61 results found
Castro P, Kaski D, Al-Fazly H, et al., 2019, Body sway during postural perturbations is mediated by the degree of vestibulo-cortical dominance, Brain Stimulation, Vol: 12, Pages: 1098-1100, ISSN: 1935-861X
Marcus HJ, Paine H, Sargeant M, et al., 2019, Vestibular dysfunction in acute traumatic brain injury, Journal of Neurology, Vol: 266, Pages: 2430-2433, ISSN: 0340-5354
Traumatic brain injury (TBI) is the commonest cause of disability in under-40-year-olds. Vestibular features of dizziness (illusory self-motion) or imbalance which affects 50% of TBI patients at 5 years, increases unemployment threefold in TBI survivors. Unfortunately, vestibular diagnoses are cryptogenic in 25% of chronic TBI cases, impeding therapy. We hypothesized that chronic adaptive brain mechanisms uncouple vestibular symptoms from signs. This predicts a masking of vestibular diagnoses chronically but not acutely. Hence, defining the spectrum of vestibular diagnoses in acute TBI should clarify vestibular diagnoses in chronic TBI. There are, however, no relevant acute TBI data. Of 111 Major Trauma Ward adult admissions screened (median 38-years-old), 96 patients (87%) had subjective dizziness (illusory self-motion) and/or objective imbalance were referred to the senior author (BMS). Symptoms included: feeling unbalanced (58%), headache (50%) and dizziness (40%). In the 47 cases assessed by BMS, gait ataxia was the commonest sign (62%) with half of these cases denying imbalance when asked. Diagnoses included BPPV (38%), acute peripheral unilateral vestibular loss (19%), and migraine phenotype headache (34%), another potential source of vestibular symptoms. In acute TBI, vestibular signs are common, with gait ataxia being the most frequent one. However, patients underreport symptoms. The uncoupling of symptoms from signs likely arises from TBI affecting perceptual mechanisms. Hence, the cryptogenic nature of vestibular symptoms in TBI (acute or chronic) relates to a complex interaction between injury (to peripheral and central vestibular structures and perceptual mechanisms) and brain-adaptation, emphasizing the need for acute prospective, mechanistic studies.
Arshad Q, Ortega MC, Goga U, et al., 2019, Interhemispheric control of sensory cue integration and self-motion perception, Neuroscience, Vol: 408, Pages: 378-387, ISSN: 0306-4522
Spatial orientation necessitates the integration of visual and vestibular sensory cues, in-turn facilitating self-motion perception. However, the neural mechanisms underpinning sensory integration remain unknown. Recently we have illustrated that spatial orientation and vestibular thresholds are influenced by interhemispheric asymmetries associated with the posterior parietal cortices (PPC) that predominantly house the vestibulo-cortical network. Given that sensory integration is a prerequisite to both spatial orientation and motion perception, we hypothesized that sensory integration is similarly subject to interhemispheric influences. Accordingly, we explored the relationship between vestibulo-cortical dominance – assessed using a biomarker, the degree of vestibular-nystagmus suppression following transcranial direct current stimulation over the PPC – with visual dependence measures obtained during performance of a sensory integration task (the rod-and-disk task). We observed that the degree of visual dependence was correlated with vestibulo-cortical dominance. Specifically, individuals with greater right hemispheric vestibulo-cortical dominance had reduced visual dependence. We proceeded to assess the significance of such dominance on behavior by correlating measures of visual dependence with self-motion perception in healthy subjects. We observed that right-handed individuals experienced illusionary self-motion (vection) quicker than left-handers and that the degree of vestibular cortical dominance was correlated with the time taken to experience vection, only during conditions that induced interhemispheric conflict. To conclude, we demonstrate that interhemispheric asymmetries associated with vestibulo-cortical processing in the PPC functionally and mechanistically link sensory integration and self-motion perception, facilitating spatial orientation. Our findings highlight the importance of dynamic interhemispheric competition upon control of vestib
Britton Z, Arshad Q, 2019, Vestibular and multi-sensory influences upon self-motion perception and the consequences for human behavior, Frontiers in Neurology, Vol: 10, ISSN: 1664-2295
In this manuscript, we comprehensively review both the human and animal literature regarding vestibular and multi-sensory contributions to self-motion perception. This covers the anatomical basis and how and where the signals are processed at all levels from the peripheral vestibular system to the brainstem and cerebellum and finally to the cortex. Further, we consider how and where these vestibular signals are integrated with other sensory cues to facilitate self-motion perception. We conclude by demonstrating the wide-ranging influences of the vestibular system and self-motion perception upon behavior, namely eye movement, postural control, and spatial awareness as well as new discoveries that such perception can impact upon numerical cognition, human affect, and bodily self-consciousness.
