Animal Models & Major Depressive Disorder (DP IB Psychology): Revision Note

Animal models & MDD

• Around 29 million animals per year are used in experiments in the USA and the EU

• Animals are widely used in the biological approach, e.g., the use of pigeons, mice and rats in studies of drug tolerance and addiction

• The term ‘animal models’ refers to using animals to study human conditions such as MDD, e.g.,

  • Chronic mild stress (CMS) model

  • Learned helplessness model

• These models show that animals, like humans, can develop MDD-like symptoms

Value of animal models

• Ethical restrictions limit research on humans

• The use of animals as subjects allows testing that would be unethical or impractical with people

• There are some perceived similarities between human brains and animal brains

• Higher-order animals such as chimpanzees share 98.8% of their DNA with humans, making them valuable as models of human behaviour

Research support for animal models & MDD

The chronic mild stress model

• Research using this animal model has shown that animals exposed to repetitive stress display behavioural changes such as anhedonia

• It was also shown that chronic, uncontrollable stress contributes to the impairment of the brain’s reward system

•  In one study, mice were subjected to unpredictable mild stressors (e.g., rat odours, dirty straw in their cage) for 9 weeks

  • Scans showed changes in their prefrontal cortex and hippocampus, suggesting difficulties in decision-making and memory

    • Thus, chronic stress may alter brain function and lead to lack of capacity for enjoyment, which is a feature of MDD

The learned helplessness model

• Research using this animal model has shown that animals exposed to continued trauma (usually in the form of electric shocks to their electroplated cage floor) lose the power to leave the aversive situation even when escape is possible

• In one study, dogs were continually subjected to electric shocks

  • When these dogs were placed in a mixed cage with other dogs (who had not been shocked), they did not use an exit ramp to escape the cage, choosing to remain in the aversive environment

    • This research suggests that continued trauma may lead to the inability to act autonomously, which is a feature of MDD

Link to concepts

Responsibility

• Subjecting animals to aversive, harmful stimuli may be viewed as unethical, particularly if there are alternatives available

  • E.g., using fewer animals; using animals which are less sophisticated/sensitive (lower order); avoiding use of animals entirely)

Perspective

• Research using animals is generally the domain of the biological approach, although it does have some relevance to other approaches

  • E.g., learned helplessness research relates well to sociocultural topics such as domestic abuse in intimate relationships; research into memory has also used animal models (cognitive approach)