Planetary Defense team project: READI (Roadmap for EArth Defense Initiatives)

Planetary Defense is a complex problem, not well understood by policy makers and the general public. The recent Chelyabinsk incident in Russia created temporary international attention but has failed to effectively stimulate public action. The lack of long-term attention to cosmic hazards has resulted in limited funding to defend our planet. Hence, it is hard to realistically address this challenge and achieve the high test and operational readiness needed for an effective Planetary Defense strategy. To address this problem, we have created a set of recommendations for the development of a Planetary Defense Program, for the purpose of contributing to the protection of Earth from asteroids and comets. The SSP15 READI Project focused on threats for which there is only a short-term warning, specifically a warning of two years or less from detection of the object to impact. We have provided recommendations in five areas of Planetary Defense including detection and tracking, deflection techniques, global collaboration, outreach and education, and evacuation and recovery. We have applied this set of recommendations in a narrative scenario to make our report more impactful and engaging. We contrast optimistic and pessimistic outcomes for a comet threat, differing from each other in terms of the level of readiness achieved during the years leading up to the discovery of the threat. In our optimistic scenario, the deflection system has achieved high test and operational readiness. The world’s governments have realized the importance of being prepared against cosmic hazards and put in place all of the necessary measures for a successful defense, leading to a positive deflection of the comet. In contrast, in the pessimistic scenario no preparation is done before the detection, and the comet strikes a heavily populated area releasing energy equivalent to 80 times the most powerful nuclear bomb ever detonated. The recommendations that we have identified in this report constitute a roadmap to avoid this horrible outcome, and we believe they should be taken seriously and swiftly implemented

The firing characteristics of foot sole cutaneous mechanoreceptor afferents in response to vibration stimuli

Single unit microneurography was used to record the firing characteristics of the four classes of foot sole cutaneous afferents [fast and slowly adapting type I and II (FAI, FAII, SAI, and SAII)] in response to sinusoidal vibratory stimuli. Frequency (3-250 Hz) and amplitude (0.001-2 mm) combinations were applied to afferent receptive fields through a 6-mm diameter probe. The impulses per cycle, defined as the number of action potentials evoked per vibration sine wave, were measured over 1 s of vibration at each frequency-amplitude combination tested. Afferent entrainment threshold (lowest amplitude at which an afferent could entrain 1:1 to the vibration frequency) and afferent firing threshold (minimum amplitude for which impulses per cycle was greater than zero) were then obtained for each frequency. Increases in vibration frequency are generally associated with decreases in expected impulses per cycle ( < 0.001), but each foot sole afferent class appears uniquely tuned to vibration stimuli. FAII afferents tended to have the lowest entrainment and firing thresholds ( < 0.001 for both); however, these afferents seem to be sensitive across frequency. In contrast to FAII afferents, SAI and SAII afferents tended to demonstrate optimal entrainment to frequencies below 20 Hz and FAI afferents faithfully encoded frequencies between 8 and 60 Hz. Contrary to the selective activation of distinct afferent classes in the hand, application of class-specific frequencies in the foot sole is confounded due to the high sensitivity of FAII afferents. These findings may aid in the development of sensorimotor control models or the design of balance enhancement interventions. Our work provides a mechanistic look at the capacity of foot sole cutaneous afferents to respond to vibration of varying frequency and amplitude. We found that foot sole afferent classes are uniquely tuned to vibration stimuli; however, unlike in the hand, they cannot be independently activated by class-specific frequencies. Viewing the foot sole as a sensory structure, the present findings may aid in the refinement of sensorimotor control models and design of balance enhancement interventions

Cutaneous afferent innervation of the human foot sole: What can we learn from single unit recordings?

