Effect of Sensory Attenuation on Cortical Movement-Related Oscillations

This study examined the impact of induced sensory deficits on cortical, movement-related oscillations measured using electroencephalography (EEG). We hypothesized that EEG patterns in healthy subjects with induced sensory reduction would be comparable to EEG found after chronic loss of sensory feedback. EEG signals from 64 scalp locations were measured from 10 healthy subjects. Participants dorsiflexed their ankle after prolonged vibration of the tibialis anterior (TA). Beta band time frequency decompositions were calculated using wavelets and compared across conditions. Changes in patterns of movement-related brain activity were observed following attenuation of sensory feedback. A significant decrease in beta power of event-related synchronization was associated with simple ankle dorsiflexion after prolonged vibration of the TA. Attenuation of sensory feedback in young, healthy subjects led to a corresponding decrease in beta band synchronization. This temporary change in beta oscillations suggests that these modulations are a mechanism for sensorimotor integration. The loss of sensory feedback found in spinal cord injury patients contributes to changes in EEG signals underlying motor commands. Similar alterations in cortical signals in healthy subjects with reduced sensory feedback implies these changes reflect normal sensorimotor integration after reduced sensory input rather than brain plasticity

Flexor Reflex Decreases during Sympathetic Stimulation in Chronic Human Spinal Cord Injury

A better understanding of autonomic influence on motor reflex pathways in spinal cord injury is important to the clinical management of autonomic dysreflexia and spasticity in spinal cord injured patients. The purpose of this study was to examine the modulation of flexor reflex windup during episodes of induced sympathetic activity in chronic human spinal cord injury (SCI). We simultaneously measured peripheral vascular conductance and the windup of the flexor reflex in response to conditioning stimuli of electrocutaneous stimulation to the opposite leg and bladder percussion. Flexor reflexes were quantified using torque measurements of the response to a noxious electrical stimulus applied to the skin of the medial arch of the foot. Both bladder percussion and skin conditioning stimuli produced a reduction (43–67%) in the ankle and hip flexor torques (p \u3c 0.05) of the flexor reflex. This reduction was accompanied by a simultaneous reduction in vascular conductance, measured using venous plethysmography, with a time course that matched the flexor reflex depression. While there was an overall attenuation of the flexor reflex, windup of the flexor reflex to repeated stimuli was maintained during periods of increased sympathetic activity. This paradoxical depression of flexor reflexes and minimal effect on windup is consistent with inhibition of afferent feedback within the superficial dorsal horn. The results of this study bring attention to the possible interaction of motor and sympathetic reflexes in SCI above and below the T5 spinal level, and have implications for clinicians in spasticity management and for researchers investigating motor reflexes post SCI

Effects of a CPC on a Concentrated Solar Energy System

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Parallel Facilitatory Reflex Pathways from the Foot and Hip to Flexors and Extensors in the Injured Human Spinal Cord

Spinal integration of sensory signals associated with hip position, muscle loading, and cutaneous sensation of the foot contributes to movement regulation. The exact interactive effects of these sensory signals under controlled dynamic conditions are unknown. The purpose of the present study was to establish the effects of combined plantar cutaneous afferent excitation and hip movement on the Hoffmann (H) and flexion reflexes in people with a spinal cord injury (SCI). The flexion and H-reflexes were elicited through stimulation of the right sural (at non-nociceptive levels) and posterior tibial nerves respectively. Reflex responses were recorded from the ipsilateral tibialis anterior (TA) (flexion reflex) and soleus (H-reflex) muscles. The plantar cutaneous afferents were stimulated at three times the perceptual threshold (200 Hz, 24-ms pulse train) at conditioning–test intervals that ranged from 3 to 90 ms. Sinusoidal movements were imposed to the right hip joint at 0.2 Hz with subjects supine. Control and conditioned reflexes were recorded as the hip moved in flexion and extension. Leg muscle activity and sagittal-plane joint torques were recorded. We found that excitation of plantar cutaneous afferents facilitated the soleus H-reflex and the long latency flexion reflex during hip extension. In contrast, the short latency flexion reflex was depressed by plantar cutaneous stimulation during hip flexion. Oscillatory joint forces were present during the transition phase of the hip movement from flexion to extension when stimuli were delivered during hip flexion. Hip-mediated input interacts with feedback from the foot sole to facilitate extensor and flexor reflex activity during the extension phase of movement. The interactive effects of these sensory signals may be a feature of impaired gait, but when they are appropriately excited, they may contribute to locomotion recovery in these patients

