Improved proprioceptive function by application of subsensory electrical noise: Effects of aging and task-demand.

The application of subsensory noise stimulation over the lower limbs has been shown to improve proprioception and postural control under certain conditions. Whereas the effect specificity seems to depend on several factors, studies are still needed to determine the appropriate method for training and rehabilitation purposes. In the current study, we investigated whether the application of subsensory electrical noise over the legs improves proprioceptive function in young and older adults. We aimed to provide evidence that stronger and age-related differential effects occur in more demanding tasks. Proprioceptive function was initially assessed by testing the detection of passive ankle movement (kinesthetic perception) in twenty-eight subjects (14 young and 14 older adults). Thereafter, postural control was assessed during tasks with different sensory challenges: i) by removing visual information (eyes closed) and; ii) by moving the visual scene (moving room paradigm). Tests performed with the application of electrical noise stimulation were compared to those performed without noise. The results showed that electrical noise applied over the legs led to a reduction in the response time to kinesthetic perception in both young and older adults. On the other hand, the magnitude of postural sway was reduced by noise stimulation only during a more challenging task, namely, when the optical flow was changing in an unpredictable (nonperiodic) manner. No differential effects of stimulation between groups were observed. These findings suggest that the relevance of proprioceptive inputs in tasks with different challenges, but not the subjects' age, is a determining factor for sensorimotor improvements due to electrical noise stimulation.

Age-related differences in EEG beta activity during an assessment of ankle proprioception.

The aim of this work was to compare cortical beta oscillatory activity between young (YA) and older (OA) adults during the assessment of ankle proprioception. We analyzed the response time (RT) to kinesthetic perception and beta event-related desynchronization/synchronization (ERD/ERS) in response to passive ankle movement applied at a slow speed, 0.5°/s. The relationship between ERD/ERS and RT was investigated by classifying the signals into fast-, medium-, and slow-RT. The results showed a temporal relationship between beta oscillation changes and RT for both groups, i.e., earlier ERD and ERS were obtained for trials with faster response time. ERD was larger and delayed in OA compared to the YA, and beta ERS was present only for OA. These findings suggest that a less efficient proprioceptive signaling reaching the brain of OA requires a higher level of brain processing and hence the differences in ERD potentials between YA and OA. Furthermore, the occurrence of ERS in OA might represent a compensatory strategy of active cortical resetting for adequate sensorimotor behavior due to the age-related reduced peripheral input and neuromuscular impairments. Altered balance between excitatory and inhibitory intracortical activity in older adults presumably explains the changes in beta oscillations.

Cortical correlates of response time slowing in older adults: ERP and ERD/ERS analyses during passive ankle movement.

OBJECTIVES: The response time (RT) to kinesthetic perception has been used as a proprioceptive measurement, for example, in older individuals. However, the RT cannot provide information on impairments at specific stages of the respective sensorimotor processing. In the present study, electroencephalographic (EEG) signals were recorded during passive ankle movement with and without an associated perceptual task of movement detection. The main purpose was to analyze differences between young and older adults both in terms of RT and cortical responses. Putative differences in the latter were expected to point to changes in the processing associated with neural pathways or cortical regions in the older subjects. METHODS: The EEG activity of nineteen older (OA, 65-76 years) and 19 young adults (YA, 21-32 years) was recorded during passive ankle movement, without motor voluntary response (NVR, sensory condition), and during a condition with voluntary motor response (VR, with measurement of the RT). Event-related potentials (ERP) and beta event-related desynchronization/synchronization (ERD/ERS) were recorded and analyzed in both experimental conditions. RESULTS: The RT in OA was larger than in YA (P<0.0001). EEG analyses showed that the N1 amplitude was larger in the VR than in the NVR condition (P=0.006), whereas no difference for latency was obtained between conditions (P=0.376). Comparisons between the groups revealed attenuated (P=0.019) and delayed (P=0.001) N1 in the OA group, irrespective of the condition (no interaction group vs condition). Only OA showed correlations between RT and N1, with significant correlation for both amplitude (r=-0.603, P=0.006) and latency (r=0.703, P=0.001). The ERD/ERS analyses revealed a task-dependent group effect: in NVR, significant differences were obtained only for the ERS amplitude, which was attenuated in OA (P=0.003). In VR, larger (P=0.004) and delayed (P=0.003) ERD and attenuated (P=0.029) and delayed (P=0.017) ERS peaks were observed in the older group. CONCLUSIONS: The results suggest that a larger response time to proprioceptive stimuli in older adults is associated with a weaker and delayed proprioceptive afferent inflow to the cortex. In this scenario, older adults would need a higher cognitive effort (larger ERD) to process the sensory inputs when attempting to properly perform a sensorimotor task. SIGNIFICANCE: ERP and ERD/ERS measurements during kinesthetic assessment provide new insights on identification of the origin of sensorimotor slowing in older adults.

