Article Vestibular Function, Sensory Integration, and Balance Anomalies: A Brief Literature Review Harold A. Solan, OD, MA1 John Shelley-Tremblay, PhD2 Steven Larson, O.D., PsyD1 1. State College of Optometry/SUNY 2. University of South Alabama ABSTRACT vestibular ocular refl ex (VOR), hearing impairment, The essence of this paper is to review selective research reading disability, visual function articles that relate to vestibular functioning, sensory INTRODUCTION integration, and balance anomalies in children and adults. As early as the pre-school level, an intact vestibular Studies that involve the role of the optometrist have been system contributes to sensory integration and the quite sparse. Special effort is made to distinguish between maturation of eye-movements that are required for effi cient developmental and acquired brain injuries (ABI). While reading and learning. The vestibular apparatus has been the former often are traced to pre-, peri- and postnatal identifi ed as the sensory organ that detects sensations disorders, traumatic brain injuries are the consequence concerned with an individual’s balance and equilibrium. of sports, motor vehicular and industrial accidents. The vestibulo-ocular refl ex (VOR) generates the rapid Delayed vestibular maturation correlates signifi cantly compensatory eye movements that support stable vision with sensory integration dysfunctions, slow vision while the head is in motion. That is, the VOR functions to processing, impaired hearing, and reading disability. prevent head movements from disturbing retinal images. Because of overlap in cortical systems, uncorrected Thus, the visual image is held steady on the retina allowing vestibular disorders may affect attention processes clear single vision.1, 2 During its course in the internal and result in cognitive dysfunctions. The clinical value auditory canal that it shares with the cochlear nerve, of several therapeutic procedures is discussed in the the vestibular nerve also may affect hearing through context of controlled studies. Successful rehabilitation efferent olivocochlear connections. Although either of may require treatment for vestibular and visual systems these complementary dependent variables, vision and since the former may have provided only a partial cure. hearing, may function independently, together, they Future sensorimotor research should stress Optometry’s dominate our primary learning processes role in this important aspect of vision care. The predominance of visual-vestibular control KEY WORDS of balance gives way to a somatosensory-vestibular vestibular function, sensory integration, balance, dependence by age three, but the transition to adult brain injury, rehabilitation, cognitive processing, like balance responses is not complete for all sensory conditions even by age six.3 Since vestibular responses Correspondence regarding this article can be emailed to hsolan@ are associated with eye movements and hearing, sunyopt.edu or sent to Dr. Harold A. Solan, State College of Optom- they contribute to visual and auditory processing. etry/SUNY 33 West 42nd Street New York, N.Y 10036. All statements Phylogenetically, the vestibular function appeared early; are the authors’ personal opinion and may not refl ect the opinions and ontogenetically, vestibular related tracts are one of of the College of Optometrists in Vision Development, Optometry and Vision Development or any institution or organization to which the earliest to myelinate in fetal life, at about twenty 4 they may be affi liated. Copyright 2007 College of Optometrists in weeks. In the normal healthy infant, the refl exes occur Vision Development. developmentally fi rst in the vestibular and auditory systems, but later in tactile and visual analyzers. There Solan HA, Shelley-Tremblay J, Larson S. Vestibular Function, remains a question, however, as to whether myelination Sensory Integration, and Balance Anomalies: A Brief Literature Review Optom Vis Dev 2007;38(1):13-17. Volume 38/Number 1/2007 13 serves as an index of maturation that contributes to children (M = 9.2 + 1.8) who were of normal intelligence, cognitive functioning in early postnatal life. and 15 LD participants (M = 9.4 + 1.5) with coordination Related Literature and clumsiness problems, but normal hearing. Twenty Clinical experience supports the notion that delayed of the 30 hearing impaired participants (67%) had vestibular maturation may be associated with sensory abnormal vestibulo-ocular refl exes (VOR). A majority integrative dysfunctions, slow vision processing, and of the 30 hearing-impaired children was affected, but delayed acquisition of reading skills in primary and 20% (3 of 15) of motor impaired LD children and 7% of middle grade elementary school children. According normals (4 