Serving Member Interests in Changing Markets: A Case Study of Pro-Fac Cooperative

Since the inception of Pro-Fac Cooperative (PF) in 1960, the cooperative has undergone significant structural and organizational changes. The PF case presents a unique opportunity to examine the changes in the processed fruit and vegetable industry and the strategies adopted by a producer-owned cooperative to best represent member interests in the face of the industry structural changes over the past fifty years. PF is an agricultural cooperative that markets crops primarily grown by its member-growers, including fruits (cherries, apples, blueberries, and peaches), vegetables (snap beans, beets, peas, sweet corn, carrots, cabbage, squash, asparagus and potatoes), and popcorn. Members are located principally in the states of New York, Delaware, Pennsylvania, Michigan, Washington, Oregon, Iowa, Nebraska, Florida, and Illinois. PF‟s history can be generally broken down into three distinct time periods, each representing a significant phase of restructuring. Particular attention is given to the decision to enter into the most recent and current phase of operations. Adequate financing of operations and value-added enterprises were dominant foci over all three periods and each phase involved a different approach. A variety of strategies were also used to enhance the market security for products produced by members. Initially, PF was formed to help preserve the fruit and vegetable processing industry in New York State. At that time, owning the processing facilities was a logical strategy. The development of alternative cooperative structures is often pursued to ameliorate financial constraints, while attempting to maintain member control. The evolution and restructuring of the PF cooperative can also be described using an ownership control rights typology framework (Chaddad and Cook 2004). Drawing from the property rights and incomplete contracts theories of the firm, Chaddad and Cook argue that alternative cooperative models differ in how ownership rights are defined and assigned to the agents of the firm, i.e., members, patrons, managers, and investors. In the current phase, investors acquired ownership rights in a separate legal entity that is partly owned by the cooperative, i.e. a cooperative with capital seeking entities (Chaddad and Cook 2004). As time progressed and economic conditions changed, PF members were not able to adequately capitalize value-added operations. An arrangement was struck with a private equity firm to provide a needed infusion of capital. The case examines to decision made by the board of directors to enter into this agreement. PF has increased its capacity to serve as a preferred supplier to those firms that can afford owning and operating plants while divesting its majority, ownership position in processing assets.Agricultural cooperatives, fruit and vegetable processing, private equity firms, boards of directors, financing., Agribusiness, Community/Rural/Urban Development, Crop Production/Industries,

Increased Lower Limb Spasticity but Not Strength or Function Following a Single-Dose Serotonin Reuptake Inhibitor in Chronic Stroke

Objective: To investigate the effects of single doses of a selective serotonin reuptake inhibitor (SSRI) on lower limb voluntary and reflex function in individuals with chronic stroke. Design: Double-blind, randomized, placebo-controlled crossover trial. Setting: Outpatient research setting. Participants: Individuals (N=10; 7 men; mean age ± SD, 57±10y) with poststroke hemiplegia of \u3e1 year duration who completed all assessments. Interventions: Patients were assessed before and 5 hours after single-dose, overencapsulated 10-mg doses of escitalopram (SSRI) or placebo, with 1 week between conditions. Main Outcome Measures: Primary assessments included maximal ankle and knee isometric strength, and velocity-dependent (30°/s–120°/s) plantarflexor stretch reflexes under passive conditions, and separately during and after 3 superimposed maximal volitional drive to simulate conditions of increased serotonin release. Secondary measures included clinical measures of lower limb coordination and locomotion. Results: SSRI administration significantly increased stretch reflex torques at higher stretch velocities (eg, 90°/s; P=.03), with reflexes at lower velocities enhanced by superimposed voluntary drive (P=.02). No significant improvements were seen in volitional peak torques or in clinical measures of lower limb function (lowest P=.10). Conclusions: Increases in spasticity but not strength or lower limb function were observed with single-dose SSRI administration in individuals with chronic stroke. Further studies should evaluate whether repeated dosing of SSRIs, or as combined with specific interventions, is required to elicit significant benefit of these agents on lower limb function poststroke

\u3cem\u3eEx Vivo\u3c/em\u3e Diffusion Tensor Imaging of Spinal Cord Injury in Rats of Varying Degrees of Severity

