tit-For-Tat players outperform those who Always Defect. In EGT, this fact establishes how a gene that promotes altruism successfully invaded the vampire bat gene pool:

IPD- EGT Stable Strategies (2)

Of course, iterated games don’t always have one winner. Consider the following food web (structurally similar to Rock-Paper-Scissors, of course).

Snake beats Fox. Fox beats Hawk. Hawk beats snake.

What if the size of the snake population starts out quite small? In that case, hawks and foxes predominate. Since hawks are prey to foxes, the size of the hawk population decreases. But this means the snakes have fewer natural predators.

The above traces the implications of one possible starting point. However, we can use EGT maths to model the entire dynamical system, as follows (image credit):

IPD- Food Web Rock Paper Scissors (1)

With this image, we can see that any starting point will eventually (after many generations), lead to a (⅓, ⅓, ⅓) divide of snakes, foxes, and hawks. This point is the locus of the “whirlpool”, it is also known as an attractor, or an evolutionarily stable state (ESS).


  • The Iterated Prisoner’s Dilemma (IPD) makes game theory more social, where many players compete for resources multiple times.
  • While one-off PD games favor selfish behavior, IPD can favor strategies that feature reciprocal altruism, such as Tit-for-Tat.
  • More generally, IPD strategies do best if they are nice, retaliating, and forgiving. This in turn explains how certain facets of our social and moral intuitions evolved.
  • Evolutionary Game Theory (EGT) extends IPD by adding replicator logic (more successful strategies are preferentially represented in future generations).
  • Evolutionary Stable States (ESS) encode dynamical attractors, which populations asymptotically approach.

Until next time.

A Dual-Process Theory of Moral Judgment

Part Of: Demystifying Ethics sequence
Content Summary: 900 words, 9 min read


An ethical theory is an attempt to explain what goodness is: to ground ethics in some feature of the world. We have discussed five such theories, including:

  • Consequentialism, which claims that goodness stems from the consequences of an action
  • Deontology, which claims that goodness stems from absolute obligations (discoverable in light of the categorical imperative)

For most behaviors (e.g., theft), both theories agree (in this case, label the act as Evil). But there do exist key scenarios which prompt these theories to disagree. Consider the switch dilemma:

Consider a trolley barreling down a track that will kill five people unless diverted. However, on the other track a single person has been similarly demobilized. Should you pull to lever to divert the trolley?

Ethical Theories- Trolley Problem (2)

Our ethical theories produce the following advice:

  • Consequentialism says: pull the lever! One death is awful, but better than five.
  • Deontology says: don’t pull the lever! Any action that takes innocent life is wrong. The five deaths are awful, but not your fault.

Would you pull the lever? Good people disagree. However, if you are like most people, you will probably say “yes”. 

Things get interesting if we modify the problem as follows. Consider the footbridge dilemma:

Consider a trolley barreling down a track that will kill five people unless diverted. You are standing on a bridge with a fat man. If you push the fat man onto the track, the trolley will derail, sparing the five people.

Dual Process Morality- Trolley Visceral Alternative (1)

Notice that the consequences for the action remain the same. Thus, consequentialism says “push the fat man!”, and deontology says “don’t push!”

What about you? Would you push the fat man? Good people disagree; however, most people confess they would not push the fat man off the bridge. 

Dual Process Morality- Conflicting Judgments (1)

Our contrasting intuitions are quite puzzling. After all, they only thing that’s different between the two cases is how close the violence is: far away (switch) vs up close (shoving).

Towards a Dual-Process Theory

Recall that there are two kinds of ethical theories.

  1. Prescriptive theories describe what goodness objectively is.
  2. Descriptive theories tell us how the brain produces moral judgments.

Consequentialism and deontology are prescriptive theories. However, we can also conceive of consequentialism and deontology as descriptive theories. Let’s call these descriptive variants folk consequentialism and folk deontology, respectively.

Sometimes, people’s judgments is better explained by folk consequentialism; other times, folk deontology enjoys more predictive success. We might entertain two hypotheses to explain this divergence:

  1. Different boundary conditions of a single neural process
  2. Two competing processes for moral judgment

As we will see, the evidence suggests that the second hypothesis, the dual-process theory of moral judgment, is correct.

