The effects of peripheral nerve impairments on postural control and mobility among people with peripheral neuropathy

Approximately 20 million Americans are suffering Peripheral Neuropathy (PN). It is estimated that the prevalence of all-cause PN is about 2.4% in the entire adult population, whereas over 8-10% in the population segment over the age of 55 (Martyn & Hughes, 1997). Peripheral Neuropathy leads to a high risk of falling, resulting from the deficits of postural control caused by the impaired peripheral nerves, especially the degenerative somatosensory system. To date, there is no effective medical treatment for the disease but pain managements. The deficits of postural control decrease the life quality of this population. The degeneration of peripheral nerves reduces sensory inputs from the somatosensory system to central nervous system via spinal reflexive loop, which should provide valuable real-time information for balance correction. Therefore, it is necessary to investigate how PN affects the somatosensory system regarding postural control. Besides that, people with PN may develop a compensatory mechanism which could be reinforced by exercise training, ultimately to improve balance and mobility in their daily life. The neuroplasticity may occur within somatosensory system by relying on relative intact sensory resources. Hence, unveiling the compensatory mechanism in people with PN may help in understanding (a) essential sensations or function of peripheral nerves to postural control, (b) effective strategy of physical treatments for people with PN, and (c) task-dependent sensory information requirements. Therefore, this dissertation discussed the roles of foot sole sensation, ankle proprioception, and stretch reflex on balance as well as gait among people with PN. Furthermore, the discussion of the coupling between small and large afferent reflexive loops may spot the compensatory mechanism in people with PN

Ankle Proprioception Correlates with Functional Mobility in People with Peripheral Neuropathy

Introduction: The ankle proprioception could influence the functional stability of ankle joint. In addition, ankle proprioception may indirectly influence postural control. Furthermore, ankle proprioception may play an important role in the impaired somatosensory system. Purpose: The purpose is to examine if ankle proprioception is correlated with functional mobility in people with Peripheral Neuropathy (PN) and health age-matched control. Methods: Twenty one people with, and twelve age-matched without PN, were recruited. Active (AAP) and passive (PAP) ankle proprioception were assessed using Biodex 3 dynamometer (Biodex Medical System, Inc, Shirley, NY, USA). Participants sat in the Biodex chair with the back of the chair positioned at 70° with lower leg parallel with the ground. The protocol of the active and passive reposition tests consisted of localizing three target positions: 15° of inversion, 0° subtalar neutral, 10° of eversion [1]. We have also tested foot sole sensation. The foot sole sensitivity (FSS) was tested at big toe (BT), 1st and 5th metatarsal (M1 and M5), midfoot (MF) and medial heel (MH) with a 5.07 monofilament [2]. The overall score of one foot was the number of its sensitive sites, ranged from 0 to 5. Functional mobility test (6-minute walk test and timed up-and-go test) were performed following standard procedures in both groups. Group effects were analyzed by ANOVA. Pearson correlation tests were used to examine the relationships between ankle proprioception tests and functional mobility measures. Results: There were significant different of AAP (PN: 28.2 ± 17.6, H: 16.8 ± 8.3), PAP (PN: 20.7 ± 12.6, H: 11.7 ± 4.3), FSS (PN: 2.5 ± 2.0, H: 4.3 ± 1.2), 6MW (PN: 426.9 ± 95.2, H: 525.3 ± 68.1), and TUG (PN: 9.7 ± 2.4, H: 6.5 ± 1.3) between two groups. No other significant group effect was observed among age, height and body mass. A significant positive correlation was observed between AAP /PAP and TUG in people with PN (R= 0.52, P\u3c.05, R= 0.75, P\u3c.05). A significant negative correlation was observed AAP/PAP and 6MW (R= -0.46, P\u3c.05, R= -0.51, P\u3c.05). No other significant correlation was observed. Discussion: Ankle proprioception is important for the functional mobility in the PN group, but not in the health control group. More accurate ankle proprioception correlates with faster walking speed in people with PN

Functional Connectivity in Gait Under Dual-Task Paradigm in Healthy Adolescents

PURPOSE: Functional connectivity can be viewed as the mechanism used to coordinate different neural networks in order to perform a complex task. Dual-task walking requires an individual to walk, while simultaneously performing a secondary task. The purpose of this study was to determine the level of functional connectivity and neuro-efficiency in adolescents under the dual-task walking. We hypothesized that we would see an increase in local and global efficiency within adolescents when transitioning from a single task gait test to a dual task gait test. METHODS: 15 healthy adolescents (12 male, age: 16.33±0.94 years, height: 1.69±0.10 m, mass: 64.08±9.81 kg) were recruited. The brain activity of the left and right prefrontal cortex (dorsal lateral, and dorsal media) were measured by fNIRS, the sampling rate of 20.3 Hz. Vicon motion capture system was used to record kinematic data, the sampling rate of 100 Hz. The first test was a single task gait test in which the subject walked at a self-selected speed between two cones 15 meters apart for 2 minutes with 10 seconds of standing as the baseline for fNIRS measures. Subjects were then tested under a dual-task paradigm (serially subtracting 7’s from randomly presented 2 or 3-digit numbers). The primary outcome measures include normalized local and global efficiency, gait speed, and stride length. Two two-way MANOVA with repeated measures were used to examine the task difference (alpha level = 0.05). RESULTS: There was a significant task effect on gait performance (F3,12 = 6.430, p = 0.008). Post hoc pairwise tests indicated that single-task presented greater average walking velocity (p \u3c 0.001, ST vs. DT: 1.33 ± 0.18 vs. 1.23 ± 0.20 m/s) and shorter stride time (p = 0.002, ST vs. DT: 1.11 ± 0.10 vs. 1.14 ± 0.12 s) than dual-task. There was no significant task effect on brain activity and neural efficiency (p \u3e 0.05). CONCLUSION: There was a significant difference in gait speed between adolescents and young adults. This is due to the task complexity affecting adolescents significantly more than adults. Young adults don’t see a change in speed but do see an increase in PFC activation. Adolescents having lower levels of functional connectivity compared to young adults could be due to the number/size of functionally connected regions measured within adolescence. Children are still developing day by day, indicating that the strength of functional connectivity seemingly develops as they age. With this information we can conclude that functional connectivity continuously changes while going through your adolescent years

