An assessment of the isoniazid preventive therapy programme for children in a busy primary healthcare clinic in Nelson Mandela Bay Health District, Eastern Cape Province, South Africa.

BACKGROUND: Tuberculosis (TB) is a significant contributor to the international and national burden of disease. Global estimates suggest that there were 10.4 million new cases of TB in 2015. Children accounted for ~10% of these cases, although in South Africa (SA) this figure is thought to be higher. Despite clear evidence that isoniazid preventive therapy (IPT) can reduce the risk of progression from TB infection to disease in TB contacts, IPT has been poorly implemented in SA national TB control programmes. OBJECTIVES: To determine current practices regarding the identification and management of child contacts (<5 years of age) at a primary care clinic in the Nelson Mandela Bay Health District, Eastern Cape Province, SA. METHODS: A cross-sectional descriptive study was conducted using a retrospective record review of infectious TB index patients aged ≥15 years. Folders of index patients with bacteriologically confirmed pulmonary TB, who started TB treatment between 21 October 2011 and 28 February 2014, were included. A sample size of 246 child contacts was required to obtain adequate power. A 95% confidence interval (CI) was used to determine statistically significant results. RESULTS: Index patient records (N=491) were assessed and 261 child contacts identified. In a high percentage of index patient folders (87.5%; n=430), contacts were documented, although only 0.53 child contacts were identified per index patient. Of the 261 child contacts identified, 184 (70.5%) were screened for TB, 2 started TB treatment and 108/184 (58.7%) started IPT. For the remaining 74 (40.2%) children, there was no documentation of further management. Only 4 (3.7%) children completed the 24-week IPT course. Male patients reported fewer child contacts (χ2 =7.31; p=0.01; odds ratio (OR) 0.6; 95% CI 0.42 - 0.86) and were less likely to bring contacts for screening (χ2=8.98; p=0.003; OR 0.41; 95% CI 0.24 - 0.72). Retreatment index patients were also less likely to bring contacts for screening (χ2=6.37; p=0.01; OR 0.45; 95% CI 0.25 - 0.81) and those who were screened were less likely to initiate IPT (χ2=4.05; p=0.04; OR 0.54; 95% CI 0.3 - 0.95). CONCLUSION: Despite contacts being well documented, child contacts were poorly identified. The fall-out of children at each step from identification to IPT completion was unacceptably high. Contacts of male patients and retreatment index patients were at greater risk of poor management. Recommendations to improve IPT delivery at national and local level include a review of the national IPT guidelines, considering the relative success of shorter courses of TB prophylaxis, the use of standardised IPT stationery, staff training and the involvement of community health workers in contact management.

Operational implementation and impact of The Union's online childhood TB training course in South Africa.

Novel, effective tuberculosis (TB) training strategies are needed in developing settings to scale up training and improve TB management at facility level. This study evaluated the feasibility of implementing an online childhood TB training course for community-based health-care workers in the Eastern Cape Province, South Africa, and measured its impact on knowledge. Training sessions were convened and participants completed the course independently. A total of 220 primary care participants completed pre- and post-training tests. The mean knowledge increase was 8% (95% confidence interval 7.0-8.8, P < 0.001). The course proved an acceptable, versatile option for decentralised training in childhood TB, provided that the technology requirements can be met.

De nouvelles stratégies efficaces de formation à la tuberculose (TB) sont requises dans les pays en développement afin d'accélérer la formation et d'améliorer la prise en charge de la TB au niveau des structures de santé. Cette étude a évalué la faisabilité de la mise en œuvre d'un cours de formation en ligne à la TB de l'enfant pour les travailleurs de santé en communauté dans la province du Cap Est, Afrique du Sud, et a mesuré l'impact sur les connaissances. Des séances de formation ont été organisées et les participants ont terminé le cours indépendamment. Un total de 220 participants travaillant en soins de santé primaires ont fait les tests avant et après la formation. L'augmentation moyenne des connaissances a été de 8% (intervalle de confiance 95% 7,0­8,8 ; P < 0,001). Le cours s'est avéré une option acceptable et souple pour une formation décentralisée à la TB de l'enfant si les exigences techniques le permettent.

