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Abstract of the Week

December Topic of the month: Affect of Vision on VOR

No 499: December 11, 2019


Tamás LT, Lundberg YW, Büki B. Vergence increases the gain of the human angular vestibulo-ocular reflex during peripheral hyposensitivity elicited by cold thermal irrigation. J Vestib Res. 2018;27(5-6):265-270. doi: 10.3233/VES-170629.
OBJECTIVE:  The aim of this study was to determine if convergence increases the gain during peripheral hyposensitivity elicited by cold thermal irrigation.

RESULTS:  Before caloric irrigation, near viewing (15cm) increased the average VOR gain by 28% (from 1 to 1.28). Cold (24°C) water irrigation of the right ear decreased the gain to 0.66 (far viewing) and 0.82 (near viewing) (22% difference). Although vergence also increased the gain for impulses to the left to the same degree before caloric stimulus, the caloric irrigation itself (applied to the right ear) did not influence the gain for contralateral impulses.

CONCLUSION:  In our experiments vergence increased the gain of the human angular VOR during peripheral hyposensitivity elicited by cold thermal irrigation. These results suggest that cold irrigation does not abolish the function of the nonlinear/phasic vestibular afferent pathway.
PMID: 29400687


No 498: December 5, 2019

Castro P, Sena Esteves S, Lerchundi F, Buckwell D, Gresty MA, Bronstein AM, Arshad Q. Viewing Target Distance Influences the Vestibulo-Ocular Reflex Gain when Assessed Using the Video Head Impulse Test. Audiol Neurootol. 2018;23(5):285-289. Epub 2018 Dec 11.
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.
PMID: 30537706 


November Topic of the month: Vestibular Hypofunction

No 497: November 29, 2019

Rinaudo CN, Schubert MC, Cremer PD, Figtree WVC, Todd CJ, Migliaccio AA. Improved Oculomotor Physiology and Behavior After Unilateral Incremental Adaptation Training in a Person With Chronic Vestibular Hypofunction: A Case Report. Phys Ther. 2019 Oct 28;99(10):
BACKGROUND AND PURPOSE: Traditional vestibular rehabilitation therapies are effective in reducing vestibular hypofunction symptoms, but changes to the vestibulo-ocular reflex (VOR) are minimal. This controlled case report describes an increase in VOR after 6 months of incremental VOR adaptation (IVA) training in a person with chronic unilateral vestibular hypofunction.

CASE DESCRIPTION: The participant was a 58-year-old female with a confirmed (Neurologist P.D.C.) left vestibular lesion stable for 2 years prior to entering a clinical trial examining the effects of daily IVA training. She was evaluated monthly for self-reported symptoms (dizziness handicap inventory), VOR function (video head impulse test), and VOR behavior (Dynamic Visual Acuity test). Intervention consisted of 6 months of 15 minutes per day unassisted training using the IVA training regime with a device developed in our laboratory. The take-home device enables the VOR response to gradually normalize on the ipsilesional side via visual-vestibular mismatch training. The intervention was followed by a 6-month wash-out and 3-month control period. The control condition used the same training device set to function like standard VOR training indistinguishable to the participant.

OUTCOMES: After the intervention, ipsilesional VOR function improved substantially. The VOR adapted both via a 52% increase in slow-phase response and via 43% earlier onset compensatory saccades for passive head movements. In addition, the participant reported fewer symptoms and increased participation in sports and daily activities.

DISCUSSION: Here, a participant with chronic vestibular hypofunction showing improved oculomotor performance atypical for traditional vestibular rehabilitation therapies, subsequent to using the newly developed IVA technique, is presented. It is the first time to our knowledge an improvement of this magnitude has been demonstrated as well as sustained over an extended period of time.
PMID: 31197314