Castro P, Kaskia D, Schieppati M, et al., 2019, Subjective stability perception is related to postural anxiety in older subjects, GAIT & POSTURE, Vol: 68, Pages: 538-544, ISSN: 0966-6362
Kaski D, Rust HM, Ibitoye R, et al., 2019, Theoretical framework for "unexplained" dizziness in the elderly: The role of small vessel disease, Editors: Ramat, Shaikh, Publisher: ELSEVIER SCIENCE BV, Pages: 225-240
Castro P, Sena Esteves S, Lerchundi F, et al., 2018, Viewing target distance influences the vestibulo-ocular reflex gain when assessed using the video head impulse test, Audiology and Neurotology, Vol: 23, Pages: 285-289, ISSN: 1420-3030
Gaze stabilization during head movements is provided by the vestibulo-ocular reflex (VOR). Clinical assessment of this reflex is performed using the video Head Impulse Test (vHIT). To date, the influence of different fixation distances on VOR gain using the vHIT has not been explored. We assessed the effect of target proximity on the horizontal VOR using the vHIT. Firstly, we assessed the VOR gain in 18 healthy subjects with 5 viewing target distances (150, 40, 30, 20, and 10 cm). The gain increased significantly as the viewing target distance decreased. A second experiment on 10 subjects was performed in darkness whilst the subjects were imagining targets at different distances. There were significant inverse relationships between gain and distance for both the real and the imaginary targets. There was a statistically significant difference between light and dark gains for the 20- and 40-cm distances, but not for the 150-cm distance. Theoretical VOR gains for different target distances were calculated and compared with those found in light and darkness. The increase in gain observed for near targets was lower than predicted by geometrical calculations, implying a physiological ceiling effect on the VOR. The VOR gain in the dark, as assessed with the vHIT, demonstrates an enhancement associated with a reduced target distance.
Edwards A, Guven O, Furman M, et al., 2018, Electroencephalographic correlates of continuous postural tasks of increasing difficulty, Neuroscience, Vol: 395, Pages: 35-48, ISSN: 0306-4522
Cortical involvement in postural control is well recognized, however the role of non-visual afferents remains unclear. Parietal cortical areas are strongly implicated in vestibulo-spatial functions, but topographical localization during balance tasks remains limited. Here, we use electroencephalography (EEG) during continuous balance tasks of increasing difficulty at single electrode positions. Twenty-four healthy, right-handed individuals performed four balance tasks of increasing difficulty (bipedal and unipedal) and a seated control condition with eyes closed. Subjective ratings of task difficulty were obtained. EEG was recorded from 32 electrodes; 5 overlying sensory and motor regions of interest (ROIs) were chosen for further investigation: C3, Cz, C4, P3, P4. Spectral power and coherence during balance tasks were analyzed in theta (4–8 Hz) and alpha (8–12 Hz) bands. Alpha power reduced as task difficulty increased and this reduction correlated with subjective difficulty ratings. Alpha coherence increased with task difficulty between C3–Cz–C4 electrode pairs. Differential changes in power were observed in Cz, suggestive of a distinct role at this electrode location, which captures lower limb cortical representation. Hemispheric asymmetry was observed, as reflected by greater reductions in theta and alpha power in right-sided areas. Our results demonstrate the functional importance of bilateral central and parietal cortices in continuous balance control. The hemispheric asymmetry observed implies that the non-dominant hemisphere is involved with online monitoring of postural control. Although the posterior parietal asymmetry found may relate to vestibular, somatosensory or multisensory feedback processing, we argue that the finding relates to active balance control rather than simple sensory-intake or reflex circuit activation.
