Neurons compute internal models of the physical laws of motion

Abstract

A critical step in self-motion perception and spatial awareness is the integration of motion cues from multiple sensory organs that individually do not provide an accurate representation of the physical world. One of the best-studied sensory ambiguities is found in visual processing, and arises because of the inherent uncertainty in detecting the motion direction of an untextured contour moving within a small aperture. A similar sensory ambiguity arises in identifying the actual motion associated with linear accelerations sensed by the otolith organs in the inner ear. These internal linear accelerometers respond identically during translational motion (for example, running forward) and gravitational accelerations experienced as we reorient the head relative to gravity (that is, head tilt). Using new stimulus combinations, we identify here cerebellar and brainstem motion-sensitive neurons that compute a solution to the inertial motion detection problem. We show that the firing rates of these populations of neurons reflect the computations necessary to construct an internal model representation of the physical equations of motion.

Activity of pursuit neurons in the caudal part of the frontal eye fields during static roll-tilt

“…Because the majority of FEF pursuit neurons receive otolith inputs induced by horizontal whole-body translation , and because roll-tilt also induces linear acceleration towards the tilted direction (e.g., Angelaki et al 2004), we expected that FEF neurons should also respond to roll-tilt. A possible explanation for our negative result is that, during static whole-body roll-tilt, sensitivity of FEF pursuit neurons to linear acceleration is reduced.…”

Gravity orientation tuning in macaque anterior thalamus

“…We assessed how much G and dG contribute to a cell’s firing rate by computing partial correlation coefficients 1 . Cells were classified as either G-tuned or dG-tuned based upon whether R 2 G|dG or R 2 dG|G was significantly higher than the other using a bootstrap analysis 2,3 , or as G+dG cells if neither was significantly higher.…”

“…Gravity is sensed by the otolith organs of the inner ear, but gravity and inertial accelerations must be differentiated, and this is achieved by a distributed brainstem/cerebellar circuit 1–4 using an internal model of the physical laws of nature 5–7 . We 7 have hypothesized that gravity provides a global allocentric reference for spatial orientation.…”

L’adaptation optimale du mouvement humain au milieu gravitaire

“…L'étude du mouvement humain permet la caractérisation de ces processus silencieux et inaccessibles. Après deux décennies de recherche sur le mouvement, émerge la théorie computationnelle du contrôle moteur qui permet d'unifier une grande variété de résultats obtenus empiriquement [ Le cas de l'adaptation du mouvement au milieu gravitaire Grâce à de multiples études de neurophysiologie réalisées chez le macaque [2] et chez l'homme [3], un consensus sur l'existence d'un modèle interne de la gravité terrestre dans le cerveau des primates a été trouvé. D'après ce modèle, il est possible de prévoir l'effet permanent de la gravité terrestre sur les mondes animé et inanimé, par exemple la chute d'objets ou la perte d'équilibre.…”