En los entornos poco desarrollados se precisan estrategias de capacitación innovadoras y eficaces en materia de tuberculosis (TB) con el objeto de ampliar la escala de las iniciativas de formación y mejorar la coordinación asistencial de la TB en los establecimientos de salud. El objetivo del estudio fue evaluar la factibilidad de poner en práctica un curso de capacitación en línea sobre la TB en la niñez dirigido a los agentes de salud comunitarios en la Provincia Oriental del Cabo en Suráfrica y medir su repercusión sobre el nivel de conocimientos de los profesionales. Se convocaron sesiones de formación y luego los participantes completaron por su cuenta el curso. Doscientos veinte profesionales de atención primaria participantes completaron los cuestionarios antes y después de la capacitación. Se observó un progreso promedio de los conocimientos de 8% (intervalo de confianza del 95% 7,0­8,8; P < 0,001). Se demostró que el curso representa una opción aceptable y versátil de formación descentralizada sobre la TB en la niñez, siempre y cuando se puedan cumplir los requisitos tecnológicos.

Rapid cVEMP and oVEMP responses elicited by a novel head striker and recording device.

OBJECTIVE: To develop a reliable, easy to use bedside, office, or field system that allows the rapid measurement of cervical and ocular vestibular evoked myogenic potentials (cVEMP and oVEMP) using a bone-conduction stimulus. STUDY DESIGN: Prospective bioengineering design and proof of concept of the test system with saccular and utricular otolith response studies in human subjects. SETTING: Private practice, tertiary neurotology referral center. SUBJECTS: Twenty healthy adult controls without history of auditory or vestibular dysfunction and 5 preoperative and postoperative patients with confirmed superior canal dehiscence (SCD) participated. INTERVENTIONS: The subjects underwent auditory stimuli-based cVEMP and oVEMP studies using a commercially available system as well as testing with a novel bone-conduction cVEMP and oVEMP head striker system. MAIN OUTCOME MEASURES: Duration of each study, healthy subject and patient comfort, reproducibility, latency, and amplitude of auditory and striker evoked cVEMP and oVEMP responses. RESULTS: The mean age of the healthy controls was 43.8, with a range of 19 to 69 years (10 male and 10 female subjects). The mean age of the SCD patient group was 46, with a range of 25 to 54 years; all female subjects. Although the cVEMP responses were similar using either the auditory or head strike stimuli, the healthy subjects preferred the latter, but the SCD patients became more symptomatic. The oVEMP data showed more consistent responses using the striker system. A statistically significant reduction in latency for the striker-evoked cVEMP occurred compared with the auditory cVEMP evoked response in the 5 SCD preoperative patients. All normalized postoperatively. CONCLUSION: Recording the cVEMP and oVEMP responses using the striker system was much more rapid than with auditory stimuli and was more comfortable for the healthy subjects. The striker system and the acoustic method elicited strong otolithic receptor dysfunction symptoms in all SCD patients; however, they preferred the shorter striker studies. The striker system, because of the statistically shorter latency of p13 during the striker evoked cVEMP, which normalized after SCD closure, suggests that this method may be useful in identifying SCD patients before imaging studies. In addition, based on our biomechanical data, the striker was able to reliably produce a consistent and defined head striker impact.

Continuous equilibrium scores: factoring in the time before a fall.

The equilibrium (EQ) score commonly used in computerized dynamic posturography is normalized between 0 and 100, with falls assigned a score of 0. The resulting mixed discrete-continuous distribution limits certain statistical analyses and treats all trials with falls equally. We propose a simple modification of the formula in which peak-to-peak sway data from trials with falls is scaled according the percent of the trial completed to derive a continuous equilibrium (cEQ) score. The cEQ scores for trials without falls remain unchanged from the original methodology. The cEQ factors in the time before a fall and results in a continuous variable retaining the central tendencies of the original EQ distribution. A random set of 5315 Sensory Organization Test trials were pooled that included 81 falls. A comparison of the original and cEQ distributions and their rank ordering demonstrated that trials with falls continue to constitute the lower range of scores with the cEQ methodology. The area under the receiver operating characteristic curve (0.997) demonstrates that the cEQ retained near-perfect discrimination between trials with and without falls. We conclude that the cEQ score provides the ability to discriminate between ballistic falls from falls that occur later in the trial. This approach of incorporating time and sway magnitude can be easily extended to enhance other balance tests that include fall data or incomplete trials.

