The Neuroanatomical Correlates of Training-Related Perceptuo-Reflex Uncoupling in Dancers

Sensory input evokes low-order reflexes and higher-order perceptual responses. Vestibular stimulation elicits vestibular-ocular reflex (VOR) and self-motion perception (e.g., vertigo) whose response durations are normally equal. Adaptation to repeated whole-body rotations, for example, ballet training, is known to reduce vestibular responses. We investigated the neuroanatomical correlates of vestibular perceptuo-reflex adaptation in ballet dancers and controls. Dancers' vestibular-reflex and perceptual responses to whole-body yaw-plane step rotations were: (1) Briefer and (2) uncorrelated (controls' reflex and perception were correlated). Voxel-based morphometry showed a selective gray matter (GM) reduction in dancers' vestibular cerebellum correlating with ballet experience. Dancers' vestibular cerebellar GM density reduction was related to shorter perceptual responses (i.e. positively correlated) but longer VOR duration (negatively correlated). Contrastingly, controls' vestibular cerebellar GM density negatively correlated with perception and VOR. Diffusion-tensor imaging showed that cerebral cortex white matter (WM) microstructure correlated with vestibular perception but only in controls. In summary, dancers display vestibular perceptuo-reflex dissociation with the neuronatomical correlate localized to the vestibular cerebellum. Controls' robust vestibular perception correlated with a cortical WM network conspicuously absent in dancers. Since primary vestibular afferents synapse in the vestibular cerebellum, we speculate that a cerebellar gating of perceptual signals to cortical regions mediates the training-related attenuation of vestibular perception and perceptuo-reflex uncoupling

Temporoparietal encoding of space and time during vestibular-guided orientation

When we walk in our environment, we readily determine our travelled distance and location using visual cues. In the dark, estimating travelled distance uses a combination of somatosensory and vestibular (i.e., inertial) cues. The observed inability of patients with complete peripheral vestibular failure to update their angular travelled distance during active or passive turns in the dark implies a privileged role for vestibular cues during human angular orientation. As vestibular signals only provide inertial cues of self-motion (e.g., velocity, °/s), the brain must convert motion information to distance information (a process called 'path integration') to maintain our spatial orientation during self-motion in the dark. It is unknown, however, what brain areas are involved in converting vestibular-motion signals to those that enable such vestibular-spatial orientation. Hence, using voxel-based lesion-symptom mapping techniques, we explored the effect of acute right hemisphere lesions in 18 patients on perceived angular position, velocity and motion duration during whole-body angular rotations in the dark. First, compared to healthy controls' spatial orientation performance, we found that of the 18 acute stroke patients tested, only the four patients with damage to the temporoparietal junction showed impaired spatial orientation performance for leftward (contralesional) compared to rightward (ipsilesional) rotations. Second, only patients with temporoparietal junction damage showed a congruent underestimation in both their travelled distance (perceived as shorter) and motion duration (perceived as briefer) for leftward compared to rightward rotations. All 18 lesion patients tested showed normal self-motion perception. These data suggest that the cerebral cortical regions mediating vestibular-motion ('am I moving?') and vestibular-spatial perception ('where am I?') are distinct. Furthermore, the congruent contralesional deficit in time (motion duration) and position perception, seen only in temporoparietal junction patients, may reflect a common neural substrate in the temporoparietal junction that mediates the encoding of motion duration and travelled distance during vestibular-guided navigation. Alternatively, the deficits in timing and spatial orientation with temporoparietal junction lesions could be functionally linked, implying that the temporoparietal junction may act as a cortical temporal integrator, combining estimates of self-motion velocity over time to derive an estimate of travelled distance. This intriguing possibility predicts that timing abnormalities could lead to spatial disorientation

Persistent postural-perceptual dizziness: a useful new syndrome.

In this issue of Practical Neurology, Popkirov, Staab and Stone illuminate a newly defined condition—persistent postural-perceptual dizziness or ‘PPPD’, a maladaptive functional syndrome in which patients feel unbalanced despite not falling, and feel that they are moving, despite being stationary. PPPD is common in specialist dizzy clinics, accounting for 10% of cases as a primary diagnosis of dizziness. PPPD can coexist with other causes of dizziness, such as vestibular migraine or benign paroxysmal positional vertigo, and it is in this form that it most commonly presents to a specialist dizzy clinic.BMS: funded by the Medical Research Council, the NIHR Imperial Biomedical Research Centre, and the Imperial Health Charity. LP: funded by the Medical Research Council (MRC) (MR/P01271X/1) at the University of Cambridge, UK

Vestibular deficits in neurodegenerative disorders: balance, dizziness, and spatial disorientation