Dissociation-Based Evidence

Consider the crying baby dilemma:

It’s wartime. You and your fellow villagers are hiding from nearby enemy soldiers in a basement. Your baby starts to cry, and you cover your baby’s mouth to block the sound. If you remove your hand, your baby will cry loudly, and the soldiers will hear. They will find you… and they will kill all of your. If you do not remove your hand, your baby will smother to death. Is it morally acceptable to smother your baby to death in order to save yourself and the other villagers?

Here, people take a long time to answer, and show no consensus in their answers. If the dual-process theory of moral judgment is correct, then we expect the following:

  1. Everyone exhibits increased activity in the dorsal anterior cingulate (dACC). This region is known to reliably respond when two or more incompatible behavioral responses are simultaneously activated. 
  2. For those who eventually choose the folk consequentialist answer (save the most lives) should exhibit comparatively more activity in brain regions associated with working memory and cognitive control.

Both predictions turn out to be true. Here then is the circuit diagram of our dual-process, organized in the two cybernetic loops framework:

Dual-Process Morality- System Architecture

Four other streams of evidence corroborate our dual-process theory:

  • Deontological judgments are produced more quickly than consequentialist ones.
  • Cognitive distractions slow down consequentialist but not deontological judgments.
  • Patients with dementia or lesions that cause “emotional blunting” are disproportionately likely to approve of consequentialist action. 
  • People who are either high in “need for cognition” and low in “faith in intuition”, or have unusually high working memory capacity, tend to produce more consequentialist judgments.

Relation To Other Disciplines

We have previously distinguished two kinds of moral machinery:

  • Propriety frames are a memory format that retains social intuitions.
  • Social intuition generators which contribute to the contents of social judgments.

These machines map to the dual-process theory of judgment. Propriety frames are housed in cerebral cortex, which perform folk consequentialist analysis. Social intuition generators are located within the limbic system, and contribute folk deontology intuitions.

Recall that Kantian deontology attempted to ground moral facts in pure reason (the categorical imperative). While surely valuable as a philosophical exercise, in practice folk deontological judgments have little to do with reason. They are instead driven by autonomic emotional responses. It is folk consequential judgments which depend more on reason (cortical reasoning).

This is not to say that people who prefer consequential reasoning are strictly superior moral judges. But I will address the question which reasoning system should I trust more? on another day.


  • For the switch dilemma, most people reason consequentially (“save the most lives”)
  • For the footbridge dilemma, most people reason deontologically (“murder is always wrong”)
  • These contrasting styles emerge because the brain has two systems of judgment.
  • Folk consequentist reasoning is performed in cerebral cortex.
  • Folk deontology intuitions are generated from within the limbic system.

Until next time.

An Introduction to Ethical Theories

Part Of: Demystifying Ethics sequence
Content Summary: 1500 words, 15 min


Ethics discussions can occur at different levels of abstraction. The most concrete ethical discussions involve discussing specific topics; e.g., “is abortion moral”? These scenarios are called applied ethics.

Spend enough time wrestling with applied ethics, and you’ll start wondering what all of these moral intuitions have in common. An ethical theory is an answer to the question “what makes a thing good or bad”?

Meta-ethics answers a yet broader set of questions. What is right and wrong, anyways? Are moral beliefs objectively true in the same sense that the Earth orbits the sun? Or is my condemning an unethical act merely expressing an aesthetic preference (“yuck!”)?

Ethical Theory- Three Abstraction Levels

Image Credit

Today we conduct a whirlwind tour of ethical theories, touching on the most influential theories. Ethical theories are normative: they speak to what moral conclusions ought to be. However, we will see later how these theories also sometimes imperfectly anticipate the emerging science of moral cognition.

We will discuss the following:

  1. Divine Command Theory
  2. Natural Law Theory
  3. Virtue Theory
  4. Deontology
  5. Utilitarianism

The first three theories are the oldest, and have close ties to religious doctrine. The last two are the most well-known theories these days.

Divine Command Theory

Historically, religions have had a good deal to say about right and wrong. One of the oldest ethical theories is Divine Command Theory, which states:

Moral behaviors are those that are commanded (or willed) by the divine.

This theory was originally proposed in the context of Greek mythology. But since it doesn’t say much about the specific character of the divine, it was adopted by Augustine and some (but not all) modern theologians.