Age-related differences in postural control: effects of the complexity of visual manipulation and sensorimotor contribution to postural performance.

Patterns of adaptive changes to the exposure to a sinusoidal visual stimulus can be influenced by stimulus characteristics as well as the integrity of the sensory and motor systems involved in the task. Sensorimotor deficits due to aging might alter postural responses to visual manipulation, especially in more demanding tasks. The purpose of this study was to compare postural control between young and older adults at different levels of complexity and to examine whether possible sensory and/or motor changes account for postural performance differences in older adults. Older and young adults were submitted to the following tests: postural control assessments, i.e., body sway during upright stance and induced by movement of a visual scene (moving room paradigm); sensory assessments, i.e., visual (acuity and contrast sensitivity) and somatosensory (tactile foot sensitivity and detection of passive ankle motion); and motor assessments, i.e., isometric ankle torque and muscular activity latency after stance perturbation. Older adults had worse sensory and motor performance, larger body sway amplitude during stance and stronger coupling between body sway and moving room motion than younger adults. Multiple linear regression analyses indicated that the threshold for the detection of passive ankle motion contributed the most to variances in body sway and this contribution was more striking when visual information was manipulated in a more unpredictable way. The present study suggests that less accurate information about body position is more detrimental to controlling body position, mainly for older adults in more demanding tasks.

Sensory and motor differences between young and older adults: somatosensory contribution to postural control.

OBJECTIVES: The aim of this study was to compare the performance of the sensory and motor systems and the contributions of possible differences to postural control. METHODS: Twenty older adults (68.9+/-3.7 years of age) and twenty young adults (21.9+/-2.1 years of age) underwent visual, somatosensory (tactile and kinesthetic sensitivity), motor tests (joint torque and muscle activation latency) and postural control assessments (upright semi-tandem posture). RESULTS: MANOVA and ANOVA indicated that older adults had a poorer performance in the sensory tests: visual acuity (p=0.001), visual contrast sensitivity (p=0.009), tactile sensitivity (p<0.001) and kinesthetic sensitivity of the knee (p<0.001) and ankle (<0.001); and in the motor tests: female (p=0.010) and male (p<0.001) knee flexion torque; female (p=0.002) and male (p<0.001) knee extension torque; female (p=0.029) and male (p=0.006) ankle dorsiflexion torque; female (p=0.004) and male (p=0.004) ankle plantar flexion torque; and muscle activation latency (p<0.001). The older adults also had greater body sway amplitude on the anterior-posterior direction (p=0.035). Multiple regression analysis revealed that perception of passive motion was the only variable that contributed to greater body sway on the anterior-posterior direction among older adults (R(2)=0.142; p<0.05). CONCLUSIONS: There are differences in sensory and motor performance between young adults and older adults, and attention should be directed toward the contribution of the proprioceptive system to postural control among older adults.

