"Evolution built us to punish cheaters." That's how Judge Morris Hoffman began his brilliant book The Punisher's Brain: The Evolution of Judge and Jury (2014). In that book, Hoffman laid out the evidence and reasoning for the claim that social life and human civilization generally depend on our evolved instinct to punish ourselves and others when we or other people violate those social norms of cooperation that sustain any social order.
I have written about Hoffman's book in a previous post. I have suggested that what Hoffman says about the natural instinct for punishing those who disobey social norms corresponds to what John Locke identifies as the natural right of all people to punish those who transgress the law of nature, which is that "no one ought to harm another in his Life, Health, Liberty, or Possessions" (Second Treatise, 6). This Lockean law of nature corresponds to what Hoffman calls the three rules of right and wrong rooted in our evolved human nature to secure property and promises. Rule 1: Transfers of property must be voluntary. Rule 2: Promises must be kept. Rule 3: Serious violations of Rules 1 and 2 must be punished. Like Locke, Hoffman interprets "property" in a broad sense as starting with self-ownership and encompassing one's life, health, and possessions, as well as the life, health, and possessions of one's family and others to whom one is attached. Understood in this broad way, Rule 1 embraces criminal law and tort law, while Rule 2 embraces contract law.
Hoffman and Locke also agree in identifying three levels of natural punishment. Through self-punishment or first-party punishment, we punish ourselves through conscience and guilt. Through second-party punishment, we punish those who harm us by immediately retaliating against them or by later taking revenge against them. Through third-party punishment, we punish those who have harmed other people.
If Hoffman is right in claiming that biological evolution has built our brains to express this kind of punishment, then we should expect to see neural correlates for punishment at all three levels. Hoffman surveys the neuroscientific evidence for this.
In this post, I am beginning a series of posts reviewing this evidence, some of which was mentioned by Hoffman, but also some that has emerged over the past eight years.
Let's start with self-punishment. We punish ourselves by blaming ourselves for our misconduct, which is expressed through feelings of conscience and guilt. In feeling guilt, we blame ourselves for our past misconduct: we recognize that we have wrongly harmed others, and that they can rightly punish us. In feeling a conscience, we imagine blaming ourselves for some future misconduct, and this gnaw of conscience can motivate us to refrain from that misconduct.
From Charles Darwin to Edward Westermarck to Jonathan Haidt, evolutionary psychologists have explained these feelings of conscience and guilt as instinctive evolutionary adaptations for human beings as social animals who need to enforce the social norms of cooperation by punishing themselves for cheating. If this is true, then we should see evidence for these evolutionary adaptations in the human brain.
To search for such evidence, we need to somehow see the mind thinking in the brain. That became possible for the first time in the late 1970s with the invention of the positron camera and positron emission tomography (PET scan). Like magnetic resonance imaging (MRI), the PET scan depends on a fundamental postulate--"neurovascular coupling"--first proposed by neurologist Charles Sherrington in 1890: the most active parts of the brain will show an increase in blood flow in the vessels supplying them, because greater neural firing requires greater energy provided by the oxygen and glucose in the increased blood flow. This postulate was confirmed in the 1950s by the neurosurgeon Wilder Penfield: while operating on people with severe epilepsy, he would wake them up during the surgery, ask them to move their fingers, and he could see changes in color from an influx of blood to regions of the brain active in motor control. In the 1970s, neuroscientists David Ingvar and Niels Lassen developed a brain imaging method, by which a radioactive gas was injected into the carotid artery, so that a scintillation camera at the side of the subject's head could record the circulation of blood, which became the first functional imaging of the brain at work (Le Bihan 2015).
The PET scan also depends on radioactivity. Water that has been made radioactive in a cyclotron is injected in a vein of the arm. When the oxygen nucleus of water has been rendered radioactive, it ejects a positron (a positively charged electron) for a few minutes. When the radioactive water reaches the brain, the positron camera can record the higher quantity of positrons in those regions of the brain with increased blood flow.
In 2000, experimenters used PET scanning for the first neuroimaging study of guilt (Shin et al. 2000). They tested eight male participants for their experience of guilt. The participants were asked to write descriptions of two kinds of past personal events--one emotionally charged event that make them feel the most guilt they had ever experienced and two other events that created no deep emotion. These descriptions were then modified so that they were written in the second person and in the present tense. These scripts were read and tape-recorded in a neutral male voice for playback in the PET scanner. They were asked to listen carefully to the scripts and imagine the event as vividly as possible. After coming out of the scanner, they were asked to rate the intensity of their emotional states during the readings of the guilt and neutral scripts on a scale from 1 to 10.
Their average subjective rating for guilt was 8.8 for the guilt script and 0 for the neutral script. For shame, the average was 7.4 for the guilt script and 0 for the neutral script. For disgust, the average was 6.5 for the guilt script and 0 for the neutral script.
As compared with the neutral script, the PET scans showed increased blood flow to three areas of the paralimbic regions of the brain: the anterior (front) temporal poles, the anterior cingulate gyrus, and the anterior insular cortex/inferior frontal gyrus.
The paralimbic cortex surrounds the middle and lower parts of the brain's two hemispheres. It is a network of brain structures associated with emotional processing, goal setting, motivation, and self-control. This PET scanning study suggests that some of the neural circuitry in this paralimbic network supports the human experience of guilt by which we punish ourselves for violating social norms. And once we have learned how guilty we feel from our past misconduct, we will feel the pangs of conscience when we contemplate some similar misconduct in the future.
