Our emotions could be arranged in the brain according to a geometric organization.
Joy, anger, and sadness seem very different. Yet we can also compare them using simple questions: are they pleasant or unpleasant? Are they calm or intense? These reference points make it possible to locate many emotions mathematically.
Yumeng Ma and Philip Kragel studied the brain activity of volunteers while they followed the evolution of their emotions. The researchers used faces whose expressions changed gradually, as well as sequences of sentences.
To observe the brain, they used functional magnetic resonance imaging. This method detects changes in blood flow associated with the activity of brain regions.
In a region located toward the front and underside of the brain, the researchers detected a distinctive pattern. Activity varied according to six preferred directions. Mathematically, this corresponds to an organization comparable to the directions of a hexagonal “radar” chart.
Geometric coding of the emotional space in the prefrontal cortex
Why six directions? A hexagonal chart makes it possible to navigate in several regularly spaced directions. Similar signatures have already been studied when the brain represents movements through space. Here, the researchers are instead examining movements between emotional states.
The phenomenon appeared with both faces and sentences. This detail matters: it indicates that the signal did not depend solely on the images observed or the words read. It could reflect a more general way of representing relationships between emotions.
Another result opens up new avenues of research: in this same region, certain signals related to the distance between emotions were associated with judgments in each trial. It also remains to be determined whether this organization operates in other situations, for example when we anticipate other people's reactions or interpret our own feelings.