A rat’s guide to virtual reality
Testing rats in a virtual reality (VR) maze uncovers a specific neural mechanism behind navigation, offering an insight into the pathogenesis of neurodegenerative diseases.
In a recent study, senior author Mayank Mehta and his team from the University of California, Los Angeles (UCLA; CA, USA) monitored dorsal CA1 neuronal activity in the hippocampus of rats while the animals navigated a maze in VR. By developing our understanding of the underlying neural circuitry, this study paves the way for treating hippocampus dysfunction–related neurological disorders including Alzheimer’s, schizophrenia, and epilepsy.
“The hippocampus is one of the first regions to be affected in memory-based diseases like Alzheimer’s,” commented lead author Jason Moore (UCLA). “So it is crucial to understand its functionality, flexibility and limits.” To address these gaps in our understanding of the hippocampus, Mehta’s team sought to explain why people with damage to the hippocampus have difficulty with memory tasks as well as spatial tasks.
If you have ever used a VR headset for an extended period, for instance to play video games, you would likely have experienced how it can cause symptoms including dizziness, disorientation, and nausea. Whilst tiny VR headsets for rats would be adorable, the rats were tested in a more feasible and more comfortable setup for repeat experiments.
To accomplish this Mehta’s lab placed rats in a box with mirror projected images on the box’s floor and walls to simulate the VR maze around the rats. Inside the box was a small quiet spherical treadmill that the rats were placed on which would allow their movement in the desired direction. The rats were fixed in the same physical space so they would not run into the box’s walls and ruin their immersion in the VR maze.
Understanding Alzheimer’s disease: answering some frequently asked questions
Alzheimer’s disease is an age-related neurodegenerative disorder, named after the first doctor to identify the disease, Alois Alzheimer. What are the causes of Alzheimer’s? What is its pathology? Find the answers to these questions and so much more, HERE
The goal for the virtual maze runners was to run through the VR maze to find the reward zone with navigational performance measured in rewards per meter traveled. Four rats were implanted with tetrodes to measure their CA1 neuron activity throughout.
Since the test was conducted in a VR maze the rats only had visual cues that they could use to navigate without relying on sound or smell. This demanded the rat’s use of spatial reasoning to make it to the reward, by determining their location in relation to the virtual surroundings and their direction and distance to their prize.
Over several weeks of repeatedly testing the rats in the VR environment, researchers observed how neuronal responses changed as the rats learned to navigate the VR mazes. The CA1 neurons in the hippocampus encoded several aspects of the rat’s location: where it is in space, the angle of its body relative to its reward, and how far it has moved along its path.
“We found that in the virtual maze, the neurons carry very little information about the rat’s position,” explained Mehta (UCLA). “Instead, most neurons encode for other aspects of navigation, such as distance traveled and which direction the body is heading.”
The longer the rats spent in the VR maze, the more precisely and dependably their neurons remembered the navigation route, which the researchers attributed to a process mediated by the neuroreceptor NMDAR, known as Hebbian learning. This was confirmed by comparing the performance in the VR maze of six additional non-implanted rats before and after injecting them with NMDAR antagonists, which resulted in impaired performance compared with saline injection.
By replacing reality and transporting you somewhere else, VR is allowing many exciting applications for future research. Mehta’s team aims to apply this technique in both rats and humans testing to determine whether VR can be used for the early diagnosis of memory and learning disorders and evaluate treatment effectiveness.
