Sensory Reweighting

Sensory Systems and Postural Control

Overview

  • Course: PT 603

  • Instructors: Prue Plummer, PhD, PT, MSCS & Ehsan Sinaei, MSc, PT

  • Institution: MGH Institute of Health Professions

Visual and Vestibular Information for Postural Control

Vestibular System

  • Function: The vestibular system is critical for maintaining the stability of vision during head movements. It plays a crucial role in postural control and the regulation of eye movements, allowing individuals to maintain orientation and balance in response to changes in head position.

  • Components: It consists of the semicircular canals and otolith organs, which detect angular and linear accelerations of the head, respectively. The system integrates this information to help the central nervous system (CNS) orient the body in space.

Postural Control

  • Definition: Postural control is defined as the ability to balance the body over its base of support. It functions as the sensor for gravity and contributes to overall stability during various activities.

  • Mechanism: The integration of vestibular and other sensory inputs is essential for the CNS to create a comprehensive understanding of body position and motion. This integration facilitates coordinated postural responses and adjustments during dynamic tasks and everyday movements, enhancing overall physical performance and safety.

Sensory Systems' Contributions to Position and Motion Sensing

Key Sensory Systems:

  1. Vestibular:

    • Purpose: Determines head movement and its position in relation to gravity.

    • Sensitivity: Most sensitive to fast head movements, particularly those processed through the semicircular canals (SCC). However, it has limitations in distinguishing between neck tilt and body flexion, which can lead to challenges in balance during complex movements.

  2. Visual:

    • Role: Provides crucial feedback regarding head position relative to the surrounding environment. It is particularly effective in conditions involving slow head movements and helps distinguish otolith signals related to gravity versus linear translations.

    • Challenges: Vision can be compromised in low-light conditions or obstructed environments, making it difficult to assess spatial orientation accurately.

  3. Somatosensory:

    • Function: Detects body position in relation to the support surface, as well as position among body parts. It plays an essential role in proprioception, allowing for awareness of limb and body position, which is vital for balance and coordinated movement.

Weighting Sensory Information

  • Dependence: The reliance on sensory information for postural alignment is significantly influenced by the availability of environmental information.

  • Normal Conditions:

    • Under stable support and adequate lighting conditions, the CNS effectively integrates information from all sensory modalities.

    • Typical Reliance:

      • 70% from somatosensory systems

      • 20% from vestibular systems


      • 10% from visual systemsThis relative dependence is referred to as weighting, which is vital for adaptive postural control strategies.

Effects of Incongruent Sensory Information

  • When sensory inputs become inconsistent—such as during rapid movements or when the support surface is unstable—the ability to maintain postural control and alignment can be severely affected.

  • Postural Instability: Discrepancies between sensory modalities can lead to postural instability and increase the risk of falls, particularly in individuals with compromised sensory function.

Changes in Sensory Weighting

  • Altered Conditions:

    • In response to variations in the support surface, whether compliant or uneven, the CNS adjusts sensory reliance, as follows:

      • 70% reliance on vestibular information

      • 20% reliance on visual information

      • 10% reliance on somatosensory information

    • CNS Compensation: The CNS compensates by increasing reliance on vestibular information in situations where support and visual inputs are compromised, ensuring stability and postural integrity.

Lab Group Activity

  • Explore how sensory systems are utilized across various activities and determine the relative reliance of these systems for:

    • Ice Skating

    • Walking on the Beach at Dusk

    • Shooting a Basketball

    • Playing the Piano

    • Standing on a Crowded Subway Train

    • Crossing a Stream by Stepping from Rock to Rock

This activity aims to deepen understanding of how different environments and tasks can alter sensory system contributions to postural control, promoting critical thinking about balance and movement in complex situations.