not blind to emotion

Nature | Two patients, partially blind because of damage to one side of their brain, were able to sense, and respond to, emotions expressed by people in pictures presented to their blind sides.

A study by an international team of researchers found that the patients unconsciously twitched a facial muscle uniquely involved in smiling when a picture showed a happy person, and a muscle involved in frowning when the person depicted looked fearful1.

The patients, both from the United Kingdom, have the very rare condition known as partial cortical blindness. Their eyes are intact but they have damage to the visual cortex on one side of their brain. This means that they cannot process information from the visual field on the opposite side of their nose.

The scientists, who were led by Marco Tamietto and Beatrice de Gelder at Tilburg University in the Netherlands, say the results show that our spontaneous tendency to synchronize our facial expressions with those of other people in face-to-face situations - known as emotional contagion - occurs even if we cannot consciously see them.

"This is interesting evidence that we can recognize the emotions of others without needing to be visually aware of them," says neuroscientist Christian Keysers, an expert in the neurophysiology of emotion at the University of Groningen, the Netherlands, who was not involved in the study.

Mixed picture?
Much of the visual input from the retina goes directly to the visual cortex, which processes the information so that we consciously perceive the image we are looking at. But a small part goes directly to the midbrain, through an evolutionarily primitive subcortical pathway that processes emotion and other information central to survival - and that is intact in the two patients.

So it seems that emotional contagion can be implemented via evolutionarily ancient neural structures, says Tamietto, and does not necessarily require the involvement of higher brain regions, visual awareness or the mirror neurons that are active when we recognize the physical actions of others.

But Keysers cautions that it remains to be determined whether the subcortical and higher cortical pathways for recognizing emotions operate in parallel. Emotion recognition could use several types of available information, he says.