When navigating an unfamiliar room in the dark, humans may fumble around to gauge their surroundings. In contrast, many animals, like mice, can move efficiently in darkness by using their whiskers to feel walls and obstacles. Fan Wang, a brain and cognitive sciences professor at MIT and a McGovern Institute for Brain Research investigator, has identified how neurons in a mouse’s brainstem utilize signals from its whiskers to calculate an object’s distance from its face.<\/p>\n
The research, published on June 25 in the journal Neuron, reveals critical brain circuitry that defines the space immediately around the body. The discovered circuit is part of the brain’s mechanism for creating an egocentric map, which helps determine the location of objects relative to oneself. Neuroscientists understand that different brain circuits are used for this internal mapping compared to those employed for mapping space using external landmarks.<\/p>\n
In their investigation, Wang and her team examined how the brain perceives the space closest to the body, known as peripersonal space. This area is essential for movement and interaction, as it helps individuals understand the spatial relationship of objects to their bodies. Mice serve as an ideal model for this research due to their whiskers, which act like built-in rulers as they explore their environment.<\/p>\n
The study aimed to determine whether the brain uses whisker signals to create a detailed internal representation of distance, beyond just “near” or “far.” Graduate student Wenxi Xiao and Research Scientist Kyle Severson observed neural activity in a brainstem region where tactile whisker signals are first processed. They investigated how neurons reacted when mice walked on a treadmill, brushing their whiskers against walls at varying distances.<\/p>\n
Some neurons in this region responded to whisker bending based on proximity to the face, creating a distance code. Others were tuned to specific distances, firing only when the wall was within a certain range. “Each of these neurons represents a specific distance,” Wang notes, likening them to tick marks on a ruler, collectively forming a “map code.”<\/p>\n
Wang’s team explored how the brain translates whisker proximity signals into an accurate map of object distances from the head. By using computational modeling and manipulating neural signals, they demonstrated how distances could be calculated by comparing sensory neuron inputs. Each brainstem neuron involved in the map code receives both excitatory and inhibitory inputs, allowing the brainstem to compare inputs and determine distance.<\/p>\n
Wang explains that this process of subtraction between inputs provides an intermediate value, offering a straightforward method to convert tactile input into a discrete distance representation. She emphasizes that although this body-centered spatial representation is crucial, it has not been extensively studied compared to allocentric mapping. Wang is keen to explore how the egocentric map code integrates with other brain systems to influence movement and behavior, hoping to inspire further research in this area.<\/p>\n