Roberts R, Ahmad H, Patel M, et al., 2018, An fMRI study of visuo-vestibular interaction in Vestibular Neuritis, NeuroImage: Clinical, Vol: 20, Pages: 1010-1017, ISSN: 2213-1582
Vestibular neuritis (VN) is characterised by acute vertigo due to a sudden loss of unilateral vestibular function. A considerable proportion of VN patients proceed to develop chronic symptoms of dizziness, including visually induced dizziness, specifically during head turns. Here we investigated whether the development of such poor clinical outcomes following VN, is associated with abnormal visuo-vestibular cortical processing. Accordingly, we applied functional magnetic resonance imaging to assess brain responses of chronic VN patients and compared these to controls during both congruent (co-directional) and incongruent (opposite directions) visuo-vestibular stimulation (i.e. emulating situations that provoke symptoms in patients). We observed a focal significant difference in BOLD signal in the primary visual cortex V1 between patients and controls in the congruent condition (small volume corrected level of p < .05 FWE). Importantly, this reduced BOLD signal in V1 was negatively correlated with functional status measured with validated clinical questionnaires. Our findings suggest that central compensation and in turn clinical outcomes in VN are partly mediated by adaptive mechanisms associated with the early visual cortex.
Bednarczuk N, Arshad Q, Fluri S, et al., 2018, Vestibulo-cortical hemispheric dominance: the link between anxiety and the vestibular system?, European Journal of Neuroscience, Vol: 47, Pages: 1517-1724, ISSN: 0953-816X
Vestibular processing and anxiety networks are functionally intertwined, as demonstrated by reports of reciprocal influences upon each other. Yet whether there is an underlying link between these two systems remains unknown Previous findings have highlighted the involvement of hemispheric lateralisation in processing of both anxiety and vestibular signals. Accordingly, we explored the interaction between vestibular cortical processing and anxiety by assessing the relationship between anxiety levels and the degree of hemispheric lateralisation of vestibulo‐cortical processing in 64 right‐handed, healthy individuals. Vestibulo‐cortical hemispheric lateralisation was determined by gaging the degree of caloric‐induced nystagmus suppression following modulation of cortical excitability using trans‐cranial direct current stimulation targeted over the posterior parietal cortex, an area implicated in the processing of vestibular signals. The degree of nystagmus suppression yields an objective biomarker, allowing the quantification of the degree of right vestibulo‐cortical hemisphere dominance. Anxiety levels were quantified using the Trait component of the Spielberger State‐Trait Anxiety Questionnaire. Our findings demonstrate that the degree of an individual's vestibulo‐cortical hemispheric dominance correlates with their anxiety levels. That is, those individuals with greater right hemispheric vestibulo‐cortical dominance exhibited lower levels of anxiety. By extension, our results support the notion that hemispheric lateralisation determines an individual's emotional processing, thereby linking cortical circuits involved in processing anxiety and vestibular signals respectively.
