Hippocampal volume in patients with bilateral and unilateral peripheral vestibular dysfunction.

Previous studies have found that peripheral vestibular dysfunction is associated with altered volumes in different brain structures, especially in the hippocampus. However, published evidence is conflicting. Based on previous findings, we compared hippocampal volume, as well as supramarginal, superior temporal, and postcentral gyrus in a sample of 55 patients with different conditions of peripheral vestibular dysfunction (bilateral, chronic unilateral, acute unilateral) to 39 age- and sex-matched healthy controls. In addition, we explored deviations in gray-matter volumes in hippocampal subfields. We also analysed correlations between morphometric data and visuo-spatial performance. Patients with vestibular dysfunction did not differ in total hippocampal volume from healthy controls. However, a reduced volume in the right presubiculum of the hippocampus and the left supramarginal gyrus was observed in patients with chronic and acute unilateral vestibular dysfunction, but not in patients with bilateral vestibular dysfunction. No association of altered volumes with visuo-spatial performance was found. An asymmetric vestibular input due to unilateral vestibular dysfunction might lead to reduced central brain volumes that are involved in vestibular processing

Executive functions in patients with bilateral and unilateral peripheral vestibular dysfunction.

Previous research suggests that patients with peripheral vestibular dysfunction (PVD) suffer from nonspatial cognitive problems, including executive impairments. However, previous studies that assessed executive functions are conflicting, limited to single executive components, and assessments are confounded by other cognitive functions. We compared performance in a comprehensive executive test battery in a large sample of 83 patients with several conditions of PVD (34 bilateral, 29 chronic unilateral, 20 acute unilateral) to healthy controls who were pairwise matched to patients regarding age, sex, and education. We assessed basic and complex executive functions with validated neuropsychological tests. Patients with bilateral PVD performed worse than controls in verbal initiation and working memory span, while other executive functions were preserved. Patients with chronic unilateral PVD had equal executive performance as controls. Patients with acute unilateral PVD performed worse than controls in the exact same tests as patients with bilateral PVD (verbal initiation, working memory span); however, this effect in patients with acute PVD diminished after correcting for multiple comparisons. Hearing loss and affective disorders did not influence our results. Vestibular related variables (disease duration, symptoms, dizziness handicap, deafferentation degree, and compensation) did not predict verbal initiation or working memory span in patients with bilateral PVD. The results suggest that bilateral PVD not only manifests in difficulties when solving spatial tasks but leads to more general neurocognitive deficits. This understanding is important for multidisciplinary workgroups (e.g., neurotologists, neurologists, audiologists) that are involved in diagnosing and treating patients with PVD. We recommend screening patients with PVD for executive impairments and if indicated providing them with cognitive training or psychoeducational support

Cognitive Rehabilitation in Bilateral Vestibular Patients: A Computational Perspective

There is evidence that vestibular sensory processing affects, and is affected by, higher cognitive processes. This is highly relevant from a clinical perspective, where there is evidence for cognitive impairments in patients with peripheral vestibular deficits. The vestibular system performs complex probabilistic computations, and we claim that understanding these is important for investigating interactions between vestibular processing and cognition. Furthermore, this will aid our understanding of patients’ self-motion perception and will provide useful information for clinical interventions. We propose that cognitive training is a promising way to alleviate the debilitating symptoms of patients with complete bilateral vestibular loss (BVP), who often fail to show improvement when relying solely on conventional treatment methods. We present a probabilistic model capable of processing vestibular sensory data during both passive and active self-motion. Crucially, in our model, knowledge from multiple sources, including higher-level cognition, can be used to predict head motion. This is the entry point for cognitive interventions. Despite the loss of sensory input, the processing circuitry in BVP patients is still intact, and they can still perceive self-motion when the movement is self-generated. We provide computer simulations illustrating self-motion perception of BVP patients. Cognitive training may lead to more accurate and confident predictions, which result in decreased weighting of sensory input, and thus improved self-motion perception. Using our model, we show the possible impact of cognitive interventions to help vestibular rehabilitation in patients with BVP

High-current galvanic vestibular stimulation impairs working memory span, but not other executive functions.

