Reduced Vestibulo-Ocular Reflex During Fast Head Rotation in Complete Darkness.

The human vestibulo-ocular reflex (VOR) leads to maintenance of the acuity of an image on the retina and contributes to the perception of orientation during high acceleration head movements. Our objective was to determine whether vision affects the horizontal VOR by assessing and comparing the performance at the boundaries of contribution of: (a) unrestricted visual information and (b) no visual information. Understanding how the VOR performs under both lighted and unlighted conditions is of paramount importance to avoiding falls, perhaps particularly among the elderly. We tested 23 participants (M age = 35.3 years, standard error of mean (SEM) = 2.0 years). The participants were tested with the video Head Impulse Test (vHIT), EyeSeeCam from Interacoustics™, which assesses whether VOR is of the expected angular velocity compared to head movement angular velocity. The vHIT tests were performed under two conditions: (a) in a well-lit room and (b) in complete darkness. The VOR was analyzed by evaluating the gain (quotient between eye and head angular velocity) at 40, 60 and 80 ms time stamps after the start of head movement. Additionally, we calculated the approximate linear gain between 0-100 ms through regression. The gain decreased significantly faster across time stamps in complete darkness (p < .001), by 10% in darkness compared with a 2% decrease in light. In complete darkness, the VOR gain gradually declined, reaching a marked reduction at 80 ms by 10% (p < .001), at which the head velocities were 150°/second or faster. The approximate linear gain value was not significantly different in complete darkness and in light. These findings suggest that information from the visual system can modulate the high velocity VOR. Subsequently, fast head turns might cause postural imbalance and momentary disorientation in poor light in people with reduced sensory discrimination or motor control, like the elderly.

Long-term postural control in elite athletes following mild traumatic brain injury.

Background: Traumas to the head and neck are common in sports and often affects otherwise healthy young individuals. Sports-related concussions (SRC), defined as a mild traumatic brain injury (mTBI), may inflict persistent neck and shoulder pain, and headache, but also more complex symptoms, such as imbalance, dizziness, and visual disturbances. These more complex symptoms are difficult to identify with standard health care diagnostic procedures. Objective: To investigate postural control in a group of former elite athletes with persistent post-concussive symptoms (PPCS) at least 6 months after the incident. Method: Postural control was examined using posturography during quiet stance and randomized balance perturbations with eyes open and eyes closed. Randomized balance perturbations were used to examine motor learning through sensorimotor adaptation. Force platform recordings were converted to reflect the energy used to maintain balance and spectrally categorized into total energy used, energy used for smooth corrective changes of posture (i.e., <0.1 Hz), and energy used for fast corrective movements to maintain balance (i.e., >0.1 Hz). Results: The mTBI group included 20 (13 males, mean age 26.6 years) elite athletes with PPCS and the control group included 12 athletes (9 males, mean age 26.4 years) with no history of SRC. The mTBI group used significantly more energy during balance perturbations than controls: +143% total energy, p = 0.004; +122% low frequency energy, p = 0.007; and +162% high frequency energy, p = 0.004. The mTBI subjects also adapted less to the balance perturbations than controls in total (18% mTBI vs. 37% controls, p = 0.042), low frequency (24% mTBI vs. 42% controls, p = 0.046), and high frequency (6% mTBI vs. 28% controls, p = 0.040). The mTBI subjects used significantly more energy during quiet stance than controls: +128% total energy, p = 0.034; +136% low-frequency energy, p = 0.048; and +109% high-frequency energy, p = 0.015. Conclusion: Athletes with previous mTBI and PPCS used more energy to stand compared to controls during balance perturbations and quiet stance and had diminished sensorimotor adaptation. Sports-related concussions are able to affect postural control and motor learning.

Strategic alterations of posture are delayed in Parkinson's disease patients during deep brain stimulation.