Cutaneous afferents convey exteroceptive information about the interaction of the body with the environment and proprioceptive information about body position and orientation. Four classes of low-threshold mechanoreceptor afferents innervate the foot sole and transmit feedback that facilitates the conscious and reflexive control of standing balance. Experimental manipulation of cutaneous feedback has been shown to alter the control of gait and standing balance. This has led to a growing interest in the design of intervention strategies that enhance cutaneous feedback and improve postural control. The advent of single-unit microneurography has allowed the firing and receptive field characteristics of foot sole cutaneous afferents to be investigated. In this review, we consolidate the available cutaneous afferent microneurographic recordings from the foot sole and provide an analysis of the firing threshold, and receptive field distribution and density of these cutaneous afferents. This work enhances the understanding of the foot sole as a sensory structure and provides a foundation for the continued development of sensory augmentation insoles and other tactile enhancement interventions

Why is Essential Tremor so Difficult to Treat? A Literature Review

Essential tremor (ET) is the most common movement disorder and affects tens of millions of individuals worldwide. It is characterized by isolated upper-limb tremors for at least three years without other neurological signs or tremors in other locations. Despite ET being a widespread movement disorder, its etiology and pathophysiology are poorly understood. This lack of understanding poses significant challenges towards the development of treatments and cures. There is no cure for ET, and current treatments for ET are limited and are often insufficient. ET symptoms can differ greatly between patients, and phenotyping is the only method for diagnosis. ET often overlaps with other disorders including dystonia and Parkinson’s disease, which further complicates diagnosis and treatment. Current treatments begin with pharmacotherapy, and progress to surgical options in drug-resistant patients. There is ongoing research into non-invasive electrical stimulation treatments that may prove to be safe and effective; however, further research is needed. The aim of this review is to assess the literature and summarize why ET is so difficult to treat. We evaluate the efficacy of current treatments, and the potential of future treatments. We summarize four reasons why ET remains so difficult to treat: 1) the unknown etiology and pathophysiology, 2) the lack of a suitable animal model, 3) difficulties with diagnosis, and 4) absence of personalized treatments. Despite the current challenges, ET remains an active area of research and novel experimental treatments may produce safe and effective non-invasive therapeutic options for ET

Why is Essential Tremor so Difficult to Treat? A Literature Review

Essential tremor (ET) is the most common movement disorder and affects tens of millions of individuals worldwide. It is characterized by isolated upper-limb tremors for at least three years without other neurological signs or tremors in other locations. Despite ET being a widespread movement disorder, its etiology and pathophysiology are poorly understood. This lack of understanding poses significant challenges towards the development of treatments and cures. There is no cure for ET, and current treatments for ET are limited and are often insufficient. ET symptoms can differ greatly between patients, and phenotyping is the only method for diagnosis. ET often overlaps with other disorders including dystonia and Parkinson’s disease, which further complicates diagnosis and treatment. Current treatments begin with pharmacotherapy, and progress to surgical options in drug-resistant patients. There is ongoing research into non-invasive electrical stimulation treatments that may prove to be safe and effective; however, further research is needed. The aim of this review is to assess the literature and summarize why ET is so difficult to treat. We evaluate the efficacy of current treatments, and the potential of future treatments. We summarize four reasons why ET remains so difficult to treat: 1) the unknown etiology and pathophysiology, 2) the lack of a suitable animal model, 3) difficulties with diagnosis, and 4) absence of personalized treatments. Despite the current challenges, ET remains an active area of research and novel experimental treatments may produce safe and effective non-invasive therapeutic options for ET

Both 50 and 30 Hz continuous theta burst transcranial magnetic stimulation depresses the cerebellum

