Paper Title: Medial prefrontal pathways for the contextual regulation of extinguished fear in humans
Introduction: Based on the purpose and hypothesis along with other information given what did the article try to address that was missing or needing to be done from previous research?
The article tries to address the extinction of fear as an emotional response in humans. Fear is triggered when we experience something that we perceive to be dangerous and harmful to us. In our minds, anatomical features including the ventromedial prefrontal cortex (vmPFC), amygdala, hippocampus, and the dorsomedial prefrontal cortex (dmPFC) all interact with one another to help us recognize and feel afraid in potentially threatening situations. For PTSD victims, there is an imbalance in the functioning of the vmPFC and the amygdala leading to the persistence of fear, meaning that patients are continually at a state of fear, which causes anxiety, or in this case, a renewal of fear. This research looks to study how the inter-connected brain areas interact to promote fear renewal in a way that is context-dependent but translatable to other real-life situations. They hypothesized that “skin conductance response (SCR) to the fear cue (CS+) relative to the safe cue (CS-) would increase in the question context compared to the extinction context…indicating fear renewal.” To do this, they made the assumption that SCR was a dependent measure of conditioned fear. However, perhaps SCR isn’t always indicative of fear but a way for the body anticipating the result of the stimulus about to be experienced. This is the first article that I have seen depicting this kind of research, which provides me with nothing to compare it to. The article, however, does not define what they mean by fear but have us believe that SCR is the main indicator of fear.
Methods: What are some scientific justification on some of the procedures performed in the study. If possible, list how some of the procedures could be improved if one were to repeat the study.
Upon reading this article, I noticed the unequal distribution of men to women. There were 43 total participants; 22 women and 21 men. These numbers may not seem significant, it would have been better to not only have a larger sample size of participants, but also to have an equal distribution of males to females. The study does not provide data to distinguish the effects of extinction and recall by gender, which would have been interesting to include as PTSD may affect both genders differently. Additionally, Fear-relevant stimuli (snake and spider) were used because of their relevance for anxiety disorders and because they are particularly resistant to extinction learning. However, this study did not mention whether a pre-experimental survey was done to screen participants that may or may not have a phobia to the snake/spider stimulus.
Results: Are the data presented accurately and are they supported with the appropriate statistics? Why, or why not?
The data in this experiment are presented accurately. They only observed increased responding to the CS+ than the CS- in the renewal context, which supported their hypothesis. Each statistical test was methodologically broken down and properly utilized. Both figure 3, 4 and amygdala show graphs congruent with the analysis of the data mentioned. Overall, there was higher renewal than recall, which meant that patients were more likely to remember the PTSD anxiety-like symptoms (associated with mdPFC activity). Also, an ANOVA was used for each ROI to find a significant four-way interaction (context x CS interaction). This was the only statistical calculation involved in this study.
Discussion: What future work or additional questions need to be answered to confirm or advance the inquiry further?
One of the biggest limitations to this article and this field of study is there are very few studies that support one another. fMRI signals are taken relative to pre-stimulus, which means that there is not a consistent baseline reading for each similar experiment done. Additionally, because vmPFC is broadly defined, there aren’t similar results in the different sub regions of the vmPFC. Moreover, this study also failed to adjust for the context-mediated fear renewal effects. Different cues were presented at different locations throughout the virtual environment. We do not know whether the physical context may have attributed to some of the fear response of the participants, rather than soley relying on the animal and shock as a measure of fear. As a side note, it wasn’t made clear why a shock method was employed. Symptoms of PTSD are heightened when associated with something that can trigger the experience that causes anxiety. Therefore, how do we know that it is the 3-D animation of the animal fear stimulus that causes the anxiety of the shock therapy that has conditioned the participants to feel more anxious.
Additional work and methods needed to improve this study would be the use of a high resolution fMRI, so as to reduce the amount of artifacts produced and also help to distinguish the interactive neuronal circuitry of dmPFC and vmPFC with the amygdala and hippocampus.