Does Emotion Affect Our Ability To Make Rational Decisions?

There are many types of decisions for us to make, and different brain regions are involved in the process depending on the decision types. Hu and Wang (2012) categorized decisions into four levels according to their complexity.

1. Intuitive – Representing the most basic level of decisions, these are the decisions we make in which we use familiarity, existing preferences and common sense to make decisions.
2. Empirical – These are the types of decisions we make based on trial and error, experience and estimation.
3. Heuristic – These are decisions we make based on scientific theories, rules of thumb, and beliefs.  
4. Rational – The most complex level of decision making, this can be split into static and dynamic rational decisions. These are decisions we make based on minimizing cost while maximizing benefit.

Some of the most important decisions we make are the second level decisions. These decisions are usually related to consumption. They require us to evaluate the values or expected values of the available options. Neuroimaging research show that the orbitofrontal cortex and the ventromedial prefrontal cortex in the brain (O/VMPFC) are related to these kinds of decision making. O/VMPFC is known to be responsible for reward and enjoyment in the brain of humans and primates. They connect to our sensory system in two ways. One is a direct connection and the other is an indirect pathway where it goes through the amygdala. The amygdala in the brain performs as a major role in processing emotions, which suggests thatemotions might be involved when we make level two decisions. Studies have shown that patients with the O/VMPFC lesion show lack of emotional expressions and difficulties in performing second level decision making (Hu and Wang, 2012).

This question was examined with the Ultimatum Game, where fairness is a major factor contributes to decision making. The Ultimatum Game is an economic experiment in which the first player receives a sum of money and decides how to split it up. This split is then offered to the second player, who has the choice to then accept or reject the offer. If the second player rejects the offer, then neither the player gets any money. A study done in 2006 tested whether a lesion to certain brain areas would affect a player’s ability to take an unfair, but still beneficial offer. In this experiment, the split was always unfair, where the first player kept more of the money than he offered to the second player. So for example, if $100 was allocated to the first player, they might split it up 80/20, offering the second player $20, or ⅕ of the total amount. Player 2, when offered an unfair split, often rejects the offer because it is perceived as being ‘unfair’.

The right dorsolateral prefrontal cortex (DLPFC) has shown to be related to decisions that reject the unfair offers. The study done in 2006 suggested that participants with lesion to this part of the brain lead to the acceptance of the unfair, but still beneficial offer. While any inference here is purely speculative, an interesting question to explore would be whether damage to this part of the brain, which is involved with level 2 decision-making, may lead to more rational decisions. In the Ultimatum Game, the rational decision is to accept the unfair offer since gaining some money is always better than nothing.

Not only can we as humans experience fairness, primates behave as if they understand the concept as well. In fact, animal models allow scientists to conduct more detailed research studies and to learn about the actual neuronal circuits involved in decision making. A research published in 2003 demonstrated that capuchins are able to detect unequal pay and decide to reject the inferior reward. After this study, more neuroscientists became interested in learning how “value” is encoded in the brain.  In 2005, Padoa-Schioppa and Assad published their study where they asked monkeys to choose between two unequal food rewards by looking left or right on a screen. By recording the monkeys’ eye movement, they found that some neurons in the orbitofrontal cortex (OFC) fire faster in response to a better reward which suggests these neurons encode economic value. It is also shown that OFC plays an important role in learning from unexpected outcomes and helping us alter our behaviors when decisions go wrong (Takahashi et al, 2009).

This just scratches the surface of what scientists have been able to learn about decision making throughout the years. There is a whole new interdisciplinary field emerging related to neuroeconomics. It truly amazes me how one of our most common and seemingly easy daily activities could be so difficult to explain and understand. Hopefully with the help of advanced technology we can solve this open mystery in the near future.