DSpace Repository :: Browsing by Author "Castro, Patricia"

Browsing by Author "Castro, Patricia"

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Electroencephalographic response to transient adaptation of vestibular perception
(2022) Cooke, Josephine; Guven, Onur; Castro, Patricia; Ibitoye, Richard; Pettorossi, Vito; Bronstein, Adolfo
When given a series of sinusoidal oscillations in which the two hemicycles have equal amplitude but asymmetric velocity, healthy subjects lose perception of the slower hemicycle (SHC), reporting a drift towards the faster hemicycle (FHC). This response is not reflected in the vestibular-ocular reflex, suggesting that the adaptation is of higher order. This study aimed to define EEG correlates of this adaptive response. Twenty-five subjects underwent a series of symmetric or asymmetric oscillations and reported their perceived head orientation at the end using landmarks in the testing room; this was converted into total position error (TPE). Thirty-two channel EEG was recorded before, during and after adaptation. Spectral power and coherence were calculated for the alpha, beta, delta and theta frequency bands. Linear mixed models were used to determine a region-by-condition effect of the adaptation. TPE was significantly greater in the asymmetric condition and reported error was always in the direction of the FHC. Regardless of condition, alpha desynchronised in response to stimulation, then rebounded back toward baseline values. This pattern was accelerated and attenuated in the prefrontal and occipital regions, respectively, in the asymmetric condition. Functional connectivity networks were identified in the beta and delta frequency bands; these networks, primarily comprising frontoparietal connections, were more coherent during asymmetric stimulation. These findings suggest that the temporary vestibulo-perceptual 'neglect' induced by asymmetric vestibular stimulation may be mediated by alpha rhythms and frontoparietal attentional networks. The results presented further our understanding of brain rhythms and cortical networks involved in vestibular perception and adaptation. KEY POINTS: Whole-body asymmetric sinusoidal oscillations, which consist of hemicycles with equal amplitude but differing velocities, can induce transient 'neglect' of the slower hemicycle in the vestibular perception of healthy subjects. In this study, we aimed to elucidate EEG correlates of this 'neglect', thereby identifying a cortical role in vestibular perception and adaptation. We identified a desynchronisation-resynchronisation response in the alpha frequency band (8-14 Hz) that was accelerated in the prefrontal region and attenuated in the occipital region when exposed to asymmetric, as compared to symmetric, rotations. We additionally identified functional connectivity networks in the beta (14-30 Hz) and delta (1-4 Hz) frequency bands consisting primarily of frontoparietal connections. These results suggest a prominent role of alpha rhythms and frontoparietal attentional networks in vestibular perception and adaptation.
Head shaking does not alter vestibulo ocular reflex gain in vestibular migraine
(2022) Patel, Priyani; Castro, Patricia; Kooh, Nehzat; Arshad, Qadeer; Gargallo, Lucia; Carmona, Sergio; Kaski, Diego
Vestibular Migraine (VM) is the most common cause of non-positional episodic vestibular symptoms. Patients with VM commonly report increased motion sensitivity, suggesting that vestibular responses to head movement may identify changes specific to VM patients. Here we explore whether the vestibulo-ocular reflex (VOR) gain alters in response to a clinical “headshake” maneuver in patients with VM. Thirty patients with VM in the inter-ictal phase, 16 patients with Benign Positional Paroxysmal Vertigo (BPPV) and 15 healthy controls were recruited. Patients responded to the question “Do you feel sick reading in the passenger seat of a car?” and completed a validated motion sickness questionnaire as a measure of motion sensitivity. Lateral canal vHIT testing was performed before and after headshaking; the change in VOR gain was calculated as the primary outcome. Baseline VOR gain was within normal limits across all participants. There was no significant change in VOR gain after headshaking in any group (p = 0.264). Patients were 4.3 times more likely to be in the VM group than in the BPPV group if they reported nausea when reading in the passenger seat of a car. We postulate that a headshake stimulus may be insufficient to disrupt cortical interactions and induce a change in VOR gain. Alternatively, changes in VOR gain may only be apparent in the acute phase of VM. Reading in the passenger seat of a car was considered uncomfortable in all VM patients suggesting that this specific question may be useful for the diagnosis of VM.
