Double cards discovered in the brain

In the brain’s secondary motor cortex, researchers have discovered two distinct maps that play a crucial role in spatial planning and navigation. The research, led by Dr Jeffrey Erlich, group leader at UCL’s Sainsbury Wellcome Centre, offers a new approach to studying spatial planning in rodents and could have implications for understanding neurological disorders that affect spatial attention, such as stroke.

“We found that the premotor cortex uses a self-centered coordinate system for spatial planning, but it also encodes a world-centered map that is used to determine the body’s current position in the world. This self-centered and world-centered information is combined in individual neurons in a multiplicative manner, facilitating downstream disentanglement,” says Dr. Erlich, corresponding author of the study.

The study, published in the Journal of Neurosciencedescribes how the researchers designed a new task in rats that allowed them to differentiate between self-centered and world-centered reference frames. They recorded neural activity from a brain area known as the frontal orientation field (FOF) in the rats’ secondary motor cortex and used machine learning techniques to decode the information.

“Imagine being asked where the nearest coffee shop is. You might say, ‘Go forward and turn left’ (self-centered cues) or ‘Walk north, then east’ (world-centered cues). We want to understand how the brain transitions between these frames of reference and turns them into action,” says Dr. Erlich.

The researchers developed a task involving a wall with seven portholes. The rats were trained to place their noses in a starting porthole, after which a light appeared in another porthole, designating it as the target. The rats then had to wait for an auditory cue before moving their noses to the target porthole to receive a reward. This waiting period allowed the researchers to distinguish between planning and action in the brain.

“By adding the right amount of complexity to our task, we were able to have good experimental control over the times. This approach allowed us to distinguish between different dimensions of the representation,” says Dr. Erlich.

Some trials had different movement directions that led to the same target, and some had the same movement direction but led to different targets because they had different starting points. The researchers looked at neural activity during the period between the visual and auditory cues, to establish whether the brain was planning based on direction or final position, thus determining whether the FOF was using a self-centered or world-centered map.

“We were surprised to find a world-centric map in FOF, as this had never been reported before. We want to explore what this positional information is used for and under what circumstances it becomes functionally relevant,” concludes Dr. Erlich.

The team is currently investigating how these dual maps are used in tasks where instructions are given in world-centered coordinates. They are also investigating how the brain plans more complex movement sequences. The ultimate goal of this research is to better understand the fundamentals of spatial attention and how attention is linked to the planning and execution of orienting movements. This has potential implications for neurological disorders such as hemispatial neglect after stroke, where people cannot process or shift their attention to one part of the world.