Patel M, Arshad Q, Seemungal BM, et al., 2018, Steroid injections through the eardrum reduce dizziness in Meniere’s disease, study finds - REPLY TO ADRION ET AL. ON PATEL ET AL., British Medical Journal, Vol: 355, ISSN: 0959-8138
Arshad Q, Nigmatullina Y, Siddiqui S, et al., 2017, Influence of biases in numerical magnitude allocation on human prosocial decision making, JOURNAL OF NEUROPHYSIOLOGY, Vol: 118, Pages: 3007-3013, ISSN: 0022-3077
Cronin T, Arshad Q, Seemungal BM, 2017, Vestibular deficits in neurodegenerative disorders: balance, dizziness, and spatial disorientation, Frontiers in Neurology, Vol: 8, ISSN: 1664-2295
The vestibular system consists of the peripheral vestibular organs in the inner ear and the associated extensive central nervous system projections—from the cerebellum and brainstem to the thalamic relays to cortical projections. This system is important for spatial orientation and balance, both of critical ecological importance, particularly for successful navigation in our environment. Balance disorders and spatial disorientation are common presenting features of neurodegenerative diseases; however, little is known regarding central vestibular processing in these diseases. A ubiquitous aspect of central vestibular processing is its promiscuity given that vestibular signals are commonly found in combination with other sensory signals. This review discusses how impaired central processing of vestibular signals—typically in combination with other sensory and motor systems—may account for the impaired balance and spatial disorientation in common neurodegenerative conditions. Such an understanding may provide for new diagnostic tests, potentially useful in detecting early disease while a mechanistic understanding of imbalance and spatial disorientation in these patients may enable a vestibular-targeted therapy for such problems in neurodegenerative diseases. Studies with state of the art central vestibular testing are now much needed to tackle this important topic.
Arshad Q, Bonsu A, Lobo R, et al., 2017, Biased numerical cognition impairs economic decision-making in Parkinson’s disease, Annals of Clinical and Translational Neurology, Vol: 4, Pages: 739-748, ISSN: 2328-9503
ObjectivePrevious findings suggest a context-dependent bihemispheric allocation of numerical magnitude. Accordingly, we predicted that lateralized motor symptoms in Parkinson's disease (PD), which reflect hemispheric asymmetries, would induce systematic lateralized biases in numerical cognition and have a subsequent influence on decision-making.MethodsIn 20 PD patients and matched healthy controls we assessed numerical cognition using a number-pair bisection and random number generation task. Decision-making was assessed using both the dictator game and a validated questionnaire.ResultsPD patients with predominant right-sided motor symptoms exhibited pathological biases toward smaller numerical magnitudes and formulated less favorable prosocial choices during a neuroeconomics task (i.e., dictator game). Conversely, patients with left-sided motor symptoms exhibited pathological biases toward larger numerical magnitudes and formulated more generous prosocial choices. Our account of context-dependent hemispheric allocation of numerical magnitude in PD was corroborated by applying our data to a pre-existing computational model and observing significant concordance. Notably, both numerical biasing and impaired decision-making were correlated with motor asymmetry.InterpretationAccordingly, motor asymmetry and functional impairment of cognitive processes in PD can be functionally intertwined. To conclude, our findings demonstrate context-dependent hemispheric allocation and encoding of numerical magnitude in PD and how biases in numerical magnitude allocation in Parkinsonian patients can correspondingly impair economic decision-making.
Bednarczuk NF, Ortega MC, Fluri A-S, et al., 2017, Inter-hemispheric control of vestibular thresholds, BRAIN STIMULATION, Vol: 10, Pages: 988-991, ISSN: 1935-861X
Sena Esteves S, Carvalho de Almeida J, Abrunhosa J, et al., 2017, Pig's ear: Streptococcus suis Meningitis and its associated inner ear implications., IDCases, Vol: 10, Pages: 55-57, ISSN: 2214-2509
Streptococcus suis (S. suis) is a zoonotic pathogen commonly found in Asian countries. Infection with this bacterium typically clinically presents as meningitis and individuals whom handle swine are at increased risk of developing infections. We present a case of a patient with a S. suis meningitis who worked as a butcher. The 48-year-old man was admitted to our department with headaches, fevers, nausea and bilateral hearing loss. According to his medical history, the patient had sustained a cut on his finger while preparing pork meat. A microbiological examination of the cerebrospinal fluid and blood revealed S. suis. The patient was empirically treated with ceftriaxone, vancomycin and dexamethasone. The patient made a complete recovery from the meningitic process and inflammatory markers. However, the hearing and vestibular loss persisted with considerable functional impact upon his daily life. He was elected for a right cochlear implant, 7 weeks after the presentation with a poor outcome. It is important to remember that inner-ear dysfunction can occur frequently in S. suis meningitis surviving patients. Physicians should have a high index of suspicion if risk factors are present and initiate urgent treatment to prevent serious long-term consequences.
