Newcomer et al. (1999) Study on Cortisol and Verbal Declarative Memory

Cortisol:

Cortisol is a stress hormone released by the adrenal glands in response to stress and low blood-glucose concentration. It plays a critical role in various bodily functions, including metabolism, immune response, and memory. However, high levels of cortisol, especially under stress, have been shown to impair cognitive functions such as memory.

Aim:

The aim of Newcomer et al. (1999) was to investigate whether high levels of cortisol interfere with verbal declarative memory. Verbal declarative memory refers to the ability to recall facts and information, often tested through tasks like memorizing and recalling prose or word lists.

Procedure:

1. Participants:
   • Participants were employees or students at Washington University Medical Center.
   • All participants underwent a clinical interview to ensure that they were healthy. They were excluded from the sample if they were pregnant, had a history of mental illness, had suffered head trauma, or had any illness treated with corticosteroids, as these factors could confound the results.
2. Experimental Design:
   • Double-blind design: Neither the participants nor the researchers knew which treatment each participant received, preventing bias in the results.
   • Matched pairs design: Participants were matched for age and gender and randomly assigned to one of three conditions:
     • Condition 1: High cortisol group – Participants took a tablet containing 160 mg of cortisol daily for four days. This dose mimicked the cortisol levels observed during a major stress event.
     • Condition 2: Low cortisol group – Participants took a tablet containing 40 mg of cortisol daily, producing cortisol levels similar to those experienced during minor surgical procedures (e.g., getting stitches).
     • Condition 3: Placebo group – Participants took placebo tablets with no active ingredient, serving as the control group.
3. Memory Task:
   • Participants were asked to listen to and recall a prose paragraph. The prose passages were of similar difficulty, and different passages were used on each day to avoid memorization effects.
   • Testing occurred at three points: before taking any cortisol (baseline), one day after taking the tablet, and four days later. A final test was administered six days later to assess long-term effects.
4. Baseline Test:
   • Before any cortisol or placebo tablets were taken, all participants completed a memory test to ensure there were no significant differences in memory performance between groups at the start of the experiment. This baseline test was critical to ensure that any later differences could be attributed to the cortisol treatment rather than individual memory differences.

Results:

• High Cortisol Group:
  • Participants in the high cortisol condition showed impaired verbal declarative memory performance. Their ability to recall the prose passage was significantly worse than participants in the other two conditions. This suggests that high cortisol levels interfere with memory recall, consistent with the idea that stress can negatively impact cognitive function.
  • Importantly, the memory impairment was temporary. Once participants stopped taking cortisol, their memory performance returned to normal levels.
• Low Cortisol and Placebo Groups:
  • There was no significant difference in memory performance between the low-dose cortisol group and the placebo group. Both groups showed improved memory performance over time, likely due to practice effects or procedural learning from repeated testing.

Conclusion:

The study demonstrated a clear link between high levels of cortisol and impaired verbal declarative memory. High doses of cortisol, similar to those experienced during major stress events, negatively affected the recall of prose passages. However, this effect was temporary, with memory performance returning to normal after cortisol administration ceased. The findings provide evidence that cortisol can interfere with memory, but only at high levels, as lower levels did not have the same impact.

Evaluation:

• Strengths:
  • Cause-and-effect relationship: As a laboratory experiment, the study was able to establish a clear cause-and-effect relationship between cortisol levels (IV) and memory performance (DV).
  • Baseline testing: The use of baseline testing controlled for individual memory differences, ensuring that pre-existing abilities did not confound the results.
  • Counterbalancing: The use of different prose passages on different testing days controlled for difficulty levels. The researchers counterbalanced the use of these texts, ensuring that text difficulty did not affect the memory results.
• Limitations:
  • Ecological validity: The task of memorizing a prose passage may not reflect everyday memory experiences, limiting the generalizability of the findings. While this task might explain the memory problems experienced during exam stress, it may not fully represent how memory functions in more complex or less structured situations.
  • Extraneous variables: Although the study ran over several days and was well-controlled in the lab, participants were not constantly monitored outside the lab. Daily stressors or personal experiences could have influenced cortisol levels and memory performance.
  • Ethical considerations: Participants ingested cortisol, which negatively affected their memory. However, the memory impairment was temporary, and participants provided informed consent. Ethical guidelines were followed, but the potential stress or discomfort from taking cortisol should be noted.
• Practice Effects: Participants in the placebo and low-dose cortisol groups showed improvements over time, which may have been due to procedural learning or practice effects from repeated memory tests. This is an important consideration when interpreting the data.

In conclusion, Newcomer et al.'s study demonstrated that high cortisol levels, similar to those experienced during significant stress, can temporarily impair verbal declarative memory. This finding highlights the impact of stress on memory and has implications for understanding the relationship between stress hormones and cognitive function.