One of the strongest criticisms to Divine Command Theory is the Euthyphro Dilemma, which goes as follows:

  • Is an action ethical because God commands it?
  • Or does God command it because it is ethical?

Clearly, we must affirm one of these options. But which one? Either “horn” of the dilemma extracts painful concessions:

  • On the first option, moral content becomes arbitrary. If God changes his mind about moral facts, our moral universe is turned upside down.
  • On the second, God becomes a middleman who conveys independent ethical facts. Why can’t we simply learn moral truths direct from the source?

These days, most philosophers find Divine Command Theory problematic. But there are other ethical theories available to the faithful.

Natural Law

Another approach to ethical theories, championed by Thomas Aquinas, is Natural Law Theory. Moral truths are grounded as follows:

Moral behaviors are those which promote, and do not detract from, a basic good.

A basic good is injected into human nature by God. Here are three such lists, generated by a Catholic, a Muslim, and a philosopher:

Ethical Theories- Natural Law Basic Goods (7)

Ethical actions promote the basic goods; immoral actions detract from the basic goods. This, incidentally, is why Catholics oppose all forms of birth control: they detract from the basic good of Reproduction.

How did these philosophers generate their lists of basic goods? By observing nature. For example, Life and Reproduction usually make the cut because humans naturally prioritize survival and reproductive success (this is a consequence of natural selection).

However, there is a conceptual difficulty in deriving basic goods from nature. This was clearly expressed by Hume’s Law, also called the is-ought gap: what logical procedure could possibly be used to infer normative statements (an “ought”) from descriptive facts of the words (an “is”)?

Virtue Theories

Unlike its competitors, virtue theory doesn’t spend much time telling you what to do (moral behaviors). Instead, people are the subject of moral truths. Behaviors are only good or evil insofar as they enhance or corrupt a person’s character.

Aristotle presented these ideas in Nichomachean Ethics. There he describes ethical behavior as a way to achieve eudaimonia (human flourishing or “the good life”).

A life of eudaimonia is a life of striving. It’s a life of pushing yourself to your limits, and finding success. A eudaimonistic life will be full of the happiness that comes from achieving something really difficult, rather than just having it handed to you.

Aristotle also believed that moral knowledge is learned not by navel-gazing, but instead comes from social interactions. Specifically, good character is developed by spending time with virtuous people. This theory is where the idea of a role model comes from.

So let’s get down to business. In virtue theory, moral facts are grounded as follows:

Moral people are those who have character; that is, they possess basic virtues.

Aristotle identified twelve basic virtues: Courage, Moderation, Flexibility, Cleanliness, Generosity, Ambition, Patience, Truthfulness, Wittiness, Friendliness, Modesty, and Righteous Indignation. A good person nurtures these virtues.

The Golden Mean provides some insight into how these virtues can be refined over time. A person can respond too strongly with a virtue (excess), or too weakly (deficiency). For example, one must not have too much courage, nor too little:

Ethical Theory- Golden Mean (1)

Virtue ethics is surprisingly robust to philosophical criticism. However, one scientific concern has been gaining traction recently. Empirical research in the field of situational psychology increasingly suggests that there is no such thing as character traits.

Make no mistake, seeing vices and virtues in others is a universal human instinct. But there is no guarantee that mental software works correctly (e.g., see how the brain lies to itself about visual experience). And the fact of the matter is, character information contributes zero predictive power over how a person will respond to a given situation.

Duty Theories

The first ethical theories that isn’t explicitly theistic, Immanuel Kant’s deontological (“knowledge of what is proper”) system purports to result from pure reason.

Moral behaviors are those which obey the categorical imperative.

For Kant, the categorical imperative is a procedure by which a person can discover the rigid contents of the moral universe. He presents four perspectives that independently arrive at these moral truths; the two most influential of which are:

  1. The universalizability principle instructs us to act only if you also desire that your action should become a universal law. Lying is wrong because if lying becomes universalized, meaningful communication becomes impossible.
  2. The principle of humanity instructs us to act in such a way that you treat humanity (both yourself or someone else), always also as an end and never simply as a means. This principle underlies the modern idea of human rights, and is leveraged by Nozick’s brand of libertarianism. 

