Idiothetic signal processing and spatial orientation in patients with unilateral hippocampal sclerosis

Vestibular perceptual testing from lab to clinic: a review

Not all dizziness presents as vertigo, suggesting other perceptual symptoms for individuals with vestibular disease. These non-specific perceptual complaints of dizziness have led to a recent resurgence in literature examining vestibular perceptual testing with the aim to enhance clinical diagnostics and therapeutics. Recent evidence supports incorporating rehabilitation methods to retrain vestibular perception. This review describes the current field of vestibular perceptual testing from scientific laboratory techniques that may not be clinic friendly to some low-tech options that may be more clinic friendly. Limitations are highlighted suggesting directions for additional research.

Adaptive perceptual responses to asymmetric rotation for testing otolithic function

This study aimed to test the role of the otolithic system in self-motion perception by examining adaptive responses to asymmetric off-axis vertical rotation. Self-movement perception was examined after a conditioning procedure consisting of prolonged asymmetric sinusoidal yaw rotation of the head on a stationary body with hemicycle faster than the other hemicycle. This asymmetric velocity rotation results in a cumulative error in spatial self-motion perception in the upright position that persists over time. Head yaw rotation conditioning was performed in different head positions: in the upright position to activate semicircular canals and in the supine and prone positions to activate both semicircular canals and otoliths with the phase of otolithic stimulation reversed with respect to activation of the semicircular canals. The asymmetric conditioning influenced the cumulative error induced by four asymmetric cycles of whole-body vertical axis yaw rotation. The magnitude of this error depended on the orientation of the head during the conditioning. The error increased by 50% after upright position conditioning, by 100% in the supine position, and decreased by 30% in the prone position. The enhancement and reduction of the perceptual error are attributed to otolithic modulation because of gravity influence of the otoliths during the conditioning procedure in supine and prone positions. These findings indicate that asymmetric velocity otolithic activation induces adaptive perceptual errors such as those induced by semicircular canals alone, and this adaptation may be useful in testing dynamic otolithic perceptual responses under different conditions of vestibular dysfunction.

Neuroimaging Systematic Review in Persistent Postural-Perceptual Dizziness: The Elaborate Alterations in the Delicate Network to Remain Balanced

OBJECTIVES

Persistent postural-perceptual dizziness (PPPD) is a chronic functional vestibular disorder that may have normal physical examination, clinical laboratory testing and vestibular evaluation. However, advances in neuroimaging have provided new insights in brain functional connectivity and structure in patients with PPPD. This systematic review was aimed at identifying significant structural or alterations in functional connectivity in patients with PPPD.

DATABASES REVIEWED

Science Direct, Pubmed, Embase via Ovid databases, and Cochrane library.

METHODS

This review following the guidelines of PRISMA, systematically and independently examined papers published up to March 2021 which fulfilled the predetermined criteria. PROSPERO Registration (CRD42020222334).

RESULTS

A total of 15 studies were included (MRI = 4, SPECT = 1, resting state fMRI = 4, task-based fMRI = 5, task-based fMRI + MRI = 1). Significant changes in the gray matter volume, cortical folding, blood flow, and connectivity were seen at different brain regions involved in vestibular, visual, emotion, and motor processing.

CONCLUSION

There is a multisensory dimension to the impairment resulting in chronic compensatory changes in PPPD that is evident by the significant alterations in multiple networks involved in maintaining balance. These changes observed offer some explanation for the symptoms that a PPPD patient may experience.Systematic Review Registration: This study is registered with PROSPERO (CRD42020222334).

Comorbidity Matters: Social Visual Attention in a Comparative Study of Autism Spectrum Disorder, Attention-Deficit/Hyperactivity Disorder and Their Comorbidity

Autism Spectrum Disorder (ASD) and Attention-Deficit/Hyperactivity Disorder (ADHD) represent two common neurodevelopmental disorders with considerable co-occurrence. Their comorbidity (ASD + ADHD) has been included in the latest diagnostic guidelines (DSM-V, 2013). The present study focuses on social visual attention that i) is a main aspect of social attention reflecting social cognition and ii) its atypicalities have been suggested as a potential biomarker for ASD. Considering the possible shared background of both disorders and their comorbidity, it is important to compare such traits directly. Here, 73 children and adolescents paired for age and IQ diagnosed with ASD (N = 12), ADHD (N = 21), comorbid ASD + ADHD (N = 15), and "typically developing" (TD) controls (N = 25), were shown static real-life social scenes while their gaze movements were recorded with eye-tracking. Scenes with two levels of social complexity were presented: low complexity (one person depicted) and high (four interacting individuals). Gaze fixation variables were investigated. Fixation duration on faces was significantly reduced only in ASD + ADHD which also required longer time to fixate all faces at least once. Fixation duration on faces in ASD was reduced, compared to TD, only when looking at scenes with high versus low social complexity. ADHD individuals did not differ from TD. Concluding, the observed alterations of social visual attention support the existence of possible dysfunctional particularities differentiating ASD, ADHD, and ASD + ADHD, which can be revealed with the new method of eye-tracking technique. The objective gaze measurements provided contribute to the development of biomarkers enabling early diagnosis, amelioration of care and further interventions specified for each group.