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MDD: Biological explanations

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  • Module: Major Depressive Disorder/
  • MDD: Biological explanations

Biological etiologies of Major Depressive Disorder

The biological approach argues that both genetics and neurochemistry may explain the origin of Major Depressive Disorder.  For this component of the module, you will learn about both the genetic argument and the Serotonin hypothesis.  The biological approach is often considered a reductionist approach to understanding mental health - and it is the basis for medical treatment.

Key concepts

Before completing the module below, please read the section of the textbook called Biological approach to depression. When reading this section, please make note of the following important concepts:

text

Deepening our understanding

Watch the following video and then answer the questions below. Try to answer the questions by writing a response in your notebook before looking at the "correct" answer that is provided.  This will help you to remember the material after you have left this part of the module.

Questions

1.  What is the relationship between stress and depression with regard to the brain?

Overstimulation of the HPA axis leads to an overactive amygdalar response.  This leads to aggressive behaviours often seen in depressed patients.  In addition, stress has a negative effect on both the hippocampus and the prefrontal cortex [PFC]. This may account for the poor decisions often made by people with depression and the inability to process and retain information.

2. To what extent are mice a good animal model for human depression?

We cannot know if a mouse is depressed, but prolonged stress can lead to symptoms linked to human behaviour - e.g. anxiety, less social interaction, and less interest in normally pleasurable activities.  As a mouse's brain is similar to ours, this helps us to understand the effects of stress on the brain - for example, the effect of cortisol on neurogenesis in the hippocampus.

3. Discuss the use of anti-depressants to regulate one's levels of serotonin or norepinephrine.

Improvement in people and mice can take up to several weeks.  However, it appears that SSRIs can actually "reboot" the brain and leads to increased neurogenesis/neuroplasticity.

Thinking about theories

There are three key theories that are outlined in the textbook chapter: genetic vulnerability, the serotonin hypothesis, and the cortisol hypothesis (also known as the neurogenesis hypothesis). 

Fill in the following grid (either on the downloadable sheet or simply in your notebook) based on your reading. When thinking about the "assumptions" of each theory, think about what the researchers believe is true and how this serves as a building block for their theory.

For the supporting evidence, you should think about which studies clearly show the effect of biological factors on depression. You may want to also look at the presentation below.

Finally, when looking at limitations - think about TEACUP. This will be outlined below for you.

Biological explanations comparison grid

TEACUP and the Serotonin Hypothesis

One of the ways to evaluate a theory is to use TEACUP:

  • Is the theory empirically testable?
  • Is there evidence to support the theory?  What is the quality of that evidence?
  • Are there applications of the theory?  How good are those applications?
  • What are the constructs that are relevant to the theory?  How well can psychologists measure these constructs?
  • Is the theory unbiased?  That is, is there a cultural or gender bias?
  • Does the theory predict behaviour?  Or is the theory only explanatory?

Go through the following presentation and try to give an answer to each of those questions before looking at the other side.

Checking for understanding

By now, you should have a good understanding of the strengths and limitations of the Serotonin Hypothesis. Could you do the same thing now for either the theory of genetic vulnerability or the Cortisol Hypothesis?

In the box below, write the "evaluation paragraph" in an essay where you have been asked to "Evaluate one biological explanation of one disorder." The paragraph should not include descriptions of any research - assume that this has been done in other paragraphs in the essay.  Explain two or three evaluation points with regard to the theory - do not try to do all aspects of TEACUP!

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Continue to Cognitive explanations of MDD