Perspective on the vestibular cortex throughout history

Altered functional activity of the precuneus and superior temporal gyrus in patients with residual dizziness caused by benign paroxysmal positional vertigo

Objective

Benign paroxysmal positional vertigo (BPPV) is a common clinical vertigo disease, and the most effective treatment for this disease is canal repositioning procedures (CRP). Most patients return to normal after a single treatment. However, some patients still experience residual dizziness (RD) after treatment, and this disease's pathogenesis is currently unclear. The purpose of this study is to explore whether there are abnormal brain functional activities in patients with RD by using resting-state functional magnetic resonance imaging (rs-fMRI) and to provide imaging evidence for the study of the pathogenesis of RD.

Materials and methods

The BPPV patients in the Second Affiliated Hospital of Xuzhou Medical University had been included from December 2021 to November 2022. All patients had been received the collection of demographic and clinical characteristics (age, gender, involved semicircular canal, affected side, CRP times, BPPV course, duration of RD symptoms, and whether they had hypertension, diabetes, coronary heart disease.), scale assessment, including Dizziness Handicap Inventory (DHI), Hamilton Anxiety Inventory (HAMA), Hamilton Depression Inventory (HAMD), rs-fMRI data collection, CRP treatment, and then a one-month follow-up. According to the follow-up results, 18 patients with RD were included. At the same time, we selected 19 healthy individuals from our hospital's physical examination center who matched their age, gender as health controls (HC). First, the amplitude of low-frequency fluctuations (ALFF) analysis method was used to compare the local functional activities of the two groups of subjects. Then, the brain regions with different ALFF results were extracted as seed points. Functional connectivity (FC) analysis method based on seed points was used to explore the whole brain FC of patients with RD. Finally, a correlation analysis between clinical features and rs-fMRI data was performed.

Results

Compared to the HC, patients with RD showed lower ALFF value in the right precuneus and higher ALFF value in the right superior temporal gyrus (STG). When using the right STG as a seed point, it was found that the FC between the right STG, the right supramarginal gyrus (SMG), and the left precuneus was decreased in RD patients. However, no significant abnormalities in the FC were observed when using the right precuneus as a seed point.

Conclusion

In patients with RD, the local functional activity of the right precuneus is weakened, and the local functional activity of the right STG is enhanced. Furthermore, the FC between the right STG, the right SMG, and the left precuneus is weakened. These changes may explain the symptoms of dizziness, floating sensation, walking instability, neck tightness, and other symptoms in patients with RD to a certain extent.

Audiovestibular Symptoms at the Intensive Care Unit: A Narrative Review

Vertigo, tinnitus and hearing loss are the most common audiovestibular symptoms detected in the emergency departments and outpatients settings. However, little is known about these on patients at the intensive care unit. Although these symptoms may be common in this scenario, few studies have documented their onset, triggers and other factors associated to their presentation. The evaluation of these symptoms is a challenge for intensive care unit physicians, neurologists and otolaryngologists due to several factors as consciousness, systemic comorbidities, prolonged immobility and antibiotic therapy. The frequency of audiovestibular symptoms at the intensive care unit and the related events and factors associated to their presentation will be explored in this review.

Acute and episodic vestibular syndromes caused by ischemic stroke: predilection sites and risk factors

Objective

This study was performed to investigate the predilection sites of acute vestibular syndrome (AVS) and episodic vestibular syndrome (EVS) caused by acute infarcts.

Methods

This retrospective cohort study was performed at a stroke center in a tertiary teaching hospital. We diagnosed patients with AVS/EVS caused by acute ischemic stroke using diffusion-weighted imaging (DWI) and magnetic resonance angiography.

Results

Among all patients with AVS/EVS, 68 had DWI-positive ischemic events and 113 had DWI-negative ischemic events. Of the 68 patients with positive DWI findings, 42.6% had acute infarcts in the anterior circulation and 41.2% had acute infarcts in the posterior circulation. The main stroke predilection sites were the insular cortex (22.1%) and posterior thalamus (11.8%). Large vessel stenosis/occlusion (odds ratio, 0.12; 95% confidence interval, 0.04–0.36) and focal neurological symptoms/signs (odds ratio, 0.27; 95% confidence interval, 0.10–0.72) were significantly associated with the risk of AVS/EVS in patients with acute ischemic stroke.

