A new way to measure bone movement without X-rays

Have you ever wondered how your bones move throughout your day? When we think about this, X-ray images immediately come to
our minds.
But how can we measure the bone movement of an animal that runs or jumps and interacts with its environment without using X-rays? Why is this important? Studying such free-roaming animals can give us unparalleled insight into their behavior and decisions, such as when they evade predation, seek mates, and raise offspring
.
While there have been many studies measuring animal behavior, research on the mechanisms by which to measure how they move has been lacking
.
But because activity in the central nervous system ultimately leads to decisions made through bodily actions, measuring these mechanisms and linking them to neural activity is critical
to gaining insight into brain function.

Analyzing the movement of individual bones without an X-ray machine is very challenging because the occlusion covering fur, skin, and soft tissue makes measuring bone movement very complicated
.
Recently, some advanced machine learning methods have been able to accurately measure the posture of animals and even changes in the facial expressions of animals; However, until now, none of the existing techniques have been able to track changes
in bone position and joint movement under the visible body surface.

Now the Department of Behavior and Brain Organization at the Max Planck Institute for Behavioral Neurobiology in Bonn, Germany, has developed a video-based method to 3D track
bones at the resolution of individual joints when not being tethered to their environment.
Their Anatomical Constraint Model (ACM) is based on an anatomical basal skeleton, inferring the kinematics
of the bones as animals move freely.
From this data, we can measure the moment-to-moment activity
inside the bones as animals jump, walk, stretch, and run.
This new method can be applied to a variety of furry species, such as mice and rats
of different sizes and ages.
To ensure that the data were correct, the researchers, in collaboration with colleagues from the Max Planck Institute for Biocybernetics and the Max Planck Institute for Intelligent Systems in Tübingen, scanned animals using MRI to compare the ACM model with the actual skeleton
.
"Our new method is relatively simple, doesn't require a tether, and uses an overhead camera
.
It solves many of the problems associated with tracking freely moving rodents, especially those covered in fur and covered with legs and feet
.
Jason Kerr, who conducted the study with Jakob Macke from Tübingen, said
.
The next step was to combine this method with synchronized recording of neurons in the brain, using a miniature head-mounted multiphoton microscope
developed by researchers at the Max Planck Institute for Behavioral Neurobiology.
This will allow us to accurately link neural activity to actual behavior, thus learning more about how the brain controls even complex behavior
.

The researchers will also apply their new method to measure the kinematics of other animals in a more natural environment and measure multiple interacting animals
simultaneously.
"With our new approach, on the one hand, we will further our understanding of how animals interact with their environment, and on the other hand, we want to gain knowledge of how animals interact with each other," says
Jason Kerr.