Parkinson's disease (PD) is characterized by rigidity, akinesia, postural instability and tremor. Deep brain stimulation (DBS) of the subthalamic nucleus (STN) reduces tremor but the effects on postural instability are inconsistent. Another component of postural control is the postural strategy, traditionally referred to as the ankle or hip strategy, which is determined by the coupling between the joint motions of the body. We aimed to determine whether DBS STN and vision (eyes open vs. eyes closed) affect the postural strategy in PD in quiet stance or during balance perturbations. Linear motion was recorded from the knee, hip, shoulder and head in 10 patients with idiopathic PD with DBS STN (after withdrawal of other anti-PD medication), 25 younger adult controls and 17 older adult controls. Correlation analyses were performed on anterior-posterior linear motion data to determine the coupling between the four positions measured. All participants were asked to stand for a 30 s period of quiet stance and a 200 s period of calf vibration. The 200 s vibration period was subdivided into four 50 s periods to study adaptation between the first vibration period (30-80 s) and the last vibration period (180-230 s). Movement was recorded in patients with PD with DBS ON and DBS OFF, and all participants were investigated with eyes closed and eyes open. DBS settings were randomized and double-blindly programmed. Patients with PD had greater coupling of the body compared to old and young controls during balance perturbations (p ≤ 0.046). Controls adopted a strategy with greater flexibility, particularly using the knee as a point of pivot, whereas patients with PD adopted an ankle strategy, i.e., they used the ankle as the point of pivot. There was higher flexibility in patients with PD with DBS ON and eyes open compared to DBS OFF and eyes closed (p ≤ 0.011). During balance perturbations, controls quickly adopted a new strategy that they retained throughout the test, but patients with PD were slower to adapt. Patients with PD further increased the coupling between segmental movement during balance perturbations with DBS ON but retained a high level of coupling with DBS OFF throughout balance perturbations. The ankle strategy during balance perturbations in patients with PD was most evident with DBS OFF and eyes closed. The increased coupling with balance perturbations implies a mechanism to reduce complexity at a cost of exerting more energy. Strategic alterations of posture were altered by DBS in patients with PD and were delayed. Our findings therefore show that DBS does not fully compensate for disease-related effects on posture.

Deep brain stimulation in the subthalamic nuclei alters postural alignment and adaptation in Parkinson's disease.

Parkinson's disease (PD) can produce postural abnormalities of the standing body position such as kyphosis. We investigated the effects of PD, deep brain stimulation (DBS) in the subthalamic nucleus (STN), vision and adaptation on body position in a well-defined group of patients with PD in quiet standing and during balance perturbations. Ten patients with PD and 25 young and 17 old control participants were recruited. Body position was measured with 3D motion tracking of the ankle, knee, hip, shoulder and head. By taking the ankle as reference, we mapped the position of the joints during quiet standing and balance perturbations through repeated calf muscle vibration. We did this to explore the effect of PD, DBS in the STN, and vision on the motor learning process of adaptation in response to the repeated stimulus. We found that patients with PD adopt a different body position with DBS ON vs. DBS OFF, to young and old controls, and with eyes open vs. eyes closed. There was an altered body position in PD with greater flexion of the head, shoulder and knee (p≤0.042) and a posterior position of the hip with DBS OFF (p≤0.014). With DBS ON, body position was brought more in line with the position taken by control participants but there was still evidence of greater flexion at the head, shoulder and knee. The amplitude of movement during the vibration period decreased in controls at all measured sites with eyes open and closed (except at the head in old controls with eyes open) showing adaptation which contrasted the weaker adaptive responses in patients with PD. Our findings suggest that alterations of posture and greater forward leaning with repeated calf vibration, are independent from reduced movement amplitude changes. DBS in the STN can significantly improve body position in PD although the effects are not completely reversed. Patients with PD maintain adaptive capabilities by leaning further forward and reducing movement amplitude despite their kyphotic posture.

Short-Latency Covert Saccades - The Explanation for Good Dynamic Visual Performance After Unilateral Vestibular Loss?

Background: Functional head impulse test (fHIT) tests the ability of the vestibulo-ocular reflex (VOR) to allow visual perception during head movements. Our previous study showed that active head movements to the side with a vestibular lesion generated a dynamic visual performance that were as good as during movements to the intact side. Objective: To examine the differences in eye position during the head impulse test when performed with active and passive head movements, in order to better understand the role of the different saccade properties in improving visual performance. Method: We recruited 8 subjects with complete unilateral vestibular loss (4 men and 4 women, mean age 47 years) and tested them with video Head Impulse Test (vHIT) and Functional Head Impulse Test (fHIT) during passive and active movements while looking at a target. We assessed the mean absolute position error of the eye during different time frames of the head movement, the peak latency and the peak velocity of the first saccade, as well as the visual performance during the head movement. Results: Active head impulses to the lesioned side generated dynamic visual performances that were as good as when testing the intact side. Active head impulses resulted in smaller position errors during the visual perception task (p = 0.006) compared to passive head-impulses and the position error during the visual perception time frame correlated with shorter latencies of the first saccade (p < 0.001). Conclusion: Actively generated head impulses toward the side with a complete vestibular loss resulted in a position error within or close to the margin necessary to obtain visual perception for a brief period of time in patients with chronic unilateral vestibular loss. This seems to be attributed to the appearance of short-latency covert saccades, which position the eyes in a more favorable position during head movements.

