The Clinical Significance of the Failure to Perceive Vertigo in the Postcaloric Period Despite a Robust Caloric Response

Vestibular Agnosia: Toward a Better Understanding of Its Mechanisms

Background/Objectives: Vestibular agnosia is characterized by a reduced or absent self-motion perception while demonstrating the presence of normal peripheral vestibular function following stimulation. This condition has previously been reported by previous authors in different populations and more recently in traumatic brain injury patients. However, the underlying mechanisms responsible for vestibular agnosia remain a matter of debate. The objective of this manuscript is to review and compare the behavioral and neuroanatomical findings in populations where vestibular agnosia has been demonstrated to better understand the underlying mechanism. Methods: A review of the literature was conducted using four databases: Medline, Embase, Google Scholar, and PubMed. A normal vestibulo-ocular reflex function with an impaired self-motion perception following vestibular stimulation represented the inclusion criteria used. Results: Behavioral data reviewed in the studies revealed a clear association with postural instability. However, no consensus can be drawn from neuroanatomical data due to variability in brain impairments in those populations even though impairments in the parietal cortex are often reported. Conclusions: In general, behavioral data and neuroanatomical data regarding vestibular agnosia have been poorly documented throughout the literature. However, vestibular agnosia can be observed in different populations and is present in concomitant postural control deficits, an important predictor of falls. Finally, even though the parietal cortex has been associated with vestibular agnosia, future studies are required to adequately identify the underlying mechanism. Indeed, the parietal cortex could be part of a larger network mediating vestibular agnosia. This review proposes various methods that future studies should use to overcome the present limitations.

Balance recovery and its link to vestibular agnosia in traumatic brain injury: a longitudinal behavioural and neuro-imaging study

BACKGROUND

Vestibular dysfunction causing imbalance affects c. 80% of acute hospitalized traumatic brain injury (TBI) cases. Poor balance recovery is linked to worse return-to-work rates and reduced longevity. We previously showed that white matter network disruption, particularly of right inferior longitudinal fasciculus, mediates the overlap between imbalance and impaired vestibular perception of self-motion (i.e., vestibular agnosia) in acute hospitalized TBI. However, there are no prior reports tracking the acute-longitudinal trajectory of objectively measured vestibular function for hospitalized TBI patients. We hypothesized that recovery of vestibular agnosia and imbalance is linked and mediated by overlapping brain networks.

METHODS

We screened 918 acute major trauma in-patients, assessed 146, recruited 39 acutely, and retested 34 at 6 months. Inclusion criteria were 18-65-year-old adults hospitalized for TBI with laboratory-confirmed preserved peripheral vestibular function. Benign paroxysmal positional vertigo and migraine were treated prior to testing. Vestibular agnosia was quantified by participants' ability to perceive whole-body yaw plane rotations via an automated rotating-chair algorithm. Subjective symptoms of imbalance (via questionnaires) and objective imbalance (via posturography) were also assessed.

RESULTS

Acute vestibular agnosia predicted poor balance recovery at 6 months. Recovery of vestibular agnosia and linked imbalance was mediated by bihemispheric fronto-posterior cortical circuits. Recovery of subjective symptoms of imbalance and objective imbalance were not correlated.

CONCLUSION

Vestibular agnosia mediates balance recovery post-TBI. The link between subjective dizziness and brain injury recovery, although important, is unclear. Therapeutic trials of vestibular recovery post-TBI should target enhancing bi-hemispheric connectivity and linked objective clinical measures (e.g., posturography).