The categorical imperative promotes a kind of moral absolutism: if actions are right or wrong intrinsically, their moral status is invariant to the consequences of an action. And this inflexibility can produce counterintuitive judgments.

For example, consider a house shielding a Jewish family from the Nazis. If a soldier comes to the door asking about its residents, most of use think it would be morally acceptable to lie. Kant, however, claims that lying is wrong in all situations, even ones such as these.

Consequentialist Theories

Deontological theories are invariant to behavioral outcome. But there are many moral situations where outcome seems to matter. Consider the trolley problem, where a trolley is currently barreling down a track and should kill five people unless diverted. However, on the other track one person has been similarly demobilized:

Ethical Theories- Trolley Problem (1)

Kant would say that pulling the lever is simply murder. That five people die is regrettable, but their death does not incriminate the person at the switch. If the person does divert the trolley, the guilt of the single person’s death is on his head.

However, most people think that the number of deaths – the consequence of an action – matters. Consequentialist theories make this intuition explicit:

Moral behaviors are those that bring the most good to the most people.

Consequentialist theories vary on how they define “the most good” (personal well-being) and “the most people” (societal well-being). 

For example, classical utilitarianism, advocated by Jeremy Bentham and John Stuart Mill, which takes the following stances:

  1. Personal well-being originates from hedonism: actions are moral if they increase pleasure and/or decrease pain.
  2. Societal well-being is taken as the sum total of the well-being of constituent individuals.

Many people condemn utilitarianism for its hedonism (“don’t immoral behaviors often feel pleasurable?”). However, this criticism loses some of its force when you remember to distinguish higher pleasures (eg., aesthetic experience) versus baser pleasures. 

The problem of figuring out societal well-being, how to optimize outcomes for communities, is much more challenging. The repugnant conclusion, aka the mere addition paradox, is a particularly damning criticism. A large society with barely tolerable quality of life (e.g., urban sweat shops) doesn’t feel morally equivalent to happier, smaller societies. 

Ethical Theories- Repugnant Conclusion

Thus, maximizing total well-being may be problematic. But different problems emerge if we instead optimize against average well-being. To this day, designing aggregation functions to compute societal well-being remains an essentially unsolved problem.


Today, we discussed the following theories:

Ethical Theories- Summary

There exist other theories besides these, of course. For example, Hobbes’ contractualism makes important contributions to the conversation. 

To date, no ethical theory has emerged as a clear favorite. A recent survey of professional philosophers reveals considerable support for three of the above theories:

Ethical Theories- Philosopher Opinions

Next time, we will explore whether we should view these normative theories as competitors, or complementary solutions to different concerns. Until then.

An Overview of Moral Cognition

Part Of: Demystifying Ethics sequence
Content Summary: 1000 words, 10 min read

Propriety Frames

Main Article: An Introduction To Propriety Frames

The primate brain contains a diverse set of memory structures. For example, episodic and semantic memory store narratives and facts, respectively.

Propriety frames are a memory format that retains social intuitions. This form of memory permits normative judgments, or which behaviors are appropriate or inappropriate.

Propriety frames are organized by situational context. A Restaurant frame provides the social intuitions for restaurant interactions. Frames are the substrate of rituals.

Frames are organized hierarchically to promote reuse. For example, the Eating frame is relevant in contexts besides restaurant dining.

Propriety Frames- Restaurant Example (2)

When a mother instructs her son to not yell in the store, the child installs an update to his Shopping frame. When a family exchanges gossip around a campfire, they are doing so in part to synchronize their propriety frames.

Intuition Generators

Main Article: Moral Foundations Theory

The contents of our social intuitions is not arbitrary. Our environment does not fully determine our moral sense. The brain also possesses innate social intuition generators, which contribute to the contents of social judgments.

As outlined in Moral Foundations theory, there are six such generators: authority, care, loyalty, fairness, autonomy, and sanctity.

People are genetically and environmentally disposed to respond to certain generators more strongly than others. Let social matrices be the emotional intensities elicited by each generator.

People with similar matrices tend to gravitate towards similar political parties. When you measure the social matrices of American citizens, you can see large differences between the social intuitions of Democrats and Republicans.

Theory of Normatives- Social Matrices by Political Party (1)

These differences in social matrices explain much of American politics.