Patients with peripheral vestibular dysfunction (PVD) suffer not only from physical problems such as imbalance or vertigo but also from neuropsychological difficulties, including executive deficits. However, it is unclear whether the PVD directly causes executive problems. To examine the causal vestibular influence on executive functions, we induced either high-current (2 mA), low-current (0.8 mA), or sham current (0 mA) galvanic vestibular stimulation (GVS) in 79 healthy participants. Participants solved three tasks, measuring the core executive components (working memory, inhibition, cognitive flexibility) before and during GVS. High-current GVS impaired working memory span, but not inhibition and cognitive flexibility performance. Low-current GVS did not influence executive performance. Results indicate a causal vestibular influence on working memory span. Joint cortical areas of vestibular and working memory processing are discussed. Since high-current GVS in healthy participants serves as a model for an artificial vestibular dysfunction, our results could improve the diagnostics and therapy of patients with PVD

Effects of galvanic vestibular stimulation on non-spatial cognitive functions in healthy participants

There is growing evidence that cognitive deficits in peripheral vestibular patients are not limited to spatial cognitive domains. Deficits seem to be present also in non-spatial cognitive tasks such as executive functions. Executive functions are comprised of several distinct components, and it is important to know which of those components are affected by vestibular impairment. Further, it is not clear whether executive deficits are causally linked to vestibular impairment. We used the method of galvanic vestibular stimulation (GVS) to induce mild vestibular impairment in healthy participants. Fifty-four participants solved two executive tasks (n-back task and Stroop task), assessing core components of executive functions (working memory, inhibition and cognitive flexibility). These tasks were solved twice, before and during simultaneous bilateral bipolar GVS. The stimulation protocol was varied between participants: The participants were either exposed to suprashreshold GVS (2mA, comparable to mild vestibular impairment), subthreshold GVS (0.8mA) or sham GVS (0mA). Results indicate that participants receiving suprathreshold GVS got worse in performance of working memory compared to participants receiving subthreshold or sham GVS. Conversely, performance in inhibition and cognitive flexibility was comparable between groups. These results indicate deficits in specific executive functions due to vestibular impairment. This finding has clinical potential: It might be reasonable to screen patients with peripheral vestibular loss for impairments in specific executive tasks. In addition, cognitive training could target specific executive components to support rehabilitation

Influence of vestibular stimulation on executive functions

Purpose: There is growing evidence that patients with peripheral vestibular loss show impairments in non-spatial cognitive domains like executive functioning. However, it is unclear which executive components are affected by vestibular loss and whether there is a causal link between vestibular loss and impaired executive functions. Therefore, the aim of this experiment was to investigate the effect of induced mild vestibular impairment in healthy participants on performance in tasks assessing executive functions. Methods: Fifty-four participants solved executive tasks twice, before and during simultaneous bilateral bipolar galvanic vestibular stimulation (GVS). Suprathreshold GVS (inducing mild vestibular impairment), subthreshold GVS or sham GVS were applied. Core components of executive functions (working memory, inhibition, cognitive flexibility) were measured with two executive tasks (n-back task, Stroop task). Results: Results indicate impaired performance in the working memory task during suprathreshold stimulation when compared to the groups receiving subthreshold or sham GVS. Performance in inhibition and cognitive flexibility showed no differences between groups. These results suggest that artificially induced mild vestibular impairment in healthy participants can lead to selective impairments in executive functions. Conclusions: To investigate the causal influence of vestibular stimulation on the performance in executive tasks in healthy participants helps to explain executive deficits in patients with vestibular loss. Since executive functions are a composite of several distinct functions, it is important to more specifically determine the executive components which are affected by vestibular impairment. This can help to screen patients with vestibular loss, and ultimately provide cognitive training methods that are tailored to their pattern of performance

