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5-Min Science: The Brady Executive Monkey Study

BioSource Faculty

Updated: Feb 9


rhesus monkey


The Dawn of Stress Research


In the 1950s, as scientists were beginning to unravel the mysteries of how our bodies respond to stress, a fascinating but controversial set of experiments emerged that would shape psychological research for decades to come.


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Joseph Brady's executive monkey studies contributed to scientific misinformation regarding the impact of perceived control on how human health outcomes.


Brady's Executive Monkey Study is a cautionary tale in research design and shows that flawed research has a long half-life, especially when it supports a popular belief.


The Experimental Design: A Tale of Two Monkeys


Picture this: 16 monkeys, paired into eight groups, each facing a stark choice. One monkey, dubbed the "executive," sits before a lever that could prevent an impending electric shock. Their partner, the "yoked" monkey, faces the same physical threat but lacks any control over the situation. When a warning light flashed, the executive monkey had a critical 5-second window to press the lever and prevent the shock. If they failed to respond in time, both monkeys would receive a 0.5-second shock at an intensity of 5 milliamperes. The yoked monkey, despite experiencing identical physical stressors, had no means to influence the outcome, creating a stark contrast in psychological burden between the pairs.


These stress trials weren't fleeting moments but grueling six-hour sessions conducted twice daily. The monkeys, isolated in sparse individual cages, endured this routine for weeks. Brady's findings seemed clear: the executive monkeys, burdened with the responsibility of control, developed gastric ulcers at an alarming rate, while their powerless counterparts remained relatively healthy (Brady, 1958).


Brady study


Methodological Flaws

Selection Bias


However, beneath this seemingly straightforward narrative lay significant methodological problems that would later cast shadows over Brady's conclusions. The most glaring issue? Brady confounded his study with selection bias. After measuring their reaction times to a warning light, he made the fastest responders executives. These monkeys might have been naturally more susceptible to stress-related illness, regardless of their role in the experiment. Indeed, Sines, Cleeland, and Adkins (1963) found that animals more prone to ulcers learned avoidance responses faster than those less susceptible. Brady's executives were the twitchiest 9 of 18 monkeys.



Analytical Flaws


Responsibility or Work-Rest Cycle?

Brady hypothesized that responsibility for preventing shock caused ulcer development. But what if the culprit was the work-rest cycle? Tsuda and Hirai (1975) found in rats that ulcers developed only under a 6-hour work and 6-hour rest cycle. Rats exposed to either a 1-hour or 3-hour work-rest schedule did not develop ulcers, indicating that the ulceration might be more related to the specific schedule rather than the stress of being an executive.



Monkeys Are Not Small Humans


Despite sharing 93-94% of our DNA sequencing with rhesus monkeys (Yun, Ahn, & Kim, 2011), we can't generalize Brady's findings to humans. As we will see in the next section, Brady's findings were not replicated in rats or humans.


Replication and Modern Understanding


Subsequent research has painted a starkly different picture of control and stress. Weiss (1971) randomly assigned rats to executive and yoked conditions, finding that control over stressors actually protected against stress-related illnesses – a direct contradiction to Brady's findings.

Likewise, Tsuda and Hirai (1975) failed to replicate Brady's results.


Human studies have consistently shown that greater perceived control correlates with better health outcomes. Langer and Rodin's (1976) research with nursing home residents demonstrated that increased control over daily decisions improved health and survival rates. Gale et al. (2008) found lower cardiovascular disease risk and mortality among individuals with a higher sense of control.



Key Takeaways


  1. Historical Context: Early stress research in the 1950s, exemplified by Brady’s executive monkey study, laid the groundwork for understanding stress responses despite its later debunking.


  2. Experimental Design: Brady’s study paired monkeys into "executive" and "yoked" roles to examine control over stress, suggesting that having control led to increased stress-related illness.


  3. Methodological Flaws: Significant issues—including selection bias and confounding work-rest cycles—undermined the study’s conclusions and misrepresented the role of control in stress.


  4. Replication and Contradiction: Subsequent research in animals and humans has consistently shown that perceived control acts as a protective factor against stress-related illnesses, reversing Brady’s original findings.


  5. Scientific Caution: The enduring influence of Brady’s flawed study serves as a reminder of the importance of rigorous research design and critical evaluation to avoid perpetuating scientific misconceptions.




Conclusion


The legacy of Brady's Executive Monkey Studies represents both a cautionary tale and a catalyst for scientific progress. While Brady's research was fundamentally flawed due to selection bias and methodological issues, it sparked crucial conversations about the relationship between control and stress that continue to influence research today. The subsequent studies by Weiss, Tsuda and Hirai, and others didn't just fail to replicate Brady's findings—they revealed an entirely opposite pattern: having control typically protects against stress-related illness rather than exacerbating it.


