Neuroscience discipline science plan

Over the past two decades, NASA's efforts in the neurosciences have developed into a program of research directed at understanding the acute changes that occur in the neurovestibular and sensorimotor systems during short-duration space missions. However, the proposed extended-duration flights of up to 28 days on the Shuttle orbiter and 6 months on Space Station Freedom, a lunar outpost, and Mars missions of perhaps 1-3 years in space, make it imperative that NASA's Life Sciences Division begin to concentrate research in the neurosciences on the chronic effects of exposure to microgravity on the nervous system. Major areas of research will be directed at understanding (1) central processing, (2) motor systems, (3) cognitive/spatial orientation, and (4) sensory receptors. The purpose of the Discipline Science Plan is to provide a conceptual strategy for NASA's Life Sciences Division research and development activities in the comprehensive area of neurosciences. It covers the significant research areas critical to NASA's programmatic requirements for the Extended-Duration Orbiter, Space Station Freedom, and exploration mission science activities. These science activities include ground-based and flight; basic, applied, and operational; and animal and human research and development. This document summarizes the current status of the program, outlines available knowledge, establishes goals and objectives, identifies science priorities, and defines critical questions in the subdiscipline areas of nervous system function. It contains a general plan that will be used by NASA Headquarters Program Offices and the field centers to review and plan basic, applied, and operational intramural and extramural research and development activities in this area

Postural control in childhood: investigating the neurodevelopmental gradient hypothesis

Neurodevelopmental disorders (NDDs) have been suggested to lie on a gradient continuum, all resulting from common brain disturbances, but with different degrees of impairment severity. This case-control study aimed to assess postural stability against such hypothesis in 104 children/adolescents aged 5-17, of whom 81 had NDDs and 23 were healthy controls. Compared to healthy controls, Autism Spectrum Disorder (ASD) resulted in the most severely impaired neurodevelopmental condition, followed by Attention Deficit Hyperactive Disorder (ADHD) and Tourette Syndrome (TS). In particular, while ASD children/adolescents performed worse than healthy controls in a number of sensory conditions across all parameters, ADHD children/adolescents performed worse than healthy controls only in the sway area for the most complex sensory conditions, when their vision and somatosensory functions were both compromised, and performance in Tourette Syndrome (TS) was roughly indistinguishable from that of healthy controls. Finally, differences were also observed between clinical groups, with ASD children/adolescents, and to a much lesser extent ADHD children/adolescents, performing worse than TS children/adolescents, especially when sensory systems were not operationally accurate. Evidence from this study indicates that poor postural control may be a useful biomarker for risk assessment during neurodevelopment, in line with predictions from the gradient hypothesis

Doctor of Philosophy

dissertationIntegration of sensory inputs by the central nervous system (CNS) is necessary for adequate postural stability, but diminishes with age and is further impaired in Parkinson disease (PD). As a result, the CNS cannot appropriately weight sensory stimuli to facilitate postural responses to sudden changes in sensory input. Training the sensorimotor system to ignore or rapidly adapt to aberrant postural cues may improve postural control in PD. We evaluated the influence of acute and repeated exposure to galvanic vestibular stimulation (GVS) on postural responses during static and dynamic tasks to determine whether training improved these responses. We hypothesized that individuals with PD would demonstrate impaired postural recovery responses to acute GVS relative to healthy controls and that individuals with PD and healthy elders would demonstrate diminished adaptive responses to repeated GVS compared to young adults. Twelve individuals with PD (PD group), 15 healthy young adults (HY group), and 11 healthy elders (HE group) participated. Timing of GVS was randomly applied during each task. Fifteen acquisition and nine retention trials with GVS were compared to assess learning. The PD group took longer to stabilize their center of pressure (COP) in quiet stance following GVS acutely compared to controls. The PD and HE groups had lower sample entropy (SaEn) compared to the HY. Neither the PD nor HE groups demonstrated changes in SaEn or meaningful improvements in postural control during acquisition or retention. SaEn in the HY group acutely decreased and then increased at retention which coincided with a meaningful improvement in postural control. The PD group had impaired motor planning, postural preparation, and postural stability during a rise to toes task following acute GVS, but these constructs returned to baseline at later acquisition and retention time points. Controls suppressed GVS acutely Postural coordination decreased acutely in the PD group during tether release. This persisted and an adaptive trend in BOS transition was noted with repeated GVS exposure in this group. No changes were observed in the control groups. Taken together, these results demonstrated that acute GVS differentially affects postural control in individuals with PD. Our results support the hypothesis that reweighting of sensory stimuli is impaired in PD. We also show that individuals with PD are able to suppress attention to a vestibular illusion and demonstrate adaptive responses to a postural threat