Diagnostic accuracy of dynamic posturography testing after short-duration spaceflight.

INTRODUCTION: Astronauts face transient disruptions of sensorimotor functions after spaceflight. Computerized dynamic posturography (CDP) testing has been used to document functional recovery; however, its objective value in return-to-duty decision-making has not been established. Therefore, we studied the diagnostic accuracy of CDP to determine the most effective test components for probing post-spaceflight sensorimotor deficits. METHODS: There were 11 first-time astronauts and 11 matched controls who were evaluated by CDP before and after spaceflight (controls did not fly). All CDP testing was conducted with eyes closed while standing on a computer-controlled force plate. Somatosensory influences were either unperturbed (stationary force plate) or altered (unstable force plate), and vestibular influences were either unperturbed (head erect) or altered by static (head pitched forward or back by 200) or dynamic (head pitched voluntarily in cadence with an auditory signal: +/- 20 degrees at 0.33 Hz) challenges. Using equilibrium (EQ) scores derived from peak A-P sway as the dependent measure, we determined the sensitivity and specificity of each test condition and then constructed receiver operator characteristic (ROC) curves to determine their diagnostic accuracies. RESULTS: The greatest diagnostic accuracy was obtained from the test requiring the subject to make dynamic head movements while standing on an unstable force plate (94.9% sensitivity 96.6% specificity, area under ROC curve = 0.991). By contrast, the estimated ROC area for the standard clinical Romberg test (fixed support, head erect), which is often used to make postflight return-to-duty decisions, was 0.718. CONCLUSION: We recommend that results from this test paradigm be considered during postflight return-to-duty decision-making.

The role of folate receptor alpha (FRalpha) in the response of malignant pleural mesothelioma to pemetrexed-containing chemotherapy.

BACKGROUND: The standard treatment of choice for malignant pleural mesothelioma is chemotherapy with pemetrexed and platinum, but the clinical outcome is poor. This study investigates the response to pemetrexed in a panel of eight mesothelioma cell lines and the clinical outcome for patients treated with pemetrexed in relation to folate receptor alpha (FRalpha). METHODS: Cell lines were treated with pemetrexed to determine the concentration that reduced growth to 50% (GI(50)). FRalpha expression was determined by western blotting and that of FRalpha, reduced folate carrier (RFC) and proton-coupled folate transporter (PCFT) by real-time quantitative RT-PCR. Immunohistochemistry for FRalpha was carried out on 62 paraffin-embedded samples of mesothelioma from patients who were subsequently treated with pemetrexed. RESULTS: A wide range of GI(50) values was obtained for the cell lines, H2452 cells being the most sensitive (GI(50) 22 nM) and RS5 cells having a GI(50) value greater than 10 microM. No FRalpha protein was detected in any cell line, and there was no relationship between sensitivity and expression of folate transporters. FRalpha was detected in 39% of tumour samples, generally in a small percentage of cells. There was no correlation between the presence of FRalpha and the outcome of pemetrexed treatment, and no significant difference between histological subtypes. CONCLUSION: Response to treatment with pemetrexed does not depend on the presence of FRalpha.

Vestibular effects on cerebral blood flow.

