In a lab mouse version The Truman Showresearchers at Harvard Medical School built a small world for a new paper. A platform eight inches wide, raised 20 inches off the ground, stood in the center, covered with a mouse mat. A tall LED screen curved around, blank until a white, disorienting bar flashed to one side or the other.
Researchers have been looking for head direction cells in the mouse that act as an internal compass in the brains of humans, insects, animals and fish. Although not a proper magnetic compass, this neural compass acts as a relative compass based on landmarks instead of the Earth’s magnetic field. In humans, it involves several different areas of the brain, including the anterodorsal thalamus, the area targeted in the mouse study.
Internal compass
All neural compasses involve brain cells with preferred firing directions, meaning they fire continuously and release neurotransmitters when the head is pointed in a certain direction. But how do they know when this is happening?
First, there is visual data from the eyesaccording to a magazine article Hippocampus. Second, the brain relies on proprioceptive sensation, which tracks limb position.
Third, the compass takes into account the important vestibular system (inner ear), which uses fluid-filled loops to estimate head position.
Mice in the dark
IN mouse studyresearchers identified compass cells covering all 360 degrees and noticed some quirks in how they functioned.
On the one hand, a rotated visual cue that moved around the screen had a special power over the mice. After about two minutes, the mobile replica hijacked their compass and canceled other types of input, including the mice’s own movement.
When subjected to darkness, the mice’s compass wandered, sometimes aimlessly and sometimes in a pattern influenced by previous cues. Deprived of landmarks, the mice stuck to traces of the old, making them easier to revive.
Beyond the basic functioning of the compass, the researchers discovered an additional layer of network activity they called “amplification” that helped the system quickly change and sort out conflicting landmarks.
Finding our way
The human brain maintains a map of where the body is and uses many senses to do so, including sight, sound, the vestibular system, and proprioception. This allows us to look around the roomwe close our eyes and take five steps without bumping into anything.
The internal compass is critical to these “place” and “grid” cells and provides live information about where the person is pointing. Because we live in a three-dimensional world, the brain must also track a vertical axis, and this appears to occur in a part of the brain called the retrosplenial cortex. 2018 survey found.
But how do we make these cards? Scientists have long wondered whether observation is enough, whether one should simply gaze at a landscape or should walk on the ground. In 2022 concludes a study that rats can do the latter and learn cage structure simply by watching a friend.