Dissipation characteristics of quantized spin waves in nano-scaled magnetic ring structures

The spatial profiles and the dissipation characteristics of spin-wave quasi-eigenmodes are investigated in small magnetic Ni$_{81}$Fe$_{19}$ ring structures using Brillouin light scattering microscopy. It is found, that the decay constant of a mode decreases with increasing mode frequency. Indications for a contribution of three-magnon processes to the dissipation of higher-order spin-wave quasi-eigenmodes are found

The sharp-interface limit for the Navier--Stokes--Korteweg equations

We investigate the sharp-interface limit for the Navier--Stokes--Korteweg model, which is an extension of the compressible Navier--Stokes equations. By means of compactness arguments, we show that solutions of the Navier--Stokes--Korteweg equations converge to solutions of a physically meaningful free-boundary problem. Assuming that an associated energy functional converges in a suitable sense, we obtain the sharp-interface limit at the level of weak solutions

Serving performance in a suprapostural visual signal detection task: context-dependent and direction-specific control of body sway with fingertip light touch

Keeping gaze fixed on a target during visual smooth pursuit or touch light during fingertip contact while standing may resemble the goals of a suprapostural task with the implicit demands to minimize self-imposed sensorimotor variability. To test whether the principle of a suprapostural task generalizes to more complex sensorimotor stimulus-response mappings, we investigated how the control of body sway is influenced by an implicit feedback coupling (IFC) between the variability of touch forces at the contact point and perceptual difficulty, that is vertical jitter of a horizontally oscillating Landolt-C, in a visual signal detection task (VSDT). Mediolateral (ML) body sway of ten young healthy adults was assessed in four IFC conditions: (1) LT with independent jitter (LT-IJ), (2) LT with jitter depending on LT contact force (LT-CF), (3) LT with jitter depending on body sway (LT-BS), and (4) no contact with jitter depending on body sway (NT-BS). We assumed that the postural control system would be responsive to IFC and therefore reduce body sway in both IFC conditions. Resulting mediolateral body sway differed between the IFC conditions. Reduced sway was found in LT-CF and LT-BS compared to LT-IJ and in LT-BS compared to NT-BS. Our results demonstrate that processes controlling body sway can reduce postural variability below a variability level achieved by LT augmentation of body sway-related feedback alone. Both direct (LT-CF) and indirect (LT-BS) IFC involvement of fingertip contact minimized sway, which implies that no hierarchy existed for whole body sway or precision of fingertip contact (integration of both control processes) or that they can be reversed flexibly (one facilitating the other) if it serves the implicit goal of reduced perceptual noise and enhanced performance within the context of our suprapostural VSDT

Short-term effects of unilateral lesion of the primary motor cortex (M1) on ipsilesional hand dexterity in adult macaque monkeys

Although the arrangement of the corticospinal projection in primates is consistent with a more prominent role of the ipsilateral motor cortex on proximal muscles, rather than on distal muscles involved in manual dexterity, the role played by the primary motor cortex on the control of manual dexterity for the ipsilateral hand remains a matter a debate, either in the normal function or after a lesion. We, therefore, tested the impact of permanent unilateral motor cortex lesion on the manual dexterity of the ipsilateral hand in 11 macaque monkeys, within a time window of 60 days post-lesion. For comparison, unilateral reversible pharmacological inactivation of the motor cortex was produced in an additional monkey. Manual dexterity was assessed quantitatively based on three motor parameters derived from two reach and grasp manual tasks. In contrast to the expected dramatic, complete deficit of manual dexterity of the contralesional hand that persists for several weeks, the impact on the manual dexterity of the ipsilesional hand was generally moderate (but statistically significant) and, when present, lasted less than 20 days. Out of the 11 monkeys, only 3 showed a deficit of the ipsilesional hand for 2 of the 3 motor parameters, and 4 animals had a deficit for only one motor parameter. Four monkeys did not show any deficit. The reversible inactivation experiment yielded results consistent with the permanent lesion data. In conclusion, the primary motor cortex exerts a modest role on ipsilateral manual dexterity, most likely in the form of indirect hand postural control

Prognostic value of cortically induced motor evoked activity by TMS in chronic stroke: caveats from a very revealing single clinical case

Background: We report the case of a chronic stroke patient (62 months after injury) showing total absence of motor activity evoked by transcranial magnetic stimulation (TMS) of spared regions of the left motor cortex, but near-to-complete recovery of motor abilities in the affected hand. Case presentation: Multimodal investigations included detailed TMS based motor mapping, motor evoked potentials (MEP), and Cortical Silent period (CSP) as well as functional magnetic resonance imaging (fMRI) of motor activity, MRI based lesion analysis and Diffusion Tensor Imaging (DTI) Tractography of corticospinal tract (CST). Anatomical analysis revealed a left hemisphere subinsular lesion interrupting the descending left CST at the level of the internal capsule. The absence of MEPs after intense TMS pulses to the ipsilesional M1, and the reversible suppression of ongoing electromyographic (EMG) activity (indexed by CSP) demonstrate a weak modulation of subcortical systems by the ipsilesional left frontal cortex, but an inability to induce efficient descending volleys from those cortical locations to right hand and forearm muscles. Functional MRI recordings under grasping and finger tapping patterns involving the affected hand showed slight signs of subcortical recruitment, as compared to the unaffected hand and hemisphere, as well as the expected cortical activations. Conclusions: The potential sources of motor voluntary activity for the affected hand in absence of MEPs are discussed. We conclude that multimodal analysis may contribute to a more accurate prognosis of stroke patients

