Facial expressions are a common way for people to communicate emotions. Some have argued that facial expressions are such a frequent and important way for people to communicate emotions that the human brain may have specialized, specific systems allocated to understanding the emotional meaning of these unique visual stimuli. One way to demonstrate such a possibility is to find individuals in whom brain damage has specifically impaired only the ability to understand the emotional meaning of facial expressions, leaving all other functions intact.
Ralph Adolphs and colleagues (1994) described a case history of just such a patient, known by the initials S.M. Patient S.M. was a thirty-year-old woman of average intelligence who suffered from the rare Urbach-Wiethe disease, which destroys the amygdala on both sides of the brain while leaving other brain areas unharmed.
Compared to twelve people of similar intelligence but with other kinds of brain damage and to seven normal people (i.e., with no brain damage) of similar intelligence, S.M. had difficulty interpreting the emotional meaning of faces she saw. When shown pictures of faces that were either making facial expressions or appearing emotionally neutral, she rated the expressions as less intense than did both the brain-damaged and normal controls. In addition, compared to both brain-damaged and normal controls, S.M. had difficulty recognizing which emotional label belonged to the correct facial expression, especially for faces showing fear-type emotions.
In contrast to these problems in recognizing emotion in facial expressions, S.M. did not herself suffer from emotional problems—her mood was generally cheerful and stable. Moreover, S.M. was normal in her capacity to see and recognize faces more generally. When shown pictures of various friends, S.M. was able to recognize their faces easily, even if she had not seen a friend for many years. S.M. also was easily able to learn new faces. Thus, S.M. appeared to present a relatively specific deficit limited to the ability to interpret the emotional meaning of facial expressions, especially those related to fear.