Andrea Green

• Université de Montréal

Many daily behaviors rely on estimates of our body's motion and orientation in space. Vestibular signals are essential for such estimates, but to contribute appropriately, two key computations are required. First, ambiguous motion information from otolith organs must be combined with spatially transformed rotational signals (e.g., from the canals)...

Accurate interaction with the environment relies on the integration of external information about the spatial layout of potential actions and knowledge of their costs and benefits. Previous studies have shown that when given a choice between voluntary reaching movements, humans tend to prefer actions with lower biomechanical costs. However, these s...

Many daily behaviors rely critically on estimates of our body's motion and orientation in space. Vestibular signals are essential for such estimates but to contribute appropriately two key sets of computations are required. First, ambiguous motion information from the otolith organs must be combined with spatially transformed rotational signals (e....

Studies of reach control with the body stationary have shown that proprioceptive and visual feedback signals contributing to rapid corrections during reaching are processed by neural circuits that incorporate knowledge about the physical properties of the limb (an "internal model"). However, among the most common spatial and mechanical perturbation...

Neurophysiological studies suggest that when decisions are made between concrete actions, the selection process involves a competition between potential action representations in the same sensorimotor structures involved in executing those actions. However, it is unclear how such models can explain situations, often encountered during natural behav...

Many daily behaviors rely critically on estimates of our body motion. Such estimates must be computed by combining neck proprioceptive signals with vestibular signals that have been transformed from a head- to a body-centered reference frame. Recent studies showed that deep cerebellar neurons in the rostral fastigial nucleus (rFN) reflect these com...

The motor system shows a remarkable capacity to generalize learned behavior to new contexts while simultaneously permitting learning of multiple and sometimes conflicting skills. To examine the influence of proprioceptive state on this capacity, we compared the effectiveness of changes in workspace location and limb orientation (horizontal vs. para...

We investigated whether target position relative to the body modifies the postural adjustments produced when reaching movements are perturbed by unexpected displacements of the support surface. Eleven healthy participants reached to a target located at their midline, acromion height and at 130 % their outstretched arm length. They stood on two forc...

To contribute appropriately to voluntary reaching during body motion, vestibular signals must be transformed from a head- to a body-centered reference frame. We quantitatively investigated the evidence for this transformation during online reach execution by using galvanic vestibular stimulation (GVS) to simulate rotation about a head-fixed, roughl...

Brain-computer interfaces (BCIs) extract signals from neural activity to control remote devices ranging from computer cursors to limb-like robots. They show great potential to help patients with severe motor deficits perform everyday tasks without the constant assistance of caregivers. Understanding the neural mechanisms by which subjects use BCI s...

Multisensory integration plays several important roles in the nervous system. One is to combine information from multiple complementary cues to improve stimulus detection and discrimination. Another is to resolve peripheral sensory ambiguities and create novel internal representations that do not exist at the level of individual sensors. Here we fo...

The nodulus and uvula (lobules X and IX of the vermis) receive mossy fibers from both vestibular afferents and vestibular nuclei neurons and are thought to play a role in spatial orientation. Their properties relate to a sensory ambiguity of the vestibular periphery: otolith afferents respond identically to translational (inertial) accelerations an...

The vestibular system is vital for motor control and spatial self-motion perception. Afferents from the otolith organs and the semicircular canals converge with optokinetic, somatosensory and motor-related signals in the vestibular nuclei, which are reciprocally interconnected with the vestibulocerebellar cortex and deep cerebellar nuclei. Here, we...

Do neurons in primary motor cortex encode the generative details of motor behavior, such as individual muscle activities, or do they encode high-level movement attributes? Resolving this question has proven difficult, in large part because of the sizeable uncertainty inherent in estimating or measuring the joint torques and muscle forces that under...

The ability to orient and navigate through the terrestrial environment represents a computational challenge common to all vertebrates. It arises because motion sensors in the inner ear, the otolith organs, and the semicircular canals transduce self-motion in an egocentric reference frame. As a result, vestibular afferent information reaching the br...

