Scientists say they have located the parts of the brain that help us 'unlearn' our fears.
One of the main areas involved is the same as that used to learn fears in the first place, experiments by the New York University team showed.
This brain region for 'forgetting' fears - the amygdala - had already been found in animals but not in humans.
The findings may help doctors better treat phobias, hope the authors of the study appearing in the journal Neuron.
There has been a great deal of research into how fears are learned and how they can be treated, but far less research into understanding how fears are naturally diminished.
For example, children can be afraid of the dark when they are young but grow out of this fear.
Dr Elizabeth Phelps and colleagues used magnetic resonance imaging to look at what happens in the brain as fears are "unlearned".
They "taught" volunteers to associate seeing an image of a coloured square with a mild electric shock.
How we forget
This created a "conditional" fear, similar to a phobia, in which seeing the coloured square would produce mild anxiety.
The researchers then reversed this fear by presenting the same coloured square previously associated with the shock, but with smaller and smaller shocks until no shock followed the image.
When they looked at the brain scans they saw the amygdala was active when the fear was being learned, which was to be expected from previous research.
The amygdala was also active when the volunteers were "unlearning" their fear, along with another part of the brain called the ventral medial prefrontal cortex.
These findings support what has been previously shown in animals and suggest new avenues for treating anxiety disorders.
Dr Phelps said: "Certain drugs influence the chemicals involved in this type of unlearning in animals.
"Now we can all start to look at different things we can try in terms of treatment.
"As humans, we actively try to control our emotions. We know not to be anxious in certain circumstances but to be anxious in others.
"When we see a tiger in a zoo we know we should not be afraid.
"The question to answer now is how do we regulate that?
"We are doing that work now," she said.
Nicky Lidbetter from the National Phobics Society said: "The National Phobics Society welcomes all research into the field of anxiety disorders, and is particularly interested to hear of this new finding.
"We very much hope that the discovery that the amygdala is involved in unlearning in addition to learning fear will herald the development of new treatments for those affected by anxiety disorders."