Brain Feels Emotion From Both Sides

Jan. 15, 2003 -- In Leonardo da Vinci's famous portrait, Mona Lisa's slight smile appears on the left side of her face — the side controlled by the right side of her brain.

For years, scientists have argued that people process emotion in the right sides of their brains, and even the Mona Lisa seemed to support the idea. According to the theory, the emotion behind the mysterious smirk must stem from her right side since this hemisphere controls movement on the left.

But recent studies show it may not be all that simple.

Decoding What and How

It now appears that both the left and right sides of the brain are active as a person processes emotion — at least when it's expressed in language. Guy Vingerhoets, of Ghent University in Belgium, and colleagues recently demonstrated that while the brain's right hemisphere plays the dominant role in sensing the tone of an emotional message, the left hemisphere is important for decoding its meaning.

"When we pay attention to the what of the message (even when it's emotional), our left hemisphere is doing most of the work," Vingerhoets explained in an e-mail to ABCNEWS.com. "It appears that we have a different pattern of cerebral activity devoted to the emotional what and the emotional how of the spoken language."

The finding, which appeared in the journal, Neuropsychology, seems to agree with other work that has linked the brain's left hemisphere to language. The new research takes this further and shows that even when language expresses emotion, the brain's right hemisphere can't work alone, but depends on the left side to interpret the message.

Watching Blood Flow

To test the idea, Vingerhoets wired 36 people to a transcranial doppler ultrasonogram, an instrument that painlessly measures blood flow velocity to the brain's left and right middle cerebral arteries. The volunteers then listened to pre-recorded messages that contained various emotional meanings (happy, sad, angry or afraid).

They were asked to focus on either the actual meaning of the words or the emotional tone in which they were spoken. And the actors who read each sentence conveyed either an emotional or neutral tone.

Vingerhoets found that when the volunteers were asked to focus on the meaning of the message, blood flow to their brains' left hemispheres increased. When asked to focus on how a phrase was expressed, blood flow increased to both sides of the brain.

And when statements were read with little emotion by the actors, less blood flowed to the right side of the brain. But blood flow to the brain's left hemisphere remained constant even when strong emotion was conveyed. This suggested both sides are always active in interpreting a message's emotional tone.

Liz Phelps, a psychologist at New York University, says the finding makes sense but adds that newer technology can trace how the brain works in even greater detail.

Zeroing In

"The whole idea of left- or right-side functions is an old one," she said. "We're kind of beyond the left and the right. We have one brain — it all works together."

Using functional magnetic resonance imaging (fMRI), a more advanced (and more expensive) technology, Phelps has zeroed in on specific regions of the brain involved in emotion. So far she and other scientists have identified two regions, the amygdala at the center of the brain, and the orbital frontal cortex at the front of the brain as regions involved in emotion.

Phelps' tests show that people's right amygdalas become more active as they look at powerful, emotional images, such as war photos. But in other tests, when told they will receive a shock if they see a blue square (they don't), people's left amygdalas light up in fear when a blue square appears.

"When they have to think about the instructions and think about the symbolism of the blue square, people use the left amygdala more, even when experiencing emotion," she said.

So whether Mona Lisa's smile stemmed from the right or left side of her brain — or both — might depend on just what she was smiling about. Was it a joke told by the painter? A happy thought? A bit of flattery?

The answer remains as mysterious as her smile.