Principles of sensorimotor learning.

The exploits of Martina Navratilova and Roger Federer represent the pinnacle of motor learning. However, when considering the range and complexity of the processes that are involved in motor learning, even the mere mortals among us exhibit abilities that are impressive. We exercise these abilities when taking up new activities - whether it is snowboarding or ballroom dancing - but also engage in substantial motor learning on a daily basis as we adapt to changes in our environment, manipulate new objects and refine existing skills. Here we review recent research in human motor learning with an emphasis on the computational mechanisms that are involved

Whole-scalp EEG mapping of somatosensory evoked potentials in macaque monkeys

High-density scalp EEG recordings are widely used to study whole-brain neuronal networks in humans non-invasively. Here, we validate EEG mapping of somatosensory evoked potentials (SSEPs) in macaque monkeys (Macaca fascicularis) for the long-term investigation of large-scale neuronal networks and their reorganisation after lesions requiring a craniotomy. SSEPs were acquired from 33 scalp electrodes in five adult anaesthetized animals after electrical median or tibial nerve stimulation. SSEP scalp potential maps were identified by cluster analysis and identified in individual recordings. A distributed, linear inverse solution was used to estimate the intracortical sources of the scalp potentials. SSEPs were characterised by a sequence of components with unique scalp topographies. Source analysis confirmed that median nerve SSEP component maps were in accordance with the somatotopic organisation of the sensorimotor cortex. Most importantly, SSEP recordings were stable both intra- and interindividually. We aim to apply this method to the study of recovery and reorganisation of large-scale neuronal networks following a focal cortical lesion requiring a craniotomy. As a prerequisite, the present study demonstrated that a 300-mm2 unilateral craniotomy over the sensorimotor cortex necessary to induce a cortical lesion, followed by bone flap repositioning, suture and gap plugging with calcium phosphate cement, did not induce major distortions of the SSEPs. In conclusion, SSEPs can be successfully and reproducibly recorded from high-density EEG caps in macaque monkeys before and after a craniotomy, opening new possibilities for the long-term follow-up of the cortical reorganisation of large-scale networks in macaque monkeys after a cortical lesion

Velocity and Density Determination by the Electron Beam Technique

In aerothermodynamic gas flows the accurate knowledge of the velocity and the density is important as the Mach number is in the hypersonic range and relatively insensitive against real gas effects.This is true especially in the case of rarefied flows if the deviation of the continuum flow condition takes place, viscous effects have to be taken into account, and mixtures of gases have to be considered. In order to get access to these quantities the electron beam technique has been developed for space related research in the hypersonic wind tunnel of the institute. This paper summarizes the main features of the technique concerning density and veloctiy determination, typical experimental set-ups, results of some investigations, and advantages and drawbacks of the technique. Finally, as a new possibility for flow diagnostics an electron photon fluorescence technique using metastable atoms or molecules is discussed

Measurement of Vortical Structures on a Helicopter Rotor Model in a Wind Tunnel by LDV and PIV

With increasing use of civil helicopters the problem of noise emission of helicopters become more and more important within the last decade. Therefore, helicopter noise has been subject of many research projects (1). Blade Vortex Interactions (BVI) are known as a major source of impulsive noise. As BVI-noise is governed by the induced velocities of tip vorticies, it depends on vortex strength and miss-distance, which itself depends on vortex location and orientatioand convection speed relative to the path of the advancing blade. Therefore, the study of these phenomena is of particular interest for progress towards quieter helicopters. Such vortical structures at a helicopter rotor model in a wind tunnel has been studied by optical measurement techniques, since only non-intrusive techniques are capable to obtain velocity data within the rotor plane. Measurements of local flow vectors at positions close to the rotor blade tips were performed by three component Laser Doppler Velocimetry (3D-LDV) and conventional (two component) Particle Image Velocimetry (PIV)

Comparison of Vortical Structures of a Helicopter Rotor Model Measured by LDV and PIV

Flow field measurements of the blade tip vortices at a rotating helicopter rotor model were performed by three component laser-Doppler velocimetry (3D-LDV) and conventional (two component) particle image velocimetry (PIV). The results are in good correspondence in general, but alo illustrate the different properties of both techniques, such as the three-dimensional measurement capability of LDV and the unsteadyness of the flow captured by the PIV method