Resonance regimes of scattering by small bodies with impedance boundary conditions

The paper concerns scattering of plane waves by a bounded obstacle with complex valued impedance boundary conditions. We study the spectrum of the Neumann-to-Dirichlet operator for small wave numbers and long wave asymptotic behavior of the solutions of the scattering problem. The study includes the case when $k=0$ is an eigenvalue or a resonance. The transformation from the impedance to the Dirichlet boundary condition as impedance grows is described. A relation between poles and zeroes of the scattering matrix in the non-self adjoint case is established. The results are applied to a problem of scattering by an obstacle with a springy coating. The paper describes the dependence of the impedance on the properties of the material, that is on forces due to the deviation of the boundary of the obstacle from the equilibrium position

Temporal Stability and the Effects of Training on Saccade Latency in “Express Saccade Makers”

The temporal stability of saccade latency, and the effects of training, particularly in “express saccade makers” (ESMs), has received little attention. ESMs are healthy, naïve, adults, who persist in executing very many low latency “express saccades” (ES; saccades with latency of 80 ms to 130 ms), in conditions designed to suppress such responses. We investigated the stability of ES production (%ES) in 59 ESM and 54 non-ESM participants in overlap tasks. Within a single session, the intraclass correlation coefficient (ICC) for %ES in two runs of 200 trials was 0.97 (p30% of saccades over the two runs were ES, were classified as ESMs. For 60 participants tested over two sessions 12 weeks apart, and 30 participants tested in three sessions over approximately six months, the ICC for %ES was uniformly high (0.95, p<0.001 and 0.97, p<0.001 respectively) and participants behaved consistently with their initial classification. Fourteen participants (7 ESMs) were then exposed to training consisting of either gap or overlap tasks. Training increased %ES in both groups. However, when tested in overlap tasks, it was not sufficient to transform Normal participants into ESMs. We conclude that the pattern of saccade behaviour exhibited by ESMs constitutes a stable and distinct oculomotor phenotype

Motor Decline in Clinically Presymptomatic Spinocerebellar Ataxia Type 2 Gene Carriers

BACKGROUND: Motor deficits are a critical component of the clinical characteristics of patients with spinocerebellar ataxia type 2. However, there is no current information on the preclinical manifestation of those motor deficits in presymptomatic gene carriers. To further understand and characterize the onset of the clinical manifestation in this disease, we tested presymptomatic spinocerebellar ataxia type 2 gene carriers, and volunteers, in a task that evaluates their motor performance and their motor learning capabilities. METHODS AND FINDINGS: 28 presymptomatic spinocerebellar ataxia type 2 gene carriers and an equal number of control volunteers matched for age and gender participated in the study. Both groups were tested in a prism adaptation task known to be sensible to both motor performance and visuomotor learning deficits. Our results clearly show that although motor learning capabilities are intact, motor performance deficits are present even years before the clinical manifestation of the disease start. CONCLUSIONS: The results show a clear deficit in motor performance that can be detected years before the clinical onset of the disease. This motor performance deficit appears before any motor learning or clinical manifestations of the disease. These observations identify the performance coefficient as an objective and quantitative physiological biomarker that could be useful to assess the efficiency of different therapeutic agents

Effects of acupuncture on foveation characteristics in congenital nystagmus

AIMS/BACKGROUND—To examine the effects of acupuncture at the sternocleidomastoid muscles on foveation characteristics in congenital nystagmus.
METHODS—Six patients with congenital nystagmus (CN) received a series of treatments consisting of two needles inserted into each sternocleidomastoid, stimulated by tapping gently every 5 minutes, for 20 minutes per session. Their eye movements were recorded using scleral search coils and changes in their CN waveforms analysed at each point in the treatment. Changes in the stability and duration of foveation periods were examined.
RESULTS—Four of the six patients showed improved foveation at the commencement of treatment; three maintained this response throughout the treatment period and after the needles were removed. In two, the CN waveform itself was modified.
CONCLUSION—This study and others involving afferent stimulation to the neck and face suggest that projections from these areas to the reticular formation and vestibular nucleus may alter the behaviour of the pathophysiological mechanism underlying congenital nystagmus.

 Keywords: congenital nystagmus; foveation; acupunctur

Activity of Neurons in Monkey Globus Pallidus During Oculomotor Behavior Compared With That in Substantia Nigra Pars Reticulata

The basal ganglia are a subcortical assembly of nuclei involved in many aspects of behavior. Three of the nuclei have high firing rates and inhibitory influences: the substantia nigra pars reticulata (SNr), globus pallidus interna (GPi), and globus pallidus externa (GPe). The SNr contains a wide range of visual, cognitive, and motor signals that have been shown to contribute to saccadic eye movements. Our hypothesis was that GPe and GPi neurons carry similarly diverse signals during saccadic behavior. We recorded from GPe, GPi, and SNr neurons in monkeys that made memory-guided saccades and found that neurons in all three structures had increases or decreases in activity synchronized with saccade generation, visual stimulation, or reward. Comparing GPe neurons with GPi neurons, we found relatively more visual-related activity in GPe and more reward-related activity in GPi. Comparing both pallidal samples with the SNr, we found a greater resemblance between GPe and SNr neurons than that between GPi and SNr neurons. As expected from a known inhibitory projection from GPe to SNr, there was a general reversal of sign in activity modulations between the structures: bursts of activity were relatively more common in GPe and pauses more common in SNr. We analyzed the response fields of neurons in all three structures and found relatively narrow and lateralized fields early in trials (during visual and saccadic events) followed by a broadening later in trials (during reward). Our data reinforce an emerging, new consensus that the GPe and GPi, in addition to the SNr, contribute to oculomotor behavior