New research on fear learning and the experience of pain
I can imagine the gasps emitted in countless households when Sweden’s Anja Paerson wiped out on the women’s combined Alpine skiing event in Vancouver last month. Her long, violent tumble could not have felt good.
From watching sports and violent movies, to seeing your friend stub her toe, we’re regularly exposed to scenes of pain. We do not always take these scenes lightly – while we may laugh out of discomfort (or sometimes malice) we often empathize with the victims. In essence, we “feel their pain.”
It is known that when one witnesses another in pain, they experience fear. Just interview a crowd leaving a horror flick and they’ll tell you the same. However, the neurological mechanism behind learning to fear that which is not directly affecting you is a mystery (though the amygdala is surely involved…check out the work by last month’s podcast subject, Joe LeDoux).
A brand new study published in Nature Neuroscience sheds some light on this issue. It turns out that the region of the brain that responds to actually enduring something painful also responds to witnessing another’s pain. This response is hypothesized to facilitate fear learning.
Jeon et al (2010) designed an experiment wherein two mice sit across from each other in a cage separated by a translucent plastic window. One mouse was given electric shocks while the other looked on. As you would guess, the “observer” mouse was in visible fear as she watched, frozen in fright. The authors conducted electrophysiological experiments (using electrodes to measure neuronal activity) to see what was going on in various regions of the observer mouse’s brain during the sessions.
As the authors note, the amygdala surely plays a role in fear learning. The amygdala is responsible for behavioral reactions to emotionally relevant events or situations causing unpleasant consequences; indeed, the electrocution of a fellow mouse has much emotional relevance.
More interesting, however, is what was going on in other regions of the observer mouse’s brain. The anterior cingulate cortex (ACC) is known to play a role in the affective/emotional dimension of pain. In other words, it facilitates the feeling of being in pain rather than direct pain itself: If you get a paper cut, various thalamic nuclei produce the sensory aspects of pain – the feeling at the source on the sliced tip of your thumb – while the ACC gives you the affective aspect of pain, the unified whole-body experience. The ACC was noticeably active in the observer mice.
This is a very compelling finding. It suggests a mechanism by which we experience pain even when nothing is directly happening to our body. In effect, we use others as our “proxy” in order to learn what we should fear.
The story, in admittedly silly and fallaciously cognitive terms, goes something like this (parentheses here represent the most relevant neural processes/substrates):
“That guy’s in pain (sensory observation + amygdala)…Ouch, I’m now having a sensation of what that pain may be like (ACC)…I should be afraid of whatever threat is doing that to him (integration of amygdala, ACC and others; “fear learning”)…I’m getting the hell out of here! (behavioral result).”
The evolutionary advantages of this system – a system whereby a creature can learn to fear something based on its observed negative affects on the creature’s peers – are clear. The grave consequences of a failure or malfunction of this system are equally clear:
“Many aberrant social behaviors associated with psychiatric conditions, including various psychopathic or mental disorders (for example, post-traumatic stress disorders, schizophrenia, autism and dementia), feature impairment of recognition of the emotions and feelings of others and dysfunctions in the ACC have been associated with these psychiatric conditions (Jeon et al, 2010).”
Perhaps we really do feel each other’s pain. Perhaps the customary “ouch!” we emit when strangers cut their fingers, movie stars get eviscerated, or downhill skiers take hard falls, reflects a sincere exclamation of pain, not just a cultural meme. When Ms. Paerson crashed I may have felt it too…that would certainly make sense of my fear of double black diamonds.