Priming overconfidence in belief systems reveals negative return on postural control mechanisms
(2022) Castro, Patricia; Papoutselou, Efstratia; Mahmoud, Sami; Hussain, Shahvaiz; Fuentealba Bassaletti, Constanza; Kaski, Diego; Bronstein, Adolfo; Arshad, Qadeer
Background: Modulation of postural control strategies and heightened perceptual ratings of instability when exposed to postural threats, illustrates the association between anxiety and postural control. Research question: Here we test whether modulating prior expectations can engender postural-related anxiety which, in turn, may impair postural control and dissociate the well-established relationship between sway and subjective instability. Methods: We modulated expectations of the difficulty posed by an upcoming postural task via priming. In the visual priming condition, participants watched a video of an actor performing the task with either a stable or unstable performance, before themselves proceeding with the postural task. In the verbal priming paradigm, participants were given erroneous verbal information regarding the amplitude of the forthcoming platform movement, or no prior information. Results: Following the visual priming, the normal relationship between trunk sway and subjective instability was preserved only in those individuals that viewed the stable but not the unstable actor. In the verbal priming experiment we observed an increase in subjective instability and anxiety during task performance in individuals who were erroneously primed that sled amplitude would increase, when in fact it did not. Significance: Our findings show that people's subjective experiences of instability and anxiety during a balancing task are powerfully modulated by priming. The contextual provision of erroneous cognitive priors dissociates the normally 'hard wired' relationship between objective measures and subjective ratings of sway. Our findings have potential clinical significance for the development of enhanced cognitive retraining in patients with balance disorders, e.g. via modifying expectations.
Saccadic Direction Errors are Associated with Impulsive Compulsive Behaviours in Parkinson's Disease Patients
(IOS Press, 2019) Barbosa, Pedro; Kaski, Diego; Castro, Patricia; Andrew, Andrew; Warner, Thomas; Djamshidian, Atbin
Fifteen individuals with Parkinson's disease (PD) and impulsive compulsive behaviours (PD+ICB) were compared to 15 PD patients without ICBs (PD-ICB) and 15 healthy controls (HC) on a pro-saccades and an anti-saccades task to assess if ICBs are associated with distinct saccadic abnormalities. PD+ICB made shorter saccades than HC and more direction errors in the anti-saccades task than PD-ICB and HC, suggesting that patients with ICBs have greater difficulty in suppressing automatic saccades towards a given target. Saccadic assessment has the potential to evolve into a marker to guide therapeutic decisions in patients at risk of developing ICBs.
Subjective stability perception is related to postural anxiety in older subjects
(Elsevier B.V., 2019-02) Castro, Patricia; Kaski, Diego; Schieppati, Marco; Furman, Michael; Arshad, Qadeer; Bronstein, Adolfo
Background: Under static conditions, the objective and subjective measures of postural stability correlate well. However, age-related changes in postural control and task-related anxiety may modify the relationship between these subjective and objective measures. Ultimately, patients' symptoms represent subjective reports, thus understanding this relationship has clinical implications. Aims: This study investigates the relationship between subjective-objective measures of postural stability in dynamic conditions and whether this relationship is influenced by age or task-related anxiety. Methods: 50 healthy participants (aged 18-83 years) stood on a platform oscillating at variable amplitudes, with-without a fall-preventing harness to modulate task-related anxiety. Trunk sway path, hip velocity and foot lifts (objective measures) and subjective scores of instability and task-related anxiety were recorded. Results: The subjective perception of stability accurately matched objective body sway, following a logarithmic function profile (r2 = 0.72, p < 0.001). This function did not change significantly with age, harness or task presentation order. A strong relationship was observed between subjective measures of stability and task-related anxiety for all subjects (r = 0.81, p < 0.001). Task repetition reduced anxiety in the young, uncoupling anxiety changes from subjective instability, but not in the elderly who retained higher anxiety levels in line with subjective unsteadiness. Discussion: Subjects accurately rate their own instability during dynamic postural challenges, irrespective of age and actual fall risk. However, anxiety may selectively modulate the perception of instability in older subjects. The perception of stability relies upon the integration of sensory afferents but also recruits emotional-cognitive processes, particularly in older individuals. The use of a safety harness has no influence on subjective or objective postural stability.
