Human fMRI study: vmPFC encodes emotion space with a grid-like hexadirectional signal
In an fMRI study in volunteers, activity in the ventromedial prefrontal cortex followed a six-fold pattern while they tracked changes in facial expressions and phrases.
Yumeng Ma and Philip Kragel report in PLoS Biology that the ventromedial prefrontal cortex (vmPFC) encodes emotion concepts with a grid-like coordinate code. Volunteers were scanned with functional MRI while they tracked trajectories through affective space. The trajectories were conveyed by morphs of facial expressions and by sequences of phrases plos.org
PLoS Biologyplos.orgOpen source ↗.
Everyday emotional experience is organized in a continuous space defined by two dimensions: valence (pleasant or unpleasant) and arousal (calm or intense). This circumplex organization has shaped decades of research, but its neural implementation remained unclear, the authors write. They asked whether abstract emotion concepts use the same coordinate principles that the brain applies to movement through physical space.
Six-fold signal in the prefrontal cortex
Functional MRI registers changes in blood flow linked to the activity of brain regions. In the vmPFC, located in the front and lower part of the brain, the signal showed hexadirectional modulation: activity varied along six preferred directions. This is a signature of grid-like coding, which has previously been studied when the brain represents displacements in space. Here it was found for displacements between emotional states.
The effect appeared with both faces and phrases, so the coordinate representation generalized across stimulus modalities. According to the authors, this indicates abstraction beyond perceptual features plos.org
PLoS Biologyplos.orgOpen source ↗. The grid-like signal reflected a metric organization of emotion concepts independent of overt behavior.
Distance signals and judgements
In the same region, signals related to the distance between emotions predicted participants' affective judgements trial by trial. The authors conclude that emotion knowledge is structured by a grid-like coordinate system in the human brain, which can support predictive inference and flexible decision-making.
It remains to be tested whether this organization is engaged in other situations, for example when people anticipate the reactions of others or interpret their own feelings.
