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The engagement of multiple systems in classification learning in modulated by many factors including stress. The memory and learning parts of the brain get supported by different systems that are functionally and anatomically distinct. Research by various researchers suggests that stress levels can change the contributions that the set of multiple memory systems have to learn. However, the underlying mechanisms of how the contributions made by multiple memory systems in the brain remains a mystery. It is crucial to understand how the memory and the learning parts of the brain are affected by the various factors including stress. Schwabe and Wolf in their article ‘Stress Modulate the Engagement of Multiple Memory Systems in Classification Learning’ focused on discussing how stress affects the memory and learning. This essay provides the details of the study including how stress modulates the engagement of the procedural and declarative memory systems of the brain.

The memory part of the brain is made up of systems that are functionally and anatomically distinct. During the study by Schwabe and Wolf, two of these systems received their most attention: the declarative memory system and the procedural memory system. In the declarative memory system depends on the hippocampus and is supportive of the acquisition any knowledge which is flexible. The procedural memory system, on the other hand, can be termed as a rigid memory system that is determinant upon the striatum. These two memory systems have been observed to process information at the same time and in parallel while being dependent on each other. They, however, interact in behavior that is seen as competitive or cooperative. Due to the competition, then the possibility of modulating engagement comes up to optimize the behavior.  This leads to the research question in the article: does stress modulate the engagement of the declarative and procedural memory systems? If so, what are the underlying brain processes?

Several healthy participants got chosen and exposed to stress to put the question to the task. It got done before they undertook a PCL task while being observed under a scanner. The tasks were completed through single or multiple cues. This was attributed to the fact that the declarative memory system and the procedural memory system supported the simple cues. To find out which strategy was being used by each, mathematical methods got used. During the case, the authors hypothesized that by passing the participants through stress, the PCL would be shifted from the hippocampal to striatal control, that task knowledge for the declarative memory got reduced, and the usage of strategies that are multi-cue got promoted.

During the selection of the participants, 60 participants were selected. All the participants were right-handed with their vision being normal or corrected-to-normal. Of the 60 participants, thirty were men, and thirty were women, with an average age of 23.83 years. Additionally, to participate, the age limit was placed between 18-30 years old. Additionally, other limitations placed included: non-smokers, people with no previous history of any neurological or psychiatric disorders, and women using any form of contraception. During the case, a woman’s data was excluded due to technical problems during the scan.

During the process, stress was inducted into each of the participants. To ensure that the diurnal variations of the stress control, the experiment was conducted between 12:30 pm and 6:30 pm. Each of the participants was randomly assigned a stress condition. After this, each of the members was told to immerse their right hand in ice-cold water for three minutes. During this time, they were being filmed and observed. To evaluate the effectiveness of the stress condition, blood pressure, saliva among others were measured. The measurement of the blood pressure was conducted before the experiment, during the experiment, and immediately after the experiment. On the other hand, the measurement of saliva occurred before and immediately after the experiment. To evaluate how stressful the experiment was, each subject was asked to respond to a scale of 0- 100 (not at all and very much) how much they found the experiment as painful, unpleasant, and stressing.

After stress induction, the participants took up the PCL task. The task was taken 25 minutes after stress was inducted. During the time of the task, the participants were monitored using a scanner. The reason why the task was taken after 25 minutes was to let the stress hormone be secreted (cortisol). The task included showing the participants different cards and asking them to describe the weather based on the cards that they were shown. This was referred to as the weather prediction task. In each trial, 1-3 cards appeared giving rise to 14 cue patterns. The patterns had either of two outcomes: sun or rain. All participants went through 100 trials. As a response to the task, the participants responded with a right button click for the sun and a left button click for the rain. After the PCL task, a questionnaire was filled by the participants without the presence of a scanner.

To identify and perform an analysis of the learning strategy, a mathematical strategy was used. The responses provided were compared with a typical response if a particular strategy was adopted in an ideal situation. Another task, the visual motor control task was used. In this task, participants were required to show by clicking the left-hand button if the cards shown were less than two, and by a right button click to show that that the cards shown were either two or more than two.

For the imaging during the PCL task, imaging was shown using an MRI. The equipment in use was a scanner of the 3T Phillips Achieva model. A high-resolution scan was required for each participant. The first three scans taken were done away with to ensure the T1 equilibration.

As the research was being conducted, results were noted that were discussed in the form of two line graphs. In the first graph, the percent correct responses were plotted against the number of trials. It was noted that as the number of trials increased, the number of correct responses also increased from the tasks. The other line graph plotted was the reaction time in seconds against the number of trials. It was noted that the reaction time for the PCL task decreased with the increase in the number of trials. Additionally, two bar graphs were also plotted during the study. In the first bar graph, the declarative knowledge was decreased by the stress levels. The second bar graph shows the percentage of participants who used a specific strategy during the PCL task. Different stress levels changed the strategies used during the task. For those who were exposed to high-stress levels, then more complex strategies were used associated with the procedural system and used less of the simple strategies that are associated with the declarative system. From the above discussion, it is clear that stress levels affected how the participants went on with the task. In the line graphs, continued training of the tasks led to a decreased response time as well as an increase in the number of correct responses. This can be compared to the results of the bar graphs that indicate that by increasing the level of stress, then the complex strategies were used as compared to when participants did not use any form of stress.

From the above research, it was clear that the learning process may be controlled by the procedural or declarative memory systems. When the participants were exposed to stress before the learning process, the engagement of the two systems becomes modulated as well as how they contribute to the task performance. However, stress did not in any way affect the accuracy of the classification. It did, however, affect change the nature of learning. For the individuals who got exposed to stress before the task, fewer details of the task were remembered as well as shown a more significant use of the complex procedural memory system. From this study, it is clear that learning under stress is for the complex procedural memory system in comparison to the declarative system.

Additionally, in the finding that stress had no effect on the striatal activity, it is clear that it is not the strength of one of the systems that control the learning process but is the relativity of one of the systems in comparison with the other. During this test, the hippocampal system was disrupted by stress leading to an increase of the relativity of the other system in controlling behavior. The most interesting this is that the hippocampal was correlated positively with classification performance while it was correlated negatively with the performance itself. Since the participants did not get impaired in the accuracy in classification shows that healthy people use both memory systems. All said, applying stress performed alternations on the nature of learning by shifted the classification of learning from the control of the hippocampal to that of the striatal. For the first time, evidence was shown that stress modulates how different memory systems are affected.

During the study, participants whom stress had been induced did not show signs of impairment in classification accuracy proves the point that healthy people use memory systems in a parallel manner. Both memory systems (striatal and the hippocampal) can be used to support the tasks provided in the study. When classification learning was transferred to the striatal memory from the hippocampal memory, the shift of how learning takes place was shown. Single-cued strategies were reduced by stress inducement before the learning process. It also reduced the level of declarative knowledge of the said task. For acquired knowledge to be used, then it appeared that a declarative knowledge of the task needed to be known. Therefore, inducing stress towards procedural learning can lead to having less flexible knowledge. This knowledge is non-transferrable to situations when people have never been in such a situation again.

In conclusion, there is a need to understand how the memory system in the brain works. Such can be understood by knowing how two of these memory systems: the declarative system and the procedural system work. To do so, the modulation of both of these systems during learning needs to be tested. This can be done by using stress as a control factor. In this case, participants are exposed to stress before the learning process. It is after this that they take upon a PCL task and the process of learning is scanned to know which parts of the brain are used. From the study, it can be concluded that various stress levels by the participants led to a different way of handling the task. The engagement of each of the two systems became modulated and also how each of the participants was able to contribute to the performance of the task.

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