The arm and hand contain a few dozen muscles innervated by a few thousand spinal motor neurons, but tens of millions of neurons in several motor cortical areas contribute to their control. Because of this redundancy, it is theoretically possible for the response properties of single cortical neurons to change with time while the global cortical out...

To construct an appropriate motor command from signals that provide a representation of desired action, the nervous system must take into account the dynamic characteristics of the motor plant to be controlled. In the oculomotor system, signals specifying desired eye velocity are thought to be transformed into motor commands by an inverse dynamic m...

An accurate internal representation of our current motion and orientation in space is critical to navigate in the world and execute appropriate action. The force of gravity provides an allocentric frame of reference that defines one's motion relative to inertial (i.e., world-centered) space. However, movement in this environment also introduces par...

The identification of potential sites for plasticity in the VOR has thus far been limited mainly to the investigation of very specific signal components that are modified following a particular reflex-training paradigm (i.e., broadband reflex training). Yet, the richness of different behavioral observations associated with different training paradi...

Our inner ear is equipped with a set of linear accelerometers, the otolith organs, that sense the inertial accelerations experienced during self-motion. However, as Einstein pointed out nearly a century ago, this signal would by itself be insufficient to detect our real movement, because gravity, another form of linear acceleration, and self-motion...

The ability to navigate in the world and execute appropriate behavioral and motor responses depends critically on our capacity to construct an accurate internal representation of our current motion and orientation in space. Vestibular sensory signals are among those that may make an essential contribution to the construction of such 'internal model...

Under natural conditions, the vestibular and pursuit systems work synergistically to stabilize the visual scene during movement. How translational vestibular signals [translational vestibuloocular reflex (TVOR)] are processed in the premotor pathways for slow eye movements continues to remain a challenging question. To further our understanding of...

The ability to navigate in the world and execute appropriate behavioral responses depends critically on the contribution of the vestibular system to the detection of motion and spatial orientation. A complicating factor is that otolith afferents equivalently encode inertial and gravitational accelerations. Recent studies have demonstrated that the...

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 m...

The vestibulo-ocular reflex (VOR) comprises an outstanding system to perform studies that probe possible cerebellar roles in motor learning. Novel VOR gains can be induced (learned) by the wearing of minifying or magnifying lenses, and learning requires the presence of the cerebellum. Previously, it was shown that Purkinje cells change their head v...

The ability to simultaneously move in the world and maintain stable visual perception depends critically on the contribution of vestibulo-ocular reflexes (VORs) to gaze stabilization. It is traditionally believed that semicircular canal signals drive compensatory responses to rotational head disturbances (rotational VOR), whereas otolith signals co...

Rotational and translational vestibulo-ocular reflexes (RVOR and TrVOR) function to maintain stable binocular fixation during head movements. Despite similar functional roles, differences in behavioral, neuroanatomical, and sensory afferent properties suggest that the sensorimotor processing may be partially distinct for the RVOR and TrVOR. To inve...

A common goal of the translational vestibuloocular reflex (TVOR) and the rotational vestibuloocular reflex (RVOR) is to stabilize visual targets on the retinae during head movement. However, these reflexes differ significantly in their dynamic characteristics at both sensory and motor levels, implying a requirement for different central processing...

Vestibular adaptation can be induced optically or by chemical or physical injury to the vestibular apparatus or the brain stem. In searching for the sites or mechanisms of vestibular adaptation, neurophysiologists often rely on comparing central resting (background) activities and central modulations (sensitivity) during vestibular stimulation, bef...

We present an anatomically and neurophysiologically relevant mathematical model for visual-vestibular interaction which reproduces the short-term adaptive behavior of the vestibulo-ocular reflex (VOR) with target distance and eccentricity. Adaptive changes are shown to anticipate acquisition of a spatial goal, circumventing the delays associated wi...

Traditionally, the vestibulo-ocular reflex (VOR) has been considered a stereotyped ocular counterrotation response to head movement that stabilizes a visual image on the retinae. However, during natural head movements, the appropriate magnitudes and directions of compensatory ocular deviations depend on viewing context. Moment-to-moment adjustments...