vHIT Testing of Vertical Semicircular Canals With Goggles Yield Different Results Depending on Which Canal Plane Being Tested.

Objective: The use of goggles to assess vertical semicircular canal function has become a standard method in vestibular testing, both in clinic and in research, but there are different methods and apparatus in use. The aim of this study was to determine what the cause of the systematic differences is between gain values in testing of the vertical semicircular canals with two different video head impulse test (vHIT) equipment in subjects with normal vestibular function. Study Design: Retrospective analysis of gain values on patients with clinically deemed normal vestibular function (absence of a corrective eye saccade), tested with either Interacoustics or Otometrics system. Prospective testing of subjects with normal vestibular function with the camera records the eye movements of both eyes. Finally, 3D sensors were placed on different positions on the goggles measuring the actual vertical movement in the different semicircular planes. Results: In the clinical cohorts, the gain depended on which side and semicircular canal was tested (p < 0.001). In the prospective design, the combination between the stimulated side, semicircular canal, and position of the recording device (right/left eye) highly influenced the derived gain (p < 0.001). The different parts of the goggles also moved differently in a vertical direction during vertical semicircular canal testing. Conclusion: The gain values when testing the function of the vertical semicircular canals seem to depend upon which eye is recorded and which semicircular plane is tested and suggests caution when interpreting and comparing results when different systems are used both clinically as well as in research. The results also imply that further research and development are needed to obtain accurate vertical semicircular canal testing, in regard to both methodology and equipment design.

Gait Flexibility among Older Persons Significantly More Impaired in Fallers Than Non-Fallers-A Longitudinal Study.

Gait disorders are a relevant factor for falls and possible to measure with wearable devices. If a wearable sensor can detect differences in gait parameters between fallers and non-fallers has not yet been studied. The aim of this study was to measure and compare gait parameters, vestibular function, and balance performance between fallers and non-fallers among a group of older persons. Participants were senior members (n = 101) of a Swedish non-profit gymnastic association. Gait parameters were obtained using an inertial measurement unit (IMU) that the participants wore on the leg while walking an obstacle course and on an even surface. Vestibular function was assessed by the Head-shake test, the Head impulse test, and the Dix-Hallpike maneuver. Balance was assessed by the Timed Up and Go, the Timed Up and Go manual, and the Timed Up and Go cognitive tests. Falls during the 12-month follow-up period were monitored using fall diaries. Forty-two persons (41%) had fallen during the 12-month follow-up. Fallers had more limited ability to vary their gait (gait flexibility) than non-fallers (p < 0.001). No other differences between fallers and non-fallers were found. The use of gait flexibility, captured by an IMU, seems better for identifying future fallers among healthy older persons than Timed Up and Go or Timed Up and Go combined with a cognitive or manual task.

Spectral analysis of body movement during deep brain stimulation in Parkinson's disease.

BACKGROUND: The characteristics of Parkinson's disease (PD) include postural instability and resting tremor. However, reductions of tremor amplitude do not always improve postural stability. RESEARCH QUESTION: What is the effect of deep brain stimulation (DBS) of the subthalamic nucleus (STN) on spectral analysis of body movement in patients with PD when tested without anti-PD medication? The effect of visual cues was also studied. METHODS: Ten patients with PD (mean age 64.3 years, range 59-69 years) and 17 control participants (mean age 71.2 years, range 65-79 years) were recruited. Spectral power following a period of quiet stance (35 s) was analysed in three different spectral power bands (0-4 Hz, 4-7 Hz and 7-25 Hz). Motion markers were secured to the head, shoulder, hip, and knee, which recorded movements in two directions, the anteroposterior and lateral. RESULTS: DBS STN significantly changed the spectral distribution pattern across the body in the anteroposterior (p = 0.029) and lateral directions (p ≤ 0.003). DBS predominantly reduced spectral power at the head (p ≤ 0.037) and shoulder (p ≤ 0.031) in the lateral direction. The spectral power of the lower and upper body in patients with PD, with DBS ON, were more similar to the control group, than to DBS OFF. Visual cues mainly reduced spectral power in the anteroposterior direction at the shoulder (p ≤ 0.041) in controls and in patients with PD with DBS ON. SIGNIFICANCE: There is an altered postural strategy in patients with PD with DBS ON as shown by an altered spectral power distribution pattern across body segments and a reduction of spectral power in the lateral direction at the head and shoulder. A reduction of spectral power in controls and in patients with PD with DBS ON suggests that visual cues are able to reduce spectral power to some extent, but not with DBS OFF where postural sway and power are larger.

