PSYC3051 – Comparison of Two Articles: Fear Learning and Memory of Rats
This paper discusses the comparison of two published articles on the behavioral mechanisms for fear extinction in rats. The first article was entitled, “Different Mechanisms of Fear Extinction Dependent on Length of Time since Fear Acquisition”, which was written by in 2006. On the other hand, the other article was entitled “Recent Fear is Resistant to Extinction”, which was written by and in 2006.
Aims and Rationale
The aim of the study of (2006) is to study the hypothesis that states that the mechanism of fear extinction in animals, likewise in humans, may differ depending on the time at which the extinction training is provided. It also aims to study the neurological basis for the mechanism of fear conditioning and extinction based on the experiments. The reason behind this study is the lack of information and relevant studies on the neural mechanisms and pathways of the acquisition, consolidation, and expression of fear, which have profound effects to the psychological and biological changes of an organism. Such would also be useful in clinical interventions and study.
On the other hand, the aim of the study of and (2006) is to study and make conclusions on whether early interventions would be more effective than delayed interventions in reducing posttraumatic stress after a relentless incident. It also aims to examine the effects of levels of fear present to the efficacy of fear extinction. The rationale behind such aims is to determine the efficacy of whether providing early or delayed intervention to fearful and stressful experiences that may lead to psychological and emotional disorders. In addition, this study was also conducted to provide better psychological treatment in the clinical and medical field.
Methods and Results
The study of (2006) used male Sprague-Dawley rats, which weighed 350-450 grams. Such animals were subjected to four consecutive experiments to be able to obtain their responses with regards of fear acquisition and extinction. For fear acquisition, the study used light as a conditioned stimulus and footshock as an unconditioned stimulus. The extinction training of the rats was divide into 4 intervals, namely, 10min, 1h, 24h, and 72h, wherein light was used as a conditioned stimulus without the presence of the footshock. Testing of the fear responses of the rats was examined through fear-potentiated startles, which can be observed after the extinction training. The presence and the absence of the fear-potentiated startles were used as basis for the retention of fear of the rats.
The first experiment in this study was conducted to examine the effects of reinstatement of fear in the rats. Result of this experiment suggests that rats following 24h and 72h of fear extinction after fear acquisition showed signs of forceful fear recovery to the conditioned stimulus, followed by the absence of the footshock. On the other hand, the rats following 10min and 1h of fear extinction training after fear acquisition showed signs of little or no recovery of fear. In this regard, it can be deduced from the experiment that long periods of not exposure to fear stimulus leads to more robust fear recovery, while more frequent exposure to fear leads to lesser or lack of fear recovery. The second experiment done under this study was to examine the effects of renewal of fear in rats. The renewal of fear in rats was done by exposure of rats in different contexts. This result suggest that differences can be observed in the different contexts, such that the lack of significant renewal in the short-interval groups displayed lack or reduced reinstatement of fear, while animals with more fear renewal displayed more robust fear recovery. In this regard, the interval or time of exposure of rats to the source of fear determines their response. The third experiment done under this study was aimed at examining the effects of spontaneous recovery of fear in the rats, which involves the reappearance of the conditioned stimulus followed by its extinction. Result of this experiment are still similar with the results of the other two experiments, wherein the 72h group exhibited forceful recovery of fear over time, the 1h group displayed smaller but notable recovery of fear, and the 10min group displayed the lack of fear recovery. Lastly, the fourth experiment done under this study was to examine the magnitude of extinction in the 10min group, for further understanding of its lack of fear recovery. The experiment suggests that the lack or reduced fear-potentiated startle of the rats in the 10min group is attributed to the amount of fear acquired by the rats, as opposed to the efficacy of extinction. As such, it can be suggested that the amount of fear of the rats in the 10min group is relatively low compared to the other groups.
The study of the other article was done using male Long-Evan rats, weighing 250-330 grams, which was subjected to five consecutive experiments. In contrast to the other study, fear acquisition was administered using footshock as the conditioned stimulus and tone as the unconditioned stimulus. The extinction of fear was administered with the intervals of 15min and 24h, wherein conditioned stimulus was presented without the presence of the unconditioned stimulus. Differences ranged on the amount of tone administered for each experiment. Levels of fear of the rats were observed through freezing.