  • Why do Democrats praise entitlements, but Republicans denounce them? Because Democrats heavily emphasize Care for the poor, whereas Republicans more strongly reverberate to questions of Fairness (exploitation and moral hazard).
  • Why are Democrats more skeptical of patriotism than their Republican counterparts? Perhaps because they respond to Loyalty to country less.

For more information, see Graham et al (2009). Liberals and conservatives rely on different sets of moral foundations.

Generators vs Frames

Main Article: A Dual-Process Theory of Moral Judgment

Two mechanisms contribute to social intuitions: propriety frames, and intuition generators.

Theory of Normatives- Frame vs Generator (1)

Generators are located subcortically, and thus produce intuitions quickly and automatically. Frames are stored in the cortical mantle, and are thus slower, and more amenable to conscious awareness.

As the work of Joshua Greene shows, deontological (rule-based) attitudes are generated rapidly; whereas consequential theories of morality are slower and more vulnerable to distraction. This suggests a relatively straightforward mapping:

  • People with a deontological style rely more heavily on their Generators.
  • People with a consequentialist style lean instead on their Frames.

Frames and Generators can influence one another, albeit slowly. Moral argumentation can change one’s mind, and these frame updates can percolate down to change one’s social matrices (intuition weights). Call this frame internalization.

Similarly, if one’s private intuitions diverge from a culturally inherited norm, that frame can be updated to be more consistent with one’s personality. Call this frame refinement.

For more information, see Cushman, Young, Greene (2010). Our multi-system moral psychology: Towards a consensus view

Cultural Regimes

Main Article: The Relational Sphere Hypothesis

Human communities generate emergent networks known as cultural regimes. These emerge as distinct categories of frames and intuition generators.

regime categories

Language made regime accretion possible. No longer is expertise confined to the skull of the individual. No longer is death a Full Restart button. Our species sends cultural expertise down through the generations.  This knowledge – these frames – have become increasingly sophisticated over the course of human history.

Hominid evolution has also seen the advent of regime diversification. Modern religions (of the Axial Age) were successful because they improved on our ability to trust strangers. This in turn dramatically increased the size of feasible social groups.

Theory of Normativity- Evolution of Regimes (3)

Moral Tagging

We have so far only been speaking about social attitudes (should / should not). What about moral attitudes (good / evil)?

Moral attitudes are nothing more than a kind of social attitude. I know of no moral attitude that can be divorced from a social context.

Moral attitudes are constructed by moral tagging, which endows a subset of social attitudes with anger and disgust reactions (as opposed to the more typical reputation appraisal, gossiping, shaming).

Further, moral tagging produces appraisal inflexibility. Moral violations are viewed as wrong everywhere, in every context. This is in contrast to other social violations, for which it is easier to see circumstances in which the behavior would seem less bad.

The boundary between Virtuous and Tolerable is smooth, reflecting the flexibility of our intuition generators. In contrast, the boundary between Tolerable and Intolerable is sharp.

Moral Flinch- Latitudes of Acceptance (2)
A similar distinction appears amidst disagreement. There are two kinds of ways people’s judgments can diverge:

  • Moral disagreement: is a given behavior Evil?
  • Social disagreement: is a given behavior Inappropriate?

moral vs social disagreement

For more information, see Tetlock et al (2000). The psychology of the unthinkable: taboo trade-offs, forbidden base rates, and heretical counterfactuals.

Norm Synchronization

The space of possible social intuitions is vast. However, group living only became possible with relatively homogenous norms. How do individual brains synchronize propriety frames and social matrices within a group?

At least four mechanisms provide norm synchronization.

  • Natural language and facial expressions are used to communicate social and emotional information.
  • Reputation systems benefit social beings who are especially adept at learning & conforming to the frames of their peers.
  • First-order punishment emotions (anger at transgressor) incentivizes people to not violate implicit societal expectations.
  • Second-order punishment (anger at those who are accepting of transgressor) incentivize a community to respond to, and develop a unified response to, dyadic disagreements.


  • In Propriety Frames, we saw how the brain retains social information.
  • Limbic machinery, such as the Care module, generate normative intuitions.
  • Generators and frames interact to facilitate both top-down and bottom-up learning.
  • A subset of social violations are tagged as morally intolerable.
  • Several emotion devices work to consolidate normatives within a group. 

