Background: We control the movements of our body and limbs through our muscles. However, the forces produced by our muscles depend unpredictably on the commands sent to them. This uncertainty has two ...sources: irreducible noise in the motor system's processes (i.e., motor noise) and variability in the relationship between muscle commands and muscle outputs (i.e., model uncertainty). Any controller, neural or artificial, benefits from estimating these uncertainties when choosing commands. Methods: To examine these benefits, we used an experimental preparation of the rat hindlimb to electrically stimulate muscles and measure the resulting isometric forces. We compare a functional electric stimulation (FES) controller that represents and compensates for uncertainty in muscle forces with a standard FES controller that neglects uncertainty. Results: Accounting for uncertainty substantially increased the precision of force control. Conclusion: Our study demonstrates the theoretical and practical benefits of representing muscle uncertainty when computing muscle commands. Significance: The findings are relevant beyond FES as they highlight the benefits of estimating statistical properties of muscles for both artificial controllers and the nervous system.
Whole genome sequencing (WGS) was introduced into Swiss antimicrobial resistance monitoring in 2022 as an additional method to phenotypic antimicrobial susceptibility testing by broth microdilution ...to characterize presumptive third-generation cephalosporin-resistant (3GC-R) Escherichia coli. Caecal samples from Swiss slaughter calves and fattening pigs, as well as beef and pork meat from Swiss retail taken in 2021, were analyzed for the presence of 3GC-R E. coli according to European harmonized protocols. In 2021, 3GC-R E. coli was detected in 23,8 % of slaughter calves, 5,9 % of fattening pigs, and 0 % of meat. Comparative analysis of the antimicrobial resistance results obtained by phenotypic measurement and those obtained by the detection of corresponding underlying molecular mechanisms by WGS showed very high agreement (99 %). Resistance to third-generation cephalosporins (3GCs) was mainly associated with the presence of blaCTX-M-15 in E. coli isolates from calves and blaCTX-M-1 in E. coli isolates from pigs and mutations in the ampC-promoter (g.-42 C>T) in E. coli isolates from both animal species. Moreover, WGS data were used for phylogenetic analysis based on multi locus sequence types (MLST) and core genome MLST(cgMLST) revealing that 3GC-R E. coli isolated from Swiss slaughter calves and fattening pigs were genetically diverse. In this study, it was shown that using WGS alone to monitor antimicrobial resistance could detect trends in known molecular antimicrobial resistance mechanisms while also providing other valuable information about the isolates, such as genetic relatedness. However, only by combining phenotypic susceptibility testing and WGS early detection of previously unknown resistance mechanisms will be possible.
Combining modules for movement Bizzi, E; Cheung, V.C.K; d'Avella, A ...
Brain Research Reviews,
01/2008, Letnik:
57, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract We review experiments supporting the hypothesis that the vertebrate motor system produces movements by combining a small number of units of motor output. Using a variety of approaches such ...as microstimulation of the spinal cord, NMDA iontophoresis, and an examination of natural behaviors in intact and deafferented animals we have provided evidence for a modular organization of the spinal cord. A module is a functional unit in the spinal cord that generates a specific motor output by imposing a specific pattern of muscle activation. Such an organization might help to simplify the production of movements by reducing the degrees of freedom that need to be specified.
After spinal cord injury (SCI), reflexes become hyperexcitable, leading to debilitating muscle spasms and compromised motor function. Previous work has described adaptations in spinal systems that ...might underlie this hyperexcitability, including an increase in constitutively active 5-HT
receptors in spinal motoneurons. That work, however, examined adaptations following complete transection SCI, whereas SCI in humans is usually anatomically and functionally incomplete. We therefore evaluated whether constitutive activity of 5-HT
receptors contributes to reflex hyperexcitability in an incomplete compression model of SCI and to spasms in vitro and in vivo. Our results confirm that 5-HT
receptor constitutive activity contributes to reflex excitability after incomplete SCI. We also evaluated whether constitutive activity could be altered by manipulation of neural activity levels after SCI, testing the hypothesis that it reflects homeostatic processes acting to maintain spinal excitability. We decreased neural activity after SCI by administering baclofen and increased activity by administering the selective serotonin reuptake inhibitor (SSRI) fluoxetine. We found that drug administration produced minimal alterations in in vivo locomotor function or reflex excitability. Similarly, we found that neither baclofen nor fluoxetine altered the contribution of constitutively active 5-HT
receptors to reflexes after SCI, although the contribution of 5-HT
receptors to reflex activity was altered after SSRIs. These results confirm the importance of constitutive activity in 5-HT
receptors to spinal hyperexcitability following SCI in the clinically relevant case of incomplete SCI but suggest that this activity is not driven by homeostatic processes that act to maintain overall levels of spinal excitability.
After spinal cord injury (SCI), most people will develop muscle spasms below their level of injury that can severely impact function. In this work, we examine the adaptations that occur within the spinal cord after SCI that contribute to these motor dysfunctions. We also evaluate one hypothesis about how these adaptations develop, which will potentially lead to intervention strategies to improve functional outcomes in persons with SCI.