Effects of Deep Brain Stimulation on Postural Control in Parkinson's Disease.

The standard approach to the evaluation of tremor in medical practice is subjective scoring. The objective of this study was to show that signal processing of physiological data, that are known to be altered by tremor in Parkinson's disease (PD), can quantify the postural dynamics and the effects of DBS. We measured postural control and its capacity to adapt to balance perturbations with a force platform and perturbed balance by altering visual feedback and using pseudo-random binary sequence perturbations (PRBS) of different durations. Our signal processing involved converting the postural control data into spectral power with Fast-Fourier Transformation across a wide bandwidth and then subdividing this into three bands (0-4 Hz, 4-7 Hz and 7-25 Hz). We quantified the amount of power in each bandwidth. From 25 eligible participants, 10 PD participants (9 males, mean age 63.8 years) fulfilled the inclusion criteria; idiopathic PD responsive to l-Dopa; >1 year use of bilateral STN stimulation. Seventeen controls (9 males, mean age 71.2 years) were studied for comparison. Participants with PD were assessed after overnight withdrawal of anti-PD medications. Postural control was measured with a force platform during quiet stance (35 s) and during PRBS calf muscle vibration that perturbed stance (200 s). Tests were performed with eyes open and eyes closed and with DBS ON and DBS OFF. The balance perturbation period was divided into five sequential 35-s periods to assess the subject's ability to address postural imbalance using adaptation. The signal processing analyses revealed that DBS did not significantly change the dynamics of postural control in the 0-4 Hz spectral power but the device reduced the use of spectral power >4 Hz; a finding that was present in both anteroposterior and lateral directions, during vibration, and more so in eyes open tests. Visual feedback, which usually improves postural stability, was less effective in participants with PD with DBS OFF across all postural sway frequencies during quiet stance and during balance perturbations. The expected adaptation of postural control was found in healthy participants between the first and last balance perturbation period. However, adaptation was almost abolished across all spectral frequencies in both the anteroposterior and lateral directions, with both eyes open and eyes closed and DBS ON and OFF in participants with PD. To conclude, this study revealed that DBS altered the spectral frequency dynamics of postural control in participants through a reduction of the power used >4 Hz. Moreover, DBS tended to increase the stabilizing effect of vision across all spectral bands. However, the signal processing analyses also revealed that DBS was not able to restore adaptive motor control abilities in PD.

Exploring the effects of deep brain stimulation and vision on tremor in Parkinson's disease - benefits from objective methods.

BACKGROUND: Tremor is a cardinal symptom of Parkinson's disease (PD) that may cause severe disability. As such, objective methods to determine the exact characteristics of the tremor may improve the evaluation of therapy. This methodology study aims to validate the utility of two objective technical methods of recording Parkinsonian tremor and evaluate their ability to determine the effects of Deep Brain Stimulation (DBS) of the subthalamic nucleus and of vision. METHODS: We studied 10 patients with idiopathic PD, who were responsive to L-Dopa and had more than 1 year use of bilateral subthalamic nucleus stimulation. The patients did not have to display visible tremor to be included in the study. Tremor was recorded with two objective methods, a force platform and a 3 dimensional (3D) motion capture system that tracked movements in four key proximal sections of the body (knee, hip, shoulder and head). They were assessed after an overnight withdrawal of anti-PD medications with DBS ON and OFF and with eyes open and closed during unperturbed and perturbed stance with randomized calf vibration, using a randomized test order design. RESULTS: Tremor was detected with the Unified Parkinson's Disease Rating Scale (UPDRS) in 6 of 10 patients but only distally (hands and feet) with DBS OFF. With the force platform and the 3D motion capture system, tremor was detected in 6 of 10 and 7 of 10 patients respectively, mostly in DBS OFF but also with DBS ON in some patients. The 3D motion capture system revealed that more than one body section was usually affected by tremor and that the tremor amplitude was non-uniform, but the frequency almost identical, across sites. DBS reduced tremor amplitude non-uniformly across the body. Visual input mostly reduced tremor amplitude with DBS ON. CONCLUSIONS: Technical recording methods offer objective and sensitive detection of tremor that provide detailed characteristics such as peak amplitude, frequency and distribution pattern, and thus, provide information that can guide the optimization of treatments. Both methods detected the effects of DBS and visual input but the 3D motion system was more versatile in that it could detail the presence and properties of tremor at individual body sections.

