On Prefrontal Guilt

The field of Neuroeconomics has become quite popular in recent years. There are several reasons for this surge in interest; amongst these are: (1) the inevitable intrigue generated by scientific considerations of currency, (2) the utility of studying behaviors contingent on well defined rewards and punishments (losses), and (3) the value of scientifically exploring a human behavior that has been studied and theorized about for hundreds of years (namely by economists and others not specifically interested in the neurological bases of these behaviors).

One particularly rewarding research tactic has been the employment of economic games (a subset of those falling under the heading of game theory, widely associated with the mathematician John Nash). One example of such a game is the following: I (the "house") flip a coin. If it's heads, I pay you a dollar. If it's tails, I flip it again. If it's heads on the second toss, I give you 2 dollars. If it's tails, I flip it again. If it's heads on this second toss, I give you 4 dollars, et cetera. Thus, if you get a head on the nth roll, you receive $2ⁿ. The question is: how much would you be willing to pay initially to be a player in this game? Most people are only willing to pay perhaps $10-20 for the privilege, however, statistically (on average), the earnings in this game are infinite. If you play enough times, you will earn an infinite amount of money. This concept was quoted hundreds of years ago to give credence to the notion that when it comes to estimation of value, we operate far from optimally.

This sort of heuristic - describing performance in a prescribed setting - can be rendered quantitative in such a way that an individual's decision making in a particular game can be used to estimate parameters about their over-all behavior: how risk-averse they are, how benevolent, and even how likely they are to feel guilty.




A paper appearing in the Journal of Neuroscience addresses this last point in the context of relevant brain areas and brain damage. Krajbich et al compared the performance of individuals with certain types of brain damage (along with normal controls) in an economic game. As can be seen in the table above (from their paper), they concluded that those with damage to the prefrontal cortex (PFC) are far less likely to experience feelings of guilt¹.



Those familiar with the story of Phineas Gage may hear the ring of truth in this result. Phineas Gage was a railroad worker responsible for tamping down explosives into holes drilled in pieces of rock, using a long metal rod. During one such episode, the explosives went off, and the rod entered his head below the left eye socket, exiting through the top of the skull and destroying most of his PFC (see image, above). Amazingly, he survived, but with the intriguing effect that his personality changed completely. Before the accident, he was described by his employers as "a great favorite" and "the most efficient and capable foreman in their employ." After the accident, he was so changed that they subsequently "considered the change in his mind so marked that they could not give him his place again." He was furthermore said to be a "braggadocio,and "manifesting but little deference for his fellows, impatient of restraint or advice when it conflicts with his desires, at times pertinaciously obstinate, yet capricious and vacillating.²"

It is likely that the experience of guilt is not the only function of the PFC; it is associated with planning functions and reasoning in general. However, this type of exploration and estimation of the parameters of human behavior is quite novel and powerful, and its utility will only increase as the complexity of our models and understanding of the parameters relevant to the generation of such behaviors increases.

References:
1. Krajbich I, Adolphs R, Tranel D, Denburg NL, Camerer CF. Economic Games Quantify Diminished Sense of Guilt in Patients with Damage to the Prefrontal Cortex. J Neurosci 29: 2188-2192, 2009.
2. Harlow JM. Recovery from the Passage of an Iron Bar through the Head. Pubs Mass Med Soc 2: 327-347, 1868.