Aug 142008
ResearchBlogging.orgHow does the human brain react to the communication of emotion? Does the observation or imagination of emotions have anything in common with the personal experience of them? It is possible that the brain uses a setup in which seeing a person experience an emotion, imagining that emotion, and feeling that same emotion all use completely independent circuitry. Yet since all of these experiences make references to the same emotional state, it is also reasonable to think that some of the pathways are shared. In a recent article from PLoS ONE, a team of researchers uses functional Magnetic Resonance Imaging (fMRI) to determine similarities and differences in the patterns of brain activation following various means of communicating disgust. PLoS ONE is open access, so go ahead and open the article up in another window.

First, a word about fMRI, for those unfamiliar with it. As the name would suggest, fMRI is an elaboration of the standard MRI techniques used image the interior of your body without the use of potentially harmful radioactivity. Neuronal activity in the brain causes a local depletion of oxygen from the blood, followed by a localized increase in blood flow. Because the magnetic properties of iron in the blood change with its oxygenation state, it is possible to detect these hemodynamics using magnetic resonance imaging. Thus, fMRI is able to indirectly detect neural activity, although the fMRI signal lags behind activity by a few seconds. A given fMRI signal also encompasses a large number of individual neurons and therefore can only serve as a rough map to where things are happening in the brain. These temporal and spatial limitations limit the conclusions that can be drawn reliably from fMRI, but the observed correlations can provide valuable insights.

Jabbi et al. used fMRI to map the neural response of subjects to various encounters with disgust. Previous research had shown that a particular region of the brain (the IFO) showed increased activity when subjects either tasted something disgusting, or viewed a short clip of someone else tasting something disgusting. For this study, Jabbi et al. had participants read short scripts (samples can be found in the supplementary materials) intended to make the reader imagine being disgusted, pleased, or not feeling anything. They found that reading disgusting passages induced a neural response in this region of interest, just as it had for the cases of tasting or observing disgust.

While this may seem completely unsurprising, it bears some consideration. The experience of personal disgust differs significantly from the experience of observing disgust in others. Similarly, imagining or reading about disgust creates a very different subjective experience than, say, drinking quinine. Given that these are all quite different feelings, it is somewhat surprising that a single area is activated by all three.

Of course, there is a fine line to consider here — the passages meant to make the subjects imagine disgust may have actually disgusted them. The paragraphs that the authors make available in the supplementary materials are written in second person and involve things like accidentally ingesting animal waste. Because the subjects are reading passages that ask them to imagine themselves being disgusted, and the passages are themselves disgusting, the act of imagination may be contaminated by an immediate personal experience of disgust. In a more elaborate experiment it might be of value to use passages written in the third person. Additionally, it might be useful to employ passages in which the characters, because of particular phobias or personal experiences, are disgusted by items or actions the reader is likely to find innocuous.

Whether the readers where themselves disgusted or not, the overall response in the brain differed for each of the stimuli, as shown by a map of correlated activity (Figure 2). While the area outside the IFO activated by observation was relatively small, both the disgusting taste and the disgusting scripts produced widespread activity relative to a neutral taste or script. In general there was not much overlap between the networks, except for a small region shared by the imagination and experience groups. The authors propose that the similarities of imagining, observing, and experiencing emotion are due to the common activation of the IFO, while the differences between these are due to the largely distinct networks of correlated activity. Different modes of exposure to disgust may therefore act in complementary, rather than independent, ways.

Additionally, this result appears to be consistent with the view that our recognition of observed disgust and our imagination of disgust rely on an internal simulation of our own feelings of disgust. However, these experiments cannot establish exactly what a particular region of the brain is doing, so this remains an open question.

While this research does not indicate whether these results can be generalized to other emotional states, this finding may interest developers of media that make use of multiple modes of communication, specifically video games. Games often rely on video cutscenes to convey story and emotion, but this approach may be wasting a significant amount of potential. The participatory nature of games makes it possible to approach emotional communication not only through the observational route, but also the experiential route.

Consider the case of Agro’s fall in Shadow of the Colossus. Observing the cutscene, and hearing the voice of Wander, the player can understand that Wander feels grief at this event, in much the same way that anyone watching a movie could understand it. Additionally, the emptiness of the game’s landscape and the forced collaboration between the player and the Agro AI has helped to create a relationship between the player and the horse. Thus, in observing Agro’s fall, the player may feel his own sense of grief at the event, increasing the emotional resonance of the moment.

This suggests a possible, if lengthy, experiment. It would be interesting to compare the fMRI profile of a subjects observing Agro’s fall under two conditions: one in which they have actually played the game up to that point, and another in which they have watched the game as a movie, with exploration and battles recorded previously from an expert player’s run. Would the first group have activity in both the observational and experiential networks, or would each group activate a different network? What implications might these outcomes have for the development of emotionally fulfilling games?

Of course fMRI studies are not some holy grail that makes everything clear. The work of Jabbi et al. has given us a rough map to where things are happening, but understanding exactly what is happening and how it is happening will require additional experiments and possibly new investigative techniques. Nonetheless, this is an interesting piece of the puzzle, and perhaps some food for thought.

Mbemba Jabbi, Jojanneke Bastiaansen, Christian Keysers (2008). A Common Anterior Insula Representation of Disgust Observation, Experience and Imagination Shows Divergent Functional Connectivity Pathways PLoS ONE, 3 (8) DOI: 10.1371/journal.pone.0002939

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