Changes in cerebral activation in individuals with and without visual vertigo during optic flow: A functional near-infrared spectroscopy study

Abstract

Background and purpose: Individuals with visual vertigo (VV) describe symptoms of dizziness, disorientation, and/or impaired balance in environments with conflicting visual and vestibular information or complex visual stimuli. Physical therapists often prescribe habituation exercises using optic flow to treat these symptoms, but it is not known how individuals with VV process the visual stimuli. The primary purpose of this study was to use functional near-infrared spectroscopy (fNIRS) to determine if individuals with VV have different cerebral activation during optic flow compared with control subjects.

Methods: Fifteen individuals (5 males and 10 females in each group) with VV seeking care for dizziness and 15 healthy controls (CON) stood in a virtual reality environment and viewed anterior-posterior optic flow. The support surface was either fixed or sway-referenced. Changes in cerebral activation were recorded using fNIRS during periods of optic flow relative to a stationary visual environment. Postural sway of the head and center of mass was recorded using an electromagnetic tracker.

Results: Compared with CON, the VV group displayed decreased activation in the bilateral middle frontal regions when viewing optic flow while standing on a fixed platform. Despite both groups having significantly increased activation in most regions while viewing optic flow on a sway-referenced surface, the VV group did not have as much of an increase in the right middle frontal region when viewing unpredictable optic flow in comparison with the CON group.

Discussion and conclusions: Individuals with VV produced a pattern of reduced middle frontal cerebral activation when viewing optic flow compared with CON. Decreased activation in the middle frontal regions of the cerebral cortex may represent an alteration in control over the normal reciprocal inhibitory visual-vestibular interaction in visually dependent individuals. Although preliminary, these findings add to a growing body of literature using functional brain imaging to explore changes in cerebral activation in individuals with complaints of dizziness, disorientation, and unsteadiness. Future studies in larger samples should explore if this decreased activation is modified following a rehabilitation regimen consisting of visual habituation exercises.

Keywords: Balance; Brain function; Brain imaging; Near-infrared spectroscopy; Neuroimaging.

Fig. 1

The participant was exposed to two types of anterior-posterior optic flow while standing in a three-screen wide field-of-view virtual reality environment.

Fig. 2

The participant wore a fNIRS head cap that consisted of 11 sources (red with capital letters A-K) and 20 detectors (blue with numbers 1–20) on the scalp, distributed between the left temporal (left), occipital (center), and right temporal (right) regions. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 3

Anterior-posterior (AP) head sway normalized path length (NPL) between stationary and optic flow periods for patients with visual vertigo and healthy controls. Error bars represent standard error.

Fig. 4

Anterior-posterior head sway normalized path length (NPL) during stationary (light blue) and optic flow (dark blue) visual stimulation periods during four testing conditions. Error bars represent standard error. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)