Summary: Neurons in the ventral intraparietal (VIP) area of the brain can flexibly switch the coordinate system they use to represent object motion. This adaptive coding allows the same neural population to represent motion relative to the head or relative to the world depending on the task, a finding that may inform future neural prosthetics and therapies for disorders that affect sensory integration.
Source: University of Rochester
How the brain represents motion across different reference frames
Our brains use different reference frames, or coordinate systems, to represent where things are and how they move. These coordinate systems are chosen to make certain tasks easier. For example, latitude and longitude are useful for locating a fixed address on Earth, while a sun-centered coordinate system would be impractical for that purpose because positions would shift with the planet’s rotation. In the same way, the brain must select and switch between reference frames that are appropriate for perception and action.
Sensory signals arrive encoded in different coordinates: visual information is first encoded relative to the eyes (eye-centered), and sounds are initially anchored to the head (head-centered). To form a unified perception of a scene and to guide behavior—such as reaching, catching, or navigating—the brain needs mechanisms to combine and transform these different representations. A central question is whether the neurons that encode spatial and motion signals are fixed to a single reference frame or can change depending on what the task requires.
In research published in Nature Neuroscience, neuroscientists at the University of Rochester, including Gregory C. DeAngelis, examined how neurons represent object motion while an observer is also moving. They asked whether neurons retain a single, fixed reference frame or whether they flexibly code motion in head-centered or world-centered coordinates depending on the task.
Are neurons fixed or flexible?
Consider playing soccer as an illustration. If you are running and you want to head the ball, your brain must compute the ball’s trajectory relative to your head so you can intercept it—this is a head-centered problem. If, instead, you are tracking whether a teammate’s kick is on target for the goal, you must judge the ball’s motion relative to the goal, which is fixed in world-centered coordinates. Successful behavior requires the brain to represent motion in the coordinate system that matches the goal of the task.
The researchers trained animals to report object motion using either head-centered or world-centered coordinates and to switch between these reference frames from trial to trial in response to cues. They recorded neural activity from two brain areas while the subjects performed the task. The most striking result came from the ventral intraparietal area (VIP), a region in the parietal lobe that integrates visual, auditory, and vestibular inputs.
Neurons in VIP did not remain tied to a single, fixed reference frame. Instead, their responses shifted depending on the instruction: the same population of VIP neurons represented object motion in head-centered coordinates when the task demanded judgments relative to the head, and represented motion in world-centered coordinates when the task required judgments relative to the world. In short, VIP neurons flexibly switched their coding to match the task’s reference frame.
This flexible coding simplifies downstream readout: downstream circuits can extract the needed information for either task from the same neural population rather than routing signals from distinct, fixed-frame neurons. By contrast, recordings from another tested region, the lateral portion of the medial superior temporal area, showed responses that primarily reflected head-centered motion, indicating regional differences in how reference frames are represented across the brain.
“This is the first demonstration that neural representations of spatial information can change according to task instructions,” says Gregory DeAngelis. The finding reveals how a single population of neurons can support multiple behaviors by dynamically reconfiguring its reference frame.
Potential applications: neural prosthetics and clinical relevance
Understanding where flexible representations exist in the brain could guide the development of neural prosthetics and brain–machine interfaces. For devices that must interpret motion-related signals—for example, to control a robotic limb or a vehicle—tapping into signals from brain areas that flexibly represent object motion, such as VIP, could allow more versatile and robust control across different behavioral contexts.
Although this particular study does not directly target a clinical disorder, the underlying capacity to combine sensory cues and infer their causes—called causal inference—is known to be impaired in conditions such as autism and schizophrenia. The researchers note that ongoing and future work will investigate the neural basis of causal inference and how interactions between self-motion and object motion are represented, which could illuminate mechanisms relevant to these conditions.
About this research
Original research article: “Flexible coding of object motion in multiple reference frames by parietal cortex neurons.” Authors: Ryo Sasaki, Akiyuki Anzai, Dora E. Angelaki & Gregory C. DeAngelis. Published in Nature Neuroscience. DOI: 10.1038/s41593-020-0656-0.
Institutional contact: University of Rochester. Media contact listed as Lindsey Valich – University of Rochester. Image adapted from the University of Rochester news release.
Abstract (summary)
Neurons encode spatial information in a variety of reference frames, but it has been unclear whether neural reference frames can shift with task demands and whether such shifts can explain behavior. This study examined how parietal neurons represent the direction of a moving object while subjects alternated trial-by-trial between reporting object direction in head-centered and world-centered coordinates. Computing object motion in world coordinates requires integrating self-motion information, whereas judging motion in head coordinates does not. Neural activity in the ventral intraparietal area is modulated by the instructed reference frame: population responses represent object direction in either head- or world-centered coordinates depending on the task. In contrast, neurons in the lateral medial superior temporal area primarily represent object motion in head coordinates. These results show that neural representations of object motion can flexibly change with behavioral demands.