Related Work

  • Graham, Haidt, Nosek (2009). Liberals and conservatives rely on different sets of moral foundations.
  • Cushman, Young, Greene (2010). Our multi-system moral psychology: Towards a consensus view
  • Tetlock et al (2000). The psychology of the unthinkable: taboo trade-offs, forbidden base rates, and heretical counterfactuals.

Two Cybernetic Loops

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

What Is Perception About?

Consider Aristotle’s five senses: vision, hearing, smell, touch, and taste. We know that senses are windows into physical reality. But what aspects of reality do these represent?

Vision and hearing have a special property: despite receptors being located within the body (proximal), they carry information about phenomena outside of the body (distal). They carry information about the world. In contrast, smell, touch, and taste only represent events close to the body; these encode the interaction between body and world.

This distinction is a neural primitive: the brain encodes World and Interaction in extrapersonal and peripersonal space, respectively.

However, there is a significant lacuna within this binary system: none of these concern the body. Body sensation is a crucial “sixth sense”:


Making Sense of Anatomy

We spend a lot of time discussing the nervous system. But the body houses eight other anatomical systems: reproductive, integumentary (skin), muscular, skeletal, endocrine (hormones), digestive (incl. urinary and excretory subsystems), circulatory (incl. immune and lymphatic subsystems), and respiratory.

To regulate these systems, your brain recruits the following peripheral nervous systems:

  1. Somatic, which contains spinal nerves and cranial nerves
  2. Autonomic, incl. the sympathetic “fight/flight” and parasympathetic “rest/ digest” 
  3. Neuroendocrine, incl. the HPA, HPG, HPT, and Neurohypophyseal axes
  4. Enteric, also called the “second brain”, a large mass of digestion-oriented neurons
  5. Neuroenteric, connects enteric nervous system via microbiome-gut-brain axis
  6. Neuroimmune, recently discovered, primarily mediated by glial cells
  7. Glymphatic, recently discovered, which removes metabolites via CSF during sleep
  8. Neurogaseous, recently discovered, mediated by gasotransmission

The CNS must coordinate all of these to respond to sense data and regulate anatomical systems. A complex undertaking. How might we understand such a process?

With the above trichotomy { world, interaction, body }, anatomical and sensory systems can be organized into meaningful categories:


The Interlocking Loop Hypothesis posits the existence of two perception-action loops, inhabiting a gradient of abstraction:

  1. The somatic “cold” loop, world- and interaction-oriented, from exteroception to movement.
  2. The visceral “hot” loop, body-oriented, from interoception to body regulation.

Loops As Organizing Principle

Evidence for the Interlocking Loop Hypothesis comes from two anatomical principles of organisation:

First, the Bell Magendie Law is based on the observation that, in all chordates, sensory information is processed at the back of the brain, and behavioral processes are at the front (“posterior perception, anterior action”):

Cybernetics- Posterior Perception, Anterior Action

Second, the Medial Viscera Principle is the observation that visceral processes tend to reside in the center of the brain (medial regions):


Thus we can see our loops clustering at different levels of the abstraction hierarchy.

We can also see our loops’ primary site of convergence:

Anatomically, the two loops converge on the basal ganglia, in which both somatic and visceral processes are blended to yield coherent behavior.


The above quote & image are from Panksepp (1998), Affective Neuroscience.

The Basis of Motivation

Why should our two loops converge on the basal ganglia? The basal ganglia is the substrate of motivation, or “wanting”. It also participates in reinforcement learning, and its mathematical interpretation as Markov Decision Processes (MDPs).

Historically, the reward function in MDPs has proven difficult to interpret biologically; however, this task becomes straightforward on the Interlocking Loop Hypothesis. Of course the cold loop would tune its behavior to promote the hot loop’s efforts to keep the organism alive.


The Basis of Consciousness

In Can Consciousness Be Explained?, I wrote:

Let me put forward a metaphor. Consciousness feels like the movies. More specifically, it comprises:

  1. The Mental Movie. What is the content of the movie? It includes data captured by your eyes, ears, and other senses.
  2. The Mental Subject. Who watches the movie? Only one person, with your goals and your memories – you!

