Last Friday, Dr. Gregory J. Quirk spoke at the fourth annual Bob Leaton Lecture.
Quirk began his talk with the following quotation (courtesy of Marie Curie): “Nothing in life is to be feared, it is only to be understood.” This sentiment of rational enquiry over irrational fear was well reflected in his presentation, “Translational studies of prefrontal control of fear expression and extinction.”
Quirk began by explaining the first Pavlovian experiment he designed to examine “conditioned” fear, meaning fear by repeated painful experiences. Placing rats in separate cages, Quirk conditioned rats to associate a high-pitched tone with an electric shock, such that when the tone was sounded without an accompanying stimulus, the rodents would freeze in anticipation of the pain.
He explained that repeating this auditory cue to excess, without an electric shock to go with it, would lead the rats to abandon their conditioned behavior, a common phenomenon known as “extinction.”
Using this basic experiment in conjunction with brain-scanning technology, Quirk developed a number of observations about the role of specific regions of the brain in the extinction of fear. First, he noted that the rats’ memories of the electric shock generally remained even after extinction was apparently complete, except in young rats whose fear memories can be erased due to their developing amygdalas.
Quirk discovered that the conditioned rodents’ memories of extinction could be induced in the prefrontal cortex via electrodes or an infusion of brain-derived neurotropic factor (BDNF), a protein used to support neuron growth. Lastly, Quirk observed that briefer pain stimulations led to a significantly lowered extinction and thus to less forgettable fear memories.
In addition to the rat experiment, Dr. Quirk studied the fear expression and extinction habits of monkeys living on an island off the coast of Puerto Rico. The researcher would show a monkey a grape, place it in an innocuous box with a pop-up rubber snake inside (without revealing it to the monkey), and observe the monkey’s reaction to the perceived threat.
Since there was a limited amount of information about the monkeys’ individual genetic, social, and experience backgrounds, the study produced one main conclusion. In general, most older monkeys, regardless of gender, developed extinction much more quickly than did their younger counterparts.
Quirk explained that this could be due to the older monkeys’ greater knowledge and experience of threats, but for now, there are too many other possible phenotypical and genotypical factors to draw any definite conclusion.
Quirk’s studies are valuable to the field of mental health because of their implications for the treatment of such human problems as post-traumatic stress disorder. With further inquiry into this field, it will hopefully be possible for traumatized people to overcome their bad experiences and to move on from fear.