No 496: November 20, 2019

Hermann R.  Pelisson D.  Dumas O, Urquizar C, Truy E. Tilikete C.  Are Covert Saccade Functionally Relevant in Vestibular Hypofunction? Cerebellum. 2018 Jun;17(3):300-307
The vestibulo-ocular reflex maintains gaze stabilization during angular or linear head accelerations, allowing adequate dynamic visual acuity. In case of bilateral vestibular hypofunction, patients use saccades to compensate for the reduced vestibulo-ocular reflex function, with covert saccades occurring even during the head displacement. In this study, we questioned whether covert saccades help maintain dynamic visual acuity, and evaluated which characteristic of these saccades are the most relevant to improve visual function. We prospectively included 18 patients with chronic bilateral vestibular hypofunction. Subjects underwent evaluation of dynamic visual acuity in the horizontal plane as well as video recording of their head and eye positions during horizontal head impulse tests in both directions (36 ears tested). Frequency, latency, consistency of covert saccade initiation, and gain of covert saccades as well as residual vestibulo-ocular reflex gain were calculated. We found no correlation between residual vestibulo-ocular reflex gain and dynamic visual acuity. Dynamic visual acuity performance was however positively correlated with the frequency and gain of covert saccades and negatively correlated with covert saccade latency. There was no correlation between consistency of covert saccade initiation and dynamic visual acuity. Even though gaze stabilization in space during covert saccades might be of very short duration, these refixation saccades seem to improve vision in patients with bilateral vestibular hypofunction during angular head impulses. These findings emphasize the need for specific rehabilitation technics that favor the triggering of covert saccades. The physiological origin of covert saccades is discussed
PMID: 29248983


No 495: November 15, 2019

Roller RA, Hall CD. A speed-based approach to vestibular rehabilitation for peripheral vestibular hypofunction: A retrospective chart review. J Vestib Res. 2018;28(3-4):349-357. doi: 10.3233/VES-180633.
BACKGROUND: Current vestibular rehabilitation for peripheral vestibular hypofunction is an exercise-based approach that improves symptoms and function in most, but not all patients, and includes gaze stabilization exercises focused on duration of head movement. One factor that may impact rehabilitation outcomes is the speed of head movement during gaze stability exercises.

OBJECTIVE: Examine outcomes of modified VOR X1 exercises that emphasize a speed-based approach for gaze stabilization while omitting substitution and habituation exercises. Balance training focused on postural realignment and hip strategy performance during altered visual and somatosensory inputs.

METHODS: A retrospective chart review of 159 patients with vestibular deficits was performed and five outcome measures were analyzed.

RESULTS: All outcomes - self-report dizziness and balance function, dynamic gait index, modified clinical test of sensory interaction and balance, and clinical dynamic visual acuity improved significantly and approached or achieved normal scores.

CONCLUSIONS: The combination of modified VOR X1 gaze stability exercises, wherein patients achieved high-velocity head movement (240°/s) during short exercise bouts, with "forced use" gait and balance exercises for postural realignment and hip strategy recruitment, achieved 93-99% of normal scores for all five outcomes. These results compare favorably to the outcomes for current VR techniques and warrant further investigation.
PMID: 29689764


No 494: November 7, 2019

Michel L, Laurent T, Alain T. Rehabilitation of dynamic visual acuity in patients with unilateral vestibular hypofunction: earlier is better. Eur Arch Otorhinolaryngol. 2019 Oct 21.

PURPOSE: Patients with acute peripheral unilateral hypofunction (UVH) complain of vertigo and dizziness and show posture imbalance and gaze instability. Vestibular rehabilitation therapy (VR) enhances the functional recovery and it has been shown that gaze stabilization exercises improved the dynamic visual acuity (DVA). Whether the effects of VR depend or not on the moment when it is applied remains however unknown, and investigation on how the recovery mechanisms could depend or not on the timing of VR has not yet been tested.

METHODS: Our study investigated the recovery of DVA in 28 UVH patients whose unilateral deficit was attested by clinical history and video head impulse test (vHIT). Patients were tested under passive conditions before (pre-tests) and after (post-tests) being subjected to an active DVA rehabilitation protocol. The DVA protocol consisted in active gaze stabilization exercises with two training sessions per week, each lasting 30 min, during four weeks. Patients were sub-divided into three groups depending on the time delay between onset of acute UVH and beginning of VR. The early DVA group (N = 10) was composed of patients receiving the DVA protocol during the first 2 weeks after onset (mean = 8.9), the late group 1  (N=9) between the 3rd and the 4th week (mean = 27.5 days after) and the late group 2 (N = 9) after the 1st month (mean: 82.5 days). We evaluated the DVA score, the angular aVOR gain, the directional preponderance and the percentage of compensatory saccades during the HIT, and the subjective perception of dizziness with the Dizziness Handicap Inventory (DHI). The pre- and post-VR tests were performed with passive head rotations done by the physiotherapist in the plane of the horizontal and vertical canals.

RESULTS: The results showed that patients submitted to an early DVA rehab improved significantly their DVA score by increasing their passive aVOR gain and decreasing the percentage of compensatory saccades, while the late 1 and late 2 DVA groups 1 and 2 showed less DVA improvement and an inverse pattern, with no change in the aVOR gain and an increase in the percentage of compensatory saccades. All groups of patients exhibited significant reductions of the DHI score, with higher improvement in subjective perception of dizziness handicap in the patients receiving the DVA rehab protocol in the first month.