Allen D, Ribeiro L, Arshad Q, et al., 2017, Age-Related Vestibular Loss: Current Understanding and Future Research Directions, Frontiers in Neurology, Vol: 8, ISSN: 1664-2295
The vestibular system sub-serves a number of reflex and perceptual functions, comprisingthe peripheral apparatus, the vestibular nerve, the brainstem and cerebellarprocessing circuits, the thalamic relays, and the vestibular cerebral cortical network.This system provides signals of self-motion, important for gaze and postural control,and signals of traveled distance, for spatial orientation, especially in the dark. Currentevidence suggests that certain aspects of this multi-faceted system may deteriorate withage and sometimes with severe consequences, such as falls. Often the deterioration investibular functioning relates to how the signal is processed by brain circuits rather thanan impairment in the sensory transduction process. We review current data concerningage-related changes in the vestibular system, and how this may be important for cliniciansdealing with balance disorders.
Allen D, Ribeiro L, Arshad Q, et al., 2017, Age-Related Vestibular Loss: Current Understanding and Future Research Directions (vol 7, 231, 2016), FRONTIERS IN NEUROLOGY, Vol: 8, ISSN: 1664-2295
Ahmad H, Roberts E, Patel M, et al., 2017, Downregulation of early visual cortex excitability mediates oscillopsia, Neurology, Vol: 89, Pages: 1179-1185, ISSN: 0028-3878
Objective; Identifying the neurophysiological mechanisms that mediate adaptation to oscillopsia in patients with bilateral-vestibular failure (BVF); an observational study. Methods; We directly probe the hypothesis that adaptive changes which mediate oscillopsia suppression implicate the early visual-cortex (V1/V2). Accordingly, we investigated (V1/V2) excitability using transcranial magnetic stimulation (TMS) in 12 avestibular patients and 12 healthy controls. Specifically, we assessed TMS-induced phosphene thresholds at baseline and cortical excitability changes whilst performing a visual-motion adaptation paradigm during the following conditions: (i) BASELINE measures (i.e. static), (ii) during visual-motion (i.e. MOTION PRE ADAPTATION) and, (iii) during visual-motion following 5 minutes of unidirectional visual-motion adaptation (i.e. MOTION ADAPTED). Results: Patients had significantly higher baseline phosphene-thresholds, reflecting an underlying adaptive mechanism. Individual thresholds were correlated with oscillopsia symptom load. During the visual-motion adaptation condition, no differences in excitability at BASELINE were observed but, during both MOTION PRE ADAPTATION and MOTION ADAPTED conditions, we observed significantly attenuated cortical excitability in patients. Again this attenuation in excitability was stronger in less symptomatic patients.Conclusion; Our findings provide neurophysiological evidence that cortically-mediated adaptive mechanisms in V1/V2 play a critical role in suppressing oscillopsia in patients with bilateral vestibular failure.
Arshad Q, 2017, DYNAMIC INTERHEMISPHERIC COMPETITION AND VESTIBULO-CORTICAL CONTROL IN HUMANS; A THEORETICAL PROPOSITION, NEUROSCIENCE, Vol: 353, Pages: 26-41, ISSN: 0306-4522
Cousins S, Kaski D, Cutfield N, et al., 2017, Predictors of clinical recovery from vestibular neuritis: a prospective study, Annals of Clinical and Translational Neurology, Vol: 4, Pages: 340-346, ISSN: 2328-9503
We sought to identify predictors of symptomatic recovery in vestibular neuritis. Forty VN patients were prospectively studied in the acute phase (median = 2 days) and 32 in the recovery phase (median = 10 weeks) with vestibulo-ocular reflex, vestibular-perceptual, and visual dependence tests and psychological questionnaires. Clinical outcome was Dizziness Handicap Inventory score at recovery phase. Acute visual dependency and autonomic arousal predicted outcome. Worse recovery was associated with a combination of increased visual dependence, autonomic arousal, anxiety/depression, and fear of bodily sensations, but not with vestibular variables. Findings highlight the importance of early identification of abnormal visual dependency and concurrent anxiety.
