Sounds of laughter

When you laugh, the whole world laughs with you, or so the saying goes. Scientists have revealed through functional MRI that positive, nonverbal vocal sounds such as laughter or a triumphant “whoop” trigger a response in the brain that automatically primes us to smile or laugh.

It is known that individuals often mirror each other’s gestures and vocabulary while in conversation. The new research shows that the sound of laughter, apart from its visual attributes, has a similar “infectious” quality that may help us in our social interactions, particularly in the creation of strong bonds among individuals in a group.

These functional MRI images show regions of the brain (in dark green) where activations were modulated by the kind of expressed emotion that participants heard, and when they smiled in response to a command. The images demonstrate the combined auditory-perceptual effects of listening to nonverbal, emotional vocalizations and motor responses during facial movement. Reprinted with permission of the Journal of Neuroscience.

Led by Sophie K. Scott, researchers at University College London and Imperial College London played a series of emotional vocalizations to 20 participants and measured their brains’ responses with a Philips Inters 3.0 tesla MRI scanner. Using headphones in a controlled environment, the subjects listened to sounds of triumph, amusement, fear and disgust as well as to an acoustically manipulated control sound. They found that all of the sounds triggered a response in the premotor cortical region that was greater for positive sounds than for negative ones.

The investigators obtained the brain imagery by using a strong magnetic field and recording small local field changes that are associated with paramagnetic molecules. Blood is immediately directed to the part of the brain where neural activity occurs. The scientists detected this process through changes in the oxyhemoglobin/deoxyhemoglobin ratios, which have different paramagnetic properties. Statistical parametric mappingsoftware was used to build up whole-brain images to identify under what conditions there was significant brain activity, and in what part of the brain it took place.

A complementary study using an electromyogram was conducted to determine whether subjects were involuntarily generating overt facial movements in response to hearing the vocalizations.

Scott said that the group will continue to investigate how we use nonverbal expressions to convey emotions. It is interested in studying individual differences in this area as well as related brain pattern variations in autism.

The study is detailed in the Dec. 13 issue of Journal of Neuroscience.