The cerebellum is implicated in the pathophysiology of numerous movement disorders, which makes it an attractive target for noninvasive neurostimulation. Continuous theta burst stimulation (cTBS) can induce long lasting plastic changes in human brain; however, the efficacy of different simulation protocols has not been investigated at the cerebellum. Here, we compare a traditional 50-Hz and a modified 30-Hz cTBS protocols at modulating cerebellar activity in healthy subjects. Seventeen healthy adults participated in two testing sessions where they received either 50-Hz (cTBS50) or 30-Hz (cTBS30) cerebellar cTBS. Cerebellar brain inhibition (CBI), a measure of cerebello-thalamocortical pathway strength, and motor evoked potentials (MEP) were measured in the dominant first dorsal interosseous muscle before and after (up to ~ 40 min) cerebellar cTBS. Both cTBS protocols induced cerebellar depression, indicated by significant reductions in CBI (P < 0.001). No differences were found between protocols (cTBS50 and cTBS30) at any time point (P = 0.983). MEP amplitudes were not significantly different following either cTBS protocol (P = 0.130). The findings show cerebellar excitability to be equally depressed by 50-Hz and 30-Hz cTBS in heathy adults and support future work to explore the efficacy of different cerebellar cTBS protocols in movement disorder patients where cerebellar depression could provide therapeutic benefits

Cutaneous mechanoreceptor feedback from the hand and foot can modulate muscle sympathetic nerve activity

Stimulation of high threshold mechanical nociceptors on the skin can modulate efferent sympathetic outflow. Whether low threshold mechanoreceptors from glabrous skin are similarly capable of modulating autonomic outflow is unclear. Therefore, the purpose of this study was to examine the effects of cutaneous afferent feedback from the hand palm and foot sole on efferent muscle sympathetic nerve activity (MSNA). Fifteen healthy young participants (9 male; 25 ± 3 years [range: 22-29]) underwent microneurographic recording of multi-unit MSNA from the right fibular nerve during 2 minutes of baseline and 2 minutes of mechanical vibration (150Hz, 220μm peak-to-peak) applied to the left hand or foot. Each participant completed three trials of both hand and foot stimulation, each separated by 10 minutes. MSNA burst frequency decreased similarly during the two minutes of both hand (20.8 ± 8.9 vs. 19.3 ± 8.6 bursts/minute [ -8%], p=0.035) and foot (21.0 ± 8.3 vs. 19.5 ± 8.3 bursts/minute [ -8%], p=0.048) vibration but did not alter normalized mean burst amplitude or area (All p>0.05). Larger reductions in burst frequency were observed during the first 10 seconds (onset) of both hand (20.8 ± 8.9 vs. 17.0 ± 10.4 [ -25%], p<0.001) and foot (21.0 ± 8.3 vs. 18.3 ± 9.4 [ -16%], p=0.035) vibration, in parallel with decreases in normalized mean burst amplitude (hand: 0.45 ± 0.06 vs. 0.36 ± 0.14% [ -19%], p=0.03; foot: 0.47 ± 0.07 vs. 0.34 ± 0.19% [ -27%], p=0.02) and normalized mean burst area (hand: 0.42 ± 0.05 vs. 0.32 ± 0.12% [ -25%], p=0.003; foot: 0.47 ± 0.05 vs. 0.34 ± 0.16% [ -28%], p=0.01). These results demonstrate that tactile feedback from the hands and feet can influence efferent sympathetic outflow to skeletal muscle

Modeling foot sole cutaneous afferents: FootSim

Summary: While walking and maintaining balance, humans rely on cutaneous feedback from the foot sole. Electrophysiological recordings reveal how this tactile feedback is represented in neural afferent populations, but obtaining them is difficult and limited to stationary conditions. We developed the FootSim model, a realistic replication of mechanoreceptor activation in the lower limb. The model simulates neural spiking responses to arbitrary mechanical stimuli from the combined population of all four types of mechanoreceptors innervating the foot sole. It considers specific mechanics of the foot sole skin tissue, and model internal parameters are fitted using human microneurography recording dataset. FootSim can be exploited for neuroscientific insights, to understand the overall afferent activation in dynamic conditions, and for overcoming the limitation of currently available recording techniques. Furthermore, neuroengineers can use the model as a robust in silico tool for neuroprosthetic applications and for designing biomimetic stimulation patterns starting from the simulated afferent neural responses