Arshad Q, Roberts RE, Ahmad H, et al., 2017, Patients with chronic dizziness following traumatic head injury typically have multiple diagnoses involving combined peripheral and central vestibular dysfunction, CLINICAL NEUROLOGY AND NEUROSURGERY, Vol: 155, Pages: 17-19, ISSN: 0303-8467
Roberts RE, Arshad Q, Patel M, et al., 2016, Functional neuroimaging of visuo-vestibular interaction, Brain Structure & Function, Vol: 222, Pages: 2329-2343, ISSN: 1863-2661
The brain combines visual, vestibular and proprioceptive information to distinguish between self-and world-motion. Often these signals are complementary and indicate that the individual is moving or stationary with respect to the surroundings. However, conflicting visual motion and vestibular cues can lead to ambiguous or false sensations of motion. In this study, we used functional magnetic resonance imaging to explore human brain activation when visual and vestibular cues were either complementary or in conflict. We combined a horizontally moving optokinetic stimulus with caloric irrigation of the right ear to produce conditions where the vestibular activation and visual motion indicatedthe same (congruent) or opposite directions of self-motion (incongruent). Visuo-vestibular conflict was associated with increased activation in a network of brain regions including posterior insular and transverse temporal areas, cerebellar tonsil, cingulate and medial frontal gyri. In the congruent condition there was increased activation in primary and secondary visual cortex. These findings suggest that when sensory information regarding self-motion is contradictory, there is preferential activation of multisensoryvestibular areas to resolve this ambiguity. When cues are congruent there is a bias towards visual cortical activation. The data support the view thata network of brain areas including the posterior insular cortex may play animportant role in integrating and disambiguating visual and vestibular cues.
Patel M, Agarwal K, Arshad Q, et al., 2016, Intratympanic methylprednisolone versus gentamicin in patients with unilateral Ménière's disease: a randomised, double-blind, comparative effectiveness trial, The Lancet, Vol: 388, Pages: 2753-2762, ISSN: 0140-6736
BACKGROUND: Ménière's disease is characterised by severe vertigo attacks and hearing loss. Intratympanic gentamicin, the standard treatment for refractory Ménière's disease, reduces vertigo, but damages vestibular function and can worsen hearing. We aimed to assess whether intratympanic administration of the corticosteroid methylprednisolone reduces vertigo compared with gentamicin. METHODS: In this double-blind comparative effectiveness trial, patients aged 18-70 years with refractory unilateral Ménière's disease were enrolled at Charing Cross Hospital (London, UK) and Leicester Royal Infirmary (Leicester, UK). Patients were randomly assigned (1:1) by a block design to two intratympanic methylprednisolone (62·5 mg/mL) or gentamicin (40 mg/mL) injections given 2 weeks apart, and were followed up for 2 years. All investigators and patients were masked to treatment allocation. The primary outcome was vertigo frequency over the final 6 months (18-24 months after injection) compared with the 6 months before the first injection. Analyses were done in the intention-to-treat population, and then per protocol. This trial is registered with ClinicalTrials.gov, number NCT00802529. FINDINGS: Between June 19, 2009, and April 15, 2013, 256 patients with Ménière's disease were screened, 60 of whom were enrolled and randomly assigned: 30 to gentamicin and 30 to methylprednisolone. In the intention-to-treat analysis (ie, all 60 patients), the mean number of vertigo attacks in the final 6 months compared with the 6 months before the first injection (primary outcome) decreased from 19·9 (SD 16·7) to 2·5 (5·8) in the gentamicin group (87% reduction) and from 16·4 (12·5) to 1·6 (3·4) in the methylprednisolone group (90% reduction; mean difference -0·9, 95% CI -3·4 to 1·6). Patients whose vertigo did not improve after injection (ie, non-responders)