Automaticity with Balance in Dual-Task Tests in Healthy Adolescents

BACKGROUND/CONTEXT: The hallmark of healthy postural control in adolescents is automaticity which is the ability of the nervous system to successfully coordinate posture with minimal use of attention-demanding executive control resources. Automaticity plays an important role in adolescents because it is necessary to perform motor skills, motor learning and reduce the risk of sport injury. Research has shown in dual-task (DT) paradigms that the ability to use postural control and cognitive skills of the brain uses both local and global functional connectivity in the Prefrontal Cortex, which controls a healthy adolescent\u27s ability to perform a dual-task test with adequate balance. PURPOSE: The purpose of our study is to examine if healthy adolescents show strong functional connectivity to compensate for the deficit in their postural control. Automaticity can be measured by presenting a healthy adolescent with a dual-task test, and observing if the brain activity is impacted in the Prefrontal Cortex (PFC), inferring a significant deficit in their postural control. The use of force plates are used to measure the sway area and the average velocity of the participants when they are given a single-task test and a dual-task test. Smaller sway area and average velocity presents a better performance in the local and global functional connectivity between regions of the brain. We hypothesized that there is no significant difference in terms of single or dual-task tests in their functional connectivity. METHODS: 15 healthy adolescents (12 male (80%), age: 16.33±0.94 years, height: 1.69±0.10 m, mass: 64.08±9.81 kg) were recruited. Activity of the left/right prefrontal cortex (dorsal lateral and dorsal medial regions) were monitored using fNIRS, sampling rate of 20.3 Hz. The AMTI force plate is used to measure the center of pressure (CoP), sampling rate of 2000 Hz. Participants performed two standing trials on force plates for 30 seconds in single task (ST) and dual task (DT: concurrent cognitive task subtracting by 7’s) conditions. There was a 10-second quiet standing before each trial to serve as the baseline for the fNIRS signals. Our dependent variable included the HbO2 level, local and global efficiency of the prefrontal cortex and the 95% sway area and average CoP velocity. Three two-way MANOVA with repeated measures were used to examine the task difference (alpha level = 0.05). OUTCOMES: There was no significant task effect on balance performance (F3,12 = 4.048, p = 0.033). Post pairwise tests indicated that single-task tests presented a smaller average CoP velocity in the anterior posterior (p = 0.037, ST vs DT: 6.78 ± 2.39 vs. 10.22 ± 5.80 cm/s) and medial lateral (p = 0.048, ST vs DT: 4.38 ± 1.44 vs. 6.31 ± 3.79 cm/s) directions than in dual-task test. There was no significant task effect on HbO2 level, local and global efficiency (p \u3e 0.05). IMPACT: There was no significant task effect on brain efficiency in balance performance. We observed a worse balance performance under dual-task tests compared to single-task tests while the functional connectivity remains the same. These results suggest that adolescents are still developing their automaticity in balance when compared to the healthy young adults who would have the same balance performance under the dual-task tests

The Contribution of Small and Large Sensory Afferents to Postural Control in Patients With Peripheral Neuropathy

Peripheral neuropathy (PN) is a multifarious disorder that is caused by damage to the peripheral nerves. Although the symptoms of PN vary with the etiology, most cases are characterized by impaired tactile and proprioceptive sensation that progresses in a distal to proximal manner. Balance also tends to deteriorate as the disorder becomes more severe, and those afflicted are substantially more likely to fall while walking compared with those who are healthy. Most patients with PN walk more cautiously and with greater stride variability than age-matched controls, but the majority of their falls occur when they must react to a perturbation such as a slippery or uneven surface. The purpose of this study was to first describe the role of somatosensory feedback in the control of posture and then discuss how that relationship is typically affected by the most common types of PN. A comprehensive review of the scientific literature was conducted using MEDLINE, and the relevant information was synthesized. The evidence indicates that the proprioceptive feedback that is conveyed primarily through larger type I afferents is important for postural control. However, the evidence indicates that the tactile feedback communicated through smaller type II afferents is particularly critical to the maintenance of balance. Many forms of PN often lead to chronic tactile desensitization in the soles of the feet and, although the central nervous system seems to adapt to this smaller type II afferent dysfunction by relying on more larger type I afferent reflex loops, the result is still decreased stability. We propose a model that is intended both to help explain the relationship between stability and the smaller type II afferent and the larger type I afferent feedback that may be impaired by PN and to assist in the development of pertinent rehabilitative interventions