This reversal of understanding highlights the vital importance of rigorous methodology in scientific research. Brady's selection of naturally reactive monkeys as "executives" and the specific work-rest cycle he employed likely created artifacts that led to misleading conclusions. Yet perhaps the greatest lesson from this scientific journey is the danger of accepting findings that conform to our intuitive beliefs without sufficient critical examination. The endurance of Brady's conclusions, despite their flaws, reminds us that scientific misconceptions can persist when they align with popular narratives about stress and responsibility.


Modern research with both animals and humans has conclusively demonstrated that a sense of control generally serves as a buffer against stress, not a burden. From Langer and Rodin's groundbreaking work with nursing home residents to Gale's studies on cardiovascular health, the evidence consistently shows that perceived control correlates with better health outcomes. This evolution in our understanding of stress and control not only corrects a historical misconception but also provides valuable insights for promoting health and well-being in contemporary society.



Glossary


control monkey: in Brady’s study, the “yoked” monkey that received the same shocks as the executive monkey but had no ability to control or prevent them. This role highlighted the contrast in psychological burden between the monkeys.


duodenal ulcer: a type of ulcer occurring in the duodenum, often associated with high stress and observed in the executive monkeys during Brady’s experiments.


executive monkey: a monkey in Brady’s experiment responsible for pressing a lever to prevent electric shocks for itself and its yoked partner. This monkey carried the psychological stress of control.


generalization: the application of findings from a study, often inaccurately, to a broader population. Brady’s findings were inappropriately generalized to human workplace stress without sufficient evidence.


gastrointestinal lesions: damage to the stomach or intestinal lining, including ulcers, caused or exacerbated by stress, as observed in the executive monkeys.


lever-press task: the mechanism in Brady’s study where the executive monkey had to press a lever within five seconds of a warning light to prevent electric shocks.


perceived control: the belief in one's ability to influence events, often linked to better health outcomes. This contrasts with Brady’s findings, which suggested control was detrimental.


replication: the process of repeating a study to verify its findings. Replications of Brady’s work, such as Weiss’s rat studies, often failed to support his conclusions.


selection bias: a methodological flaw in which subjects are not randomly assigned, leading to skewed results. Brady’s assignment of monkeys based on reaction times introduced this bias.


six-hour work-rest cycle: the schedule used in Brady’s experiments, where monkeys alternated between six hours of lever-pressing and six hours of rest. This cycle was later implicated as a stressor contributing to ulcer development.


stress trials: sessions in Brady’s experiments involving exposure to electric shocks, with varying psychological burdens depending on the monkey’s role.


ulcers: painful sores in the stomach or intestine linked to stress and observed in Brady’s executive monkeys but not in yoked controls.


warning light: a signal used in Brady’s study to indicate an impending shock, giving the executive monkey a five-second window to respond.



Google Illuminate Discussion


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References


Brady, J. V. (1958). Ulcers in "executive" monkeys. Scientific American, 199(4), 95-100. https://doi.org/10.1038/scientificamerican0458-95


Gale, C. R., Batty, G. D., & Deary, I. J. (2008). Locus of control at age 10 years and health outcomes and behaviors at age 30 years: The 1970 British Cohort Study. American Journal of Epidemiology, 168(1), 30-36. https://doi.org/10.1093/aje/kwn413


Langer, E. J., & Rodin, J. (1976). The effects of choice and enhanced personal responsibility for the aged: A field experiment in an institutional setting. Journal of Personality and Social Psychology, 34(2), 191-198. https://doi.org/10.1037/0022-3514.34.2.191


Sines, J. 0., Cleeland, C., & Adkins, J. The behavior of normal and stomach lesion susceptible rats in several learning situations. Genetic Psychology, 102, 91-94.


Tsuda, A., & Hirai, H. (1975). Effects of the amount of required coping response tasks on gastrointestinal lesions in rats. Japanese Psychological Research, 17, 119-132. https://doi.org/10.4992/PSYCHOLRES1954.17.119

Weiss, J. M. (1971). Effects of coping behavior in different warning signal conditions on stress pathology in rats. Journal of Comparative and Physiological Psychology, 77(1), 1-13. https://doi.org/10.1037/h0031582

Yun, S., Ahn, K., & Kim, H. (2011). Molecular analysis of alternative transcripts of CCDC94 gene in the brain tissues of rhesus monkey. Journal of Life Science, 21, 459-463. https://doi.org/10.5352/JLS.2011.21.3.459




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