The construction of movement by the spinal cord Bizzi, Emilio; Tresch, Matthew C; Saltiel, Philippe
Nature neuroscience,
199902, 1999-Feb, 1999-2-00, 19990201, Letnik:
2, Številka:
2
Journal Article
Recenzirano
We used a computational analysis to identify the basic elements with which the vertebrate spinal cord constructs one complex behavior. This analysis extracted a small set of muscle synergies from the ...range of muscle activations generated by cutaneous stimulation of the frog hindlimb. The flexible combination of these synergies was able to account for the large number of different motor patterns produced by different animals. These results therefore demonstrate one strategy used by the vertebrate nervous system to produce movement in a computationally simple manner.
We describe the responses evoked by microstimulation of interneuronal regions of the spinal cord in unanesthetized rats chronically spinalized at T10-T12. One to three weeks after spinalization, ...sites in the lumbar spinal cord were stimulated using trains of low current microstimulation. The isometric force produced by stimulation of a spinal site was measured at the ankle. Responses were reliably observed from stimulation of a region within the first 1250 microm from the dorsal surface of the spinal cord. These responses were clearly not due to direct motoneuronal activation and were maintained after chronic deafferentation. The force evoked by microstimulation and measured at the ankle varied smoothly across the workspace. Simultaneous stimulation of two sites in the spinal cord produced a response that was a simple linear summation of the responses evoked from each of the sites alone. Microstimulation generally produced a highly non-uniform distribution of response directions, biased toward responses which pulled the limb toward the body. Within these distributions there appeared to be two main types of responses. These different types of responses were preferentially evoked by microstimulation of different rostrocaudal regions of the spinal cord. This anatomical organization paralleled the spinal cutaneous somatotopy, as assessed by recording cutaneous receptive fields of neurons at sites to which the microstimulation was applied. This relationship was maintained after chronic deafferentation. The findings described here in the rat spinal cord in large part replicate those previously described in the frog.
This paper relates to the problem of the existence of muscle synergies, that is whether the CNS command to muscles is simplified by controlling their activity in subgroups or synergies, rather than ...individually. We approach this problem with two methods that have been recently introduced: intraspinal N-methyl-D-aspartate (NMDA) microstimulation and a synergy-extracting algorithm. To search for a common set of synergies encoded for by the spinal cord whose combinations would account for a large range of electromyographic (EMG) patterns, we chose, rather than examining a large range of natural behaviors, to chemically microstimulate a large number of spinal cord interneuronal sites in different frogs. A possible advantage of this complementary method is that it is task-independent. Visual inspection suggested that the NMDA-elicited EMG patterns recorded from 12 leg muscles might indeed be constructed from smaller subgroups of muscles whose activity co-varied, suggestive of synergies. We used a modification of our extracting computational algorithm whereby a nonnegative least-squares method was employed to iteratively update both the synergies and their coefficients of activation in reconstructing the EMG patterns. Using this algorithm, a limited set of seven synergies was found whose linear combinations accounted for more than 91% of the variance in the pooled EMG data from 10 frogs, and more than 96% in individual frogs. The extracted synergies were similar among frogs. Further, preferred combinations of these synergies were clearly identified. This was found by extracting smaller sets of four, five, or six synergies and fitting each synergy from those sets as a combination from the set of seven synergies extracted from the same frog; the synergy combinations from each frog were then pooled together to examine their frequency of occurrence. Concordance with this method of identifying synergy combinations was found by examining how the synergies from the set of seven correlated pair-wise as they reconstructed the EMG data. These results support the existence of muscle synergies encoded within the spinal cord, which through preferred combinations, account for a large repertoire of spinal cord motor output. These findings are contrasted with previous approaches to the problem of synergies.
New perspectives on spinal motor systems Bizzi, Emilio; Tresch, Matthew C; Saltiel, Philippe ...
Nature reviews. Neuroscience,
11/2000, Letnik:
1, Številka:
2
Journal Article
Recenzirano
The production and control of complex motor functions are usually attributed to central brain structures such as cortex, basal ganglia and cerebellum. In traditional schemes the spinal cord is ...assigned a subservient function during the production of movement, playing a predominantly passive role by relaying the commands dictated to it by supraspinal systems. This review challenges this idea by presenting evidence that the spinal motor system is an active participant in several aspects of the production of movement, contributing to functions normally ascribed to 'higher' brain regions.
The vertebrate nervous system produces a wide range of movement flexibly and efficiently, even though the simplest of these movements is potentially highly complex. The strategies by which the ...nervous system overcomes these complexities have therefore been of interest to motor physiologists for decades. In this review, the authors present a number of recent experiments that propose one strategy by which the nervous system might simplify the production of movement. These experiments suggest that spinal motor systems are organized in terms of a small number of distinct motor responses, or "modules." These distinct modules can be combined together simply to produce a wide range of different movements. Such a modular organization of spinal motor systems can potentially allow the nervous system to produce a wide range of natural behaviors in a simple and flexible manner.
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