of 54) also had depressed vestibular function to Ayres,5 among learning disabled (LD) children, as measured by VOR tests. These motor-impaired LD the presence of hearing impairment may compound children were at least two years delayed in two or more the assessment and interpretation of the relationship subjects. They were not diagnosed as minimal brain between vestibular disorders and gross motor-balance damaged (MBD), but could be classifi ed as experiencing activities such as rail-walking and one-foot standing. signifi cant neuro-maturational lags associated with Although the ubiquitous vestibular system primarily is a sensory-motor defi cits.11 somatosensory and motor system, sensation, digestion, In summary, two-thirds of hearing impaired subjects and state of mind may be affected. had signifi cant vestibular defi cits, and in addition twenty Malamut6 emphasizes the complexity of the vestibular percent of LD motor impaired children (as measured system. It involves interconnections with the inner- with the Bruininks-Oseretsky Test12) had peripheral ear, superior temporal cortex, insula and the temporal- vestibular disabilities. Predictably, the hearing impaired parietal junction within the cortex, and the postural and and the LD samples showed signifi cant diffi culties in extraocular muscle systems, all of which contribute organizing vestibular inputs.8,13 These results revealed to balance and vestibular refl exes. In part, because of a vestibular hypofunction in the hearing impaired group the overlap in cortical systems, uncorrected vestibular with accompanying balance defi cits. However, the disorders may ultimately affect attention processing study fails to focus on reciprocal interaction between the and result in cognitive dysfunctions.7,8 Smith, Zheng, visual and vestibular systems. Horii, and Darlington7 have reviewed extensive animal It has become increasingly clear that stimulation of and human studies. They provide evidence that, in one sensory system may affect other sensory systems addition to more commonly known defi cits in balance (See Figure 1). For example, Dieterich and Brandt13 and posture, problems with vestibular function can be reported that vestibular stimulation deactivates the seen to be associated with defi cits in object recognition, visual cortex, and visual stimulation deactivates the spatial navigation, learning and memory. Most severely vestibular cortex. Fortunately, the system as a whole can affected in these studies were tasks directly measuring withstand and adapt to signifi cant amounts of peripheral attention, such as the Digit Span test from the Weschler vestibular dysfunction. Often vestibular dysfunctions Intelligence Scale for Adults. These authors conclude appearing early are ameliorated in the course of normal that one mechanism by which vestibular disorders neuromaturation. adversely affect attention is the distracting infl uence of However, it is important to recognize that mental increased body sway and postural lean. Additionally, the development and learning are different phenomena psychological sequelae of vestibular disorders, which and each is infl uenced by distinct antecedents. Piaget may include anxiety and depression, could negatively conceptualized mental development as embryogenesis.14 affect the cognitive resources available for information processing. Sensory Input Central Processing Motor Output There are major differences between developmental vestibular Visual and traumatic acquired brain injuries Primary processor Eye movements Motor neurons (ABI). The latter, traumatic brain (Vestibular Vestibular Postural injuries (TBI), are more often nuclear complex) movements the consequence of sports, motor vehicular, and industrial accidents.9 Proprioceptive They include closed and penetrating head injuries as compared to a history Adaptive of prenatal and neonatal complications processor of pregnancy in children. (Cerebellum) Horak, Shumway-Cook, Crow, and Black10 reported signifi cant differences when they compared 54 normal children, ages 7–12 years (M = 9.2 + 2.3), with 30 hearing impaired Figure 1. Block diagram illustrating the organization of the vestibular system. 14 Optometry and Vision Development It is open-ended and is concerned with the development different balance related competencies. Furthermore, and maturation of the nervous system, e.g.: synaptogenesis, competency in one area does not indicate competence axonal branching, and dendritic elaboration. Each in another. Therefore, vestibular rehabilitation should element of learning occurs as a function of the include several activities to treat vertigo, balance individual’s total developmental framework. Therefore, problems, functional limitations, and disabilities caused embryogenesis is the neuroanatomical