The model of fear extinction originated from the Pavlovian classical conditioning paradigm in the early 1900s. Defined as a reduction in a conditioned fear response following a non reinforced exposure to a feared conditioned stimulus, fear extinction is known to involve the amygdala and medial prefrontal cortex (mPFC).
It's also a frequently striven-for goal in cognitive behavioral therapy during the treatment of various phobias including arachibutyrophobia; the fear of peanut butter sticking to the roof of the mouth, or barophobia; the fear of gravity.
Unfortunately, extinguished fear responses sometimes reappear with the passage of time (spontaneous recovery), through a shift of context (renewal), or by unsignaled presentations of the unconditioned stimulus (reinstatement). However, the likelihood of these events happening after a few intense sessions of fear exposure may differ significantly depending on the age of the patient according to a new study published in this weeks Journal of Neuroscience.
Kim, Hamlin, and Richardson investigated the role of the mPFC during fear extinction among postnatal 24 day rats (P24) and postnatal 17 day rats (P17). They found that temporary inactivation of the mPFC during extinction training blocked extinction retention the following day in P24 rats but not in P17 rats.
Furthermore, through immunohistochemical analyses they observed that extinction of conditioned fear involved an increased number of phosphorylated MAPK-immunoreactive (pMAPK-IR) neurons in the mPFC and amygdala in P24 rats. However, an elevation of these neurons was only seen in the amygdala of P17 rats. The results indicate that the mPFC has no part in the neural circuitry underlying fear extinction in P17 rats.
The authors suggest that fear extinction is essentially the process of unlearning for the younger rats. In other words, they're "erasing" their fear altogether!
These important findings may significantly impact the future treatment of phobias; targeting and treating fears earlier rather than later in life. Perhaps one day we can teach little barophobic Johnny why the force of gravity isn't really such a scary thing after all.
Kim JH, Hamlin AS, & Richardson R (2009). Fear extinction across development: the involvement of the medial prefrontal cortex as assessed by temporary inactivation and immunohistochemistry. The Journal of neuroscience : the official journal of the Society for Neuroscience, 29 (35), 10802-8 PMID: 19726637