On this view, to explain consciousness one must explain the origins, mechanics, and output of both Movie and Subject. (Of course, one must be careful that the Subject is not a homunculus, on pain of recursion!)

The Interlocking Loop hypothesis offers an obvious foothold in the science of consciousness:

  • The world-centric cold loop generates the Mental Movie (“a world appears”). 
  • The body-centric hot loop creates the Subject (“narrative center of gravity”)

Thus, we are no longer surprised that opioid anomalies (a visceral loop instrument) are linked to depersonalization disorders; whereas dopamine (the promoter of somatic behavior) is associated with subjective time dilation effects.


First, we introduced the Interlocking Loop Hypothesis:

  • Some perceptions are about the world, others are about the body.
  • The CNS is a visceral body-centric hot loop, and a somatic world-centric cold loop
  • Bell-Magendie Law: perception for both loops is posterior, action is anterior.
  • Medial Viscera Principle: hot loop is located medially, while cold loop is more lateral.

Then, we examined its implications:

  • Motivation, as generated by the basal ganglia, is loop communication software; it allows the hot loop to influence cold loop behavior.
  • Consciousness has two components: the Mental Movie and Mental Subject. These are supported by cold and hot loops, respectively.

Until next time.

Relevant Materials

  • Northoff & Panksepp (2008). The trans-species concept of self and the subcortical–cortical midline system


Evolution of the Basal Ganglia

Part Of: [Neuroeconomics] sequence
Followup To: [An Introduction to the Basal Ganglia]

Natural History

The Earth accreted from a protoplanetary disc 4.5 billion years ago (Ga). Geologists break up Earth’s history into four eons: the Hadeon, Archaean, Proterozoic, and Phanerozoic eons.

At 3.8 Ga, abiogenesis occurred, and the sea was awash with bacteria. Since then, there have been five major events in the history of life.

  1. At 1.85 Ga, bacterial inbreeding (symbiogenesis) led to the advent of eukaryotes, whose organelles improved cellular flexibility
  2. At 800 Ma, the advent of multicellularity: some eukaryotes discovered ways to act meaningfully in groups.
  3. At 580 Ma, animal-like adaptations, such as motility and ability to consume other living matter (heterotrophy), set off the Cambrian Explosion.
  4. At 380 Ma, some animals developed four limbs (tetrapods) and the ability to become terrestrial animals.
  5. At 320 Ma, some terrestrial animals developed mammary glands, and saw the spark of the mammals.


We can use the tree of life to better understand these anatomical milestones. Since all life on this planet is related (common descent), we can represent familial relations just as you would on ancestry.com. Key innovations in organism body-plans can be embedded in such graphics, as follows:


When confronted with some biological structure, we can employ comparative anatomy to discover its origin. If an adaptation is shared across multiple species, we can infer either homology (the innovation of some common ancestor) or homoplasy (an adaptation appearing independently, a.k.a “convergent evolution”).  

For example, the spine is a homology; whereas homeothermy (warm-bloodedness) and multicellularity are homoplasies. 

Full Circuit in Vertebrates

Last time, we discussed the basal ganglia, a brain structure that is intimately involved in motivation and behavior. Here, we use comparative anatomy to discover the evolutionary origin of the basal ganglia. By dissecting brains from eight representative species, we can infer that the basal ganglia dates back to the origin of vertebrates:


Specifically, here are the frontal sections of the eight species. By employing sophisticated histochemistry techniques such as TH-immunostaining, we are able to directly visualize the striatal and pallidal regions of the representative basal ganglia.

bg-evolution-frontal-sections-representative-species-1This investigation was conducted by Anton Reiner in his aptly-titled 2009 paper, You cannot have a vertebrate brain without a basal ganglia. The basal ganglia is not the “reptile brain”, contra the triune brain hypothesis. It is, in fact, much older.

Ancient Subcortical Loops

One of the key structures in the midbrain is the corpora quadrigemina (Latin for “four bodies”). It is composed of bilateral expressions of the superior colliculus (SC), and the inferior colliculus (IC). Anatomically, these structures are four bumps at the posterior of the midbrain; for this reason, the corpora quadrigemina is also called the tectum (Latin for “roof”).


The SC receives inputs from the retina, via input from the LGN nucleus of the thalamus. The IC receives input from the auditory system, and projects to the MGN nucleus of the thalamus. For this reason, it is easy to describe these structures as a vision center, and audio center, respectively.