Co-morbidities to Vestibular Impairments-Some Concomitant Disorders in Young and Older Adults.

Background: Dizziness and pain are common complaints that often appear concomitantly, with or without a causal relationship. However, these symptoms might maintain and exacerbate each other and other co-morbidities. Therefore, adequate rehabilitation may have to include an expanded focus on other deficits and preconditions, especially in older adults and in patients. Objective: To understand how frequently vestibular dysfunction coincided with medical conditions and aging, we studied two categories: Study 1: patients referred to a vestibular unit and Study 2: senior members in a fitness association. Method: Study 1: 49 patients [34 females/15 males; mean age 52 years (SEM 2.0)] seeking health care for balance disorders and vestibular deficits were asked in questionnaires about their perception of dizziness and pain, and emotional and functional strains. Study 2: 101 senior members in a fitness association [91 females/10 males; mean age 75 years (SEM 0.6)], were assessed for vestibular and balance deficits and for any co-morbidities. The participants were monitored for falls for 12 months after the initial assessments. Result: Study 1: Co-morbidity often existed between dizziness and pain (65%). The patients reported high emotional and functional strain related to their dizziness and pain. Patients older than 60 years reported longer durations of pain (p ≤ 0.028) but less emotional strain (p = 0.036), compared to younger patients. Study 2: 84% of the participants had a vestibular impairment, often without noticing any symptoms. Furthermore, 40% reported cardiovascular illnesses, 12% musculoskeletal disorders, and 63% reported other medical conditions. Forty-two percent experienced falls within 1 year after the initial assessments (thereof 42% in the group with vestibular deficits and 38% in the group without vestibular deficits). Conclusion: To enhance and preserve postural control, both in patients with vestibular deficits and in older adults, we suggest an expanded clinical perspective. Hence, we recommend detailed examinations of the vestibular system but simultaneously probing for possible co-morbidities. Since aging often entails deterioration of multimodal processes related to maintained mobility and postural stability, our results add focus on the importance of addressing balance disorders together with additional medical conditions.

Dizziness and localized pain are often concurrent in patients with balance or psychological disorders.

Background and aims Symptoms of dizziness and pain are both common complaints and the two symptoms often seem to coincide. When symptoms appear concomitant for sustained periods of time the symptoms might maintain and even exacerbate each other, sometimes leading to psychological distress. In order to evaluate such comorbidity we studied patients referred to a vestibular unit and to a psychiatric outpatient clinic with respectively balance disorders and psychological issues. Methods Consecutive patients referred to a vestibular unit (n = 49) and a psychiatric outpatient clinic (n = 62) answered the Dizziness Handicap Inventory (DHI) questionnaire and a questionnaire detailing occurrence of dizziness and pain. Results The experience of dizziness and pain often coincided within individuals across both clinical populations, especially if the pain was located to the neck/shoulder or the back (p = 0.006). Patients who reported dizziness had significantly more often pain (p = 0.024); in the head (p = 0.002), neck/shoulders (p = 0.003) and feet (p = 0.043). Moreover, patients who reported dizziness stated significantly higher scoring on emotional (p < 0.001) and functional (p < 0.001) DHI sub-scales. Furthermore, patients who reported an accident in their history suffered significantly more often from dizziness (p = 0.039) and pain (p < 0.001); in the head (p < 0.001), neck/shoulders (p < 0.001) and arms (p = 0.045) and they scored higher on the emotional (p = 0.004) and functional (p = 0.002) DHI sub-scales. Conclusions The findings suggest comorbidity to exist between dizziness and neck/shoulder or back pain in patients seeking health care for balance disorders or psychological issues. Patients suffering from dizziness and pain, or with both symptoms, also reported higher emotional and functional strain. Thus, healthcare professionals should consider comorbidity when determining diagnosis and consequent measures. Implications Clinicians need to have a broader "receptive scope" in both history and clinical examinations, and ask for all symptoms. Although the patients in this study visited a vestibular unit respectively a psychological clinic, they commonly reported pain conditions when explicitly asked for this symptom. A multimodal approach is thus to favor, especially when the symptoms persist, for the best clinical management.

