As you may know from Star Trek, Spock is half-Vulcan and Vulcans are purely logical: they don’t let fluffy stuff like emotions get in the way of making coolly rational choices.

But here’s a counter-intuitive truth, care of neuroscience: emotions are essential to making rational decisions.

Highly illogical?

In his book Descartes’ Error, neuroscientist Antonio Damasio describes Elliot, a patient who had it all; he was a successful businessman, a good husband and father. Then he developed a tumor in his brain that had to be surgically removed. It resulted in damage to a part of the brain associated with emotion, called the ventromedial frontal lobe.

Soon, Damasio says, Elliot became an “uninvolved spectator” in his own life: Even though his marriage collapsed and each business venture folded, he remained controlled. Damasio spoke with Elliot for many hours, but he never noticed sadness, impatience, or frustration.

Nor did he see any decisiveness. Small choices like which pen to use, when to make an appointment, or which restaurant to eat at led to circling deliberations.

Which, curiously enough, sounds a lot like a decision-making meeting run purely on logic. As Damasio writes in Descartes’ Error:

In the high-reason view, you take the different scenarios apart… and perform a cost/benefit analysis of each of them. You infer logically what is good and what is bad. For instance, you consider the consequences of each option at different points in the projected future and weigh the ensuing losses and gains.

Sounds great, right? A Spock-like precision of decision-making, clean of the messiness of emotions. The only problem is that it won’t work. As Damasio continues: