Animal experimentation is contentious. Some argue they’re valuable and worthwhile, while others question their validity and ethicality. The fundamental issue with animal research is that animals cannot provide informed consent. Most animals are euthanised at the end of the experiment. This is especially true when studying the brain. But what if researchers could use brain scanners on live rats so they didn’t have to kill them? That’s what happened here.
This was not the first study to use fMRI on an animal. Previous studies had used fMRI on rats, mice, pigeons and dogs. However, in all these studies the animals were anaesthetised. Remember in an fMRI you have to be perfectly still or the scan won’t work. Imagine trying to get a pigeon to sit still in an fMRI! This is why they prefer to knock them unconscious and scan there brains. Of course, this is a big issue because the whole point of fMRI is to see what’s happening in brain while performing actual tasks. This study trained the mice to get comfortable with the fMRI so they could perform the scans while they were awake.
This study features in the chapter “Criminology” in IB Psychology: A Student’s Guide (2nd Ed.)
The harmless sound of a concierge bell can become a fear creating stimulus if it’s paired enough times with something scary.
To fully comprehend the study, you need to understand fear conditioning, a type of classical condition (also called Pavlovian conditioning). Fear conditioning is when someone (or some animal) is taught over time to be afraid of something. I always demonstrate in class using a student in the front row (let’s call him Adam), a long stick and a concierge bell. If I ring the bell, nothing happens. Adam just sits there looking at me. Now I ring the bell and poke him in the ribs with the stick (not really, we pretend). He flinches, naturally. I make a buzzing sound as if I’m electrocuting him, too. It would work better if the stick gave a little shock, but I can’t do that because, well, ethics. We do this repeatedly: ring bell and poke ribs, ring bell and poke ribs. If you do this enough times, when I ring the bell Adam will flinch even without the stick. The harmless bell (a once neutral stimulus) has become a conditioned stimulus because he has learned to be afraid of it. He has developed a conditioned response. In animal studies, like this mouse fMRI one, they use lights or sounds and electrified cages that shock the animals feet.
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Using fMRI to See Fear Conditioning in Mice (Brydges et al. 2013)
This was the first fMRI study on brain activity during learned behaviours in awake non-human animals. The researchers wanted to see how fear and early life stress affects the amygdala in awake rats.
Methods:
On Day 1 and Day 3 of the study, the rats were placed in a fake rat fMRI scanner. This was to get them used to the scanner so that they wouldn’t move during the real thing.
The researchers also used Pavlovian fear conditioning to train them to fear a blue light. They put the rats in special cages for 25 minutes and a blue light blinked for 10 seconds every five minutes. Each time the blue light stopped, the cage floor was electrified and the rats got a small shock. This conditioned them to fear the blue light because they learned when it stopped they would get a shock.
A second group of mice were used as a control. This group had a flashing light and foot shocks, but they were at random, different times. That means the mice in this group wouldn’t learn to associate the lights with the shock.
They also had a group of rats who had “early life stress” to see the effects on the brain during fear conditioning. At four weeks old, these rats were periodically dropped in buckets of water for 10 mins, held in plastic rat restraint tubes for 30 mins at a time or put in a “shock chamber” where they were randomly shocked over three minute intervals.
On Day 5, rats were placed in the fMRI and the same blue light was flashed. The researchers measured their brain activity while this happened.
This is an anaesthetised rat being placed in a special rat fMI (Image Research Gate Anne-Karine Bouzier-Sore – Permission pending).
Results:
The fMRI showed the mice’s amygdalae were activated when they saw the blue light. They also found that animals who suffered early life stress had greater activity in their amygdala than control mice.
Conclusions and Applications:
- This study supports earlier studies that shows the amygdala plays an important role in fear conditioned. Also, early life stress increases the activity in the amygdala during this process.
- The study also demonstrates how fMRI can be used to measure brain activity during learned behaviours like conditioned fear and provides an animal model for disorders like PTSD – early life stress changes amygdala response to conditioned fears.
- We can also use this study to explain the Three Rs of ethics in animal research: reuse, reduce and replace. Using fMRI meant the rats didn’t have to be euthanised. This means they can be reused in future research. The fMRI is also replacing other, more harmful methods, like removing or damaging amygdalae and then doing the fear conditioning task.
Critical Thinking Considerations
- A carefully controlled experiment like this can show causality. For example, early life stress causes increased amygdala activity during fear conditioning. However, do you think we could apply this to humans? Why or why not?
- Using fMRI is in one way more ethical than euthanising rats. Can you see any other ethical issues in this study? Do you think it’s responsible for the researchers to still use these kinds of methods?
References
- Harris, A. P., Lennen, R. J., Marshall, I., Jansen, M. A., Pernet, C. R., Brydges, N. M., Duguid, I. C., & Holmes, M. C. (2015). Imaging learned fear circuitry in awake mice using fMRI. The European journal of neuroscience, 42(5), 2125–2134. https://doi.org/10.1111/ejn.12939
Travis Dixon is an IB Psychology teacher, author, workshop leader, examiner and IA moderator.