IB Docs (2) Team
Animal research: Hormones
Animal research on hormones and behaviour
After completing this lesson, you should be able to:
- Evaluate two studies that show how animals are used to study the relationship between hormones and behaviour
- Explain the limitations of animal research
In this section, we will be revising some key concepts from the biological approach.
- Cortisol
- The HPA-axis and the human stress response
Exam tip
On your exam, the IB may ask you to discuss the value of animal models in "the study of hormones and/or pheromones." In order to answer this question, you need to do two things. First, you need to discuss the use of animal models. This is what we looked at in the first component of this module. Then, you need to be able to discuss an example. That example should look at animal or human research from the unit on hormones and/or pheromones. Regardless of which study you choose, it is important that there be a clearly identified behaviour in the explanation of the study.
Two studies that we have looked at in other parts of the course can be used to answer this question. We will also look at two new studies. For the exam, you should be able to discuss one behaviour - so, having one animal and one human study would be enough for this exam question.
Revising research
Before we begin looking at how to approach this question, let's take a few minutes to review the role of cortisol in memory consolidation and impairment.
Thinking about research
Before answering the questions below, take some time to re-read the following two studies about the effect of cortisol on memory.
1. Why did it make sense to use rats in Meaney's study?
Meaney needed to see how high levels of glucocorticoids in childhood affected the cognitive abilities of an ageing rat. Rats have a relatively short lifespan - between one and two years. In addition, as you heard Meaney say in the video, although rats can swim, they don't really like water. This made the water maze an appropriate way to measure spatial memory.
2. Although this is a study of hormones, it is also a study of the brain and behaviour - and a study of genetics. Explain how that is true.
The higher cortisol levels had an effect on the hippocampus - and this is the area of the brain that helps to encode and retrieve spatial memory. In addition, it seems that when the mother strokes her baby rats, this leads to gene expression for a gene that helps to regulate the stress response. Neglect meant that these genes were not expressed, leading to higher sustained levels of glucocorticoids. This is an example of epigenetics - the grooming process “turns on” the genes which help the young rat cope with stress - which then leads to stronger cognitive skills in old age.
3. How is Newcomer's study different from Meaney's study - besides the fact that used a human sample?
Unlike Meaney, the study is focused on semantic memory, not on spatial memory. In addition, Newcomer is actually able to regulate the amount of cortisol experienced in the different conditions. Meaney's study is also longitudinal. Newcomer's study is of a much shorter duration, demonstrating only the short-term effects of cortisol on memory. A longer-term study that could potentially lead to cognitive impairment in Newcomer's study would have been unethical.
4. What were the key findings in Newcomer's study?
The participants who received the highest level of cortisol also showed the worst performance in verbal declarative memory. It appears that high levels of cortisol interfered with the recall of the prose passage, whereas moderate levels of cortisol may have actually assisted in the recall of the passage. This makes sense as there are cortisol receptor sites on the hippocampus, which is responsible for the transfer of information from STM to LTM and vice versa.
Studying memory in animals
What's up with all the spatial memory studies? One of the great debates in psychology is what types of memory can be observed in animals. We know that animals are capable of procedural memory, but what about episodic memory? Episodic memory is the ability to recall and mentally re-experience specific episodes from one's personal past. Episodic memory does not just recall what happened, but when and where it happened. Psychologists have argued that animals do not have this type of memory, but more and more evidence seems to support that something similar exists - what researchers call "episodic-like memory."
Episodic memory is not only recalling the "what", "when", and "where" - but also showing flexibility - that is, the ability to use the information in a versatile way.
Watch the following video on "crow funerals." What does this tell us about episodic-like memory in crows?
The original study can be accessed here.
If you have done the health option on obesity, you will have studied Friedman's discovery of leptin. The discovery of leptin was possible through animal research - however, the ethics of the study are highly questionnable. If you would like to review this study - or are interested to know more - you can watch the video below.
This is a good example of where the animal model has not been a great predictor of human behaviour. Heymsfield et al (1999) carried out a study of a leptin substitute in human weight loss. Although leptin reduced the weight of obese mice by better regulating their hunger, the study by Heymsfield did not find the same results.
There study involved 54 people who were of normal weight and 73 who were obese. The participants were randomly assigned to inject themselves daily for a month with either leptin or, as a control, saltwater for four weeks. The leptin injections ranged for low to high levels of the hormone. In the second part of the study, only obese participants continued with the injections for another 20 weeks. The obese patients were also asked to follow a weight-loss diet.
Leptin had little effect except at the highest dose tested, when two out of eight patients lost about 35 pounds each in 24 weeks. The others lost much less, and one gained nearly 20 pounds. This incredible variance in the results challenges the rat as a good animal model for leptin as a regulator of eating behaviour in humans.
Exam question: Discuss the value of animal models in the study of hormones and/or pheromones and behaviour.
Criterion B. Knowledge and understanding
Marks are awarded here for showing an understanding of animal models.
You should explain what is meant by an animal model and why researchers choose to use animals in the study of hormones and behaviour. This would include - the similar physiology of animals and humans, the ethical considerations of research on humans, and the relatively easy access to participants.
Criterion C. Use of research
Marks are awarded here for both the choice of research and its explicit link to the question.
It is appropriate to have one study with animals and one with humans in order to show how the research in animals is confirmed in human research.
You should explicitly identify the behaviour that is being studied in each study.
Noting key differences between the animal and human studies will be important for critical thinking.
Criterion D. Critical thinking
Marks are awarded here for critical thinking with regard to the question.
Do not simply evaluate the studies. Critical thinking should focus on the value of animal models. The strengths and limitations of animal models should be clearly addressed.
Critically thinking about research
Psychologists have said that research on animals, such as Meaney's research on rats, may be used as a model for how we understand Alzheimer's disease. The role of stress in the deterioration of hippocampal cells may give us some insight into potential prevention and/or treatments for the disease. First, watch the short video below on the nature of Alzheimer's disease.
Then, write a response in the box below to the following question. Which study - Meany's or Newcomer's - do feel is the better model for Alzheimer's disease? What are your concerns, if any, about using animals to better understand the nature of the disease?
Continue to Animal research: Genetics
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