BACKGROUND: Humans demonstrate a number of unique adaptations that allow for the maintenance of blood pressure and brain blood flow when upright. While several physiological systems, including cerebral autoregulation, are involved in this adaptation the unique role the vestibular system plays in helping to maintain brain blood flow is just beginning to be elucidated. In this study, we tested the hypothesis that stimulation of the vestibular system, specifically the otoliths organs, would result in changes in cerebral blood flow. RESULTS: To test our hypothesis, we stimulated the vestibular organs of 25 healthy subjects by pitch tilt (stimulates both canals and otoliths) and by translation on a centrifuge (stimulates otoliths and not the canals) at five frequencies: 0.5, 0.25, 0.125 and 0.0625 Hz for 80 sec and 0.03125 Hz for 160 sec. Changes in cerebral flow velocity (by transcranial Doppler) and blood pressure (by Finapres) were similar during both stimuli and dependent on frequency of stimulation (P < 0.01). However, changes in cerebral blood flow were in opposition to changes in blood pressure and not fully dependent on changes in end tidal CO2. CONCLUSION: The experimental results support our hypothesis and provide evidence that activation of the vestibular apparatus, specifically the otolith organs, directly affects cerebral blood flow regulation, independent of blood pressure and end tidal CO2 changes.

Loss of otolith function with age is associated with increased postural sway measures.

Loss of balance and increased fall risk is a common problem associated with aging. Changes in vestibular function occur with aging but the contribution of reduced vestibular otolith function to fall risk remains unknown. We examined a population of 151 healthy individuals (aged 21-93) for both balance (sway measures) and ocular counter-rolling (OCR) function. We assessed balance function with eyes open and closed on a firm surface, eyes open and closed on a foam surface and OCR during +/-20 degree roll tilt at 0.005 Hz. Subjects demonstrated a significant age-related reduction in OCR and increase in postural sway. The effect of age on OCR was greater in females than males. The reduction in OCR was strongly correlated with the mediolateral measures of sway with eyes closed. This correlation was also present in the elderly group alone, suggesting that aging alone does not account for this effect. OCR decreased linearly with age and at a greater rate in females than males. This loss of vestibular otolith-ocular function is associated with increased mediolateral measures of sway which have been shown to be related to increased risk of falls. These data suggest a role for loss of otolith function in contributing to fall risk in the elderly. Further prospective, longitudinal studies are necessary to confirm these findings.

Electrotactile feedback of sway position improves postural performance during galvanic vestibular stimulation.

The purpose of this study was to assess the influence of electrotactile feedback on postural control performance during binaural galvanic vestibular stimulation (GVS). Postural equilibrium was measured with a computerized hydraulic platform in 10 healthy adults (6M, 4F, 24-65 y). Feedback of anterior-posterior (AP) and mediallateral (ML) body sway was derived from a 2-axis linear accelerometer mounted on a torso belt and displayed on a 144-point electrotactile array held against the anterior dorsal tongue. Subjects were trained to use the tongue electrotactile feedback (TEF) by voluntarily swaying to draw figures on their tongue, both with and without GVS. Subjects performed 24 randomized trials (20-s duration with eyes closed, 2 trials per condition), including 4 support surface conditions (fixed, rotational sway-referenced, translating the support surface proportional to AP sway, and combined rotational-translational support-platform sway referencing), and 3 feedback conditions (baseline, GVS, and GVS with TEF). Postural performance was assessed using deviations from upright (peak-to-peak and root-mean-square sway) and convergence toward stability limits (time and distance to limit of support boundaries). Postural stability was impaired (with respect to baseline) during GVS in all platform conditions, with larger decrements in performance during trials with rotation sway-referencing. Electrotactile feedback improved performance with GVS toward non-GVS levels, especially during trials with rotation sway-referencing. These results demonstrate the effectiveness of TEF in providing sensory substitution to maintain postural stability during vestibular disturbances.

Antibiotic treatment interruption of suspected lower respiratory tract infections based on a single procalcitonin measurement at hospital admission--a randomized trial.

Recent studies have suggested that procalcitonin (PCT) is a safe marker for the discrimination between bacterial and viral infection, and that PCT-guided treatment may lead to substantial reductions in antibiotic use. The present objective was to evaluate the effect of a single PCT measurement on antibiotic use in suspected lower respiratory tract infections (LRTIs) in a Danish hospital setting. In a randomized, controlled intervention study, 223 adult patients admitted to the hospital because of suspicion of LRTI were included with 210 patients available for analysis. Patients were randomized to either PCT-guided treatment or standard treatment. Antibiotic treatment duration in the PCT group was based on the serum PCT value at admission. The cut-off point for recommending antibiotic treatment was PCT > or =0.25 microg/L. Physicians could overrule treatment guidelines. The mean duration of hospital stay was 5.9 days in the PCT group vs. 6.7 days in the control group (p 0.22). The mean duration of antibiotic treatment during hospitalization in the PCT group was 5.1 days on average, as compared to 6.8 days in the control group (p 0.007). In a subgroup analysis of chronic obstructive pulmonary disease patients, the mean length of stay was reduced from 7.1 days in the control group to 4.8 days in the PCT group (p 0.009). It was concluded that the determination of a single PCT value at admission in patients with suspected LRTIs can lead to a reduction in the duration of antibiotic treatment by 25% without compromising outcome. No effect on the length of hospital stay was found.

Effects of eccentric rotation on the human pitch vestibulo-ocular reflex.

CONCLUSION: The pitch plane vestibulo-ocular reflex (VOR) gain and symmetry at low frequencies (< or =0.3 Hz) are enhanced by otoliths and/or somatosensory sensory cues during combined angular and linear stimuli. We conclude that neural processing of these linear motion cues is used to improve the VOR when stimulus frequencies are below the optimal range for the canals. OBJECTIVE: The purpose of this study was to examine the effects of eccentric rotation on the passive pitch VOR responses in humans. SUBJECTS AND METHODS: Eleven subjects were placed on their left sides (90 degrees roll position) and rotated in the pitch plane about an earth-vertical axis at 0.13, 0.3, and 0.56 Hz. The inter-aural axis was either aligned with the axis of rotation (no modulation of linear acceleration) or offset from it by 50 cm (centripetal linear acceleration directed feet-ward). The modulation of pitch VOR responses was measured in the dark with a binocular videography system. RESULTS: The pitch VOR gain was significantly increased and the VOR asymmetry was significantly reduced at the lowest stimulus frequencies during eccentric rotation. There was no effect of eccentric rotation on the pitch gain or asymmetry at the highest frequency tested.

Test of memory malingering (TOMM) trial 1 as a screening measure for insufficient effort.

The identification of insufficient effort is critical to neuropsychological evaluation, and several existing instruments assess effort on neuropsychological tasks. Yet instruments designed to detect insufficient effort are underutilized in standard neuropsychological assessments, perhaps in part because they typically require significant administration time and are, therefore, not ideally suited to screening contexts. The Test of Memory Malingering (TOMM) is a commonly administered, well-validated symptom validity test. This study evaluates the utility of TOMM Trial 1 as a relatively brief screening measure of insufficient effort. Results suggest that TOMM Trial 1 demonstrates high diagnostic accuracy and is a viable option for screening insufficient effort. Diagnostic accuracy estimates are presented for a range of base rates. The need for more comprehensive SVT assessment in most clinical and forensic situation is discussed.

Malingering in toxic exposure: classification accuracy of reliable digit span and WAIS-III Digit Span scaled scores.

This study examined the sensitivity and false-positive error rate of reliable digit span (RDS) and the WAIS-III Digit Span (DS) scaled score in persons alleging toxic exposure and determined whether error rates differed from published rates in traumatic brain injury (TBI) and chronic pain (CP). Data were obtained from the files of 123 persons referred for neuropsychological evaluation related to alleged exposure to environmental and industrial substances. Malingering status was determined using the criteria of Slick, Sherman, and Iverson (1999). The sensitivity and specificity of RDS and DS in toxic exposure are consistent with those observed in TBI and CP. These findings support the use of these malingering indicators in cases of alleged toxic exposure and suggest that the classification accuracy data of indicators derived from studies of TBI patients may also be validly applied to cases of alleged toxic exposure.

Psychomotor testing predicts rate of skill acquisition for proficiency-based laparoscopic skills training.