Reflex control of the spine and posture: a review of the literature from a chiropractic perspective

OBJECTIVE: This review details the anatomy and interactions of the postural and somatosensory reflexes. We attempt to identify the important role the nervous system plays in maintaining reflex control of the spine and posture. We also review, illustrate, and discuss how the human vertebral column develops, functions, and adapts to Earth's gravity in an upright position. We identify functional characteristics of the postural reflexes by reporting previous observations of subjects during periods of microgravity or weightlessness. BACKGROUND: Historically, chiropractic has centered around the concept that the nervous system controls and regulates all other bodily systems; and that disruption to normal nervous system function can contribute to a wide variety of common ailments. Surprisingly, the chiropractic literature has paid relatively little attention to the importance of neurological regulation of static upright human posture. With so much information available on how posture may affect health and function, we felt it important to review the neuroanatomical structures and pathways responsible for maintaining the spine and posture. Maintenance of static upright posture is regulated by the nervous system through the various postural reflexes. Hence, from a chiropractic standpoint, it is clinically beneficial to understand how the individual postural reflexes work, as it may explain some of the clinical presentations seen in chiropractic practice. METHOD: We performed a manual search for available relevant textbooks, and a computer search of the MEDLINE, MANTIS, and Index to Chiropractic Literature databases from 1970 to present, using the following key words and phrases: "posture," "ocular," "vestibular," "cervical facet joint," "afferent," "vestibulocollic," "cervicocollic," "postural reflexes," "spaceflight," "microgravity," "weightlessness," "gravity," "posture," and "postural." Studies were selected if they specifically tested any or all of the postural reflexes either in Earth's gravity or in microgravitational environments. Studies testing the function of each postural component, as well as those discussing postural reflex interactions, were also included in this review. DISCUSSION: It is quite apparent from the indexed literature we searched that posture is largely maintained by reflexive, involuntary control. While reflexive components for postural control are found in skin and joint receptors, somatic graviceptors, and baroreceptors throughout the body, much of the reflexive postural control mechanisms are housed, or occur, within the head and neck region primarily. We suggest that the postural reflexes may function in a hierarchical fashion. This hierarchy may well be based on the gravity-dependent or gravity-independent nature of each postural reflex. Some or all of these postural reflexes may contribute to the development of a postural body scheme, a conceptual internal representation of the external environment under normal gravity. This model may be the framework through which the postural reflexes anticipate and adapt to new gravitational environments. CONCLUSION: Visual and vestibular input, as well as joint and soft tissue mechanoreceptors, are major players in the regulation of static upright posture. Each of these input sources detects and responds to specific types of postural stimulus and perturbations, and each region has specific pathways by which it communicates with other postural reflexes, as well as higher central nervous system structures. This review of the postural reflex structures and mechanisms adds to the growing body of posture rehabilitation literature relating specifically to chiropractic treatment. Chiropractic interest in these reflexes may enhance the ability of chiropractic physicians to treat and correct global spine and posture disorders. With the knowledge and understanding of these postural reflexes, chiropractors can evaluate spinal configurations not only from a segmental perspective, but can also determine how spinal dysfunction may be the ultimate consequence of maintaining an upright posture in the presence of other postural deficits. These perspectives need to be explored in more detail

Sensorimotor postural control in healthy and pathological stance and gait

Postural control during standing and walking is an inherently unstable task requiring the interaction of various biomechanical, sensory, and neurophysiological mechanisms to shape stable patterns of whole-body coordination that are able to counteract postural disequilibrium. This thesis focused on the examination of central aspects of the functional roles of these mechanisms and the modes of interaction between them. A further aim was to determine the conditions of dynamic stability for healthy standing and walking performance as well as for certain balance and gait disorders. By studying movement fluctuations in the walking pattern it could be demonstrated that dynamic stability during walking depends on gait speed and is differentially regulated for the medio-lateral and the fore-aft walking planes. Stability control in the fore-aft walking plane exhibits attractor dynamics typical for a dynamical system. Accordingly, the most stable pattern of movement coordination in terms of minimal fluctuations in the order parameter (i.e., the relative phase between the two oscillating legs) can be observed at the attractor of self-paced walking. Critical fluctuations occur at increasingly non-preferred speeds, indicating a loss of dynamic gait stability close to the speed boundaries of the walking mode. Moreover, stability control during slow walking is critically dependent on sensory feedback control, whereas dynamic stability during fast walking relies mainly on the smooth operation of cerebellar pacemaker regions. Disturbances of sensory and cerebellar locomotor control in certain gait disorders could be further linked to a loss of dynamic gait stability, in particular an increased risk of falls. Furthermore, this thesis examined alterations in the sensorimotor postural control scheme that may trigger the experience of subjective imbalance and vertigo in the conditions of phobic postural vertigo and visual height intolerance. Both conditions are characterized by an inadequate mode of balance regulation featuring increased levels of open-loop balance control and a precipitate integration of closed-loop sensory feedback into the postural control scheme. This inadequate balance control strategy is accompanied by a stiffening of the anti-gravity musculature and is elicited by specific influences of attention and sensory feedback control. The findings of this thesis contribute to the understanding of central sensorimotor mechanisms involved in the control of dynamic postural stability during standing and walking. They further provide relevant information for the differential diagnosis and fall risk estimation of certain balance and gait disorders

