Thus, they have performed experiments that reveal for the first time in humans details of the brain regions that become most active as fears are unlearned. The findings show that the walnut-sized brain region called the amygdala, which is a key structure in learning fears, is also involved in unlearning them. Also, they found that a connected area, called the ventral medial prefrontal cortex (vmPFC), appears to be critical for the retention of the extinction of fear.
Importantly, said the researchers, their findings mirror those of animal studies, providing one of the first demonstrations that the mechanisms of "extinction learning" may be preserved across species.
In their studies, the researchers asked volunteers to submit to experiments in which they would see either blue or yellow squares, with one color associated with a mild electric shock to the wrist, while the other was not. Before the experiments, the volunteers were allowed to set the level of the shock themselves so that it would be uncomfortable but not painful. The subjects' fear response was determined by measuring their skin conductance, which would increase with greater fear due to a rise in perspiration.
The subjects were first given a session in which the fear response was acquired. Then, on two subsequent days, they underwent sessions in which the fear response was extinguished. The extinction of the fear response was done by presenting the colored square previously associated with the shock, but without the following shock. Importantly, the researchers slowed extinction using a "partial reinforcement paradigm" in which the shock association with the square was gradually reduced, rather than immediately eliminated. Otherwise, said the research
Contact: Heidi Hardman