BACKGROUND: Laparoscopic simulator training translates into improved operative performance. Proficiency-based curricula maximize efficiency by tailoring training to meet the needs of each individual; however, because rates of skill acquisition vary widely, such curricula may be difficult to implement. We hypothesized that psychomotor testing would predict baseline performance and training duration in a proficiency-based laparoscopic simulator curriculum. METHODS: Residents (R1, n = 20) were enrolled in an IRB-approved prospective study at the beginning of the academic year. All completed the following: a background information survey, a battery of 12 innate ability measures (5 motor, and 7 visual-spatial), and baseline testing on 3 validated simulators (5 videotrainer [VT] tasks, 12 virtual reality [minimally invasive surgical trainer-virtual reality, MIST-VR] tasks, and 2 laparoscopic camera navigation [LCN] tasks). Participants trained to proficiency, and training duration and number of repetitions were recorded. Baseline test scores were correlated to skill acquisition rate. Cutoff scores for each predictive test were calculated based on a receiver operator curve, and their sensitivity and specificity were determined in identifying slow learners. RESULTS: Only the Cards Rotation test correlated with baseline simulator ability on VT and LCN. Curriculum implementation required 347 man-hours (6-person team) and 795,000 dollars of capital equipment. With an attendance rate of 75%, 19 of 20 residents (95%) completed the curriculum by the end of the academic year. To complete training, a median of 12 hours (range, 5.5-21), and 325 repetitions (range, 171-782) were required. Simulator score improvement was 50%. Training duration and repetitions correlated with prior video game and billiard exposure, grooved pegboard, finger tap, map planning, Rey Figure Immediate Recall score, and baseline performance on VT and LCN. The map planning cutoff score proved most specific in identifying slow learners. CONCLUSIONS: Proficiency-based laparoscopic simulator training provides improvement in performance and can be effectively implemented as a routine part of resident education, but may require significant resources. Although psychomotor testing may be of limited value in the prediction of baseline laparoscopic performance, its importance may lie in the prediction of the rapidity of skill acquisition. These tests may be useful in optimizing curricular design by allowing the tailoring of training to individual needs.

The prevalence of cognitive malingering in persons reporting exposure to occupational and environmental substances.

OBJECTIVE: Directly estimate the prevalence of cognitive malingering in persons claiming exposure to occupational and environmental substances. METHODS: Retrospective review of 128 neuropsychological cases with financial incentive. Estimates were based on two methods: (1) clinical identification using the Slick, Sherman and Iverson criteria for malingered neurocognitive dysfunction (MND), and (2) statistical modeling based on patient performance on several individual psychometric indicators of malingering. RESULTS: The prevalence based on the clinical method was 40%. The statistically based estimates ranged from 30% to more than 45% depending on model parameters. Different incentive parameters may influence prevalence. CONCLUSIONS: Cognitive malingering in toxic exposure is common and must be adequately addressed in the clinical neuropsychological assessment of toxic exposure and in research on its neurocognitive effects or findings will likely over-estimate the degree of cognitive impairment and related disability.

Classification accuracy of the Test of Memory Malingering in persons reporting exposure to environmental and industrial toxins: Results of a known-groups analysis.

This study used a known-groups design to examine the classification accuracy of the Test of Memory Malingering in detecting cognitive malingering in patients claiming cognitive deficits due to exposure to environmental and industrial toxins. Thirty-three patients who met Slick et al. criteria for Malingered Neurocognitive Dysfunction were compared to 17 toxic exposure patients negative for evidence of malingering, 14 TBI patients and 22 memory disorder patients, both groups without incentive. The original cutoffs (<45) for Trial 2 and Retention demonstrated perfect specificity (0% false positive error rate) and impressive sensitivity (>50%). These findings indicate the TOMM can be used with confidence as an indicator of negative response bias in cases of cognitive deficits attributed to exposure to alleged neurotoxic substances.

Hearing loss in patients with vestibulotoxic reactions to gentamicin therapy.