The first experiment done aimed at examining the effects of immediate or delayed extinction of fear after conditioning, which compared two different times. Result of this experiment suggests that rats provided with extinction training 15min after fear acquisition displayed higher levels of freezing, while rats provided with extinction training 24h after fear acquisition displayed delayed extinction. Such findings are the opposite of the findings of the other experiment, as this experiment suggests that forceful fear recovery can be observed in rats that underwent extinction training shortly after fear acquisition, while rats less or reduced fear recovery can be observed in rats that underwent extinction training after longer periods following fear acquisition. The second experiment was done by equalizing the test interval in the immediate and delayed extinction groups, wherein the retention of the fear of both groups was examined 48h after extinction training. The result of this experiment was similar to the result of the first experiment, wherein rats in the immediate extinction condition displayed forceful fear retention and weak fear extinction, while rats in the delayed extinction condition exhibited stronger fear extinction and less fear retention. The third experiment done compared the results of massed or distributed extinction trials after fear acquisition. Result of the experiment suggests that neither massed nor distributed extinction trials are effective in fear retention in the rats if administered shortly after fear acquisition. The aim of the fourth experiment was to reduce the level of fear before the onset of extinction training. This experiment suggests that reducing the levels of fear of the rats before extinction training produces significant reduction in fear retention. The last experiment was done to prove if arousing the fear of the rats before extinction training would impair their extinction memory. This experiment suggests that recent fear appears to lessen the long-term extinction memory of the rats.
Main Conclusions
From the different experiments done, both studies arrived at contrasting conclusions. The main conclusions derived by (2006) in their study is that fear extinction is greatly achieved if extinction training is provided at an interval of 10min after fear acquisition, while fear extinction is not achieved if extinction training is given at a later period. Te extinction of fear was explained by the authors using the neurochemical process, as the extinction of fear in the 10min group is due to synaptic depotentiation, where the expression of protein phosphatase calcineurin is increased, and through the L-VGCC-independent mechanism, which is also associated with depotentiation. On the other hand, the conclusion of and (2006) suggests rather a contrary statement, as they point out that fear extinction is minimal when extinction training is administered shortly after fear acquisition, while fear extinction would be greatly achieved when extinction training is administered after longer periods following fear acquisition. In addition, the authors also suggest that fear extinction is dependent on the level of fear prior to extinction training, rather than the time interval.
Clinical Implications
Both studies are relevant in psychological and clinical fields, and can be both used in the treatment of anxiety disorders, such as Post Traumatic Stress Disorders and phobias. However, the first study, because it delved more on the neurobiological aspect of fear acquisition and extinction, its implication would be more on the field of biopsychology, where biological processes and functions are significantly related to the many theories and concepts of psychology. In this regard, the use of this study is not only limited to addressing anxiety disorders, but also is also relevant in addressing other psychological disorders, such as psychoneurosis, which is also mainly due to anxiety. It has been mentioned that the second study is directed at providing better treatment to PTSD or Post Traumatic Stress Disorder. Because it is directed at providing conclusions on how to address and provide treatment or interventions on PTSD, its implication, similar to the first study, would not only be focused on PTSD, but on other psychological disorders as well. Most of the psychological disorders stem from a number of fearful and stressful events in the environment. Thus, such events are considered one of the leading causes of mental disorders. In this regard, this study can be used in the provision of treatment and intervention for clients having psychological problems and illnesses.
Evaluation of Reasons of Differences in Results
Experiments in the study done by (2006) present a trend of poorer extinction in the short-interval groups, compared in the long-interval groups, which is determined by higher levels of fear-potentiated startle in the post-extinction test. Reasons provided in the study indicate that the 10min group was used as a control group, and that the difference in its response lies on the fact that its mechanism of fear retention and extinction is different from the other groups. In addition, the authors also emphasized that both qualitative and quantitative differences must be taken note off, for short-interval extinction is determined through inhibitory learning mechanism and happens to be much stronger or more efficient than long-interval extinction. Similarly, the mechanism of short-interval extinction presents a qualitative difference from long-interval extinction, which involves the process of erasure. On the other hand, the study of and (2006) also expressed differences in results due to the different levels of retention of the extinction memory. This difference was explained by the authors as being due to the levels of fear of the rats during the extinction training, rather than the time interval following fear acquisition. The time interval of administering the extinction training does not indicate the level of retention of extinction memory because both fear extinction and conditioning produces excitatory and inhibitory memories, such that they compete with each other for expression in behavior of the organism. In this regard, the extinction of fear does not erase its memory, thus, emphasizing the differences.
Other Reasons for Differences
Primarily, the conditioned and unconditioned stimuli used by the two studies are very different from one another. Because fear extinction of the rats depends on the level of fear, it can be assumed that the level of fear of the rats in the study of (2006) was of different degree, compared to the level of fear of the rats in the study of and (2006). Second, the effect of the use of electricity or shocks can also be taken note off. The amount of electric shocks used in both studies is different from one another, thus, may become a source of the retention of the extinction memory. In this regard, the effect of electricity can be emphasized, as to have effects in the retention of memory. Recent researches have found out that minimal electric shocks to the brain may improve memory retention. However, it can be assumed that increase in the amount of electric shock may lead to severe tissue damage and memory loss. Third difference can be accounted for the difference in the time intervals used in the two studies. Fear extinction training was administered in four intervals in the study of (2006), while extinction training was only done in two intervals in the study of and (2006).
References
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