Field of Science

Your brain knows when you should be afraid, even if you don't

I just got back to my desk after an excellent talk by Paul Whalen of Dartmouth College. Whalen studies the amygdala, an almond-shaped region buried deep in the brain. Scientists have long known that the amygdala is involved in emotional processing. For instance, when you look at a person whose facial expression is fearful, your amygdala gets activated. People with damage to their amygdalas have difficulty telling if a given facial expression is "fear" as opposed to just "neutral."

It was an action-packed talk, and I recommend that anybody interested in the topic visit his website and read his latest work. What I'm going to write about here are some of his recent results -- some of which I don't think have been published yet -- investigating whether you have to be consciously aware of seeing a fearful face in order for your amygdala to become activated.

The short answer is "no." What Whalen and his colleagues did was use an old trick called "masking." If you present one stimulus (say, a fearful face) very quickly (say, 1/20 of a second) and then immediately present another stimulus (say, a neutral face) immediately afterwards, the viewer typically reports only having seen the second stimulus. Whalen used fMRI to scan the brains of people while they viewed emotional faces (fearful or happy) that were masked by neutral faces. The participants said they only saw neutral faces, but the brain scans showed that their amygdalas knew different.

One question that has been on researcher's minds for a while is what information does the amygdala care about? Is it the whole face? The color of the face? The eyes? Whalen ran a second experiment which was almost exactly the same, but he erased everything from the emotional faces except the eyes. The amygdala could still tell the fearful faces from the happy faces.

You could be wondering, "Does it even matter if the amygdala can recognize happy and fearful eyes or faces that the person doesn't remember seeing? If the person didn't see the face, what effect can it have?"

Quite possibly plenty. In one experiment, the participants were told about the masking and asked to guess whether they were seeing fearful or happy eyes. Note that the participants still claimed to be unable to see the emotional eyes. Still, they were able to guess correctly -- not often, but more often than if they were guessing randomly. So the information must be available on some level.

There are several ways this might be possible. In ongoing research in Whalen's lab, he has found that people who view fearful faces are more alert and more able to remember what they see than people who view happy faces. Experiments in animals show that when you stimulate the amygdala, various things happen to your body such as your eyes dilating. Whalen interprets this in the following way: when you see somebody being fearful, it's probably a clue that there is something dangerous in the area, so you better pay attention and look around. It's possible that subjects who guessed correctly [this is my hypothesis, not his] were tapping into the physiological changes in their bodies in order to make these guesses. "I feel a little fearful. Maybe I just saw a fearful face."

For previous posts about the dissociation between what you are consciously aware of from what your brain is aware of, click here, here and here.

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