Imprecise perception of hand position during early motor adaptation.

Localizing one's body parts is important for movement control and motor learning. Recent studies have shown that the precision with which people localize their hand places constraints on motor adaptation. Although these studies have assumed that hand localization remains equally precise across learning, we show that precision decreases rapidly during early motor learning. In three experiments, healthy young participants (n = 92) repeatedly adapted to a 45° visuomotor rotation for a cycle of two to four reaches, followed by a cycle of two to four reaches with veridical feedback. Participants either used an aiming strategy that fully compensated for the rotation (experiment 1), or always aimed directly at the target, so that adaptation was implicit (experiment 2). We omitted visual feedback for the last reach of each cycle, after which participants localized their unseen hand. We observed an increase in the variability of angular localization errors when subjects used a strategy to counter the visuomotor rotation (experiment 1). This decrease in precision was less pronounced in the absence of reaiming (experiment 2), and when subjects knew that they would have to localize their hand on the upcoming trial, and could thus focus on hand position (experiment 3). We propose that strategic reaiming decreases the precision of perceived hand position, possibly due to attention to vision rather than proprioception. We discuss how these dynamics in precision during early motor learning could impact on motor control and shape the interplay between implicit and strategy-based motor adaptation.NEW & NOTEWORTHY Recent studies indicate that the precision with which people localize their hand limits implicit visuomotor learning. We found that localization precision is not static, but decreases early during learning. This decrease is pronounced when people apply a reaiming strategy to compensate for a visuomotor perturbation and is partly resistant to allocation of attention to the hand. We propose that these dynamics in position sense during learning may influence how implicit and strategy-based motor adaption interact.

Strategy-based motor learning decreases the post-movement ß power.

Motor learning depends on the joint contribution of several processes including cognitive strategies aiming at goal achievement and prediction error-driven implicit adaptation. Understanding this functional interplay and its clinical implications requires insight into the individual learning processes, including at a neural level. Here, we set out to examine the impact of learning a cognitive strategy, over and above implicit adaptation, on the oscillatory post-movement ß rebound (PMBR), which typically decreases in power following (visuo)motor perturbations. Healthy participants performed reaching movements towards a target, with online visual feedback replacing the view of their moving hand. The feedback was sometimes rotated, either relative to their movements (visuomotor rotation) or invariant to their movements (and relative to the target; clamped feedback), always for two consecutive trials interspersed between non-rotated trials. In both conditions, the first trial with a rotation was unpredictable. On the second trial, the task was either to re-aim, and thereby compensate for the rotation experienced in the first trial (visuomotor rotation; Compensate condition), or to ignore the rotation and keep on aiming at the target (clamped feedback; Ignore condition). After-effects did not differ between conditions, indicating that the amount of implicit learning was similar, while large differences in movement direction in the second rotated trial between conditions indicated that participants successfully acquired re-aiming strategies. Importantly, PMBR power following the first rotated trial was modulated differently in the two conditions. Specifically, it decreased in both conditions, but this effect was larger when participants had to acquire a cognitive strategy and prepare to re-aim. Our results therefore suggest that the PMBR is modulated by cognitive demands of motor learning, possibly reflecting the evaluation of a behaviourally significant goal achievement error.

[Pancytopenia, arthralgia and myeloneuropathy due to copper deficiency]. / Kupfermangel als seltene Ursache von Panzytopenie, Arthralgien und Gangstörungen.

BACKGROUND: Copper deficiency leads to hematologic disorders like pancytopenia. In addition, myeloneuropathy was described in a few cases reports. CASE REPORT: A 71-year-old woman was hospitalized because of increasing pancytopenia and ataxic gait, that resulted in a near-complete inability to walk without assistance. Additional symptoms included arthralgia, reduced appetite and weight loss. Laboratory studies revealed a proteinuria of 3,700 mg/day. Magnetic resonance imaging of the cervical and thoracic spine revealed a wedge-shaped signal intensity in the dorsal part as a sign of damage in this area. A copper deficiency was then identified as the likely underlying cause for the low blood cell counts and neurologic deficits. In this patient, the copper deficiency may have resulted from a disturbance in absorption due to a partial gastrectomy (modified Billroth I) 10 years ago and due to urinary copper loss in view of mesangioproliferative glomerulonephritis. A therapy with copper gluconate 3 x 3 mg/day was initiated. Within 2 weeks, blood cell counts normalized and appetite became normal again; just so, arthralgia disappeared. The neurologic symptoms persisted, even though the copper substitution continued for 6 months. CONCLUSION: Copper deficiency may be a differential diagnosis for hematologic abnormalities like pancytopenia, even if a disorder of intestinal resorption or a proteinuria occurs. Myeloneuropathy is a rare complication of this deficiency. Hemograms may become normal after treatment with oral copper gluconate, but at least in the case presented here, neurologic symptomes did not show any improvement.

Inscription of optical waveguides in crystalline silicon by mid-infrared femtosecond laser pulses.

For the first time to the authors' knowledge, optical waveguides have been inscribed in bulk crystalline silicon by ultrafast laser radiation. Femtosecond laser pulses of 40-nm spectral bandwidth, 1-kHz repetition rate, and 1.7-microJ on-target energy were applied at a mid-infrared wavelength of 2.4 microm to induce nonlinear absorption in the focal volume of the beam. By scanning the laser beam with respect to the sample, buried optical waveguides have been created that were single mode at 1550 and 1320 nm and guided light only with its polarization perpendicular to the sample's surface. Propagation losses with an upper limit of 1.2 dB/cm or less were observed throughout the optical telecommunications band.

Discrete diffraction in two-dimensional arrays of coupled waveguides in silica.

The propagation of light in 5 x 5 and 7 x 7 cubic lattices of evanescently coupled waveguides is investigated for the first time, to the authors' knowledge. The results reveal ideal discrete diffraction and demonstrate the excellent quality of the waveguide arrays, which were manufactured in fused silica by femtosecond-laser-induced refractive-index modifications.

Optical properties of waveguides fabricated in fused silica by femtosecond laser pulses.

With tightly focused femtosecond laser pulses, waveguides are fabricated in fused silica. The guiding and attenuation properties of these waveguides at wavelengths of 514 nm and 1.5 microm are studied. We demonstrate that by changing only the writing speed, waveguides with a controllable mode number can be produced.