Have you ever been inside an MRI scanner? I recently got in one and it was quite the experience. After a short introduction to the process, including a question about whether I was claustrophobic, they gave me earplugs – because it’s NOISY inside the machine, yes, in capitals – and then they proceeded to slide me into the scanner.

Once there, there’s not much for you to do other than stay still. You keep hearing a sort of white noise, digital beeps from time to time, and looking at your surroundings. As you don’t have a lot to do, it is normal for your mind to wander a lot. So, I could not stop myself from realizing how similar the donut-like chamber was to the spaceship depicted in 2001 a space odyssey, remembering a short show of a cute parrot riding a bike, and I even considered to start counting imaginary sheeps jumping around me, but decided not to, to avoid falling asleep.

It was easy to realize how challenging it could be if I were claustrophobic. Still, with all the instructions and clarifications of what to expect, that uncommon and slightly uncomfortable situation was quite bearable. But can you imagine how the experience would have felt without instructions or a good understanding of what was going on? I can tell you, I probably would have freaked out!

Scanning animal brains

We often see reports that include brain imaging techniques in humans. It might be more surprising that there are protocols for scanning animal brains, including those of non-human primates, birds, and rabbits.

As these techniques require animals to stay still for prolonged periods, the protocols often involve movement restriction or surgically implanted devices that can be physically attached to the experimental device. This may not come as a surprise, considering that we can’t simply instruct animals, explain to them what is about to happen, and politely request that they stay still.

The idea, however, leaves me feeling uneasy. Not only is it easy to see the high-stress situation animals go through, but it also brings methodological difficulties to the forefront: If we are interested in studying behavior and brain functions, stress can be immediately identified as a variable to control, and potential workarounds such as the use of sedative – while likely being helpful to control movement and/or artificially decrease stress – would themselves interfere with normal behavioral and brain processes.

With these considerations in mind, Camille Pluchot, Hans Adriaensen, Céline Parias, Didier Dubreuil, Cécile Arnould, Elodie Chaillou, and Scott A. Love developed a highly innovative protocol that allows capturing structural MRI acquisitions of sheep brains without anesthesia or physical restraint.

They describe it in Sheep (Ovis aries) training protocol for voluntary awake and unrestrained structural brain MRI acquisitions, recently published in Behavior Research Methods, one of the official journals of the Psychonomic Society.

Snacks and cuddles

The authors developed a training protocol in two phases. One where the sheep trained in an environment using a mock MRI scanner, and a second one interacting with the real equipment.

The protocol was based on positive reinforcement, such as using food rewards, verbal encouragement, cuddling, and stroking. The interest was leveraging a positive human-animal relationship and voluntary cooperation of the animals. As such, the sheep could always move freely, were never forcefully attached to the experimental devices, and could leave the training session at any time.

In short, it is possible to shape very complex behaviors by reinforcing successive behavioral approximations to the desired one. In a similar way to our biking parrot from the introduction, this allows the gradual training of sheep to participate in the MRI scanning protocol voluntarily.

In the first phase, the sheep gradually developed important behavioral components that would allow them to ultimately take part in the real study. These included climbing a ramp leading to the custom-made mock MRI table, staying still while it moved back and forth, and staying motionless. As they progressed in their training, the authors also played MRI sounds through Bluetooth speakers while the sheep performed the desired behaviors (to get them accustomed to the sounds they could expect in the real environment).

Below, you can see Ted and Léonard —two of the adorable sheep of the study—training for their mission in the mock MRI equipment and the number of training sessions it took them to complete the first training phase.

In the second training phase, sheep were taught to walk towards a waiting pen beside the MRI room and perform similar behaviors as in the mock experimental setup. They also needed to adapt to additional conditions in the new environment, such as lighting, sounds, a scanning table that moved up and down, and to accept wearing headphones to protect their hearing from the much more intense sounds in the real scanner.

Below, you can see Brook and Ted—wearing white wool suits—training for their mission in the real MRI setup along with their trainers—wearing blue protective suits—and the number of sessions it took them to complete the second training phase successfully.

You can see two short videos of the training protocol here (heads-up, the sound of the real equipment is loud!).

A clear picture of the next steps

Success in the second phase of training was defined as a correctly captured MRI structural scan of the sheep brain without a need for anesthesia or restraint. Below, you can compare the brain scans of our friends Brook, Ted, and Léonard, as well as their wooly friends who successfully completed the training at the time of writing the article. As you can see, the results are comparable to scans under anesthetized conditions.

This protocol demonstrates that it is possible to train sheep to take part in MRI imaging studies, opening the possibility to go beyond structural imaging protocols in the future and perform scans during cognitive experiments. In the words of the authors:

“The idea of a sheep lying motionless in an MRI scanner while it makes 100 dB noise does sound like a crazy idea. But if you think about it, it’s also a little crazy that humans and dogs are willing to do it – so why not sheep? We thought that the benefits to the welfare of the sheep and to science outweighed the cost of trying. And now, we have the proof-of-concept that sheep can voluntarily participate in an MRI experiment. This work will serve as a springboard for future welfare-friendly animal cognitive neuroimaging.”

Psychonomic Society’s article featured in this post

Pluchot, C., Adriaensen, H., Parias, C., Dubreuil, D., Arnould, C., Chaillou, E. & Love, S.A. (2024) Sheep (Ovis aries) training protocol for voluntary awake and unrestrained structural brain MRI acquisitions. Behavior Research Methods. https://doi.org/10.3758/s13428-024-02449-6