Now a new set of volunteers watched a series of images while undergoing an fMRI brain scan. Participants watched each video clip or still image for three seconds, with about one-second breaks between each presentation.
In addition, some scrambled and upside-down images were added to the sequence, with the observers being told to press a button every time they saw an upside-down image. This helped ensure they watched each presentation and collected scans of the observers’ brains while pressing a button, which helped filter out irrelevant brain activity later. This image shows how the experiment worked:
After the scan portion of the study, the volunteers watched all the clips again and said whether the actor was angry or neutral in each clip. As expected, viewers were significantly more accurate at judging the emotion of the actors when they were moving compared to the still images: 95 percent of the dynamic angry images were correctly judged, while only 80 percent of static images were correctly judged.
But what about the brain scans? Whenever you read about a brain scan study where some portion of the brain “lights up,” the first question you should be asking is “compared to what?” There is always activity in the brain, even when you are sleeping. So what an fMRI study typically does is subtract one or more measures of brain activity from another.
In this study, if you compared the fMRI results of viewer of an angry dynamic image to that viewer watching a blank screen, you would find that many parts of the brain show increased activity. But some of that activity is devoted to recognizing that there is a human and a door in the image, which is not what we are interested in. So the key to understanding the results is understanding what is being compared to what.
First Pichon and his colleagues looked at the difference between brains watching moving angry people and still images of angry people. Here’s an example:
This is a horizontal slice through the middle of a brain (remember, the brain is three-dimensional, so any image you see of a brain scan typically covers only a two-dimensional slice). In this slice, the right amygdala (circled) shows more activity than other brain regions. The amygdala is known to be an area for processing emotion, so it makes sense that there is activity here. But what this particular section is actually showing is that there isÂ more activity here when viewing the moving actor compared to a still image. In fact, the researchers also found more amygdala activity for static images showing anger compared to neutral images.
In a similar fashion, the researchers identified several other regions of the brain where dynamic expressions of anger led to more activity than static or neutral expressions: The fusiform gyrus (associated with face perception and perception of body gestures), the lateral orbitofrontal cortex (associated with perception of facial and vocal expressions of emotion), and areas such as the hypothalamus, associated with defense reactions.
So in responding to bodily expressions of anger, and especially when the angry body is in motion, the brain appears to be incorporating the same responses it does to facial and vocal expressions of anger. It not only identifies the emotion, it also begins to prepare a response to that emotion, even when the viewer is distracted by a seemingly unrelated task. And all this is done when the viewer can’t see the actor’s faces or hear their voices. Such is the power of the human brain — and the critical importance of detecting and responding to a potentially dangerous emotion.
Pichon S., de Gelder B. & GrĂ¨zes J. (2008). Emotional modulation of visual and motor areas by dynamic body expressions of anger, Social Neuroscience, 3 (3-4) 199-212. DOI: http://dx.doi.org/10.1080/17470910701394368