CONCLUSION: Our data provide the first demonstration in UVH patients that earlier is better to improve DVA and passive aVOR gain. Gaze stabilization exercises would benefit from the plastic events occurring in brain structures during a sensitive period or opportunity time window to elaborate optimal functional reorganizations. This result is potentially very important for the VR programs to restore the aVOR gain instead of recruiting compensatory saccades assisting gaze stability.
PMID:  31637477


October Topic of the month: Neural Correlates of Dizziness

No 493: October 23, 2019

Micarelli A, Chiaravalloti A, Schillaci O, Ottaviani F, Alessandrini M. Aspects of cerebral plasticity related to clinical features in acute vestibular neuritis: a "starting point" review from neuroimaging studies. Acta Otorhinolaryngol Ital 2016, Apr;36(2):75-84. doi: 10.14639/0392-100X-642. Epub 2016 Apr 29.

Vestibular neuritis (VN) is one of the most common causes of vertigo and is characterised by a sudden unilateral vestibular failure (UVF). Many neuroimaging studies in the last 10 years have focused on brain changes related to sudden vestibular deafferentation as in VN. However, most of these studies, also due to different possibilities across diverse centres, were based on different times of first acquisition from the onset of VN symptoms, neuroimaging techniques, statistical analysis and correlation with otoneurological and psychological findings. In the present review, the authors aim to merge together the similarities and discrepancies across various investigations that have employed neuroimaging techniques and group analysis with the purpose of better understanding about how the brain changes and what characteristic clinical features may relate to each other in the acute phase of VN. Six studies that strictly met inclusion criteria were analysed to assess cortical-subcortical correlates of acute clinical features related to VN. The present review clearly reveals that sudden UVF may induce a wide variety of cortical and subcortical responses - with changes in different sensory modules - as a result of acute plasticity in the central nervous system.
PMID:  27196070


No 492: October 16, 2019

Van Ombergen A, Heine L, Jillings S, Roberts RE, Jeurissen B, Van Rompaey V, Mucci V, Vanhecke S, Sijbers J, Vanhevel F, Sunaert S, Bahri MA, Parizel PM, Van de Heyning PH, Laureys S, Wuyts FL. Altered functional brain connectivity in patients with visually induced dizziness. Neuroimage Clin 2017, Feb 28;14:538-545. doi: 10.1016/j.nicl.2017.02.020. eCollection 2017.

BACKGROUND: Vestibular patients occasionally report aggravation or triggering of their symptoms by visual stimuli, which is called visually induced dizziness (VID). These patients therefore experience dizziness, discomfort, disorientation and postural unsteadiness. The underlying pathophysiology of VID is still poorly understood.

OBJECTIVE: The aim of the current explorative study was to gain a first insight in the underlying neural aspects of VID.

METHODS: We included 10 VID patients and 10 healthy matched controls, all of which underwent a resting state fMRI scan session. Changes in functional connectivity were explored by means of the intrinsic connectivity contrast (ICC). Seed-based analysis was subsequently performed in visual and vestibular seeds.

RESULTS: We found a decreased functional connectivity in the right central operculum (superior temporal gyrus), as well as increased functional connectivity in the occipital pole in VID patients as compared to controls in a hypothesis-free analysis. A weaker functional connectivity between the thalamus and most of the right putamen was measured in VID patients in comparison to controls in a seed-based analysis. Furthermore, also by means of a seed-based analysis, a decreased functional connectivity between the visual associative area and the left parahippocampal gyrus was found in VID patients. Additionally, we found increased functional connectivity between thalamus and occipital and cerebellar areas in the VID patients, as well as between the associative visual cortex and both middle frontal gyrus and precuneus.