Galvanic vestibular stimulation and executive functions

Patients with peripheral vestibular disease have problems in executive functions but there is not much knowledge about the direct vestibular influence on executive functioning. We used the method of galvanic vestibular stimulation (GVS) to induce a mild vestibular impairment in healthy participants and investigated its effect on core domains of executive functions (inhibition, working memory, cognitive flexibility). Seventy-nine healthy participants solved two executive tasks (n-back task, Stroop task) twice, first as a baseline measure and then again during the application of bilateral bipolar sinusoidal GVS. Participants were randomly assigned to three different stimulation protocols: 1.) Suprathreshold GVS (2mA) to induce the vestibular impairment, 2.) subthreshold GVS (0.8mA) or 3.) sham GVS (0mA). Participants receiving suprathreshold GVS showed an impaired performance in the working memory task whereas participants in the subthreshold GVS or the sham GVS group did not show an impaired working memory performance. Inhibition and cognitive flexibility performance did not differ between groups. Our results show that artificially induced vestibular impairment leads to a selective negative effect on working memory performance. This knowledge can help to understand executive deficits in patients with peripheral vestibular disease and should guide new treatment options

Galvanic vestibular stimulation impairs specific executive functions

Recent research suggests that patients with peripheral vestibular disease have problems in executive functions, but to date, not much is known about the direct vestibular influence on executive functioning. We artificially induced mild vestibular impairment in healthy participants by suprathreshold galvanic vestibular stimulation (GVS) and measured their performance in core executive functions. Seventy-nine participants solved two executive tasks (n-back task and Stroop task), assessing core components of executive functions (working memory, inhibition and cognitive flexibility). These tasks were solved twice, before and during simultaneous bilateral bipolar sinusoidal GVS. Participants were randomly assigned to three different stimulation protocols: They were either exposed to suprathreshold GVS (2mA, comparable to mild vestibular impairment), subthreshold GVS (0.8mA) or to sham GVS (0mA). Participants receiving suprathreshold GVS showed diminished performance in working memory ability when compared to participants receiving subthreshold GVS or sham GVS. Performance in inhibition and cognitive flexibility did not differ between groups. These results indicate that artificially induced mild vestibular impairment has a selective negative effect on working memory performance. The results provide important evidence about the specific effects vestibular impairment can have on executive functions, and this in turn can help the design of new treatment options for patients with peripheral vestibular disease

Executive functions in patients with bilateral and unilateral peripheral vestibular dysfunction

Patients with peripheral vestibular dysfunction (PVD) suffer from cognitive difficulties in several visuo-spatial as well as non-visuo-spatial domains. Associations of PVD and executive problems have been made, but no study investigated a range of different executive domains in patients with PVD. We administered a broad neuropsychological test battery of basic and complex executive functions to 84 patients with different kinds of PVD (34 chronic bilateral, 29 chronic unilateral, 21 acute unilateral) and 49 healthy controls matched for age, education, sex, and handedness. Descriptive data analysis showed that patients with PVD scored lower in specific executive domains than healthy controls. Results indicate that patients with PVD should be screened for specific executive impairments and could benefit from a cognitive training targeting executive functions

Development of executive functions from childhood to adolescence in very preterm-born individuals - A longitudinal study.

Preterm-born individuals are at risk for poorer executive functions. Longitudinal studies investigating whether preterm-born individuals present persistent cognitive deficits, or a transient delay of development are scarce. We assessed developmental trajectories of executive functions (inhibition, working memory, cognitive flexibility) in 29 very preterm-born individuals (<32 weeks' gestation) and 25 term-born controls longitudinally over two time points, namely in childhood (7-12 years of age, TP1) and adolescence (13-16 years of age, TP2). Individual changes in executive functions were examined using relative difference scores (TP2 - TP1) / TP1). There was a significantly stronger improvement of inhibition (U = 477, p = .024) and cognitive flexibility (U = 312, p = .029) between childhood and adolescence in very preterm-born individuals than in term-born controls. Preterm-born individuals improved their performance in the domain of cognitive flexibility significantly more often (76%) between childhood and adolescence than controls (31%, χ = 8.6, p = .003). Controls worsened significantly more often (36%) in the domain of inhibition than the preterm group (14%, χ = 4.8, p = .028). Results indicate that healthy preterm-born individuals show prolonged development of executive functions throughout childhood up into adolescence