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Cortisol And Working Memory

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Category: Psychology

Autor: anton 07 November 2010

Words: 1403 | Pages: 6

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Research has shown that there is a definite connection between cognitive function and hormones that are released in the human body during moments of exacerbated stress or emotion. It has been suggested that an individual’s working memory, “the cognitive mechanism that allows us to keep a limited amount of information active for a limited period of time,” (Elzinga & Roelofs, 2005; Baddeley, 1996) is significantly affected by the release of cortisol. “Recent findings from studies in animals suggest that that influence of GC’s on memory functioning depends on the level of training-induced emotional arousal and/or adrenergic activity during memory performance.” (Okuda, Roozendall, & McGaugh, 2004; Elzinga & Roelofs, 2005) Intrigued by these findings, the authors decided to conduct a study to determine whether or not cortisol released in humans during stressful or emotional situations requires adrenergic activity to have an effect on working memory. They believed their research would indicate that working memory is impaired during “acute psychosocial stress” (Elzinga & Roelofs, 2005), which casues both elevated cortisol levels and more significant amounts of adrenergic activity.

Methods: Elzinga & Roelofs recruited a total of 44 college students, who were either paid or given course credit for participating in the study. Participants were screened for psychiatric disorders, substance abuse, clinically signigicant medical disease, and use of medication. All participants were between the ages of 18 and 37. Female participants were only allowed if they were in days 21-25 of their menstrual cycle; “there are indications that during this phase, stress-induced cortisol levels do not differ between men and women.” (Kirschbaum, Kudielka, Gaab, Schommer, & Hellhammer, 1999; Elzinga & Roelofs, 2005). Participants were instructed to

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refrain from physical exercise, large meals, smoking, and ingesting coffee or low pH beverages, as these things are known to influence cortisol levels.

Participants were given a version of the Trier Social Stress Test (TSST). The TSST is an exercise that consists mainly of public speaking and mental arithmetic tasks in front of an audience. Heart rate, blood pressure, and salivary cortisol are usually measured to determine the subject’s stress level. Participants in this study were told that they would be pretending to apply for a research assistant position at a university. They were given 5 minutes to prepare, and were expected to deliver a 5 minute speech to an audience of 3 psychologists. They were told that their speech would be videotaped, they were to speak for the entire 5 minutes, that the psychologists were trained to monitor nonverbal behavior related to speech, that a voice frequency analysis would be performed, and that their speech would be judged based on its content and the way in which it was presented. For the mental arithmetic task, participants were asked to subtract 13 from 1587 serially (1587-13, 1574-13, etc.). When any mistake was made, participants were instructed by a member of the judging panel to repeat the task from the beginning.

Working memory was tested by use of the Digit Span subtest of the Wechsler Adult Intelligence Scale – Revised (Wechsler, 1987). Five series of numbers, increasing in length, were read to the participant at the rate of one digit per second. The participant was then asked to repeat the sequence of numbers both in the original order given and backwards. This test was administered three times: once for a baseline reading without an audience present, once

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immediately following the TSST with the audience still present, and once after the TSST without an audience.

Starting 45 minutes prior to the introduction of the first stressor, and again every 15 minutes thereafter until 50 minutes after the last stressor, salivary cortisol samples, heart rates, and blood pressure readings were taken.

Results: After collecting all the data, the authors found that all participants demonstrated higher heart rates and blood pressure levels during the highest stress phase of the study and were back to baseline levels by 50 minutes later. Average cortisol levels increased significantly over time in the stress group, while they decreased over time in the control group. Additionally, the stress group showed a marked variance between cortisol levels right before the TSST and right after the TSST, with the readings afterward being much higher, whereas the control group showed a significant decrease in cortisol levels. These findings lead the authors to divide the stress group of participants into two categories: cortisol responders and nonresponders. “Responders showed elevated cortisol levels from right after the TSST until the end of the experiment.” (Elzinga & Roelofs, 2005) Prior to the TSST, the two groups did not exhibit any differences.

The authors found that cortisol responders did not perform as well using working memory during the TSST. During baseline and recovery phases of the experiment, responders and nonresponders were considered equal in terms of working memory performance. Therefore, the authors concluded that the increase in cortisol levels was “the best and only significant predictor of working memory performance.” (Elzinga & Roelofs, 2005)

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This study was conducted in an effort to determine whether or not a stress-induced increase in cortisol levels must be accompanied be adrenergic activity in order to impair working memory in humans. The authors clearly state that “the fact that responders were exclusively distinguishable from nonresponders on the basis of their cortisol responses, and not on the basis of any other stress response, either sympathetic or subjective, suggests that the working memory impairments during stress were primarily associated with stress-induced cortisol levels.” (Elzinga & Roelofs, 2005) Later in their discussion, the authors state that because cortisol levels and/or adrenergic activity alone did not lead to significant working memory impairment in this study, it is safe to deduce that “stress-induced cortisol elevations require sympathetic activation for working memory impairments to occur.” (Elzinga & Roelofs, 2005) They further go on to compare their study to others, noting that their own findings are “remarkably consistent.” (Elzinga & Roelofs, 2005) They state that the findings of other studies, when taken into consideration with their own research, “could indicate that when acting alone, cortisol may diminish working memory only at extremely high levels, whereas within the physiological range, cortisol may induce working memory impairment only when secreted under conditions of acute stress.”

In reviewing their discussion, it seems that the authors of the study are conflicted as to the indications of their findings, and how they relate to the hypothesis they set out to support. The purpose of their study, as they clearly stated, was to determine whether or not adrenergic activity is required in order for cortisol to impair working memory. They have given several statements that support the already well-documented idea that cortisol can impair working

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memory in humans in high stress or emotional situations. They even go so far as to state that the participants in their study who were recognized as “distinguishable” were recognized as such because of their cortisol levels alone, and not because of any other “sympathetic or subjective stress response.” (Elzinga & Roelofs, 2005) Adrenergic activity is clearly a sympathetic response related to cortisol levels, according to the research the authors themselves used as a basis for the purpose of their study. Therefore, ruling out any sympathetic activity seems contradictory to the purpose of their research.

Additionally, it would have been helpful to learn a bit more about the control group the authors used in the study. For example, how the control group was chosen, what tasks they were given or not given, what readings were taken and when they were taken, and perhaps even the screening process for the control group participants might have been useful information when reviewing this study. The authors made no mention of the control group until the results of the study were mentioned. It is not likely that a proper control group was not utilized, but it would lend more validity to the research if the authors were clear about how and when a control group was used.

Overall, the study itself provides an interesting concept. The authors simply need to be more precise, either about their research or about how it is presented.

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