Stress Levels Escalate When Repeatedly Performing Tasks Involving Threats.

Police work may include performing repeated tasks under the influence of psychological stress, which can affect perceptual, cognitive and motor performance. However, it is largely unknown how repeatedly performing stressful tasks physically affect police officers in terms of heart rate and pupil diameter properties. Psychological stress is commonly assessed by monitoring the changes in these biomarkers. Heart rate and pupil diameter was measured in 12 male police officers when performing a sequence of four stressful tasks, each lasting between 20 and 130 s. The participants were first placed in a dimly illuminated anteroom before allowed to enter a brightly lit room where a scenario was played out. After each task was performed, the participants returned to the anteroom for about 30 s before performing the next sequential task. Performing a repeated sequence of stressful tasks caused a significant increase in heart rate (p = 0.005). The heart rate started to increase already before entering the scenario room and was significantly larger just after starting the task than just before starting the task (p < 0.001). This pattern was more marked during the first tasks (p < 0.001). Issuance of a verbal "abort" command which terminated the tasks led to a significant increase of heart rate (p = 0.002), especially when performing the first tasks (p = 0.002). The pupil diameter changed significantly during the repeated tasks during all phases but in a complex pattern where the pupil diameter reached a minimum during task 2 followed by an increase during tasks 3 and 4 (p ≤ 0.020). During the initial tasks, the pupil size (p = 0.014) increased significantly. The results suggest that being repeatedly exposed to stressful tasks can produce in itself an escalation of psychological stress, this even prior to being exposed to the task. However, the characteristics of both the heart rate and pupil diameter were complex, thus, the findings highlight the importance of studying the effects and dynamics of different stress-generating factors. Monitoring heart rate was found useful to screen for stress responses, and thus, to be a vehicle for indication if and when rotation of deployed personnel is necessary to avoid sustained high stress exposures.

Postural instability in an immersive Virtual Reality adapts with repetition and includes directional and gender specific effects.

The ability to handle sensory conflicts and use the most appropriate sensory information is vital for successful recovery of human postural control after injury. The objective was to determine if virtual reality (VR) could provide a vehicle for sensory training, and determine the temporal and spatial nature of such adaptive changes. Twenty healthy subjects participated in the study (10 females). The subjects watched a 90-second VR simulation of railroad (rollercoaster) motion in mountainous terrain during five repeated simulations, while standing on a force platform that recorded their stability. The immediate response to watching the VR movie was an increased level of postural instability. Repeatedly watching the same VR movie significantly reduced both the anteroposterior (62%, p < 0.001) and lateral (47%, p = 0.001) energy used. However, females adapted more slowly to the VR stimuli as reflected by higher use of total (p = 0.007), low frequency (p = 0.027) and high frequency (p = 0.026) energy. Healthy subjects can significantly adapt to a multidirectional, provocative, visual environment after 4-5 repeated sessions of VR. Consequently, VR technology might be an effective tool for rehabilitation involving visual desensitisation. However, some females may require more training sessions to achieve effects with VR.

Different Visual Weighting due to Fast or Slow Vestibular Deafferentation: Before and after Schwannoma Surgery.