Functional Connectivity in Tactile Object Discrimination—A Principal Component Analysis of an Event Related fMRI-Study

BACKGROUND: Tactile object discrimination is an essential human skill that relies on functional connectivity between the neural substrates of motor, somatosensory and supramodal areas. From a theoretical point of view, such distributed networks elude categorical analysis because subtraction methods are univariate. Thus, the aim of this study was to identify the neural networks involved in somatosensory object discrimination using a voxel-based principal component analysis (PCA) of event-related functional magnetic resonance images. METHODOLOGY/PRINCIPAL FINDINGS: Seven healthy, right-handed subjects aged between 22 and 44 years were required to discriminate with their dominant hand the length differences between otherwise identical parallelepipeds in a two-alternative forced-choice paradigm. Of the 34 principal components retained for analysis according to the 'bootstrapped' Kaiser-Guttman criterion, t-tests applied to the subject-condition expression coefficients showed significant mean differences between the object presentation and inter-stimulus phases in PC 1, 3, 26 and 32. Specifically, PC 1 reflected object exploration or manipulation, PC 3 somatosensory and short-term memory processes. PC 26 evinced the perception that certain parallelepipeds could not be distinguished, while PC 32 emerged in those choices when they could be. Among the cerebral regions evident in the PCs are the left posterior parietal lobe and premotor cortex in PC 1, the left superior parietal lobule (SPL) and the right cuneus in PC 3, the medial frontal and orbitofrontal cortex bilaterally in PC 26, and the right intraparietal sulcus, anterior SPL and dorsolateral prefrontal cortex in PC 32. CONCLUSIONS/SIGNIFICANCE: The analysis provides evidence for the concerted action of large-scale cortico-subcortical networks mediating tactile object discrimination. Parallel to activity in nodes processing object-related impulses we found activity in key cerebral regions responsible for subjective assessment and validation

The cognitive neuroscience of prehension: recent developments

Prehension, the capacity to reach and grasp, is the key behavior that allows humans to change their environment. It continues to serve as a remarkable experimental test case for probing the cognitive architecture of goal-oriented action. This review focuses on recent experimental evidence that enhances or modifies how we might conceptualize the neural substrates of prehension. Emphasis is placed on studies that consider how precision grasps are selected and transformed into motor commands. Then, the mechanisms that extract action relevant information from vision and touch are considered. These include consideration of how parallel perceptual networks within parietal cortex, along with the ventral stream, are connected and share information to achieve common motor goals. On-line control of grasping action is discussed within a state estimation framework. The review ends with a consideration about how prehension fits within larger action repertoires that solve more complex goals and the possible cortical architectures needed to organize these actions

Networks involved in motor cognition : Physiology and pathophysiology of apraxia.

Unter dem Begriff Apraxie werden unterschiedliche Störungen höherer motorischer Fähigkeiten zusammengefasst, die nicht durch elementare sensomotorische Defizite (z. B. Paresen oder Ataxie) erklärt werden. Charakteristische, im klinischen Alltag gut zu erfassende Merkmale sind Schwierigkeiten bei pantomimisch dargestelltem oder tatsächlichem Werkzeuggebrauch sowie bei der Imitation bedeutungsloser Gesten. Apraxien sind bilaterale, deshalb kognitiv-motorische Störungen, die meist (jedoch nicht ausschließlich) nach linkshemisphärischen Läsionen auftreten; zudem gibt es Apraxien bei neurodegenerativen Erkrankungen (z. B. kortikobasales Syndrom, M. Alzheimer). Apraktische Defizite können zu gravierenden Einschränkungen bei den Aktivitäten des täglichen Lebens führen, weshalb die Diagnose von großer Bedeutung ist. Auf funktionell-anatomischer Ebene werden unterschiedliche kognitiv-motorische Fähigkeiten durch zumindest teilweise verschiedene Netzwerke ermöglicht. Hier werden ein ventraler Verarbeitungspfad für semantische Handlungskomponenten wie Zuordnungen zwischen Handlungen und Objekten, ein ventrodorsaler Pfad für sensomotorische Programme erlernter Bewegungen sowie ein dorsodorsales System für Bewegungskontrolle und wahrscheinlich auch Imitation bedeutungsloser Gesten unterschieden. Hierbei kommt es zu partiellen Überlappungen mit sprachrelevanten Regionen, während sich zwischen apraktischen und räumlichen Aufmerksamkeitsdefiziten deutlichere Dissoziationen finden. Bei der Therapie apraktischer Störungen rücken neben rein verhaltensbasierten Therapieansätzen zunehmend nichtinvasive neuromodulatorische Verfahren sowie auch computerbasierte Assistenzsysteme in den Fokus