For the experiment, scientists conditioned patients to be afraid of a certain face by showing them a picture of the face along with a specific smell and then administering an electric shock. Patients would eventually learn to fear not only the image of the face but also the associated smell. The smell would trigger fear even when the patient was asleep and not being shocked, but after so many exposures, the fearful reaction would fade away. In effect, the exposure to the smell would do away with the fear.
This study sheds more light on the strong relationship between emotion and smell. Some scientists suggest that this is because the olfactory bulb where smells are processed is close to the amygdala and hippocampus, where emotion and memory are processed. Other experiments have been conducted that confirm the relationship, too. Last year, for instance, scientists showed 70 women a traumatic video while the smell of cassis was pumped into the room. A week later, the women were asked to recall the contents of the video, and some were exposed to the cassis again. Those who smelled the cassis could recall more from the video than those who were not exposed to the scent.
The relationship gets even more interesting. A few years ago, Norwegian artist Sissel Tolaas collected the sweat of various men after they'd been exposed to fear-inducing stimuli and chemically reproduced it. The resultant smell was then installed in a gallery setting using a process called microencapsulation, which is similar to how Scratch'n'sniff products are made. In the gallery, people could scratch or rub the walls and literally smell fear. The public's reaction to the art varied widely as many had visceral reactions to the smell, some of whom couldn't even walk into the room. Scientists are increasingly learning that people can't help but have visceral reactions to smell. Our brains are just wired that way. More here.