Conclusions

The main predilection sites of AVS/EVS caused by ischemic stroke are the insular cortex and posterior thalamus. The risk of AVS/EVS is associated with large vessel stenosis and focal symptoms.

Acute dizziness with potential life-threatening event: A case series from single ICU

BACKGROUND

Whether the acute dizziness would be associated with potentially life-threatening event, which was previously unknown.

METHODS

Between Jan 2014 and Dec 2016, We performed a retrospective survey to investigate the clinical data of patients with acute dizziness from an intensive care unit (ICU) in China. Inclusion criteria for all cases were presented with acute dizziness at onset, and then with a potentially life-threatening event. Baseline data and 30-days outcomes were collected.

RESULTS

Approximately 1.0% of ICU patients had an acute dizziness with potentially life-threatening events. The median age of patients was 60 years (range 23 to 81 years), male: female ratio was 1.8:1. The causes of acute dizziness included focal cerebral hemorrhage in 15 cases (60%), shock in 7cases (28%), and cerebral infarction in 3 cases (12%). The most frequent potentially life-threatening event was acute brain failure (24/25), and the most common cause leading to brain failure was the lesion enlarged (54.2%, including hematoma enlargement in 8 cases, large area infarction or new infarction in 3 cases, and intraventricular hemorrhage in 2 cases). The second potentially life-threatening event was septic shock/secondary sepsis (45.8%). The fatality rate for all life- threatening events was in 64%. Compared with the survival group, the patients with lesion enlarged (56.3% vs. 11.1%, p < 0.05), acute respiratory failure (93.8% vs. 55.6% p < 0.05), lactate level (5.3 mmol/l vs. 1.3 mmol/l, p < 0.05), and Sequential Organ Failure Assessment (SOFA) score (6.9 vs. 3.4, p < 0.0001) in the non-survival group were significantly higher, while late mean arterial blood pressure (84.6 mmHg vs.124 mmHg, p < 0.0001), GCS score (5.0 score vs. 15 score, p < 0.0001) in the non-survival group were significantly lower.

CONCLUSION

Acute dizziness with potentially life-threatening events accounts for about 1% of adult ICU patients. Acute dizziness in ICU patients is associated with a high risk of death within 30 days of onset.

Short-term memory impairment in vestibular patients can arise independently of psychiatric impairment, fatigue, and sleeplessness

Vestibular dysfunction is associated with visual short-term memory impairment; however, it remains unclear if this impairment arises as a direct result of the vestibular dysfunction or is a consequence of comorbid changes in mood, affect, fatigue, and/or sleep. To this end, we assessed the concurrence and interdependence of these comorbidities in 101 individuals recruited from a tertiary balance clinic with a neuro-otological diagnosis. Over fifty per cent of the sample showed reduced visuospatial short-term memory, 60% and 37% exceeded cut-off on the Beck Anxiety and Depression Inventories, respectively, 70% exceeded cut-off on the Fatigue Severity Scale, 44% reported daytime sleepiness on the Epworth Sleepiness Scale, and 78% scored above cut-off on the Pittsburgh Sleep Quality Index. The high concurrence of these symptoms gives reason to infer the existence of a vestibular cognitive affective syndrome. Structural equation modelling indicated that the significant statistical association between general unassisted posture (a marker of chronic vestibular dysfunction and strong predictor of falls risk) and short-term memory was not mediated by mood and wakefulness. Instead, the memory impairment related more directly to vestibular dysfunction. From a rehabilitation perspective, the implication is that if the vestibular disorder is treated successfully then the memory problem will likewise improve.

Perception of Upright: Multisensory Convergence and the Role of Temporo-Parietal Cortex

We inherently maintain a stable perception of the world despite frequent changes in the head, eye, and body positions. Such "orientation constancy" is a prerequisite for coherent spatial perception and sensorimotor planning. As a multimodal sensory reference, perception of upright represents neural processes that subserve orientation constancy through integration of sensory information encoding the eye, head, and body positions. Although perception of upright is distinct from perception of body orientation, they share similar neural substrates within the cerebral cortical networks involved in perception of spatial orientation. These cortical networks, mainly within the temporo-parietal junction, are crucial for multisensory processing and integration that generate sensory reference frames for coherent perception of self-position and extrapersonal space transformations. In this review, we focus on these neural mechanisms and discuss (i) neurobehavioral aspects of orientation constancy, (ii) sensory models that address the neurophysiology underlying perception of upright, and (iii) the current evidence for the role of cerebral cortex in perception of upright and orientation constancy, including findings from the neurological disorders that affect cortical function.