Lubeck AJA, Van Ombergen A, Ahmad H, et al., 2016, Differential effect of visual motion adaption upon visual cortical excitability, Journal of Neurophysiology, Vol: 117, Pages: 903-909, ISSN: 0022-3077
The objectives of this study were 1) to probe the effects of visual motion adaptation on early visual and V5/MT cortical excitability and 2) to investigate whether changes in cortical excitability following visual motion adaptation are related to the degree of visual dependency, i.e., an overreliance on visual cues compared with vestibular or proprioceptive cues. Participants were exposed to a roll motion visual stimulus before, during, and after visual motion adaptation. At these stages, 20 transcranial magnetic stimulation (TMS) pulses at phosphene threshold values were applied over early visual and V5/MT cortical areas from which the probability of eliciting a phosphene was calculated. Before and after adaptation, participants aligned the subjective visual vertical in front of the roll motion stimulus as a marker of visual dependency. During adaptation, early visual cortex excitability decreased whereas V5/MT excitability increased. After adaptation, both early visual and V5/MT excitability were increased. The roll motion-induced tilt of the subjective visual vertical (visual dependence) was not influenced by visual motion adaptation and did not correlate with phosphene threshold or visual cortex excitability. We conclude that early visual and V5/MT cortical excitability is differentially affected by visual motion adaptation. Furthermore, excitability in the early or late visual cortex is not associated with an increase in visual reliance during spatial orientation. Our findings complement earlier studies that have probed visual cortical excitability following motion adaptation and highlight the differential role of the early visual cortex and V5/MT in visual motion processing.
Ahmad H, Arshad Q, Roberts R, et al., 2016, CHRONIC DIZZINESS POST TRAUMATIC BRAIN INJURY: A CROSS-SECTIONAL STUDY, Annual Meeting of the Association-of-British-Neurologists (ABN), Publisher: BMJ PUBLISHING GROUP, ISSN: 0022-3050
Roberts RE, Da Silva Melo M, Siddiqui AA, et al., 2016, Vestibular and oculomotor influences on visual dependency., Journal of Neurophysiology, Vol: 116, Pages: 1480-1487, ISSN: 1522-1598
The degree to which a person relies on visual stimuli for spatial orientation is termed visual dependency (VD). VD is considered a perceptual trait or cognitive style influenced by psychological factors and mediated by central re-weighting of the sensory inputs involved in spatial orientation. VD is often measured using the rod-and-disk test, wherein participants align a central rod to the subjective visual vertical (SVV) in the presence of a background that is either stationary or rotating around the line of sight - dynamic SVV. Although this task has been employed to assess VD in health and vestibular disease, it is unknown what effect torsional nystagmic eye movements may have on individual performance. Using caloric ear irrigation, 3D video-oculography and the rod-and-disk test, we show that caloric torsional nystagmus modulates measures of visual dependency and demonstrate that increases in tilt after irrigation are positively correlated with changes in ocular torsional eye movements. When the direction of the slow phase of the torsional eye movement induced by the caloric is congruent with that induced by the rotating visual stimulus, there is a significant increase in tilt. When these two torsional components are in opposition there is a decrease. These findings show that measures of visual dependence can be influenced by oculomotor responses induced by caloric stimulation. The findings are of significance for clinical studies as they indicate that VD, which often increases in vestibular disorders, is not only modulated by changes in cognitive style but also by eye movements, in particular nystagmus.