Vestibular loss disrupts visual reactivity in the alpha EEG rhythm
(2023) Ibitoye, Richard; Castro, Patricia; Ellmers, Toby; Kaski, Diego; Bronstein, Adolfo
The alpha rhythm is a dominant electroencephalographic oscillation relevant to sensory-motor and cognitive function. Alpha oscillations are reactive, being for example enhanced by eye closure, and suppressed following eye opening. The determinants of inter-individual variability in reactivity in the alpha rhythm (e.g. changes with amplitude following eye closure) are not fully understood despite the physiological and clinical applicability of this phenomenon, as indicated by the fact that ageing and neurodegeneration reduce reactivity. Strong interactions between visual and vestibular systems raise the theoretical possibility that the vestibular system plays a role in alpha reactivity. To test this hypothesis, we applied electroencephalography in sitting and standing postures in 15 participants with reduced vestibular function (bilateral vestibulopathy, median age = 70 years, interquartile range = 51-77 years) and 15 age-matched controls. We found participants with reduced vestibular function showed less enhancement of alpha electroencephalography power on eye closure in frontoparietal areas, compared to controls. In participants with reduced vestibular function, video head impulse test gain - as a measure of residual vestibulo-ocular reflex function - correlated with reactivity in alpha power across most of the head. Greater reliance on visual input for spatial orientation ('visual dependence', measured with the rod-and-disc test) correlated with less alpha enhancement on eye closure only in participants with reduced vestibular function, and this was partially moderated by video head impulse test gain. Our results demonstrate for the first time that vestibular function influences alpha reactivity. The results are partly explained by the lack of ascending peripheral vestibular input but also by central reorganisation of processing relevant to visuo-vestibular judgements.
Viewing Target Distance Influences the Vestibulo-Ocular Reflex Gain when Assessed Using the Video Head Impulse Test
(2019) Castro, Patricia; Esteves, Sara Sena; Lerchundi, Florencia; Buckwell, David; Gresty, Michael A.; Bronstein, Adolfo M.; Arshad, Qadeer
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.
Visuospatial orientation: Differential effects of head and body positions
(2022) Castro, Patricia; Hussaina, Shahvaiz; Mohameda, Omer G.; Kaskia, Diego; Arshada, Qadeer; Bronsteina, Adolfo M.; Kheradmand, Amir
To orientate in space, the brain must integrate sensory information that encodes the position of the body with the visual cues from the surrounding environment. In this process, the extent of reliance on visual information is known as the visual dependence. Here, we asked whether the relative positions of the head and body can modulate such visual dependence (VD). We used the effect of optokinetic stimulation (30◦/s) on subjective visual vertical (SVV) to quantify VD as the average optokinetic-induced SVV bias in clockwise and counter-clockwise directions. The VD bias was measured in eight subjects with a head-on-body tilt (HBT) where only the head was tilted on the body, and also with a whole-body tilt (WBT) where the head and body were tilted together. The VD bias with HBT of 20◦was in the same direction of the head tilt position (left tilt VD 1.35 ±0.1.2◦; right VD 1.60 ±0.9◦), whereas the VD bias with WBT of 20◦was in a direction away from the body tilt position (left tilt VD 2.5 ±1.1◦; right tilt VD 2.1 ±0.9◦). These findings show differential effects of relative head and body positions on visual cue integration, a process which could facilitate optimal interaction with the surrounding environment for spatial orientation.

Browsing by Author "Castro, Patricia"

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