Research published in Behavioral and Brain Functions suggests that scientists may one day be able to cure phobias, everything from fear of spiders to heights, with a simple injection.

Researchers studied the cerebellum, an area of the brain thought to be involved with the development of fear. Using classical conditioning, Masayuki Yoshida and Ruriko Hirano from the University of Hiroshima taught goldfish to become afraid of a light flashed in their eyes.

By administering a low voltage electric shock every time a light was shone, the fish were taught to associate the light with being shocked, which slowed their hearts – the typical fish reaction to a fright.

"As you would expect, the goldfish we used in our study soon became afraid of the flash of light because, whether or not we actually gave them a shock, they had quickly learned to expect one," Yoshida said. "Fear was demonstrated by their heart beats decreasing, in a similar way to how our heart rate increases when someone gives us a fright."

Humans can also be 'trained' to become afraid, and in fact, simple classical conditioning rooted in our childhood and early development can explain many of our behaviors. In this study however, the team discovered that fish that had first been injected in the cerebellum with lidocaine had stable heart rates and showed no fear when the light was shone – they were unable to learn to become afraid.

Since the brains of goldfish show many similarities with those of mammals, including humans, it is hoped that with further study it may  be possible in the future to understand more about the biological and chemical processes that cause us to become afraid. For the goldfish, the effect of lidocaine is only temporary – fearless fish return to being frightened fish as soon as the anesthetic has worn off. Nevertheless, one day, our irrational phobias could become a thing of the past.

Citation: Masayuki Yoshida, Ruriko Hirano, 'Effects of local anesthesia of the cerebellum on classical fear conditioning in goldfish', Behavioral and Brain Functions, 2010; doi:10.1186/1744-9081-6-20 (in press)