Patel M, Agarwal K, Arshad Q, et al., 2016, Intratympanic steroids vs. gentamicin in unilateral Ménière's disease: a randomised double-blind comparative effectiveness trial, Lancet, ISSN: 1474-547X
Background: Ménière’s disease (MD) is characterised by severe vertigo attacks and deafness. Intratympanic gentamicin ablates vestibular function, quells vertigo and is the standard treatment for refractory MD - but it can worsen hearing. Intratympanic corticosteroids may reduce vertigo without harming hearing but no RCT comparing steroids versus gentamicin is available.Methods: In this comparative effectiveness trial, refractory unilateral MD patients, defined according to the American Academy of Otolaryngology, were double-blindly randomised (1:1 block-design) to intratympanic methylprednisolone (n=30, 62·5mg/ml) or gentamicin (n=30, 40mg/ml) and followed-up over two years at Charing Cross Hospital (Imperial NHS, London) and Leicester Royal Infirmary, Leicester, UK. Primary outcome was vertigo frequency over the final 6-months (18-24months post-injection) compared to a 6-month pre-injection baseline. Secondary outcomes were vestibular and auditory symptoms (validated questionnaires) and hearing preservation (audiometry). ClinicalTrials.gov:NCT00802529.Findings: For intention-to-treat analysis i.e., all 60 patients, number of vertigo attacks/6months (primary outcome) fell from 19·9 to 2·5 [87%] in the gentamicin arm and 16·4 to 1·6 [90%] in the steroid arm (difference in absolute number of attacks in the final 6months -0·9; 95%CI -3·4 to 1·6). Both drugs reduced the number of vertigo attacks at 2 years (P<0·0001), with equal efficacy (P=0·51). For hearing preservation (secondary outcome), there was no difference (P=0·18) between drugs for hearing thresholds (final difference -2·45decibels, 95%CI -13·4 to 8·5). Both drugs reduced auditory and vestibular symptoms equally. As protocol, patients whose vertigo did not respond post-injection (‘non-responders’) were considered for additional injections by an unblinded physician (8 patients ge
Nigmatullina Y, Siddiqui S, Khan S, et al., 2016, Lateralisation of the vestibular cortex is more pronounced in left-handers, Brain Stimulation, Vol: 9, Pages: 942-944, ISSN: 1935-861X
Arshad Q, Nigmatullina Y, Roberts RE, et al., 2016, Perceived state of self during motion can differentially modulate numerical magnitude allocation., European Journal of Neuroscience, Vol: 44, Pages: 2369-2374, ISSN: 1460-9568
Although a direct relationship between numerical-allocation and spatial-attention has been proposed, recent research suggests these processes are not directly coupled. In keeping with this, spatial attention shifts induced either via visual or vestibular motion can modulate numerical allocation in some circumstances but not in others. In addition to shifting spatial attention, visual or vestibular motion-paradigms also (i) elicit compensatory eye-movements which themselves can influence numerical-processing and (ii) alter the perceptual-state of-"self", inducing changes in bodily self-consciousness impacting upon cognitive mechanisms. Thus, the precise mechanism by which motion modulates numerical-allocation remains unknown. We sought to investigate the influence that different perceptual experiences of motion have upon numerical magnitude allocation whilst controlling for both eye-movements and task-related effects. We first used optokinetic visual-motion stimulation (OKS) to elicit the perceptual experience of either "visual world" or "self"-motion during which eye movements were identical. In a second experiment we used a vestibular protocol examining the effects of perceived and subliminal angular rotations in darkness, which also provoked identical eye movements. We observed that during the perceptual experience of "visual-world" motion, rightward OKS biased judgments towards smaller numbers, whereas leftward OKS biased judgments towards larger numbers. During the perceptual experience of "self-motion", judgments were biased towards larger numbers irrespective of the OKS direction. Contrastingly, vestibular motion perception was found not to modulate numerical magnitude allocation, nor was there any differential modulation when comparing "perceived" versus "subliminal" rotations. We provide a novel demonstration that magnitude-allocation can be differentially modulated by the perceptual state
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