Functional Organization of Human Balance Control as Basis for Rehabilitation Planning: The MCS Model

, Antonio Cesarani² and Guido Brugnoni³

(1)

“Don Carlo Gnocchi” Foundation, Milano, Italy

(2)

UOC Audiologia Dip. Scienze Cliniche e Comunità, Università degli Studi di Milano, Milano, Italy

(3)

Istituto Auxologico Italiano, Milano, Italy

Abstract

Vestibular and extra-vestibular reflexes interact in order to provide different functions that harmonically lead to finalistic and ergonomic behaviours that allow human beings to dynamically interact with other subjects and the environment. Derived abnormalities of these reflexes, functions or behaviours are represented by vertigo, dizziness and unsteadiness (VDU). In the mid-1940s, an English otolaryngologist, Sir Cawthorne, observed that some patients who experienced dizziness did better or recovered sooner when performing rapid head movements. In cooperation with a physiotherapist, Mr. Cooksey, he developed a regimen of exercises which, with some modifications, are nowadays still used. The Cawthorne–Cooksey (CC) protocol is based on the concepts of habituation and sensory substitution. We propose a rehabilitation approach to VDU based on a model of equilibrium system called MCS, acronym for mechanic, cybernetic and synergetic, as an evolution of the CC protocol.

In 1999, we proposed a model of equilibrium system called MCS [1]. MCS is the acronym for mechanic, cybernetic and synergetic. It is a model and not a theory. In fact, under an epistemological point of view, theory is a complex of logical argumentations that it is as valid as it is true. Model is a complex of logical argumentations that it is as valid as it is useful. In this way, we proposed a model aimed to the treatment of vertigo and dizziness, on the basis of neurophysiology of the vestibular system and movement control and the most recent knowledge about cognitive processing and motor learning.

As we stated in the Introduction, human equilibrium is a complex sensory–psychomotor function [2]: complex sensorial cues are processed into the vestibular nuclei and cerebellum, mainly, and, on the basis of emotional, psychological and volitional condition of the subjects, they provide adequate motor reflexes in order to interact with the environment. The vestibular system can be considered the dedicated neurophysiological system that subserves this complex sensory–psychomotor function.

In other words, vestibular and extra-vestibular reflexes interact in order to provide different functions that harmonically lead to finalistic and ergonomic behaviours that allow human beings to dynamically interact with other subjects and the environment.

Reflexes may be considered the basic elements of the human balance control. Thinking under a mechanic (M) point of view, balance results by the sum of these reflexes, the contemporary but distinct activation of some or all of the reflexes, according to the need: gaze, standing and walking. Reflexes involved in balance control can be subdivided into two groups:

Ocular reflexes: vestibulo-ocular reflex (VOR), optokinetic reflexes (OKR) and cervico-ocular reflexes (COR). These reflexes are aimed to the stabilization of the visual field.
Spinal reflexes: vestibulospinal reflexes (VSR), vestibulocollic reflexes (VCR), cervico-collic reflexes (CCR), cervicospinal reflexes (CSR) and stretch reflexes (SR). These reflexes are aimed at the maintenance of upright stance and maintenance of postural control during moving (walking, stepping, jumping, etc.).

Reflexes are activated by sensorial stimuli and act on muscles, such as the oculomotor, antigravity and dynamic muscles. The muscles arrange the different body segments or move different body long bones (arms and legs) acting through the joints. Under a mechanic point of view, also sensorial cues, muscles and joints have to be considered as basic elements. Thus, vertigo and dizziness rehabilitation has to start restoring basic element activity, that is to say, that the first phase of rehab can be considered a mechanic phase: simple vestibular stimulations, joint mobilizations, massages, muscle exercises, etc.

In neurophysiological organization each reflex is not always well distinguishable from others. Frequently peripheral cues, such as visual or labyrinthine inputs, convey on the same vestibular nuclei or the same reticular formation. In fact, Lackner [3] stated that, under natural conditions, during movement, it is not possible to activate only single peripheral input. He remembered [4, 5] that the so-called vestibular nuclei are real multisensorial relays. They are the true balance nuclei that act together with the cerebellum and reticular formations and the supratentorial structures until the parieto-temporal cortex (the so-called vestibular cortex). Norrè [6] proposed to distinguish two complex reflexes each controlled from different sensorial inputs but generally elaborated in the vestibular nuclei and cerebellum: the Balance Ocular Reflex (BOR) and the Balance Spinal Reflex (BSR).

BOR and BSR represent a higher level of physiological organization in which different reflexes dynamically interact in order to provide complex functions: oculomotor (BOR) and postural (BSR) functions. Cybernetic [7] helps in approaching this higher level of complexity. In other words, thinking under a cybernetic point of view means that all the structures, peripheral and central, that contribute to the BOR and BSR constitute a system. A system is a network of different structures interconnected to reach a common goal. In this case the goal is human balance control.

A system [8] is defined as any collection of components arranged and interconnected in a definite way and any collection of communicating materials and processes which together perform some function.

By this point of view, the labyrinths, eyes, vestibular nuclei, paravertebral receptors, antigravity extensor muscles, plantar receptors, etc. constitute a system controlling static and dynamic balance.

The behaviour of any system is determined by: