Postural control characterization according to age and auditory input in cochlear implant users.

Aims/Objectives: Understand the relationship between auditory input and balance motor control. Material and Methods: Twelve prelingual adolescent cochlear implant users (CIU) and 12 adult postlingual CIU were tested by posturography on a force platform with eyes open in two conditions, with the cochlear implant (CI) on and off. Energy consumption (EC) of the body center of pressure sway signal was measured, calculating total EC and divided into three bands of frequencies; low (B1) 0-0.1 Hz, medium (B2) 0.1-1 Hz, and high (B3)1-2 Hz. Wilcoxon and Mann-Whitney tests were used for statistical analysis and the significance level was P ≤ 0.05. Results: Prelingual CIU decrease the EC in low and high frequencies throughout the adolescence (P < 0.05) assessed with the CI turned on, while it did not show any modification with the CI off. Postlingual CIU showed a deterioration of PR related to aging when evaluated with the CIU turned off, P < 0.05 in band 1. However, with the CI turned on they had no significant increase in this age range. Conclusions and Significance: The acoustic input improved EC of postural responses in higher and lower frequencies in adolescence and with aging which suggests a relationship with gross and fine movements involved in postural control.

Auditory input modulates sleep: an intra-cochlear-implanted human model.

To properly demonstrate the effect of auditory input on sleep of intra-cochlear-implanted patients, the following approach was developed. Four implanted deaf patients were recorded during four nights: two nights with the implant OFF, with no auditory input, and two nights with the implant ON, that is, with normal auditory input, being only the common night sounds present, without any additional auditory stimuli delivered. The sleep patterns of another five deaf people were used as controls, exhibiting normal sleep organization. Moreover, the four experimental patients with intra-cochlear devices and the implant OFF also showed normal sleep patterns. On comparison of the night recordings with the implant ON and OFF, a new sleep organization was observed for the recordings with the implant ON, suggesting that brain plasticity may produce changes in the sleep stage percentages while maintaining the ultradian rhythm. During sleep with the implant ON, the analysis of the electroencephalographic delta, theta and alpha bands in the frequency domain, using the Fast Fourier Transform, revealed a diversity of changes in the power originated in the contralateral cortical temporal region. Different power shifts were observed, perhaps related to the exact position of the implant inside the cochlea and the scalp electrode location. In conclusion, this pilot study shows that the auditory input in humans can introduce changes in central nervous system activity leading to shifts in sleep characteristics, as previously demonstrated in guinea pigs. We are postulating that an intra-cochlear-implanted deaf patient may have a better recovery if the implant is maintained ON during the night, that is, during sleep.

Motor and cognitive performances in pre-lingual cochlear implant adolescents, related with vestibular function and auditory input.

BACKGROUND: Information about the role of auditory input and motor control is limited. OBJECTIVES: Assessment the relationship between auditory and vestibular information with specific motor and cognitive functions. METHODS: Posturography in 17 Pre-lingual Cochlear Implant Adolescents, (PCIA) age 14.06 ± 3.05 in four sensory conditions was analyzed: (A) eyes open, cochlear implant (CI) on, (B) eyes open, CI off, (C) eyes closed standing on a foam over a platform (ECFP) with CI on, and (D) ECFP, CI off. Gait velocity (GV) was registered by inertial sensors using a 10-meter test. Vestibulo-ocular reflex (VOR) was evaluated with the video head impulse test (VHIT) and visual spatial skill (VS) assessed with the WISC-V test. RESULTS: SV had no significant difference between conditions A and B (p = .2461). Comparing C and D, SV values decreased when CI was turned on (p = .0036). A significant linear relationship between VOR and GV (p = .0064) generating the VOR gain loss lower gait. Relationship between VOR and VS scores was no significant (p = .685). CONCLUSIONS AND SIGNIFICANCE: Auditory information is a relevant cue when somatosensory and visual inputs are modified and range of vestibular function influence in a dynamic motor activity as gait, facts which must be considered in the neurodevelopment control.

Postural strategies in normal subjects and in patients with instability due to central nervous system diseases after sudden changes in the visual flow.

CONCLUSION: The results suggest that after a sudden change in the visual input, postural adaptation is impaired in patients with instability and central nervous system disorders (CNSD). OBJECTIVE: The aim of this study was the assessment of postural adaptation, as a transient phenomenon, when sudden changes in visual perception occur in normal subjects and in patients with instability due to different CNSD. SUBJECTS AND METHODS: Horizontal optokinetic stimulation (40 s and suddenly stopped) was performed in 16 patients with CNSD, and also in 22 normal subjects. Measurements were made of the body center of pressure area (COP) and the body sway velocity (SV) during 10 s before and after the stop and labeling the COP trajectory. RESULTS: Values of COP and SV (Wilcoxon signed rank test, p=0.979 and 0.496, respectively) in normal subjects did not show any significant change before and after the stop. In 15 of the 16 assessed patients with instability associated with CNSD an increase of the COP and SV values (Wilcoxon signed test, p=0.001 and 0.004, respectively) was observed in the 10 s after the visual stop. COP labeling showed 'roaming' of the COP spatial evolution approaching the limits of stability.

Performance after cochlear implantation in DFNB1 patients.

OBJECTIVE: To evaluate the speech perception and language development with cochlear implants (CI) of DFNB1 children in comparison with non-DFNB1 deaf children. STUDY DESIGN: Retrospective case series. SETTING: Academic tertiary center. RESULTS: Thirty-one congenitally deafened children, screened for GJB2 allele variants, were followed for an average 32 months after CI. With the use of age-appropriate testing, 75% of DFNB1 and 53% of non-DFNB1 children achieved open set word recognition (speech perception category [SPC] level 6). Multivariate analysis showed that SPC was primarily dependent on duration of CI use, but not on the cause of hearing loss. In Reynell language tests, DFNB1 children showed more consistent and quicker gains than non-DFNB1 children. CONCLUSION: Although children with CI with DFNB1 show faster gains in Reynell scores, duration of CI use appears to have a greater effect on speech perception than DFNB1 status. SIGNIFICANCE: Identification of DFNB1 children is useful in counseling of CI outcomes.

Sensorimotor interaction in deaf children. Relationship between gait performance and hearing input during childhood assessed in pre-lingual cochlear implant users.

CONCLUSIONS: The results suggest that auditory input is not neutral in motor skills and the complex interaction between them is generated in the earlier stages of childhood development. Objective The assessment of gait performance in pre-lingual deaf children with cochlear implant (CI). METHODS: Gait velocity (GV), using a 10-meter test, was measured by means of three inertial sensors in 10 pre-lingual cochlear implant users (CIU) (10-16 years old) in three sensory conditions: (1) cochlear implant turned on with environmental noise (EN), (2) cochlear implant turned on with EN and with cognitive dual task (DT), and (3) CI turned off (CI-OFF). GV with EN and DT was assessed in a normal hearing control group (CG) (n = 14). Mann-Whitney and Wilcoxon Signed ranked test were used for significance validation. RESULTS: (1) GV in CG was lower in DT than with EN (p = .019). (2) GV was faster in CG with EN compared with the three conditions in CIU (EN, p = .006; DT, p = .0001; CI-OFF, p = .03). (3) CIU had slower GV walking with EN (p = .037) and with DT (p = .022). (4) Dividing the CIU sample by age, the acoustic information generates a slower gait for those implanted after 3 years old.

Postural adaptation in elderly patients with instability and risk of falling after balance training using a virtual-reality system.

Our aim in this study was to assess postural control adaptation quantitatively in unsteady elderly patients at risk of falls in open spaces and given balance training with a virtual-reality system reproducing environmental stimulation. Using a balance rehabilitation unit based on a virtual-reality system that changes sensory information (visual, vestibular, and somatosensory), we treated 26 elderly, unsteady patients who were prone to falling (age range, 73-82 years) and who were enrolled in a customized vestibular rehabilitation program. We assessed postural responses by posturography before and after 6 weeks in the vestibular rehabilitation program under two conditions: (1) standing, eyes open, static visual field, and (2) standing, eyes open, dynamic visual field through virtual-reality goggles, generating horizontal optokinetic stimulation (70 degrees per second angular velocity). We recorded postural responses with a platform measuring the confidential ellipse of the center-of-pressure distribution area and sway velocity with a scalogram analyzing postural behavior by wavelets. After 6 weeks of treatment, postural response confidential ellipse and sway velocity values were lower, evincing decreased amplitudes and sway frequency contents in the scalogram by wavelet under both stimulation paradigm conditions. These findings suggest postural adaptation under the two perceptual conditions when patients had static and dynamic visual fields. The possibility of treating elderly fallers with balance disorders using a virtual-reality environmental stimulation reproduction system is discussed.

Postural responses applied in a control model in cochlear implant users with pre-lingual hearing loss.

Conclusions The assessment of postural responses (PR) based in a feedback control system model shows selective gains in different bands of frequencies adaptable with child development. Objective PR characterization of pre-lingual cochlear implant users (CIU) in different sensory conditions. Methods Total energy consumption of the body's center of pressure signal (ECCOP) and its distribution in three bands of frequencies: band 1 (0-0.1 Hz), band 2 (0.1-0.7 Hz), and band 3 (0.7-20 Hz) was measured in a sample of 18 CIU (8-16 years old) and in a control group (CG) (8-15 years old). They were assessed in a standing position on a force platform in two sensory conditions: 1 = Eyes open. 2 = Eyes closed and standing on foam. Results In condition 1, total ECCOP of PR and its proportion of energy consumption in the three bands of frequencies were similar between CIU and CG (p > 0.05). In condition 2, CIU have significantly higher ECCOP, mainly in high frequencies (bands 2 and 3) (p < 0.05). ECCOP values decreased with age also, mainly in bands 2 and 3. This behavior is interpreted in the control system model proposed as an adaptation process related with child development.

Chronic balance disorders after acoustic neuroma surgery: assessment of gravitational vertical perception.

CONCLUSION: The head tilt response (HTR) test performed in a group of patients with chronic dizziness after acoustic neuroma surgery showed alterations in the gravitational vertical perception (GV). OBJECTIVE: The assessment of the accuracy in the GV through the HTR test in patients with long-term balance disorders after acoustic neuroma surgery. METHODS: The HTR was performed in two groups of patients that had undergone acoustic neuroma surgery: six uncompensated patients (UPs) who maintained vestibular symptoms 1 year after surgery and two compensated patients (CPs) without vestibular symptoms. Twelve healthy control adults were also tested (control group, CG). Three parameters were measured in the HTR test: steady-state error (SSE), rise time (TRS), and mean energy of the error signal per step (MEE). RESULTS: The UP group showed higher values for the TRS and MEE parameters compared with the CG (p < 0.05) when performing the HTR test to the side of the lesion and to the contralateral side, while the SSE only showed significant higher values when the patient estimated the GV towards the side of the lesion. The two patients in the CP group did not have differences in the three parameters assessed when compared with the CG.

Rol de la información auditiva en el control motor del sistema del equilibrio en pacientes con implantes cocleares / Role of auditory information in motor control of the balance system in patients with cochlear implants / Papel das informações auditivas no controle motor do sistema de equilíbrio em pacientes com implante coclear

Revisión de nuestros hallazgos experimentales sobre la relación entre audición y control motor del equilibrio en usuarios de implantes cocleares (UIC). Se realizó posturografía en 34 UIC en dos condiciones sensoriales:1- Implante encendido (ON). 2- Implante apagado (OFF) Se usó como medida el consumo de energía (CE) de la señal del centro de presión corporal. La marcha se analizó mediante la prueba de 10 m, implementada con: A - implante ON y ruido ambiental (EN), B - Implante ON, EN y Tarea dual cognitiva (DT) y C-implante OFF. Se registró la velocidad de marcha (GV) usando acelerómetros en los pies y la región retrosacra. Estadística: Se utilizaron las pruebas de Wilcoxon y Mann-Whitney y el nivel de significación fue p = 0.05. El análisis de la postura en la adolescencia mostró un ajuste adaptativo, disminuyendo la CE con el IC-ON.p = < 0,05, mientras con el CI-OFF no hubo disminución p => 0,05. En adultos, CI- OFF tuvieron valores más altos de CE en edades mayores, mientras que el CE no se incrementó con la edad con el CI-ON. En la marcha, la GV con el implante ON en EN solo disminuyó en UIC solo en aquellos que estaban implantado después de los 3 años. La UIC implantada antes de esta edad mostró un comportamiento de la marcha similar en comparación con los sujetos con audición normal como control. La información auditiva interviene en la postura y el comportamiento motor de la marcha, hechos que se analizan en esta revisión.

Review of publications of our group about the relationship between the auditory input and the balance motor control in subjects with profound hearing loss and cochlear implant users (UIC). A population of 34 UIC in which posturography in two different sensory information was performed, 1-Implant turned on (ON) giving acoustic information. 2-Implant turned off (OFF) and without auditory input. Energy consumption (CE) of the body center of pressure signal was used as measurement. Gait assessment was analyzed by the 10 m test, implemented with: A- Implant turned ON and environmental noise (EN). B- Implant ON, EN and cognitive dual task (DT) and C- Implant OFF with accelerometers in the feet and sacrum region to measure the gait velocity (GV). Statistics: Wilcoxon and Mann-Whitney test were used and significance level was p=0.05. Posture analysis for different ages in adolescence showed an adaptive adjustment, decreasing the EC significantly when the CI is ON (p<0.05). With the implant turned OFF, changes were not significant (p>0.05). In adults, (implant OFF) had higher values of CE related with age, while the CE did not show increment of CE with age when receiving auditory input with the implant ON. UIC implanted after being 3 years old showed a significant decrease in GV. The UIC implanted before this age showed similar gait behavior compared to normal hearing subjects as control. The auditory information intervenes in posture and gait motor behavior, facts which are analyzed in this review.

Revisão de publicações de nosso grupo sobre a relação entre a entrada auditiva e o controle motor do equilíbrio em indivíduos com perda auditiva profunda e usuários de implante coclear (UIC). Uma população de 34 UIC em que foi realizada a posturografia em duas informações sensoriais diferentes, o 1-Implant ativado (ON) fornece informações acústicas. 2-O implante foi desativado (OFF) e sem entrada auditiva. O consumo de energia (CE) do sinal do centro de pressão corporal foi utilizado como medida. A avaliação da marcha foi analisada pelo teste de 10 m, implementado com: A- Implante ligado e ruído ambiental (EN). B- Implante ON, EN e tarefa dupla cognitiva (TD) e C- Implante OFF com acelerômetros na região dos pés e sacro para medir a velocidade da marcha (GV). Estatísticas: Foram utilizados os testes de Wilcoxon e Mann-Whitney e o nível de significância foi de p = 0,05. A análise da postura para diferentes idades na adolescência mostrou um ajuste adaptativo, diminuindo significativamente a CE quando o IC está ligado (p <0,05). Com o implante desligado, as alterações não foram significativas (p> 0,05). Nos adultos, o (implante OFF) apresentou maiores valores de EC relacionados à idade, enquanto o CE não apresentou incremento do CE com a idade ao receber entrada auditiva com o implante ON. A UIC implantada após os 3 anos de idade mostrou uma diminuição significativa no GV. A UIC implantada antes dessa idade mostrou comportamento de marcha semelhante em relação aos indivíduos com audição normal como controle. As informações auditivas intervêm no comportamento motor da postura e da marcha, fatos analisados nesta revisão.

A multicenter observational study on the role of comorbidities in the recurrent episodes of benign paroxysmal positional vertigo.

OBJECTIVE: Primary objective of this study was to find a statistical link between the most worldwide comorbidities affecting the elderly population (hypertension, diabetes, osteoarthrosis, osteoporosis and depression) and recurrent episodes of BPPV. Secondary objective was defining possible "groups of risk" for people suffering recurrent positional vertigo related to the presence of a well documented comorbidity. METHODS: This was an observational, cross-sectional, multicenter, spontaneous, non-pharmacological study. The data of 1092 patients suffering BPPV evaluated in 11 different Departments of Otolaryngology, Otoneurology and Neurology, referring Centers for positional vertigo evaluation, were retrospectively collected. RESULTS: Regarding evaluated comorbidities (hypertension, diabetes, osteoarthrosis, osteoporosis and depression), data analysis showed the presence of at least one comorbid disorder in 216 subjects (19.8%) and 2 or more in 408 subjects (37.4%). Moreover there was a statistical significant difference between the number of comorbidities and the number of recurrences, otherwise said as comorbidity disorders increased the number of relapses increased too. CONCLUSION: The presence of a systemic disease may worsen the status of the posterior labyrinth causing a more frequent otolith detachment. This condition increases the risk for patients suffering BPPV to have recurrent episodes, even if correctly managed by repositioning maneuvers. The combination of two or more of aforementioned comorbidities further increases the risk of relapsing BPPV, worsened by the presence of osteoporosis. On the basis of this results it was possible to define "groups of risk" useful for predicting BPPV recurrence in patients with one or more comorbidity.

Effects of balance training using a virtual-reality system in older fallers.

Poor balance is considered a challenging risk factor for falls in older adults. Therefore, innovative interventions for balance improvement in this population are greatly needed. The aim of this study was to evaluate the effect of a new virtual-reality system (the Balance Rehabilitation Unit [BRU]) on balance, falls, and fear of falling in a population of community-dwelling older subjects with a known history of falls. In this study, 60 community-dwelling older subjects were recruited after being diagnosed with poor balance at the Falls and Fractures Clinic, Nepean Hospital (Penrith, NSW, Australia). Subjects were randomly assigned to either the BRU-training or control groups. Both groups received the usual falls prevention care. The BRU-training group attended balance training (two sessions/week for 6 weeks) using an established protocol. Change in balance parameters was assessed in the BRU-training group at the end of their 6-week training program. Both groups were assessed 9 months after their initial assessment (month 0). Adherence to the BRU-training program was 97%. Balance parameters were significantly improved in the BRU-training group (P < 0.01). This effect was also associated with a significant reduction in falls and lower levels of fear of falling (P < 0.01). Some components of balance that were improved by BRU training showed a decline after 9 months post-training. In conclusion, BRU training is an effective and well-accepted intervention to improve balance, increase confidence, and prevent falls in the elderly.

Postural response characterization in elderly patients with bilateral vestibular hypofunction.

CONCLUSIONS: The measurement of the energy consumption (EC) of the body's center of pressure (COP) to maintain the upright stance position was higher in elderly patients with bilateral vestibular hypofunction (BVH) compared with a control group and may be a valid parameter in the assessment of balance disorders. OBJECTIVE: The aim of the study was to evaluate the energy consumption of the COP in elderly patients with BVH. METHODS: The COP was recorded on a force platform (FP) for eight elderly patients with BVH related to aging and eight normal control group subjects. The EC of the COP was calculated using the discrete wavelet transform. The two groups were tested in standing position on the FP in three sensory conditions:1, eyes open; 2, eyes closed; and 3, standing on a foam pad placed on the force platform. Wilcoxon's rank test and multi-factor analysis of variance were used, with the level of significance set at 0.05. RESULTS: BVH patients showed higher values of EC of the COP signal measured in arbitrary units compared with the control group (conditions 1 and 2). None of the BVH patients could perform the test in condition 3. BVH patients had increased EC in the frequency band between 0.1 and 0.78 Hz when the visual information was canceled (condition 2).

Visual gravitational vertical perception in peripheral vestibular hypofunction.

CONCLUSIONS: Rise time in the estimation of the gravitational vertical in the head tilt response (HTR) test is increased in patients with peripheral vestibular lesions and residual chronic dizziness. OBJECTIVE: Assessment of the perception of the gravitational vertical in patients with peripheral vestibular lesions through the HTR. METHODS: HTR was studied in 12 patients with peripheral vestibular lesion, 8 clinically with chronic dizziness and 4 without it; 23 normal subjects were studied as control group. Two parameters of the HTR were assessed, rise time and steady-state error to characterize a dynamical system step response. The Kolmogorov-Smirnov test (alpha = 5%) was used to verify normal distribution (steady-state error, p = 0.53; rise time, p = 0.88). The three sigma ellipse was calculated for the control group. ROC curves were used to measure the sensitivity and specificity of these parameters. RESULTS: Rise time showed increased values in peripheral vestibular lesion patients with chronic dizziness. Two-dimensional analysis (rise time vs steady-state error) allows a better discrimination between patients with peripheral vestibular hypofunction with chronic dizziness and the rest of the studied population.

Influence of DFNB1 status on expressive language in deaf children with cochlear implants.

OBJECTIVE: The objective of this study was to compare the language growth of children with connexin-related deafness (DFNB1) who received cochlear implants versus the language growth of implanted children with non-DFNB1 deafness. STUDY DESIGN: A prospective longitudinal observational study and analysis. SETTING: Two tertiary referral centers. PATIENTS: There were 37 children with severe-to-profound hearing loss who received cochlear implants before the age of 5 years. INTERVENTIONS: A standardized language measure, the section for expressive language of the Reynell Developmental Language Scale was used to assess expressive language skills at 2 times postimplantation (14 and 57 mo postimplantation). Molecular screening for DFNB1 gene variants. MAIN OUTCOME MEASURES: Language quotient (LQ) scores (i.e., age-equivalent score obtained on the Reynell Developmental Language Scale divided by the child's chronological age), results of genotyping. RESULTS: The mean language age at the second time interval (mean ± standard deviation, 51.8 ± 13 mo) was greater than at the first testing session (mean ± standard deviation, 19 ± 8 mo, p < 0.001, Wilcoxon signed rank test). When divided by genotype, DFNB1 children exhibited a higher LQ and less variability in scores than non-DFNB1 children at the second testing interval (Wilcoxon sign rank test, p = 0.0034). A regression analysis (linear-fit by least squares) conducted on 26 children with preimplantation audiometric data showed that DFNB1 status was the independent variable with greater predictive effect on LQ at the second testing interval, followed by age at implantation (R2 = 0.35, p = 0.0479). CONCLUSION: Deaf children who received cochlear implants before the age of 5 years and use oral communication show substantial improvement in language abilities. In this study, DFNB1 children who use cochlear implants show greater gains in expressive language than non-DFNB1 children, independent of residual hearing, age at implantation, and duration of implant use.

Clinical characteristics of positional vertigo after mild head trauma.

CONCLUSION: This study showed that a population with benign paroxysmal positional vertigo related to mild head trauma (BPPVAT) was younger and more frequently presented with bilateral canalithiasis than another population with idiopathic etiology (IBPPV). In both groups, females presented a higher risk of BPPV. OBJECTIVE: To compare the clinical features of a population with BPPVAT and another with IBBPV. METHODS: We carried out statistical analysis of a population of 51 subjects with BPPVAT and another of 325 subjects with IBPPV, comparing age, gender, recurrence of symptoms, associated chronic dizziness (CD), and clinical presentation. Kolmogorov Smirnov test, Student's t test, Mann-Whitney test, 95% binomial confidence interval for proportions, chi-squared, and Fisher's test were used as statistical tools. A significance level of p < 0.05 was considered in all cases. RESULTS: The population affected with BPPVAT was younger and bilateral canalithiasis was also more frequent. No differences were found in gender distribution, semicircular canals involved in the symptoms, recurrence after repositioning maneuvers, or associated CD.

