The entire set of our emotions is topographically represented in a small region of the brain, a 3 centimeters area of the cortex, report scientists in a study conducted at the IMT School for Advanced Studies Lucca, Italy.
The discovery of this “map” of emotions comes from a work conducted by the Molecular Mind Laboratory (MoMiLab) directed by Professor Pietro Pietrini, and recently published in Nature Communications.
To investigate how the brain processes the distinct basic component of emotional states, the IMT School researchers asked a group of 15 volunteers enrolled in the study to express, define and rate their emotions while watching the iconic 1994 American movie Forrest Gump.
For the entire length of the film, in fact, the 15 volunteers reported scene by scene their feelings and their respective strength on a scale from 1 to 100.
Their answers were then compared to those of 15 other persons who had watched the same movie during a functional magnetic resonance imaging (fMRI) study conducted in Germany.
The imaging data were obtained through “open science”, a platform where scientists from different laboratories can share their data, so that anyone can replicate their findings or use the data for novel experiments, as in this case.
To unveil cortical regions involved in emotion processing, the “emotional ratings” were used by scientists for predicting the fMRI response of the brain. The correspondence between functional characteristics and the relative spatial arrangement of distinct patches of cortex was then used to test the topography of affective states.
As researchers found out, the activation of temporo-parietal brain regions was associated to the affective states we feel in an exact moment, providing us with the map of our emotional experience.
The analysis of the data by Giada Lettieri, first author of the study along with Giacomo Handjaras, both PhD students at the IMT School, and their collaborators shows that the polarity, complexity and intensity of emotional experiences are represented by smooth transitions in right temporo-parietal territories.
The spatial arrangement allows the brain to map a variety of affective states within a single patch of cortex.
To summarize, the right temporo-parietal junction can topographically represent the variety of the affective states that we experience: which emotions we feel in a specific moment, and how much we perceive them.
The process resembles the way senses, like sight or hearing, are represented in the brain. For this reason, the researchers proposed the definition emotionotopy as a principle of emotion coding.
Historically, emotions have often been considered a “separate” human faculty, well distinct from cognition. As a matter of fact, this point of view has been recently challenged by various studies showing how much affective responses can influence cognitive processes, such as decision-making and memory.
The IMT School study adds new details to this more recent view that the principles responsible for the representation of sensory stimuli are also responsible for the mapping of emotions.
Illustration of how emotions are represented in the brain according to the findings of the study. Results revealed the existence of an “emotionotopic” mapping in the right temporo-parietal territories, associated to the the complex and multifaceted subjective emotional experience elicited by watching the Forrest Gump movie. Image is credited to Luca Cecchetti, IMT School for Advanced Studies Lucca.
“This study is also an interesting example of open science and sharing data initiatives in neuroscience”, said Luca Cecchetti, senior author of the paper and Assistant Professor at the IMT School.
“The fMRI data were collected by Michael Hanke and colleagues at Otto von Guericke University Magdeburg and publicly released at studyforrest.org. This allowed us to exploit high-quality neuroimaging data, at the same time saving resources and time. Following the same principle, we released data and code“.
“Dissecting the brain correlates of elementary factors that modulate intensity and quality of our emotions has major implications to understand what happens when emotions get sick, as in case of depression and phobia.
These studies are getting psychiatry closer to other fields of medicine in finding objective biological correlates of feelings, which are subjective states”, commented Professor Pietro Pi
To understand our own emotions, as well as those of others, is crucial for human social interactions. Also, witnessing facts and events of others’ life sometimes prompts inner reactions related to the beliefs, intentions and desires of actors. Through years, the relevance and pervasiveness of these aspects motivated the quest for models that optimally associate behavioral responses to emotional experiences.
In this regard, seminal works pointed toward the existence of discrete basic emotions, characterized by distinctive and culturally stable facial expressions1, patterns of autonomous nervous system activity2,3 and bodily sensations4.