CONCLUSIONS: We found alterations in the visual and vestibular cortical network in VID patients that could underlie the typical VID symptoms such as a worsening of their vestibular symptoms when being exposed to challenging visual stimuli. These preliminary findings provide the first insights into the underlying functional brain connectivity in VID patients. Future studies should extend these findings by employing larger sample sizes, by investigating specific task-based paradigms in these patients and by exploring the implications for treatment.
PMID:  28331800


No 491: October 10, 2019

Helmchen C, Rother M, Spliethoff P, Sprenger A. Increased brain responsivity to galvanic vestibular stimulation in bilateral vestibular failure. Neuroimage Clin 2019, Jul 19;24:101942. doi: 10.1016/j.nicl.2019.101942

In this event-related functional magnetic resonance imaging (fMRI) study we investigated how the brain of patients with bilateral vestibular failure (BVF) responds to vestibular stimuli. We used imperceptible noisy galvanic vestibular stimulation (GVS) and perceptible bi-mastoidal GVS intensities and related the corresponding brain activity to the evoked motion perception. In contrast to caloric irrigation, GVS stimulates the vestibular organ at its potentially intact afferent nerve site. Motion perception thresholds and cortical responses were compared between 26 BVF patients to 27 age-matched healthy control participants. To identify the specificity of vestibular cortical responses we used a parametric design with different stimulus intensities (noisy imperceptible, low perceptible, high perceptible) allowing region-specific stimulus response functions. In a 2 x 3 flexible factorial design all GVS-related brain activities were contrasted with a sham condition that did not evoke perceived motion. Patients had a higher motion perception threshold and rated the vestibular stimuli higher than the healthy participants. There was a stimulus intensity related and region-specific increase of activity with steep stimulus response functions in parietal operculum (e.g. OP2), insula, superior temporal gyrus, early visual cortices (V3) and cerebellum while activity in the hippocampus and intraparietal sulcus did not correlate with vestibular stimulus intensity. Using whole brain analysis, group comparisons revealed increased brain activity in early visual cortices (V3) and superior temporal gyrus of patients but there was no significant interaction, i.e. stimulus-response function in these regions were still similar in both groups. Brain activity in these regions during (high)GVS increased with higher dizziness-related handicap scores but was not related to the degree of vestibular impairment or disease duration. nGVS did not evoke cortical responses in any group. Our data indicate that perceptible GVS-related cortical responsivity is not diminished but increased in multisensory (visual-vestibular) cortical regions despite bilateral failure of the peripheral vestibular organ. The increased activity in early visual cortices (V3) and superior temporal gyrus of BVF patients has several potential implications: (i) their cortical reciprocal inhibitory visuo-vestibular interaction is dysfunctional, (ii) it may contribute to the visual dependency of BVF patients, and (iii) it needs to be considered when BVF patients receive peripheral vestibular stimulation devices, e.g. vestibular implants or portable GVS devices. Imperceptible nGVS did not elicit cortical brain responses making it unlikely that the reported balance improvement of BVF by nGVS is mediated by cortical mechanisms.
PMID: 31382239


No 490: October 2, 2019

lsalman O, Ost J, Vanspauwen R, Blaivie C, De Ridder D, Vanneste S. The Neural Correlates of Chronic Symptoms of Vertigo Proneness in Humans. PLoS One 2016, Apr 18;11(4):e0152309. doi: 10.1371/journal.pone.0152309. eCollection 2016.
Vestibular signals are of significant importance for variable functions including gaze stabilization, spatial perception, navigation, cognition, and bodily self-consciousness. The vestibular network governs functions that might be impaired in patients affected with vestibular dysfunction. It is currently unclear how different brain regions/networks process vestibular information and integrate the information into a unified spatial percept related to somatosensory awareness and whether people with recurrent balance complaints have a neural signature as a trait affecting their development of chronic symptoms of vertigo. Pivotal evidence points to a vestibular-related brain network in humans that is widely distributed in nature. By using resting state source localized electroencephalography in non-vertiginous state, electrophysiological changes in activity and functional connectivity of 23 patients with balance complaints where chronic symptoms of vertigo and dizziness are among the most common reported complaints are analyzed and compared to healthy subjects. The analyses showed increased alpha2 activity within the posterior cingulate cortex and the precuneues/cuneus and reduced beta3 and gamma activity within the pregenual and subgenual anterior cingulate cortex for the subjects with balance complaints. These electrophysiological variations were correlated with reported chronic symptoms of vertigo intensity. A region of interest analysis found reduced functional connectivity for gamma activity within the vestibular cortex, precuneus, frontal eye field, intra-parietal sulcus, orbitofrontal cortex, and the dorsal anterior cingulate cortex. In addition, there was a positive correlation between chronic symptoms of vertigo intensity and increased alpha-gamma nesting in the left frontal eye field. When compared to healthy subjects, there is evidence of electrophysiological changes in the brain of patients with balance complaints even outside chronic symptoms of vertigo episodes. This suggests that these patients have a neural signature or trait that makes them prone to developing chronic balance problems.
PMID: 27089185

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