Compensation Following Bilateral Vestibular Damage

Bilateral loss of vestibular inputs affects far fewer patients than unilateral inner ear damage, and thus has been understudied. In both animal subjects and human patients, bilateral vestibular hypofunction (BVH) produces a variety of clinical problems, including impaired balance control, inability to maintain stable blood pressure during postural changes, difficulty in visual targeting of images, and disturbances in spatial memory and navigational performance. Experiments in animals have shown that non-labyrinthine inputs to the vestibular nuclei are rapidly amplified following the onset of BVH, which may explain the recovery of postural stability and orthostatic tolerance that occurs within 10 days. However, the loss of the vestibulo-ocular reflex and degraded spatial cognition appear to be permanent in animals with BVH. Current concepts of the compensatory mechanisms in humans with BVH are largely inferential, as there is a lack of data from patients early in the disease process. Translation of animal studies of compensation for BVH into therapeutic strategies and subsequent application in the clinic is the most likely route to improve treatment. In addition to physical therapy, two types of prosthetic devices have been proposed to treat individuals with bilateral loss of vestibular inputs: those that provide tactile stimulation to indicate body position in space, and those that deliver electrical stimuli to branches of the vestibular nerve in accordance with head movements. The relative efficacy of these two treatment paradigms, and whether they can be combined to facilitate recovery, is yet to be ascertained

Forward optic flow is prioritised in visual awareness independently of walking direction

When two different images are presented separately to each eye, one experiences smooth transitions between them-a phenomenon called binocular rivalry. Previous studies have shown that exposure to signals from other senses can enhance the access of stimulation-congruent images to conscious perception. However, despite our ability to infer perceptual consequences from bodily movements, evidence that action can have an analogous influence on visual awareness is scarce and mainly limited to hand movements. Here, we investigated whether one's direction of locomotion affects perceptual access to optic flow patterns during binocular rivalry. Participants walked forwards and backwards on a treadmill while viewing highly-realistic visualisations of self-motion in a virtual environment. We hypothesised that visualisations congruent with walking direction would predominate in visual awareness over incongruent ones, and that this effect would increase with the precision of one's active proprioception. These predictions were not confirmed: optic flow consistent with forward locomotion was prioritised in visual awareness independently of walking direction and proprioceptive abilities. Our findings suggest the limited role of kinaesthetic-proprioceptive information in disambiguating visually perceived direction of self-motion and indicate that vision might be tuned to the (expanding) optic flow patterns prevalent in everyday life

Characterizing the dynamics of vestibular reflex gain modulation using balance-relevant sensory conflict

Electrical vestibular stimulation (EVS) can be used to evoke reflexive body sways as a probe of vestibular control of balance. However, EVS introduces sensory conflict by decoupling vestibular input from actual body motion, prompting the central nervous system (CNS) to potentially perceive vestibular signals as less reliable. In contrast, light touch reduces sway by providing reliable feedback about body motion and spatial orientation. The juxtaposition of reliable and unreliable sensory cues enables exploration of multisensory integration during balance control. I hypothesized that when light touch is available, coherence and gain between EVS input and center of pressure (CoP) output would decrease as the CNS reduces the weighting of vestibular cues. Additionally, I hypothesized that the CNS would require less than 0.5 seconds to adjust weighting of sensory cues upon introduction or removal of light touch. In two experiments, participants stood as still as possible while receiving continuous stochastic EVS (with a frequency of 0-25 Hz, amplitude of ± 4 mA, and a duration of 200-300 seconds), while either: lightly touching a load cell (<2 N); holding their hand above a load cell; or intermittently switching between touching and not touching the load cell. Anterior-posterior (AP) CoP and linear accelerations from body-worn accelerometers were collected to calculate the root mean square (RMS) of AP CoP, as well as the coherence and gain between EVS input and AP CoP or acceleration outputs. Light touch led to a decrease in CoP RMS (mean 49% decrease) with and without EVS. Significant coherence between EVS and AP CoP was observed between 0.5 Hz and 24 Hz in the NO TOUCH condition, and between 0.5 Hz and 30 Hz in the TOUCH condition, with TOUCH having significantly greater coherence from 11 to 30 Hz. Opposite to coherence, EVS-AP CoP gain decreased in the TOUCH condition between 0.5-8 Hz (mean decrease 63%). Among the available acceleration data, only the head exhibited a significant increase in coherence above 10 Hz in the TOUCH condition, compared to the NO TOUCH condition. Light touch reduced CoP displacement, but increased variation in the CoP signal that can be explained by EVS input. Light touch may cause the CNS to attribute EVS signals to head movements and therefore up-weight vestibulocollic responses while downweighting vestibulospinal balance responses. Changes in coherence and gain started before the transition to the NO TOUCH condition and after the transition to the TOUCH condition. The loss of sensory information may be more destabilizing than addition, necessitating anticipatory adjustments. These findings demonstrate the ability of one sensory modality to modulate the utilization of another by the CNS, and highlight asymmetries in the timing of responses to the introduction and removal of sensory information, which may impact behavior.

