Reznikov et al analysis

Reznikov et al attempted a more representative PTSD model of humans in their paper on extinction of conditioned stimuli responses. Statistics show that only 20-30% of humans that experience a traumatic event will actually develop PTSD. This proportion was paralleled in the study with only 25% of the rats developing a weak extinction to the conditioned stimulus. The weak extinction rats therefore represented individuals with PTSD. The experimenters then raised the question of what is it that contributes to the weak versus strong extinction of conditioned stimuli? The second experiment was used to show that typical stress and anxiety tests are not indicative of which group the rats fall into, either weak or strong extinction. So the level of extinction must be related to the traumatic event.

            I feel that Reznikov and colleagues were reaching a little bit in their attempt to delineate thresholds for corticosterone levels in the rats. The data clearly shows that a low initial corticosterone level is related to weak extinction, but the authors tried to create a threshold by saying that all animals with levels above 20 ng/ml showed strong extinction. While this is true, not all animals below 20 ng/ml showed weak extinction. About half of the animals with levels below 20 ng/ml showed strong and half showed weak extinction. So I don’t know how far we can really go with the data given.

            Another area that I thought could use some improvement was the depiction of class differences in the conditioning phases of the experiment. When looking at Figure 2, it appears that there is a difference between the weak and strong extinction mice, but the graph does not show an asterisk. In the text it is stated that C2 showed significance at the p<0.05 level, which is lower than the other significant differences seen. It seems very odd to me that this is the only asterisk that is magically missing, since the difference in groups during conditioning is brought up as an area of debate later in the discussion. So was this actually a mistake or purposefully left out to make it appear that there was not much difference between the two groups during conditioning. Later in the discussion it is brought up that this difference shows a stronger conditioned stimulus and unconditioned stimulus connection in one of the groups that may have resulted from rats with learning differences or varying pain tolerances.