However, there is more to the story. SC and IC represent space topographically, and densely innervate one another. They seem to participate in coordinate transformations, which integrate multimodal sensory information. The SC and IC are actually composed of distinct anatomical regions, each of which perform specialized tasks. Importantly, the SC Deep Layer functions as a control center: basically, a predecessor of the motor cortex.


We have seen the basal ganglia processing information from the neocortex. But the neocortex is a mammalian innovation. What did the basal ganglia do before the invention of the neocortex? If you look carefully at the basal ganglia, you can actually see afferents from the GPi / SNr / VP node into the superior colliculus (SC). It turns out that the SC drives its own loop through the basal ganglia:


The basal ganglia evolved a general-purpose reinforcement learning device, assisting behavioral computations of the superior colliculus. As motor cortex M1 began to complement and compete with the SC for motor control, it was also built on top of basal ganglia loops.

For more details, see McHaffie et al (2005). Subcortical Loops in the Basal Ganglia  

Simplified Circuit in Arthropods

Insects (arthropods) have been around long before vertebrates, evolving around the Cambrian epoch. We saw above that insects (arthropods) have a nerve cord: a predecessor of the spinal cord. Each segment of the body corresponds with a nerve bundle called a ganglia. The head segment of insects, called the cephalon, is particularly important insofar as its associated ganglia (cerebral ganglion) is the direct predecessor of the brain.

Within the cerebral ganglion, we find structures called neuropiles (analogous to modern-day nuclei) which perform specific functions:


One such structure (located in the protocerebrum), is the central complex (in above diagram, called the central body, CB). The central complex contains a fan-shaped body which strikingly resembles the mammalian striatum:


The similarities do not stop there. The basal ganglia and central complex share homologous circuitry, and are even created by the same genetic material. In fact, we can conclude that they are the same structure, with different names. 


Recall that the basal ganglia contains two pathways: direct and indirect. The central complex does not have an indirect pathway! This suggests that the indirect pathway evolved later, as an elaboration of more primitive motivation circuitry.

For more information, see Strausfeld & Hirth (2013). Deep Homology of Arthropod Central Complex and Vertebrate Basal Ganglia. See this response, however, for a critique.

The Evolution of Dopamine

Dopamine plays a key role in behavioral readiness. The basal ganglia contains ten times more dopamine receptors than any other brain area. When did dopamine evolve? Recall that, as a catecholamine, dopamine (DA) is heavily related to norepinephrine (NE) and epinephrine (EPI):


In order for these neurotransmitters to influence the nervous system, neurons must have receptors responsive to the aforementioned chemicals. Our question becomes, when did these receptors evolve?

By genomic analysis, we can confirm that DA transporters (DAT) came into existence with the invention of bilateral symmetry. This basal bilaterian also contained transporters for serotenin (SERT) and a highly flexible transporter for monoamines (MAT).

In protostomes, the MAT gene was destroyed via mutation, and replaced with the octopamine transporter (OAT). Let me repeat that. Dopamine is not used by insects etc: instead, related chemicals tyramine and octopamine (bolded above) are used in its place. 

History was not much kinder for the deuterostomes, whose dopamine transporter was destroyed. However, this clade duplicated the MAT gene to resurrect dopamine receptivity in subsequence chordates (cDAT).  


The above analysis clearly demonstrates the volatility of natural selection, and how natural selection uses the resources at its disposal to construct neurotransmitter systems like dopamine. For more information, see Caveney et al (2006). Ancestry of neuronal monoamine transporters in the Metazoa.


  • Comparative anatomy dates the emergence of the basal ganglia to at least as early as the vertebrate clade.
  • The basal ganglia also supports the “control center” of the Deep Layer of the SC, which predates its support of neocortex.
  • Incredibly, the basal ganglia predate the brain, originated prior to arthropods (insects)! The central complex is the vertebrate basal ganglia.
  • The arthropod version of the basal ganglia does not include an indirect pathway. This innovation happened later.
  • Prior to the creation of the basal ganglia, dopamine assumed its role in promoting behavior near the invention of the core animal body-plan.

We will close by condensing these discoveries into a single graphic:


Until next time.