OBJECTIVES: To determine whether patients with vestibulotoxic reactions to gentamicin have hearing thresholds worse than predicted by distributions of better-ear hearing thresholds in people of the same age and sex in the general population, and, if so, to measure the severity and audiometric pattern of that hearing loss. DESIGN: Retrospective case series from previously published prospective and retrospective studies of vestibular function in patients receiving gentamicin. SETTING: Tertiary neurotological practice. PATIENTS: Convenience sample of 33 consecutive patients seen for objective evidence of vestibulotoxic reactions after systemic gentamicin therapy. Twenty-five of 33 patients underwent valid and complete audiometry. MAIN OUTCOME MEASURES: Age- and sex-corrected better-ear pure tone thresholds, 0.5 to 6.0 kHz. The better-ear audiogram was defined in 2 ways: primarily, the audiogram of the ear with the better average threshold at 0.5, 1.0, and 2.0 kHz; secondarily, the composite audiogram taking the better threshold for each frequency. RESULTS: Patients exhibiting vestibulotoxic reactions to gentamicin therapy had hearing thresholds that were similar to those seen in the general population at 0.5, 3.0, and 6.0 kHz. Median thresholds were 6 to 7 dB worse than expected at 1.0 and 2.0 kHz (95% confidence intervals, 2-13 dB and 3-12 dB, respectively). The largest median difference was 15 dB at 4.0 kHz (95% confidence interval, 3-23 dB), but this difference was not significant for the more conservative composite definition of the better ear. CONCLUSIONS: Patients with vestibulotoxic reactions to gentamicin therapy have little additional hearing loss compared with the general population. Physicians should monitor both auditory and vestibular function when aminoglycosides, especially gentamicin, must be used.

Roll rotation cues influence roll tilt perception assayed using a somatosensory technique.

We investigated how the nervous system processes ambiguous cues from the otolith organs by measuring roll tilt perception elicited by two motion paradigms. In one paradigm (tilt), eight subjects were sinusoidally tilted in roll with the axis of rotation near ear level. Stimulus frequencies ranged from 0.005 to 0.7 Hz, and the peak amplitude of tilt was 20 degrees . During this paradigm, subjects experienced a sinusoidal variation of interaural gravitational force with a peak of 0.34 g. The second motion paradigm (translation) was designed to yield the same sinusoidal variation in interaural force but did not include a roll canal cue. This was achieved by sinusoidally translating the subjects along their interaural axis. For the 0.7-Hz translation trial, the subjects were simply translated from side to side. A centrifuge was used for the 0.005- to 0.5-Hz translation trials; the subjects were rotated in yaw at 250 degrees /s for 5 min before initiating sinusoidal translations yielding an interaural otolith stimulus composed of both centrifugal and radial acceleration. Using a somatosensory task to measure roll tilt perception, we found substantial differences in tilt perception during the two motion paradigms. Because the primary difference between the two motion paradigms was the presence of roll canal cues during roll tilt trials, these perceptual differences suggest that canal cues influence tilt perception. Specifically, rotational cues provided by the semicircular canals help the CNS resolve ambiguous otolith cues during head tilt, yielding more accurate tilt perception.

Modeling postural instability with Galvanic vestibular stimulation.

In this study the effect of a pseudorandom binaural bipolar Galvanic stimulus generated by a sum of nonharmonically related sine waves on postural control was functionally assessed using computerized dynamic posturography (CDP), and the results compared to vestibulopathic patient populations and astronauts exposed to microgravity. The standardized CDP test battery comprised six sensory organization tests (SOTs) that combined three visual conditions (eyes open, eyes closed, and sway-referenced vision) with two proprioceptive conditions (fixed and sway-referenced support surfaces). Subjects (12) performed 18 randomized trials (three trials of each of the six SOTs) as a baseline, repeated the 18 trials with Galvanic vestibular stimulation (GVS), and then performed a post-GVS baseline. A 10 min rest period was inserted between each test battery. Anterioposterior postural sway increased significantly and was in the abnormal range (fifth percentile) during GVS for SOTs where visual input was compromised (sway-referenced surround) or absent. Postural stability returned to baseline when GVS was removed. An analysis of sensory input scores (somatosensory, visual, and vestibular) demonstrated the specificity of GVS in distorting vestibular input to postural control. The SOT scores observed in astronauts on landing day did not differ significantly to that generated by GVS in our normal subjects. GVS also induced a similar pattern of instability on CDP as profound bilateral vestibular loss, although not as severe. The results suggest that unpredictably varying GVS quantitatively and qualitatively models postural instability of vestibular origin.