WATCHING the Bollywood blockbuster, Deewar, one marvelled at the facial expressions of the angry young man that Amitabh Bachchan portrayed. But in case you failed to detect any emotion on Bachchan's face, or generally cannot identify any human expression, get your grey matter examined: you'll probably find that you have a damaged amygdala. This structure, the shape and size of an almond, is being seen as playing a major role in interpreting facial expressions.

This much has been borne out in animal studies. Says John Allman of the California Institute of Technology, "Although studies in epileptic patients supports amygdala's role in emotion, the determination of its functions in humans is hampered by the rarity of patients with selective amygdala lesions."

R Adolphs, D Transel, H Damasio and A Damasio of the University of Iowa College of Medicine and the Salk Institute for Biological Studies handled one such rare patient. Says Adolphs, "This patient was unable to discern fear in the facial expression, and was unable to discriminate between fine differences in other facial expressions that are easily perceived by normal humans."

Adolphs and his co-workers used photographs of faces depicting emotions such as happiness, surprise, fear and anger, plus emotionless faces. Their findings suggest that "human amygdala may be indispensable for recognising fear in facial expressions and also multiple emotions in a single facial expression".

Says Allman, "Similar findings have been reported by another scientist, who studied a patient with partial lesions in the amygdala as a consequence of treatment of epilepsy." The patient was unable to match the photographs depicting facial expressions to either the emotion portrayed or to other photographs displaying the same emotion.