Implementation of a Central Sensorimotor Integration Test for Characterization of Human Balance Control During Stance

Abstract

Balance during stance is regulated by active control mechanisms that continuously estimate body motion, via a “sensory integration” mechanism, and generate corrective actions, via a “sensory-to-motor transformation” mechanism. The balance control system can be modeled as a closed-loop feedback control system for which appropriate system identification methods are available to separately quantify the sensory integration and sensory-to-motor components of the system. A detailed, functionally meaningful characterization of balance control mechanisms has potential to improve clinical assessment and to provide useful tools for answering clinical research questions. However, many researchers and clinicians do not have the background to develop systems and methods appropriate for performing identification of balance control mechanisms. The purpose of this report is to provide detailed information on how to perform what we refer to as “central sensorimotor integration” (CSMI) tests on a commercially available balance test device (SMART EquiTest CRS, Natus Medical Inc, Seattle WA) and then to appropriately analyze and interpret results obtained from these tests. We describe methods to (1) generate pseudorandom stimuli that apply cyclically-repeated rotations of the stance surface and/or visual surround (2) measure and calibrate center-of-mass (CoM) body sway, (3) calculate frequency response functions (FRFs) that quantify the dynamic characteristics of stimulus-evoked CoM sway, (4) estimate balance control parameters that quantify sensory integration by measuring the relative contribution of different sensory systems to balance control (i.e., sensory weights), and (5) estimate balance control parameters that quantify sensory-to-motor transformation properties (i.e., feedback time delay and neural controller stiffness and damping parameters). Additionally, we present CSMI test results from 40 subjects (age range 21–59 years) with normal sensory function, 2 subjects with results illustrating deviations from normal balance function, and we summarize results from previous studies in subjects with vestibular deficits. A bootstrap analysis was used to characterize confidence limits on parameters from CSMI tests and to determine how test duration affected the confidence with which parameters can be measured. Finally, example results are presented that illustrate how various sensory and central balance deficits are revealed by CSMI testing.

Evaluating Sensory Acuity as a Marker of Balance Dysfunction After a Traumatic Brain Injury: A Psychophysical Approach

“…Sensory acuity directly relates to perceptual mechanisms and impairment to sensory afferents as well as their integration after TBI could significantly contribute to impaired sensory acuity and balance dysfunction. Limited research specifically reports objective quantification of impairments to sensory integration after TBI (Peterka et al, 2018) and no research thus far has investigated sensory acuity in the individuals with TBI. This investigation presents an objective measure of sensory acuity in terms of PPT which goes beyond the biomechanical and functional markers of balance dysfunction and it is related to the process of sensory integration.…”

“…Although the peripheral system may or may not be impaired as a secondary consequence of the same event, damage to the brain could result in impaired central motor processes such as intention to act, motor planning, and automatic postural response mechanisms (Allison, 1999). Further, impaired sensory integration, a central process, is postulated as one of the sources for imbalance after TBI (Sosnoff et al, 2011;Fino et al, 2017;Peterka et al, 2018). The body-position awareness, i.e., the detection of body-sway, is a fundamental necessity to maintain static and dynamic balance during activities of daily living (Fitzpatrick and McCloskey, 1994) and it is achieved by an accurate perception of the body's interaction with the surrounding environment.…”

“…Further, in the domain of perception and balance, sensory acuity, i.e., the ability to detect body-sway during external perturbations (Fitzpatrick and McCloskey, 1994;Richerson et al, 2003), could stem from impaired sensory integration. Limited research specifically reports objective quantification of impairments to sensory integration after TBI (Peterka et al, 2018) and no research thus far has investigated sensory acuity in the individuals with TBI. An objective assessment of the sensory acuity, i.e., the ability to perceive external perturbations, is necessary to accurately detect, quantify, and treat sensory integration deficits that could lead to poor detection of body sway and imbalance in dynamic environment.…”

Reductions in body sway responses to a rhythmic support surface tilt perturbation can be caused by other mechanisms than prediction

“…A detailed description of the analysis of the body sway responses to the tilt stimuli with pseudo-random ternary sequences can be found elsewhere (Peterka 2002;Peterka et al 2018). In brief, the first cycle of pseudo-random responses was discarded to avoid transient responses.…”

Neurophysiological mechanisms, clinical features and treatment of statodynamic disorders

“…Ранее существовавшее представление о наличии изолированной системы статодинамического контроля, функционирующей на основе ряда рефлексов, в настоящее время признано некорректным [8,9]. Полагают, что поддержание равновесия является сложным моторным навыком, не имеющим какого-либо локализованного центра в головном мозге и реализуемым при взаимодействии множества сенсомоторных процессов [10,11]. В целом статодинамический контроль может быть определен как способность управлять общим центром массы (ОЦМ) тела в пределах базы поддержки его опоры c целью предотвращения падения или потери равновесия в статическом и динамическом положениях.…”