Age Differences in Vestibular Processing: Neural and Behavioral Evidence

The vestibular system is well known for its role in balance, but its mechanisms of action in this role are not well understood. My dissertation aims to provide a better understanding of vestibular brain function, its correlation with postural control, and its alteration with advancing age. This is an important topic considering that falls are the current leading cause of injuries in older adults in the U.S., and they have negative consequences on wellbeing and independence. In this dissertation, I first review the conventional methods for studying vestibular function in the human brain, and I evaluate a novel MRI-compatible method, which relies on a pneumatic tapper. This approach successfully induces vestibular responses, while preventing the aversive effects of stimulation that are common in other approaches. Next, I assess age differences in brain responses to pneumatic vestibular stimulation, and find that older adults demonstrate less sensitivity to stimulation. Also, those with better postural control exhibit less deactivation of cross-modal sensory regions (e.g. visual and somatosensory cortices). This greater engagement of non-vestibular sensory regions in older adults with better balance could be a mechanism to compensate for inefficient vestibular processing. Consistent with this hypothesis, the relationship between postural control and deactivation of sensory regions was only evident in tasks of low difficulty (i.e. normal stance) in which compensatory neural recruitment might be most effective. After assessing the brain responses to vestibular stimulation in terms of activation and deactivation, I examine connectivity of the vestibular cortex with other regions. This last experiment demonstrates that vestibular cortex connectivity increases in response to vestibular stimulation, and young adults exhibit greater connectivity relative to older adults. Also, connectivity predicts postural stability in high difficulty tasks for young adults, and in low difficulty tasks for older adults. Better balance in young adults is associated with less vestibular connectivity (i.e. they engaged vestibular cortex more selectively), whereas better balance in older adults is associated with higher connectivity (i.e. more recruitment of other sensory regions). These findings reinforce the conclusions from the second experiment, and provide more evidence in support of the compensation related utilization of neural circuits hypothesis (CRUNCH) of neural processing in older adults.PHDKines & Psychology PhDUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/145857/1/fnoohi_1.pd

The Effects of Anxiety, Ageing, and Neurodegenerative Disease on Visual Reweighting for Postural Control

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonFor most people, the complex mechanisms of sensory reweighting and maintaining balance are effective in maintaining relative automaticity and stability. However, this optimal function can be jeopardized by a range of factors. Ageing, anxiety, changes in attention, and neurodegenerative disease are some of the factors that potentially affect sensory integration for balance. These factors are explored in this thesis over several empirical studies using visual perturbations delivered using virtual reality. First, I examined the effects of ageing and anxiety on the postural response to the erroneous visual experience of self-movement (Study 1). Secondly, I explored these effects in the context of Parkinson’s Disease with Freezing of Gait: a population with impaired non-visual sensory processing and increased anxiety related to motor control (Study 2). The final study attempts to isolate the effects of increased conscious control of movement on visual reweighting to examine the degree to which they account for the results of the previous studies (Study 3). Study 1 found that anxiety appears to relate to increased reliance on vision for balance, but it only partially accounts for greater reliance on vision in older adults. Study 2 found that people with PD+FOG take longer responding to the visual perturbation than healthy age-matched adults, and that freezing severity correlates with longer latency and possibly lower magnitude of response. Finally, Study 3 found no significant effect of increased conscious control of movement on reliance on vision for postural control. Overall, while anxiety does have the potential to increase reliance on visual input, increased visual dependency observed in older adults and people with PD is likely to have different origins, potentially related to physiological changes, rather than increased conscious control of movement. The General Discussion reviews the contribution of these findings to research on sensory integration and postural control, and discusses their implications, and directions for future research