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

Mimicking human neuronal pathways in silico: an emergent model on the effective connectivity

International audienceWe present a novel computational model that detects temporal configurations of a given human neuronal pathway and constructs its artificial replication. This poses a great challenge since direct recordings from individual neurons are impossible in the human central nervous system and therefore the underlying neuronal pathway has to be considered as a black box. For tackling this challenge, we used a branch of complex systems modeling called artificial self-organization in which large sets of software entities interacting locally give rise to bottom-up collective behaviors. The result is an emergent model where each software entity represents an integrate-and-fire neuron. We then applied the model to the reflex responses of single motor units obtained from conscious human subjects. Experimental results show that the model recovers functionality of real human neuronal pathways by comparing it to appropriate surrogate data. What makes the model promising is the fact that, to the best of our knowledge, it is the first realistic model to self-wire an artificial neuronal network by efficiently combining neuroscience with artificial self-organization. Although there is no evidence yet of the model's connectivity mapping onto the human connectivity, we anticipate this model will help neuroscientists to learn much more about human neuronal networks, and could also be used for predicting hypotheses to lead future experiments

Does primary brachial plexus surgery alter palliative tendon transfer surgery outcomes in children with obstetric paralysis?

<p>Abstract</p> <p>Background</p> <p>The surgical management of obstetrical brachial plexus palsy can generally be divided into two groups; early reconstructions in which the plexus or affected nerves are addressed and late or palliative reconstructions in which the residual deformities are addressed. Tendon transfers are the mainstay of palliative surgery. Occasionally, surgeons are required to utilise already denervated and subsequently reinnervated muscles as motors. This study aimed to compare the outcomes of tendon transfers for residual shoulder dysfunction in patients who had undergone early nerve surgery to the outcomes in patients who had not.</p> <p>Methods</p> <p>A total of 91 patients with obstetric paralysis-related shoulder abduction and external rotation deficits who underwent a modified Hoffer transfer of the latissimus dorsi/teres major to the greater tubercle of the humerus tendon between 2002 and 2009 were retrospectively analysed. The patients who had undergone neural surgery during infancy were compared to those who had not in terms of their preoperative and postoperative shoulder abduction and external rotation active ranges of motion.</p> <p>Results</p> <p>In the early surgery groups, only the postoperative external rotation angles showed statistically significant differences (25 degrees and 75 degrees for total and upper type palsies, respectively). Within the palliative surgery-only groups, there were no significant differences between the preoperative and postoperative abduction and external rotation angles. The significant differences between the early surgery groups and the palliative surgery groups with total palsy during the preoperative period diminished postoperatively (p < 0.05 and p > 0.05, respectively) for abduction but not for external rotation. Within the upper type palsy groups, there were no significant differences between the preoperative and postoperative abduction and external rotation angles.</p> <p>Conclusions</p> <p>In this study, it was found that in patients with total paralysis, satisfactory shoulder abduction values can be achieved with tendon transfers regardless of a previous history of neural surgery even if the preoperative values differ.</p

Estimation of postsynaptic potentials in rat hypoglossal motoneurones: insights for human work

Copyright © 2003 The Physiological SocietyClassical techniques for estimating postsynaptic potentials in motoneurones include spike-triggered averages of rectified surface and multiunit electromyographic recordings (SEMG and MU-EMG), as well as the compilation of peristimulus time histograms (PSTH) based on the discharge of single motor units (SMU). These techniques rely on the probability of spike occurrence in relation to the stimulus and can be contaminated by count- and synchronization-related errors, arising from postspike refractoriness and the discharge statistics of motoneurones. On the other hand, since these probability-based techniques are easy to use and require only inexpensive equipment, it is very likely that they will continue to be used in clinical and laboratory settings for the foreseeable future. One aim of the present study was to develop a modification of these probability-based analyses in order to provide a better estimate of the initial phase of postsynaptic potentials. An additional aim was to combine probability-based analyses with frequency-based analyses to provide a more reliable estimate of later phases of postsynaptic potentials. To achieve these aims, we have injected simple as well as complex current transients into regularly discharging hypoglossal motoneurones recorded in vitro from rat brainstem slices. We examined the discharge output of these cells using both probability- and frequency-based analyses to identify which of the two represented the profile of the postsynaptic potential more closely. This protocol was designed to obtain PSTHs of the responses of single motor units to repeated application of the same afferent input. We have also simulated multiunit responses to afferent input by replacing the times of spike occurrence in individual trials with a representation of either an intramuscular or surface-recording single motor unit waveform and summing many of these trials to obtain either a simulated SEMG or MU-EMG. We found that in a regularly discharging motoneurone, the rising phase of an EPSP moves the occurrence of spikes forward and hence induces a substantial peak in all probability-based records. This peak is followed immediately by a period of reduced activity (‘silent period’) due to the phase advancement of spikes that were to occur at this period. Similarly, the falling phase of an IPSP delays spikes so that they occur during the rising phase of the IPSP. During the delay, the probability-based analyses display gaps and during the occurrence of the delayed spikes they generate peaks. We found that all the probability-based analyses (SEMG, MU-EMG and PSTH) can be made useful for illustrating the underlying initial PSP by a special use of the cumulative sum (CUSUM) calculation. We have illustrated that, in most cases, the CUSUM of probability-based analyses can overcome the delay- or advance-related (i.e. the count-related) errors of the classical methods associated with the first PSP only. The probability-based records also induce secondary and tertiary peaks and troughs due to synchronization of the spikes in relation to the stimulus (i.e. the synchronization-related errors) by the first PSP to occur at fixed times from the stimulus. Special CUSUM analyses cannot overcome these synchronization-related errors. Frequency-based analysis (PSFreq) of individual and summed trials gave comparable and often better indications of the underlying PSPs than the probability-based analyses. When used in combination, these analyses compliment each other so that a more accurate estimation of the underlying PSP is possible. Since the correct identification of the connections in the central nervous system is of utmost importance in order to understand the operation of the system, we suggest that as well as the using the special CUSUM approach on probability-based records, researchers should seriously consider the use of frequency-based analyses in their indirect estimation of stimulus-induced compound synaptic potentials in human motoneurones.K. S. Türker, R. K. Power