Negro, Francesco

[["dc.bibliographiccitation.firstpage","1895"],["dc.bibliographiccitation.issue","3"],["dc.bibliographiccitation.journal","Journal of Neurophysiology"],["dc.bibliographiccitation.lastpage","1911"],["dc.bibliographiccitation.volume","114"],["dc.contributor.author","Dideriksen, Jakob Lund"],["dc.contributor.author","Negro, Francesco"],["dc.contributor.author","Farina, Dario"],["dc.date.accessioned","2018-11-07T09:52:18Z"],["dc.date.available","2018-11-07T09:52:18Z"],["dc.date.issued","2015"],["dc.description.abstract","Increasing joint stiffness by cocontraction of antagonist muscles and compensatory reflexes are neural strategies to minimize the impact of unexpected perturbations on movement. Combining these strategies, however, may compromise steadiness, as elements of the afferent input to motor pools innervating antagonist muscles are inherently negatively correlated. Consequently, a high afferent gain and active contractions of both muscles may imply negatively correlated neural drives to the muscles and thus an unstable limb position. This hypothesis was systematically explored with a novel computational model of the peripheral nervous system and the mechanics of one limb. Two populations of motor neurons received synaptic input from descending drive, spinal interneurons, and afferent feedback. Muscle force, simulated based on motor unit activity, determined limb movement that gave rise to afferent feedback from muscle spindles and Golgi tendon organs. The results indicated that optimal steadiness was achieved with low synaptic gain of the afferent feedback. High afferent gains during cocontraction implied increased levels of common drive in the motor neuron outputs, which were negatively correlated across the two populations, constraining instability of the limb. Increasing the force acting on the joint and the afferent gain both effectively minimized the impact of an external perturbation, and suboptimal adjustment of the afferent gain could be compensated by muscle cocontraction. These observations show that selection of the strategy for a given contraction implies a compromise between steadiness and effectiveness of compensations to perturbations. This indicates that a task-dependent selection of neural strategy for steadiness is necessary when acting in different environments."],["dc.description.sponsorship","EU Commission through the project NeuroTREMOR [287739]"],["dc.identifier.doi","10.1152/jn.00247.2015"],["dc.identifier.isi","000362045100049"],["dc.identifier.pmid","26203102"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/36094"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Amer Physiological Soc"],["dc.relation.issn","1522-1598"],["dc.relation.issn","0022-3077"],["dc.title","The optimal neural strategy for a stable motor task requires a compromise between level of muscle cocontraction and synaptic gain of afferent feedback"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","3427"],["dc.bibliographiccitation.issue","16"],["dc.bibliographiccitation.journal","The Journal of Physiology"],["dc.bibliographiccitation.lastpage","3441"],["dc.bibliographiccitation.volume","592"],["dc.contributor.author","Farina, Dario"],["dc.contributor.author","Negro, Francesco"],["dc.contributor.author","Dideriksen, Jakob Lund"],["dc.date.accessioned","2018-11-07T09:36:34Z"],["dc.date.available","2018-11-07T09:36:34Z"],["dc.date.issued","2014"],["dc.description.abstract","We analysed the transformation of synaptic input to the pool of motor neurons into the neural drive to the muscle. The aim was to explain the relations between common oscillatory signals sent to motor neurons and the effective component of the neural signal sent to muscles as output of the spinal cord circuitries. The approach is based on theoretical derivations, computer simulations, and experiments. It is shown theoretically that for frequencies smaller than the average discharge rates of the motor neurons, the pool of motor neurons determines a pure amplification of the frequency components common to all motor neurons, so that the common input is transmitted almost undistorted and the non-common components are strongly attenuated. The effective neural drive to the muscle thus mirrors the common synaptic input to motor neurons. The simulations with three models of motor neuron confirmed the theoretical results by showing that the coherence function between common input components and the neural drive to the muscle tends to 1 when increasing the number of active motor neurons. This result, which was relatively insensitive to the type of model used, was also supported experimentally by observing that, in the low-pass signal bandwidth, the peak in coherence between groups of motor units of the abductor digiti minimi muscle of five healthy subjects tended to 1 when increasing the number of motor units. These results have implications for our understanding of the neural control of muscles as well as for methods used for estimating the strength of common input to populations of motor neurons."],["dc.description.sponsorship","European Research Council Advanced Grant DEMOVE [267888]"],["dc.identifier.doi","10.1113/jphysiol.2014.273581"],["dc.identifier.isi","000340599200012"],["dc.identifier.pmid","24860172"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/32645"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Wiley-blackwell"],["dc.relation.issn","1469-7793"],["dc.relation.issn","0022-3751"],["dc.title","The effective neural drive to muscles is the common synaptic input to motor neurons"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","3357"],["dc.bibliographiccitation.issue","12"],["dc.bibliographiccitation.journal","Journal of Neurophysiology"],["dc.bibliographiccitation.lastpage","3369"],["dc.bibliographiccitation.volume","107"],["dc.contributor.author","Dideriksen, Jakob Lund"],["dc.contributor.author","Negro, Francesco"],["dc.contributor.author","Enoka, Roger M."],["dc.contributor.author","Farina, Dario"],["dc.date.accessioned","2018-11-07T09:09:37Z"],["dc.date.available","2018-11-07T09:09:37Z"],["dc.date.issued","2012"],["dc.description.abstract","Dideriksen JL, Negro F, Enoka RM, Farina D. Motor unit recruitment strategies and muscle properties determine the influence of synaptic noise on force steadiness. J Neurophysiol 107: 3357-3369, 2012. First published March 14, 2012; doi:10.1152/jn.00938.2011.-Motoneurons receive synaptic inputs from tens of thousands of connections that cause membrane potential to fluctuate continuously (synaptic noise), which introduces variability in discharge times of action potentials. We hypothesized that the influence of synaptic noise on force steadiness during voluntary contractions is limited to low muscle forces. The hypothesis was examined with an analytical description of transduction of motor unit spike trains into muscle force, a computational model of motor unit recruitment and rate coding, and experimental analysis of interspike interval variability during steady contractions with the abductor digiti minimi muscle. Simulations varied contraction force, level of synaptic noise, size of motor unit population, recruitment range, twitch contraction times, and level of motor unit short-term synchronization. Consistent with the analytical derivations, simulations and experimental data showed that force variability at target forces above a threshold was primarily due to low-frequency oscillations in neural drive, whereas the influence of synaptic noise was almost completely attenuated by two low-pass filters, one related to convolution of motoneuron spike trains with motor unit twitches (temporal summation) and the other attributable to summation of single motor unit forces (spatial summation). The threshold force above which synaptic noise ceased to influence force steadiness depended on recruitment range, size of motor unit population, and muscle contractile properties. This threshold was low (<10% of maximal force) for typical values of these parameters. Results indicate that motor unit recruitment and muscle properties of a typical muscle are tuned to limit the influence of synaptic noise on force steadiness to low forces and that the inability to produce a constant force during stronger contractions is mainly attributable to the common low-frequency oscillations in motoneuron discharge rates."],["dc.identifier.doi","10.1152/jn.00938.2011"],["dc.identifier.isi","000305420200013"],["dc.identifier.pmid","22423000"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/26301"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Amer Physiological Soc"],["dc.relation.issn","0022-3077"],["dc.title","Motor unit recruitment strategies and muscle properties determine the influence of synaptic noise on force steadiness"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]