The aim of this study was to characterize magnetic resonance diffusion tensor imaging (DTI) in proximal regions of the spinal cord following a thoracic spinal cord injury (SCI). Sprague–Dawley rats (n = 40) were administered a control, mild, moderate, or severe contusion injury at the T8 vertebral level. Six direction diffusion weighted images (DWIs) were collected ex vivo along the length of the spinal cord, with an echo/repetition time of 31.6 ms/14 sec and b = 500 sec/mm2. Diffusion metrics were correlated to hindlimb motor function. Significant differences were found for whole cord region of interest (ROI) drawings for fractional anisotropy (FA), mean diffusivity (MD), longitudinal diffusion coefficient (LD), and radial diffusion coefficient (RD) at each of the cervical levels ( p \u3c 0.01). Motor function correlated with MD in the cervical segments of the spinal cord (r2 = 0.80). The diffusivity of water significantly decreased throughout ‘‘uninjured’’ portions of the spinal cord following a contusion injury ( p \u3c 0.05). Diffusivity metrics were found to be altered following SCI in both white and gray matter regions. Injury severity was associated with diffusion changes over the entire length of the cord. This study demonstrates that DTI is sensitive to SCI in regions remote from injury, suggesting that the diffusion metrics may be used as a biomarker for severity of injury

Using Swing Resistance and Assistance to Improve Gait Symmetry in Individuals Post-Stroke

A major characteristic of hemiplegic gait observed in individuals post-stroke is spatial and temporal asymmetry, which may increase energy expenditure and the risk of falls. The purpose of this study was to examine the effects of swing resistance/assistance applied to the affected leg on gait symmetry in individuals post-stroke. We recruited 10 subjects with chronic stroke who demonstrated a shorter step length with their affected leg in comparison to the non-affected leg during walking. They participated in two test sessions for swing resistance and swing assistance, respectively. During the adaptation period, subjects counteracted the step length deviation caused by the applied swing resistance force, resulting in an aftereffect consisting of improved step length symmetry during the post-adaptation period. In contrast, subjects did not counteract step length deviation caused by swing assistance during adaptation period and produced no aftereffect during the post-adaptation period. Locomotor training with swing resistance applied to the affected leg may improve step length symmetry through error-based learning. Swing assistance reduces errors in step length during stepping; however, it is unclear whether this approach would improve step length symmetry. Results from this study may be used to develop training paradigms for improving gait symmetry of stroke survivors

Leg Sympathetic Response to Noxious Skin Stimuli is Similar in High and Low Level Human Spinal Cord Injury

Objective To determine if sympathetically mediated vasoconstriction in the lower extremities is injury level dependent. Although sympathetic responses have been measured in the limbs of people with high and low level SCI using blood flow measurements, including Doppler ultrasound and venous plethysmography, a direct comparison between injury levels has not been made. Methods Volunteers with chronic SCI were grouped according to injury level. Above T6: high level (HL, n = 7), and T6 and below: low level (LL, n = 6). All subjects had complete motor and sensory loss. Leg arterial flows were recorded by venous occlusion plethysmography, and continuous heart rate and mean arterial pressure (MAP) were measured. The conditioning stimulus consisted of transcutaneous stimulation to the arch of the contralateral foot. Results HL and LL subjects demonstrated a significant decrease in arterial conductance during stimulation with no significant difference found between groups. As expected, only group HL demonstrated a significant increase in MAP. Conclusions These results support our hypothesis that local (leg) sympathetic responses are similar for both high and low level SCI. Significance While low level SCI does not typically present with autonomic dysreflexia, bouts of increased reflex sympathetic activity could have ramifications for metabolism as well as renal and motor system functio

Stepping Responses to Treadmill Perturbations vary with Severity of Motor Deficits in Human SCI

In this study, we investigated the responses to tread perturbations during human stepping on a treadmill. Our approach was to test the effects of perturbations to a single leg using a split-belt treadmill in healthy participants and in participants with varying severity of spinal cord injury (SCI). We recruited 11 people with incomplete SCI and 5 noninjured participants. As participants walked on an instrumented treadmill, the belt on one side was stopped or accelerated briefly during mid to late stance. A majority of participants initiated an unnecessary swing when the treadmill was stopped in mid stance, although the likelihood of initiating a step was decreased in participants with more severe SCI. Accelerating or decelerating one belt of the treadmill during stance altered the characteristics of swing. We observed delayed swing initiation when the belt was decelerated (i.e. the hip was in a more flexed position at time of swing) and advanced swing initiation with acceleration (i.e. hip extended at swing initiation). Further, the timing and leg posture of heel strike appeared to remain constant, reflected by a sagittal plane hip angle at heel strike that remained the same regardless of the perturbation. In summary, our results supported the current understanding of the role of sensory feedback and central drive in the control of stepping in participants with incomplete SCI and noninjured participants. In particular, the observation of unnecessary swing during a stop perturbation highlights the interdependence of central and sensory drive in walking control