The experience of fear has often been closely tied to activity in the brain structure called the amygdala, which is itself a cluster of nuclei and highly involved in the processing of memory. There are two amygdalae, one on each side of the brain.
There is ample evidence that the amygdala is heavily involved in fear conditioning, the procedure whereby we learn to tag aversive experiences with feelings of fear. Fear conditioning is perfectly natural, and functions to help you avoid aversive experiences in the future. There are numerous problems that can arise because of fear conditioning, however, such as tagging healthy and innocuous experiences with a fear response (perhaps because of past trauma), making one susceptible to perpetual fear, paranoia, and misanthropy. On the whole, though, fear conditioning should facilitate your passage through life.
A recent study by Feinstein et al. found that while the amygdala is active during fearful occurrences, it is not responsible for our subjective experience of fear. Feinstein et al. found that a lady, who suffered a condition that resulted in a reduced amygdala, and subsequently seemed to lack a fear response, could be induced to experience fear by increasing her carbon dioxide intake. In fact, people who have a reduced amygdala become even more fearful than those with a healthy amygdala during these negative experiences. I would expect that CO2 triggers fear because of the impending threat of suffocation; if the body is becoming low on oxygen, any mechanism or experience that motivates the organism to take action will promote survival.
On the surface, this experiment seems to suggest that you can induce fear in those who do not typically experience it.
Naturally, this peaked my curiosity because of my interest in psychopaths. Those with psychopathy typically have a reduced amygdala and cannot experience fear. I would be curious to know if this method of inducing fear could be used to help psychopaths develop a conscious and emotional understanding of what it is to experience fear. There are still no treatments for psychopathy, but if we could induce fear in these individuals, perhaps we could trigger the beginning of a conscience?
Jack Pemment, 2013