Happiness, surprise, fear, sadness, anger and disgust represent the most frequently identified set of basic emotions5, though alternative models propose that other emotions, such as pride or contempt, should be included for their social and biological relevance6.
To prove the neurobiological validity of these models, neuroscientists investigated whether basic emotions are consistently associated with specific patterns of brain responses across subjects.
Findings show that activity in amygdala, medial prefrontal, anterior cingulate, insular, middle/inferior frontal, and posterior superior temporal cortex, is associated to the perceived intensity of emotions and supports their recognition7–10.
However, this perspective has been challenged by other studies, which failed to demonstrate significant associations between single emotions and activity within distinct cortical areas or networks11–13.
An alternative theory proposes that behavioral and physiological characteristics of emotions would be more appropriately described along a number of continuous cardinal dimensions14,15, generally one governing pleasure versus displeasure (i.e., valence) and another one the strength of the experience (i.e., arousal).
While these two dimensions have been reliably and consistently described, other models propose that additional dimensions, such as dominance or unpredictability, are needed to adequately explain affective states16,17.
Neuroimaging studies also demonstrated that stimuli varying in valence and arousal elicit specific and reliable brain responses18,19, which have been recently employed to decode emotional experiences20.
Activity recorded in insula, amygdala, ventral striatum, anterior cingulate, ventromedial prefrontal and posterior territories of the superior temporal cortex is associated to transitions between positive and negative valence and fluctuations in arousal21,22.
Of note, other than in ventromedial prefrontal regions, studies using either discrete emotion categories9,10,12 or emotion dimensions22–25have shown responses in the posterior portion of the superior temporal cortex, extending to temporo-parietal territories.
Furthermore, these temporo-parietal regions are fundamental for social cognition, as they support empathic processing26,27 and the attribution of intentions, beliefs and emotions to others28,29.
However, despite this large body of evidence, it remains to be determined whether emotional experiences are better described through discrete basic emotions or emotion dimensions. Moreover, regardless of the adopted model, it is still debated how emotion features are spatially encoded in the brain8,11,13,30–32.
As a matter of fact, while findings support the role of distinct regions7, others indicate the recruitment of distributed networks in relation to specific affective states33.
An alternative and biologically favorable perspective may be provided by the notion of gradient. Gradients have been proven a fundamental organizing principle through which the brain efficiently represents and integrates stimuli coming from the external world.
For instance, the location of a stimulus in the visual field is easily described through two orthogonal spatially overlapping gradients in primary visual cortex: rostrocaudal for eccentricity and dorsoventral for polar angle34.
Thus, using functional magnetic resonance imaging (fMRI) and retinotopic mapping, one can easily predict the location of a stimulus in the visual field considering the spatial arrangement of recruited voxels with respect to these orthogonal gradients.
Crucially, recent investigations revealed that gradients support the representation of higher-order information as well35–37, with features as animacy or numerosity being topographically arranged onto the cortical mantle35,38,39.
Following this view, we hypothesize that affective states are encoded in a gradient-like manner in the human brain. Specifically, different affective states would be mapped onto the cortical mantle through spatially overlapping gradients, which would code either the intensity of discrete emotions (e.g., weak to strong sadness) or, alternatively, the smooth transitions along cardinal dimensions (e.g., negative to positive valence).
In either case, the pattern of brain activity could be used to predict the current affective state as function of cortical topography.
Here, we test this hypothesis using moment-by-moment ratings of the perceived intensity of emotions elicited by an emotionally charged movie. To unveil cortical regions involved in emotion processing, behavioral ratings are used as predictors of fMRI activity in an independent sample of subjects exposed to the same movie.
The correspondence between functional characteristics and the relative spatial arrangement of distinct patches of cortex is then used to test the topography of affective states. Results show that three orthogonal and spatially overlapping gradients encode the polarity, complexity and intensity of emotional experiences in right temporo-parietal cortex.
As this organization resembles how primary sensory regions represent psychophysical properties of stimuli (e.g., retinotopy), we propose emotionotopy as a principle of emotion coding in the human brain.