Balance in Parkinson's disease patients changing the visual input.

The description of the postural responses in Parkinson's disease patients when visual information changes from a stable to a moving visual field analyzing the impact on balance in these patients. METHODS (CLINICAL): Limits of Stability, Body center of pressure and balance functional reserve were measured by means of the force platform in 24 Parkinson's patients in stages 1 and 2 of the Boher classification and 19 volunteers as a control group. Both groups were stimulated with 1-Static visual field and 2-horizontal optokinetic stimulation using a virtual reality system. Postural responses were analyzed using the inverted pendulum as mathematical model. RESULTS: While the control group didn't show significant differences on the postural control between the two sensory conditions (COP p=0.0017, BFR p=0.0025), Parkinson's patients presented significant differences in the area of the center of pressure and the balance functional reserve values between static visual field and optokinetic stimulation. (COP p=0.0017, BFR p=0.0025). CONCLUSIONS: The results support the hypothesis about the influence of the changes in the visual information in triggering balance control disorders in Parkinson's patients. It is discussed the interest of these fact in the assessment and the rehabilitation programs of this disease.

Dynamic modeling and experimental results for a head tilt response.

The estimation of the vertical in humans is important in everyday life although the mechanisms involved are not completely understood yet. This paper presents two sets of experiments with normal subjects, using the same virtual reality setup, aiming to help in this understanding. First, a steady state experiment is presented, which is used to determine the gravitational vertical precision while the second, a dynamical transient response experiment, is used to find dynamic models of each subject response. Results show that the dynamic models are able to reproduce the results of the steady state experiment while having the benefits that a dynamic model brings to evaluate subjects performance.

Head tilt response: A complementary test to the Subjective Visual Vertical.

This paper studies the phenomenon of the perceived vertical by means of a novel dynamic experiment. This task is inspired in the Subjective Visual Vertical test and can be regarded as complementary in terms of how the information involved varies (visual, otolithic and neck proprioception). The experiment consists in presenting a white stripe in a pair of virtual reality goggles and adjusting the roll angle of the head until the stripe is aligned with the gravitational vertical. The roll angle of the head is measured and recorded along each trial where the white stripe changes position four times, after a specific amount of time. The task was run on a group of 28 normal subjects and a small sample of 5 patients with vestibular hypofunction. Six parameters derived from Control Theory were extracted from the data to characterize the subject transient response. All parameters for normal subjects were found to be normally distributed. Experimental results show that discrimination is possible between normal subjects and patients using just one or two of the parameters studied.

Postural control and sensory perception in patients with Parkinson's disease.

CONCLUSIONS: This study suggests that patients with Parkinson's disease (PD), even in the early stages, have decreased body limits of stability (LOS) and changes in the visual input impair their postural control. OBJECTIVE: To assess the LOS and the postural responses after changes in visual input in a group of PD patients in stage 1 of the Hoehn and Yahr classification. SUBJECTS AND METHODS: Twenty PD patients in stage 1 and a group of 24 normal subjects as control were assessed in two tests: (1) the LOS and (2) measurement of the body center of pressure area (COP) 10 s before and after sudden change in visual flow velocity. We also investigated labeling of the COP trajectory in these two periods. The stimulation paradigm was a horizontal optokinetic stimulation (60 degrees /s and suddenly stopped) using a virtual reality system. RESULTS: LOS showed significant decrease in PD patients as compared with the control group (p<0.001, Kruskal-Wallis and Wilcoxon ranked test). The COP values increased significantly (p<0.001, Wilcoxon signed rank test) after sudden changes in the visual flow velocity in relation to the control group. After the visual stop the PD patient showed a spatial 'roaming' approaching the limits of stability and therefore impairing the postural control.