The sense and control of standing balance in the presence of motor noise.

This study aimed to characterize motor noise in human standing balance and uncover mechanisms that enable the nervous system to robustly sense and control upright posture despite this variability. We conducted three experiments using a robotic balance simulator. First, we quantified the natural variability of ankle torques, revealing that torque variability was stable within preferred postures and increased only at more extreme orientations.

Age-related impairments and influence of visual feedback when learning to stand with unexpected sensorimotor delays.

Background: While standing upright, the brain must accurately accommodate for delays between sensory feedback and self-generated motor commands. Natural aging may limit adaptation to sensorimotor delays due to age-related decline in sensory acuity, neuromuscular capacity and cognitive function. This study examined balance learning in young and older adults as they stood with robot-induced sensorimotor delays.

Unperceived motor actions of the balance system interfere with the causal attribution of self-motion.

The instability of human bipedalism demands that the brain accurately senses balancing self-motion and determines whether movements originate from self-generated actions or external disturbances. Here, we challenge the longstanding notion that this process relies on a single representation of the body and world to accurately perceive postural orientation and organize motor responses to control balance self-motion. Instead, we find that the conscious sense of balance can be distorted by the corrective control of upright standing.

Neural Mechanisms Underlying High-Frequency Vestibulocollic Reflexes In Humans And Monkeys.

The vestibulocollic reflex is a compensatory response that stabilizes the head in space. During everyday activities, this stabilizing response is evoked by head movements that typically span frequencies from 0 to 30 Hz. Transient head impacts, however, can elicit head movements with frequency content up to 300-400 Hz, raising the question whether vestibular pathways contribute to head stabilization at such high frequencies.

Sensorimotor Manipulations of the Balance Control Loop-Beyond Imposed External Perturbations.

Standing balance relies on the integration of multiple sensory inputs to generate the motor commands required to stand. Mechanical and sensory perturbations elicit compensatory postural responses that are interpreted as a window into the sensorimotor processing involved in balance control. Popular methods involve imposed external perturbations that disrupt the control of quiet stance.

Vestibular-Evoked Responses Indicate a Functional Role for Intrinsic Foot Muscles During Standing Balance.

Maintaining standing balance involves multisensory processing and integration to produce dynamic motor responses. Electrical vestibular stimulation (EVS) delivered over the mastoid processes can be used to explore the vestibular control of balance. The purpose of this study was to determine whether intrinsic foot muscles exhibit vestibular-evoked balance responses and to characterize the traits associated with these responses.

The internal representation of head orientation differs for conscious perception and balance control.

Key Points: We tested perceived head-on-feet orientation and the direction of vestibular-evoked balance responses in passively and actively held head-turned postures. The direction of vestibular-evoked balance responses was not aligned with perceived head-on-feet orientation while maintaining prolonged passively held head-turned postures. Furthermore, static visual cues of head-on-feet orientation did not update the estimate of head posture for the balance controller.

Gain and phase of perceived virtual rotation evoked by electrical vestibular stimuli.

Galvanic vestibular stimulation (GVS) evokes a perception of rotation; however, very few quantitative data exist on the matter. We performed psychophysical experiments on virtual rotations experienced when binaural bipolar electrical stimulation is applied over the mastoids. We also performed analogous real whole body yaw rotation experiments, allowing us to compare the frequency response of vestibular perception with (real) and without (virtual) natural mechanical stimulation of the semicircular canals.