Background: Feedback postural control depends upon information from somatosensation, vision, and the vestibular system that are weighted depending on their relative importance within the central nervous system. Following loss of any sensory component, the weighting changes, e.g., when suffering a vestibular loss, the most common notion is that patients become more dependent on visual cues for maintaining postural control. Dizziness and disequilibrium are common after surgery in schwannoma patients, which could be due to interpretation of the remaining sensory systems involved in feedback-dependent postural control and spatial orientation. Objective: To compare visual dependency in spatial orientation and postural control in patients suffering from unilateral vestibular loss within different time frames. Methods: Patients scheduled for schwannoma surgery: group 1 (n = 27) with no vestibular function prior to surgery (lost through years), group 2 (n = 12) with remaining vestibular function at the time of surgery (fast deafferentation), and group 3 (n = 18) with remaining function that was lost through gentamicin installations in the middle ear (slow deafferentation). All patients performed vibratory posturography and rod and frame investigation before surgery and 6 months after surgery. Results: Postural control improved after surgery in patients that suffered a slow deafferentation (groups 1 and 3) (p < 0.001). Patients that suffered fast loss of remaining vestibular function (group 2) became less visual field dependent after surgery (p ≤ 0.035) and were less able to maintain stability compared with group 1 (p = 0.010) and group 3 (p = 0.010). Conclusions: The nature and time course of vestibular deafferentation influence the weighting of remaining sensory systems in order to maintain postural control and spatial orientation.

Functional Head Impulse Testing Might Be Useful for Assessing Vestibular Compensation After Unilateral Vestibular Loss.

Background: Loss of the vestibulo-ocular reflex (VOR) affects visual acuity during head movements. Previous studies have shown that compensatory eye-saccades improve visual acuity and that the timing of the saccade is important. Most of the tests involved in testing VOR are made with passive head movement, that do not necessarily reflect the activities of daily living and thus not being proportionate to symptoms and distresses of the patients. Objective: To examine differences between active (self-generated) or passive (imposed by the examiner) head rotations while trying to maintain visual focus on a target. Method: Nine subjects with unilateral total vestibular loss were recruited (4 men and 5 women, mean age 47) and tested with video Head Impulse Test (vHIT) and Head Impulse Testing Device-Functional Test (HITD-FT) during passive and active movements while looking at a target. VOR gain, latencies of covert saccades, frequency of covert saccades and visual acuity were measured and analyzed. Results: Active head-impulses toward the lesioned side resulted in better visual acuity (p = 0.002) compared to conventional passive head-impulses and generated eye-saccades with significantly shorter latencies (p = 0.004). Active movements to the lesioned side generated dynamic visual acuities that were as good as when testing the intact side. Conclusion: Actively generated head impulses resulted in normal dynamic visual acuity, even when performed toward the side of total vestibular loss. This might be attributed to the appearance of short-latency covert saccades. The results show a strong relationship between self-generated movements, latencies of covert saccades and outcome in HITD-FT, i.e., a better dynamic visual function with less retinal slip which is the main function of the VOR. The method of active HITD-FT might be valuable in assessing vestibular compensation and monitoring ongoing vestibular rehabilitation.

Elevated visual dependency in young adults after chemotherapy in childhood.

Chemotherapy in childhood can result in long-term neurophysiological side-effects, which could extend to visual processing, specifically the degree to which a person relies on vision to determine vertical and horizontal (visual dependency). We investigated whether adults treated with chemotherapy in childhood experience elevated visual dependency compared to controls and whether any difference is associated with the age at which subjects were treated. Visual dependency was measured in 23 subjects (mean age 25.3 years) treated in childhood with chemotherapy (CTS) for malignant, solid, non-CNS tumors. We also stratified CTS into two groups: those treated before 12 years of age and those treated from 12 years of age and older. Results were compared to 25 healthy, age-matched controls. The subjective visual horizontal (SVH) and vertical (SVV) orientations was recorded by having subjects position an illuminated rod to their perceived horizontal and vertical with and without a surrounding frame tilted clockwise and counter-clockwise 20° from vertical. There was no significant difference in rod accuracy between any CTS groups and controls without a frame. However, when assessing visual dependency using a frame, CTS in general (p = 0.006) and especially CTS treated before 12 years of age (p = 0.001) tilted the rod significantly further in the direction of the frame compared to controls. Our findings suggest that chemotherapy treatment before 12 years of age is associated with elevated visual dependency compared to controls, implying a visual bias during spatial activities. Clinicians should be aware of symptoms such as visual vertigo in adults treated with chemotherapy in childhood.

PREHAB vs. REHAB - presurgical treatment in vestibular schwannoma surgery enhances recovery of postural control better than postoperative rehabilitation: Retrospective case series.