Epilepsy and the cortical vestibular system: tales of dizziness and recent concepts

Cortical representations of the vestibular system are now well recognized. In contrast, the fact that epilepsy can affect these systems, provoking transient vestibular symptoms, is less known. Focal seizures may nonetheless manifest by prominent vestibular changes ranging from mild unsteadiness to true rotational vertigo. Most often these symptoms are associated with other subjective manifestations. In pure vestibular forms, the diagnosis may be more difficult and is often delayed. The cortical origin of these symptoms will be discussed and compared with the known "vestibular" cortical representations. In addition, the existence of a specific "vestibular epilepsy" has been suggested in some publications. This condition affects young subjects with a frequent family history and most often a benign evolution, raising the possibility of a form of idiopathic epilepsy (Hewett etal., 2011).

The use of tDCS and CVS as methods of non-invasive brain stimulation

Transcranial direct current stimulation (tDCS) and caloric vestibular stimulation (CVS) are safe methods for selectively modulating cortical excitability and activation, respectively, which have recently received increased interest regarding possible clinical applications. tDCS involves the application of low currents to the scalp via cathodal and anodal electrodes and has been shown to affect a range of motor, somatosensory, visual, affective and cognitive functions. Therapeutic effects have been demonstrated in clinical trials of tDCS for a variety of conditions including tinnitus, post-stroke motor deficits, fibromyalgia, depression, epilepsy and Parkinson's disease. Its effects can be modulated by combination with pharmacological treatment and it may influence the efficacy of other neurostimulatory techniques such as transcranial magnetic stimulation. CVS involves irrigating the auditory canal with cold water which induces a temperature gradient across the semicircular canals of the vestibular apparatus. This has been shown in functional brain-imaging studies to result in activation in several contralateral cortical and subcortical brain regions. CVS has also been shown to have effects on a wide range of visual and cognitive phenomena, as well as on post-stroke conditions, mania and chronic pain states. Both these techniques have been shown to modulate a range of brain functions, and display potential as clinical treatments. Importantly, they are both inexpensive relative to other brain stimulation techniques such as electroconvulsive therapy (ECT) and transcranial magnetic stimulation (TMS).

Studies of caloric vestibular stimulation: implications for the cognitive neurosciences, the clinical neurosciences and neurophilosophy

OBJECTIVE

Caloric vestibular stimulation (CVS) has traditionally been used as a tool for neurological diagnosis. More recently, however, it has been applied to a range of phenomena within the cognitive neurosciences. Here, we provide an overview of such studies and review our work using CVS to investigate the neural mechanisms of a visual phenomenon - binocular rivalry. We outline the interhemispheric switch model of rivalry supported by this work and its extension to a metarivalry model of interocular-grouping phenomena. In addition, studies showing a slow rate of binocular rivalry in bipolar disorder are discussed, and the relationship between this finding and the interhemispheric switch model is described. We also review the effects of CVS in various clinical contexts, explain how the technique is performed and discuss methodological issues in its application.

METHODS

A review of CVS and related literature was conducted.

RESULTS

Despite CVS being employed with surprising effect in a wide variety of cognitive and clinical contexts, it has been a largely underutilized brain stimulation method for both exploratory and therapeutic purposes. This is particularly so given that it is well tolerated, safe, inexpensive and easy to administer.

CONCLUSION

CVS can be used to investigate various cognitive phenomena including perceptual rivalry, attention and mood, as well as somatosensory representation, belief, hemispheric laterality and pain. The technique can also be used to investigate clinical conditions related to these phenomena and may indeed have therapeutic utility, especially with respect to postlesional disorders, mania, depression and chronic pain states. Furthermore, we propose that based on existing reports of the phenomenological effects of CVS and the brain regions it is known to activate, the technique could be used to investigate and potentially treat a range of other clinical disorders. Finally, the effects of CVS (and its potential effects) on several phenomena of interest to philosophy suggest that it is also likely to become a useful tool in experimental neurophilosophy.