Researchers have discovered that bats possess a sophisticated internal navigation system, a kind of neural compass that allows them to orient themselves in three-dimensional space with remarkable precision. This finding, which builds upon decades of research into animal navigation, offers new insights into how mammalian brains, including our own, construct a sense of direction and place. The discovery of this 3D compass in the bat brain helps to explain their ability to perform complex aerial maneuvers in complete darkness without becoming disoriented.
This internal guidance system is comprised of specialized brain cells that function like a biological global positioning system. At least three types of cells work in concert: “place” cells, which create a mental map of the environment; “grid” cells, which provide a coordinate system for this map; and “head-direction” cells, which act as an internal compass, indicating the direction the animal is facing. While much of the foundational research on this system was conducted with rodents on flat surfaces, the new findings in bats reveal how this system is adapted for the complexities of flight and 3D navigation.
An Internal 3D Compass
The key to the bat’s navigational prowess lies in its “head-direction” cells, which are located in a part of the brain called the dorsal presubiculum, within the hippocampus. Researchers in Israel, led by Arseny Finkelstein at the Weizmann Institute of Science, conducted experiments with Egyptian fruit bats, using wireless devices to monitor their brain activity during both crawling and flight. The recordings revealed that the bat’s neural compass is not limited to a two-dimensional plane like a traditional magnetic compass. Instead, it encodes space in three dimensions.
The study identified different populations of neurons that were tuned to specific spatial orientations. Approximately 20% of these cells were sensitive to the bat’s pitch, or its up-and-down angle of movement. Another 10% of the cells responded to the bat’s roll, or its sideways tilt. A significant number of cells were attuned to a combination of these angles, effectively creating a comprehensive 3D representation of the bat’s orientation in space.
The Toroidal Model of Navigation
The researchers found that the activity of these head-direction cells corresponds to a toroidal, or donut-shaped, model of 3D space. As the bat moves and rotates, the neural activity shifts around this donut-shaped representation. This model is particularly well-suited to the bat’s typical movements, as they do not often roll their bodies to the side. Other animals that exhibit more rolling motions may have a more spherical neural compass. This toroidal system allows the bat to remain oriented even when performing complex maneuvers like landing upside down.
Building on Foundational Research
The discovery of the 3D neural compass in bats is the latest in a long line of research into the brain’s navigational abilities. In 1971, John O’Keefe discovered “place” cells in the hippocampus of rats, which fire when an animal is in a specific location, forming a mental map of its surroundings. This was followed in the mid-1980s by the identification of “head-direction” cells, which act as the brain’s internal compass. In 2005, May-Britt and Edvard Moser discovered “grid” cells, which provide a coordinate system for the mental map. These discoveries, which earned a Nobel Prize in 2014, laid the groundwork for understanding how mammals navigate their environment.
The Role of Memory in Navigation
Further research has revealed another layer of complexity in the bat’s navigational system, highlighting the crucial role of memory. Scientists have identified “vector neurons” in the hippocampus that allow bats to calculate their angle and distance to a specific target. In one experiment, researchers tracked the brain activity of Egyptian fruit bats as they flew towards a banana. They found that certain neurons fired more frequently as the bat approached the banana at the correct angle and distance.
To test the role of memory, the researchers then hid the banana behind an opaque curtain, which blocked both sonar signals and smell. The bats were still able to find the fruit, and the same vector neurons fired as they flew towards the hidden target. This indicates that these neurons are not simply reacting to immediate sensory input, but are guided by the bat’s memory of the banana’s location. This finding has implications for understanding human conditions such as Alzheimer’s disease, where damage to the hippocampus can lead to memory loss and disorientation.
Navigating into the Future
More recent studies have shown that the bat’s brain is not just focused on its present location, but also on where it is going. Neuroscientists at the University of California, Berkeley, have found that the activity of “place cells” in the hippocampus of flying Egyptian fruit bats is more strongly correlated with the bat’s future location than its current one. This suggests that the brain is not just creating a static map of the environment, but is actively plotting a trajectory through it.
This ability to project into the future, even by a fraction of a second, is crucial for fast-moving animals like bats. It allows them to anticipate upcoming obstacles and adjust their flight path accordingly. While it is not yet known if this future-oriented navigation is unique to bats or a more general feature of the mammalian brain, it opens up new avenues for understanding how we perceive and move through space and time.