Mechanisms underlying firing in healthy and sick human motoneurons

International audienceIn an address to the British Association for the Advancement of Science in Cambridge, Professor Sherrington introduced the terms " motor neurone " and " the final common path, " the latter term implying that all motor commands converge onto the motoneuron which integrates the incoming information and passes the net information to the muscle for contraction (Sherrington, 1904). The relative ease of access of the spinal motoneuron made it feasible to set up techniques for investigating the physiological, biophysical and molecular properties of these neurons. It became the most investigated neuron of the CNS in the twentieth century and the information gained from studies on motoneurons formed the basis for examining the other neurons of the CNS. Since the compound action potential of a muscle unit is strictly related one-to-one to the action potential arriving from the innervating motoneuron, the statistical analysis of muscle unit action potentials provides an investigator with an elegant way to probe the properties of motoneurons in behaving humans. In the following review the terms motoneuron and motor unit might be used interchangeably. Different aspects of human motoneuron investigations in health and disease are presented in 16 articles of this topic which are summarized below. An increase in the net excitatory synaptic input to the motoneuron pool results in an increase in the level of muscle contraction by recruitment of additional motor units (MUs) and an increase in firing rates of the already recruited units (Milner-Brown et al., 1973; Henneman et al., 1974). The principle of orderly recruitment of motoneurons by size was originally proposed by Henneman (1957) but was later questioned by other researchers presenting examples of selective, rather than orderly recruitment (e.g., Smith et al., 1980). These controversies are assessed by Bawa et al. (2014), and the opinion unifying the concept of orderly recruitment is presented. In humans, increases in firing rates of motor units have been shown to follow the " onion skin " pattern at lower levels of contraction, meaning that the lower-threshold motor units discharge with higher rates than higher-threshold ones. However, studies performed on the whole range of muscle forces indicated that for higher force levels the motor unit firing rate follows a " reverse onion skin " pattern. Hu et al. (2014) decided to approach this problem using small surface electrodes and step increases in force instead of the " ramp and hold " protocols used by previous authors. They showed that the " onion skin " pattern was preserved until 15% of maximal voluntary contraction, and from their results predict this pattern to be valid for the whole range of muscle forces, which is not supported by the previous published works. However, the reported rate saturation of the MUs discharging with higher rates implies that at the higher forces the " reverse onion skin " pattern may be expected. In another paper, Duchateau and Baudry (2014) show that during ballistic contractions the maximal discharge rates are higher than those observed in ramp contractions. It should be noted, however, that during ballistic contractions one deals with instantaneous rates, while during ramp and hold contractions one refers to tonic firing rates defined as the averag

Motor units as tools to evaluate profile of human Renshaw inhibition

Although Renshaw inhibition (RI) has been extensively studied for decades, its precise role in motor control is yet to be discovered. One of the main handicaps is a lack of reliable methods for studying RI in conscious human subjects. We stimulated the lowest electrical threshold motor axons (thickest axons) in the tibial nerve and analysed the stimulus‐correlated changes in discharge of voluntarily recruited low‐threshold single motor units (SMUs) from the soleus muscle. In total, 54 distinct SMUs from 12 subjects were analysed. Stimuli that generated only the direct motor response (M‐only) on surface electromyography induced an inhibitory response in the low‐threshold SMUs. Because the properties of RI had to be estimated indirectly using the background discharge rate of SMUs, its profile varied with the discharge rate of the SMU. The duration of RI was found to be inversely proportional to the discharge rate of SMUs. Using this important finding, we have developed a method of extrapolation for estimating RI as it develops on motoneurons in the spinal cord. The frequency methods indicated that the duration of RI was between 30 and 40 ms depending on the background firing rate of the units, and the extrapolation indicated that RI on silent motoneurons was ∼55 ms. The present study establishes a novel methodology for studying RI in human subjects and hence may serve as a tool for improving our understanding of the involvement of RI in human motor control

Analysis of motoneuron responses to composite synaptic volleys (computer simulation study)

This paper deals with the analysis of changes in motoneuron (MN) firing evoked by repetitively applied stimuli aimed toward extracting information about the underlying synaptic volleys. Spike trains were obtained from computer simulations based on a threshold-crossing model of tonically firing MN, subjected to stimulation producing postsynaptic potentials (PSPs) of various parameters. These trains were analyzed as experimental results, using the output measures that were previously shown to be most effective for this purpose: peristimulus time histogram, raster plot and peristimulus time intervalgram. The analysis started from the effects of single excitatory and inhibitory PSPs (EPSPs and IPSPs). The conclusions drawn from this analysis allowed the explanation of the results of more complex synaptic volleys, i.e., combinations of EPSPs and IPSPs, and the formulation of directions for decoding the results of human neurophysiological experiments in which the responses of tonically firing MNs to nerve stimulation are analyzed

Borders in historical research using GIS servers

This article presents the possibilities of using geographic information systems (GIS) by scientists analysing the process of shaping administrative borders. This still evolving and perfected technology used for introducing, collecting, processing and visualising spatial data provides the researchers with previously unattainable possibilities of data analysis. It is certainly a milestone in historical research on geographic and cultural environments as it carries many new perspectives which not only pertain to analysing spatial data, but also map-making. The examined or presented space ceases to be a “colour agreed upon” on paper, and becomes a precisely localised area that can be seen in the old and contemporary form in multiple shots. With such possibilities, history, this synonym of passing time, becomes a living picture

Replication data for raw data recorded for the study of AHP duration in stroke patients

Raw data from control subjects and poststroke patient

The Characteristics of the Documentation of the Prussian Land and Building Cadastre in the State Archives in Olsztyn

The Prussian land and building cadastre was introduced on May 21, 1861, under three laws that unified the tax system throughout the Prussian state. According to the regulations, the cadastre was to be based on measurements and calculations. Because broad field surveys were not taken into account, cadastral maps drawn up at that time were most often copies of already existing land maps. In the 1930s, the Prussian state reorganized its surveying services, aimed at introducing a uniform system of land classification in the entire German state, and consequently a single cadastral system. As a result, a unified state cadre - the Reichkataster – was to be formed throughout Germany. Unfortunately, the work did not produce the desired effect and the Reichkataster was introduced only in 1941. Further work on the national cadastre was interrupted by the Second World War. The State Archive in Olsztyn holds the cadastral documentation from the area of the former Olsztyn district, the part of the Królewiec district (primarily the area which after the Second World War was within the borders of the Polish state) and the remains of the cadastral office in Węgorzewo. The full documentation from the area of the Królewiec district is presented, consisting of cadastral office files and 9 cadastral offices in Bartoszyce, Braniewo, Gierdawy, Kętrzyn, Lidzbark Warmiński, Morąg, Pasłęk, Pruska Iława and Święta Siekierka. There are 11222 cadastral maps in the file. This documentation is an important part of the pre-war resource of Olsztyn