We should recognize, however, that neuroimaging studies like this have some serious limitations. First, the sample size is small (only eight individuals). Second, it relies on self-reporting, so that we must trust that these eight people honestly and accurately reported their experience of guilt. Third, the spatial resolution of PET is limited in ways that can create errors in neuroanatomical localization.
Neuroimaging with MRI produces clearer, more precise images. While PET relies on the oxygen nucleus of the water molecule and radioactivity, MRI relies on the hydrogen nucleus of water and magnetism. MRI uses a large magnet to create an intense magnetic field that is strong enough to magnetize the proton in the nucleus of the hydrogen atom in the water molecule. The MRI scanner uses radio waves to excite the protons so that they emit radio wave signals that can be detected by the scanner.
The hemoglobin of red blood cells attaches to oxygen in the lungs and transports the oxygen to the organs of the body through the arteries. Hemoglobin contains an atom of iron that is magnetized. As long as it is attached to oxygen, it is "diamagnetic"--it is repelled by a magnetic field. When the hemoglobin has released the oxygen, the hemoglobin becomes "paramagnetic"--it is attracted by a magnetic field and becomes like a little magnet.
In the blood vessels of the brain, some of the oxygen is released, and the red blood cells are enriched with deoxygenated hemoglobin and so magnetized. These magnetized red blood cells change the local magnetic field and disturb the magnetization of water molecules around them, which lowers the MRI signal sent by the hydrogen protons. A computer analysis of these changing signals can then generate images showing the most active parts of the brain as indicated by variation of oxygenation of the blood.
In 1992, researchers in four groups in the United States showed how this could be done so that subjects in a MRI scanner would have visual images presented to them, and the scanner could then generate images of neural activity in the back of their brains in their primary visual fields (Ogawa et al. 1992). This was the beginning of functional brain imaging by MRI (fMRI), using the method called BOLD (blood oxygen level dependent).
An fMRI Image of Human Neural Activity in the Primary Visual Fields at the Back of the Brain (the Occipital Lobe)
One systematic review of 16 fMRI studies of guilt found three kinds of methods for measuring guilt (Gifuni, Kendal, and Jollant 2017). One method was to have subjects read a script involving guilt and then evaluate the emotion evoked by the script. A second was to ask subjects to relive a guilt-causing event from their past or to imagine themselves in a imaginary guilt-causing event. A third method was to put subjects in a social situation that might elicit guilt, such as playing economic behavioral games or other kinds of interpersonal games. The MRI scanner would then identify the areas of their brains that were most active during their experience of guilt.
This review identified a distributed network of brain regions involved in processing guilt. There were 12 clusters of brain activation located in the prefrontal, temporal, and parietal regions, mostly in the left hemisphere. "Together, these interconnected regions have been associated with a wide variety of functions pertaining to guilt, including self-awareness, theory of mind, conceptual knowledge, moral values, conflict monitoring and feelings of moral disgust" (Gifuni, Kendal, and Jollant 2017, 1174).
In general, brain scanning studies have shown that moral experience elicits greater activity in brain regions for emotional processing, social cognition (including reading the minds of others), and abstract reasoning about the past and future. These regions include the ventromedial and dorsolateral prefrontal cortex, the amygdala, superior temporal sulcus, bilateral temporoparietal junction, posterior cingulate cortex, and precuneus. In other words, "many brain areas make important contributions to moral judgments although none is devoted specifically to it" (Greene and Haidt 2002, 517).
Where in the brain is morality? The answer seems to be: Everywhere and nowhere (Young and Dungan 2012). There is no specifically moral organ or moral brain set apart from the rest of the brain: in a sense, the moral brain is the whole brain, because human morality depends on "the brain's general-purpose machinery for representing value, applying cognitive control, mentalizing, reasoning, imagining, and reading social cues" (Greene and Young 2020, 1009).
This indicates that the Kantian philosophers are wrong in assuming that morality is an autonomous human activity of pure practical reason belonging to a realm of freedom that transcends the realm of nature, including the human nature of the human body and brain.
I will say more about this in future posts.
REFERENCES
Greene, Joshua, and Jonathan Haidt. 2002. "How (and Where) Does Moral Judgment Work?" Trends in Cognitive Sciences 6: 517-523.
Greene, Joshua, and Liane Young. 2020. "The Cognitive Neuroscience of Moral Judgment and Decision-Making." In David Poeppel, George R. Mangun, and Michael S. Gazzaniga, eds., The Cognitive Neurosciences, 1003-1013. 6th edition. Cambridge: MIT Press.
Gifuni, Anthony J., Adam Kendal, and Fabrice Joliant. 2017. "Neural Mapping of Guilt: A Quantitative Meta-Analysis of Functional Imaging Studies." Brain Imaging and Behavior 11: 1164-1178.
Hoffman, Morris. 2014. The Punishing Brain: The Evolution of Judge and Jury. Cambridge: Cambridge University Press.
Le Bihan, Denis. 2015. Looking Inside the Brain: The Power of Neuroimaging. Princeton, NJ: Princeton University Press.
Young, Liane, and James Dugan. 2012. "Where in the Brain is Morality? Everywhere and Maybe Nowhere." Social Neuroscience 7: 1-10.
No comments:
Post a Comment