Diferenças sensoriais e motoras entre jovens e idosos: contribuição somatossensorial no controle postural / Sensory and motor differences between young and older adults: somatosensory contribution to postural control

OBJETIVOS: Comparar o desempenho dos sistemas sensoriais e motor entre jovens e idosos e identificar as contribuições das possíveis diferenças para o controle postural. MÉTODOS: Vinte idosos (68,9±3,7 anos de idade) e 20 jovens (21,9±2,1anos de idade) realizaram testes visuais; somatossensoriais (sensibilidade cutânea e cinestésica); motores (torque articular e latência de ativação muscular) e de controle postural (postura ereta em semi-tandem). RESULTADOS: As análises de variância (ANOVAs) e as análises de multivariância (MANOVAs) indicaram desempenho inferior dos idosos nos testes sensoriais: acuidade visual (p=0,001); sensibilidade ao contraste visual (p=0,009); sensibilidade cutânea (p<0,001); sensibilidade cinestésica de joelho (p<0,001) e tornozelo (<0,001), e motores: torque em flexão de joelho feminino (p=0,010) e masculino (p<0,001); extensão de joelho feminino (p=0,002) e masculino (p<0,001); dorsiflexão de tornozelo feminino (p=0,029) e masculino (p=0,006), flexão plantar de tornozelo feminino (p=0,004) e masculino (p=0,004) e latência de ativação muscular (p<0,001). Os idosos também apresentaram maior oscilação corporal na direção ântero-posterior (p=0,035). Análise de regressão múltipla revelou que a percepção ao movimento passivo foi a única variável que contribuiu para a maior oscilação corporal na direção ântero-posterior em idosos, R²=0,142, p<0,05. CONCLUSÕES: Diferenças no desempenho sensorial e motor ocorrem entre jovens e idosos e atenção deveria ser direcionada para a contribuição do sistema proprioceptivo para o controle postural de idosos.

OBJECTIVES: The aim of this study was to compare the performance of the sensory and motor systems and the contributions of possible differences to postural control. METHODS: Twenty older adults (68.9±3.7 years of age) and twenty young adults (21.9±2.1 years of age) underwent visual, somatosensory (tactile and kinesthetic sensitivity), motor tests (joint torque and muscle activation latency) and postural control assessments (upright semi-tandem posture). RESULTS: MANOVA and ANOVA indicated that older adults had a poorer performance in the sensory tests: visual acuity (p=0.001), visual contrast sensitivity (p=0.009), tactile sensitivity (p<0.001) and kinesthetic sensitivity of the knee (p<0.001) and ankle (<0.001); and in the motor tests: female (p=0.010) and male (p<0.001) knee flexion torque; female (p=0.002) and male (p<0.001) knee extension torque; female (p=0.029) and male (p=0.006) ankle dorsiflexion torque; female (p=0.004) and male (p=0.004) ankle plantar flexion torque; and muscle activation latency (p<0.001). The older adults also had greater body sway amplitude on the anterior-posterior direction (p=0.035). Multiple regression analysis revealed that perception of passive motion was the only variable that contributed to greater body sway on the anterior-posterior direction among older adults (R²=0.142; p<0.05). CONCLUSIONS: There are differences in sensory and motor performance between young adults and older adults, and attention should be directed toward the contribution of the proprioceptive system to postural control among older adults.

Influence of imposed optic flow characteristics and intention on postural responses.

This study examined the influence of both optic flow characteristics and intention on postural control responses. Two groups of 10 adults each were exposed to the room's movement either at 0.6 cm/s (low velocity group) or 1.0 cm/s (high velocity group). All the participants stood in the upright stance inside of a moving room and were informed about the room movement only after the fourth trial as they were asked to resist to its influence. Results revealed that participants from both groups were influenced by the imposed visual stimulus in the first trials, but the coupling strength was weaker for the high velocity group. The request to resist the visual influences decreased visual influences on body sway, but only for the low velocity group. These results indicate that intention might play a role in stimulus influences on body sway but it is stimulus dependent.