OBJECT: To evaluate post-surgical postural stability when treating patients with remaining vestibular function with intratympanic gentamicin (PREHAB) prior to schwannoma surgery. METHOD: 44 consecutive patients with some form remaining vestibular function scheduled for vestibular schwannoma surgery. 20 were medically deafferented with intratympanic gentamicin before surgery and 24 were not. Both groups were of the same age, had the same tumor size, same type of surgery, and same perioperative sensory rehabilitation (training exercises), and no surgical complications. Postural stability measured as energy expenditure while standing on a force platform during vibratory stimulation of the calf muscles, performed prior to surgery (or gentamicin treatment) and 6 months after surgery. RESULTS: Patients pretreated with gentamicin had significantly better postural stability at the time for follow-up (p < 0.05) and displayed a better adaptive capacity when faced with a postural challenge (p < 0.01). They were also able to use vision more efficiently to control their stability (p < 0.05). CONCLUSIONS: By separating the sensory loss (through intratympanic gentamicin, that ablates the remaining vestibular function) from the intracranial surgical trauma, the postural control system benefited from a better short-term (adaptation) and long-term (habituation) recovery, when experiencing a postural challenge or resolving a sensory conflict. The benefits could be attributed to; active and continuous motor learning as the vestibular function slowly attenuates; no concomitant central nervous dysfunction due to effects from neurosurgery, thus allowing time for a separate unimpeded recovery process with more limited challenges and objectives; and the initiation and certain progression of sensory reweighting processes allowed prior to surgery. In contrast, worse compensation could be due to; immobilization from nausea after surgery, harmful amount of stress and cognitive dysfunction from the combination of surgical and sensory trauma and an abrupt vestibular deafferentation and its consequences on sensory reweighting.

Disturbed cervical proprioception affects perception of spatial orientation while in motion.

The proprioceptive, visual and vestibular sensory systems interact to maintain dynamic stability during movement. The relative importance and interplay between these sensory systems is still not fully understood. Increased knowledge about spatial perception and postural orientation would provide better understanding of balance disorders, and their rehabilitation. Displacement of the body in space was recorded in 16 healthy subjects performing a sequence of stepping-in-place tests without any visual or auditory cues. Spatial displacement and orientation in space were determined by calculating two parameters, "Moved distance (sagittal + lateral displacement)" and "Rotation". During the stepping-in-place tests vibration were applied in a randomized order on four different cervical muscles, and the effects were compared between muscles and to a non-vibration baseline condition. During the tests a forward displacement ("Moved distance") was found to be the normal behavior, with various degrees of longitudinal rotation ("Rotation"). The moved distance was significantly larger when the vibration was applied on the dorsal muscles (916 mm) relative to on ventral muscles (715 mm) (p = 0.003) and the rate of displacement was significantly larger for dorsal muscles (36.5 mm/s) relative to ventral (28.7 mm/s) vs (p = 0.002). When vibration was applied on the left-sided muscles, 16° rotation to the right was induced (p = 0.005), whereas no significant rotation direction was induced with right-sided vibration (3°). The rate of rotation was significantly larger for vibration applied on ventral muscles (0.44°/s) relative to on dorsal (0.33°/s) (p = 0.019). The results highlight the influence of cervical proprioception on the internal spatial orientation, and subsequent for postural control.

Decreased postural control in adult survivors of childhood cancer treated with chemotherapy.

The objective of cancer treatment is to secure survival. However, as chemotherapeutic agents can affect the central and peripheral nervous systems, patients must undergo a process of central compensation. We explored the effectiveness of this compensation process by measuring postural behaviour in adult survivors of childhood cancer treated with chemotherapy (CTS). We recruited sixteen adults treated with chemotherapy in childhood for malignant solid (non-CNS) tumours and 25 healthy age-matched controls. Subjects performed posturography with eyes open and closed during quiet and perturbed standing. Repeated balance perturbations through calf vibrations were used to study postural adaptation. Subjects were stratified into two groups (treatment before or from 12 years of age) to determine age at treatment effects. Both quiet (p = 0.040) and perturbed standing (p ≤ 0.009) were significantly poorer in CTS compared to controls, particularly with eyes open and among those treated younger. Moreover, CTS had reduced levels of adaptation compared to controls, both with eyes closed and open. Hence, adults treated with chemotherapy for childhood cancer may suffer late effects of poorer postural control manifested as reduced contribution of vision and as reduced adaptation skills. These findings advocate development of chemotherapeutic agents that cause fewer long-term side effects when used for treating children.