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

Public opinion on crime, punishment and the death penalty in Barbados

The bulk of extant research on public opinion on crime and punishment is focused on Global North nations. This article contributes a new perspective to the literature on punitivism by examining public opinion on crime, punishment and the death penalty in Barbados. The article presents insights from exploratory focus group research conducted in Barbados in 2017. These findings are particularly relevant as Barbadian lawmakers navigate reform of the nation’s death penalty law. While the focus groups reveal anxieties that echo those identified in other jurisdictions, related to nostalgia for the past and concern regarding social order for instance, they also demonstrate the specific relevance of time and place. Using approaches from Caribbean Criminology and drawing on post-colonial perspectives, the article examines the context of views on punishment in Barbados, including perceptions of ‘neo-colonial’ interference and concerns about what can be lost in the process of ‘progress’

The Effects of Supplemental and Substitutional Bee Food on the Common Eastern Bumblebee (Bombus impatiens)

This study was undertaken to determine the effect of supplemental and substitution bee food on the common eastern bumblebee (Bombus impatiens) compared to what is most commonly fed to captive bumblebees now, which is honeybee pollen. There is not an extensive amount of knowledge about the effects of supplemental or substitutional bee food and whether or not what is fed to bumblebees can have an effect on their overall success and health. Three different test groups of micro-colonies of bumblebee each with ten replicants were set up in order to test this; each were fed a different bee food: (i) 100% honeybee pollen (P), (ii) a supplemental bee food (GP) and (iii) a substitutional bee food (BP). Over the test period it was discovered that bumblebees which were fed 100% honeybee pollen consumed between 63-73% more food than those fed a supplemental or substitutional food. It was also found that there was a relationship between what is fed to bumblebees and their success, in this case the amount of eggs they laid. Those bumblebees which were fed 100% honeybee pollen (P) and those that were fed a supplemental food (GP) had comparable amounts of eggs laid; P laid 121 eggs and GP laid 112 eggs). This is despite the fact that the bees in test group GP ate 66% less food than those bees which ate 100% honeybee pollen and yet they produced a comparable amount of eggs over the course of the experiment. The amount of supplemental food eaten by GP could be compared to the amount that was eaten by those bees fed a substitutional bee food (BP) as the two test groups ate a similar amount of food. GP only ate 16% more food compared to BP. However, the amount of eggs that each of the groups laid was vastly different with bumblebees that ate a supplemental diet (GP) laying 112 eggs in total and bees fed a substitutional bee food (BP) only laying 2 eggs in total over the experimental period. These findings suggested that supplemental food may be a comparable alternative food to be fed to captive bumblebees instead of what is most commonly fed to them which is honeybee pollen

Vestibular Perception following Acute Unilateral Vestibular Lesions.

Little is known about the vestibulo-perceptual (VP) system, particularly after a unilateral vestibular lesion. We investigated vestibulo-ocular (VO) and VP function in 25 patients with vestibular neuritis (VN) acutely (2 days after onset) and after compensation (recovery phase, 10 weeks). Since the effect of VN on reflex and perceptual function may differ at threshold and supra-threshold acceleration levels, we used two stimulus intensities, acceleration steps of 0.5°/s(2) and velocity steps of 90°/s (acceleration 180°/s(2)). We hypothesised that the vestibular lesion or the compensatory processes could dissociate VO and VP function, particularly if the acute vertiginous sensation interferes with the perceptual tasks. Both in acute and recovery phases, VO and VP thresholds increased, particularly during ipsilesional rotations. In signal detection theory this indicates that signals from the healthy and affected side are still fused, but result in asymmetric thresholds due to a lesion-induced bias. The normal pattern whereby VP thresholds are higher than VO thresholds was preserved, indicating that any 'perceptual noise' added by the vertigo does not disrupt the cognitive decision-making processes inherent to the perceptual task. Overall, the parallel findings in VO and VP thresholds imply little or no additional cortical processing and suggest that vestibular thresholds essentially reflect the sensitivity of the fused peripheral receptors. In contrast, a significant VO-VP dissociation for supra-threshold stimuli was found. Acutely, time constants and duration of the VO and VP responses were reduced - asymmetrically for VO, as expected, but surprisingly symmetrical for perception. At recovery, VP responses normalised but VO responses remained shortened and asymmetric. Thus, unlike threshold data, supra-threshold responses show considerable VO-VP dissociation indicative of additional, higher-order processing of vestibular signals. We provide evidence of perceptual processes (ultimately cortical) participating in vestibular compensation, suppressing asymmetry acutely in unilateral vestibular lesions