Leonardo Abdala Elias

@article{pmid31605381,

title = {The human central nervous system transmits common synaptic inputs to distinct motor neuron pools during non-synergistic digit actions},

author = {A Del Vecchio and C M Germer and L A Elias and Q Fu and J Fine and M Santello and D Farina},

doi = {10.1113/JP278623},

issn = {1469-7793},

year  = {2019},

date = {2019-12-01},

urldate = {2019-12-01},

journal = {J Physiol},

volume = {597},

number = {24},

pages = {5935--5948},

abstract = {KEY POINTS: Neural connectivity between distinct motor neuronal modules in the spinal cord is classically studied through electrical stimulation or multi-muscle EMG recordings. We quantified the strength of correlation in the activity of two distinct populations of motor neurons innervating the thenar and first dorsal interosseous muscles during tasks that required the two hand muscles to exert matched or un-matched forces in different directions. We show that when the two hand muscles are concurrently activated, synaptic input to the two motor neuron pools is shared across all frequency bandwidths (representing cortical and spinal input) associated with force control. The observed connectivity indicates that motor neuron pools receive common input even when digit actions do not belong to a common behavioural repertoire.nnABSTRACT: Neural connectivity between distinct motor neuronal modules in the spinal cord is classically studied through electrical stimulation or multi-muscle EMG recordings. Here we quantify the strength of correlation in the activity of two distinct populations of motor neurons innervating the thenar and first dorsal interosseous muscles in humans during voluntary contractions. To remove confounds associated with previous studies, we used a task that required the two hand muscles to exert matched or un-matched forces in different directions. Despite the force production task consisting of uncommon digit force coordination patterns, we found that synaptic input to motor neurons is shared across all frequency bands, reflecting cortical and spinal inputs associated with force control. The coherence between discharge timings of the two pools of motor neurons was significant at the delta (0-5 Hz), alpha (5-15 Hz) and beta (15-35 Hz) bands (P < 0.05). These results suggest that correlated input to motor neurons of two hand muscles can occur even during tasks not belonging to a common behavioural repertoire and despite lack of common innervation. Moreover, we show that the extraction of activity from motor neurons during voluntary force control removes cross-talk associated with global EMG recordings, thus allowing direct in vivo interrogation of spinal motor neuron activity.},

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pubstate = {published},

tppubtype = {article}

}

@article{pmid31197752,

title = {Sinusoidal vibrotactile stimulation differentially improves force steadiness depending on contraction intensity},

author = {Carina Marconi Germer and Luciana Sobral Moreira and Leonardo Abdala Elias},

doi = {10.1007/s11517-019-01999-8},

issn = {1741-0444},

year  = {2019},

date = {2019-08-01},

urldate = {2019-08-01},

journal = {Med Biol Eng Comput},

volume = {57},

number = {8},

pages = {1813--1822},

abstract = {Studies have reported the benefits of sensory noise in motor performance, but it is not clear if this phenomenon is influenced by muscle contraction intensity. Additionally, most of the studies investigated the role of a stochastic noise on the improvement of motor control and there is no evidence that a sinusoidal vibrotactile stimulation could also enhance motor performance. Eleven participants performed a sensorimotor task while sinusoidal vibrations were applied to the finger skin. The effects of an optimal vibration (OV) on force steadiness were evaluated in different contraction intensities. We assessed the standard deviation (SD) and coefficient of variation (CoV) of force signals. OV significantly decreased force SD irrespective of contraction intensity, but the decrease in force CoV was significantly higher for low-intensity contraction. To the best of our knowledge, our findings are the first evidence that sinusoidal vibrotactile stimulation can enhance force steadiness in a motor task. Also, the significant improvement caused by OV during low-intensity contractions is probably due to the higher sensitivity of the motor system to the synaptic noise. These results add to the current knowledge on the effects of vibrotactile stimulation in motor control and have potential implications for the development of wearable haptic devices. Graphical abstract In this work the effects of a sinusoidal vibrotactile stimulation on force steadiness was investigated. Index finger sensorimotor tasks were performed in three levels of isometric contraction of the FDI muscle: 5, 10 and 15 %MVC. An optimal level of vibration significantly improved force steadiness, but the decrease in force CoV caused by vibration was more pronounced in contractions at 5 %MVC.},

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pubstate = {published},

tppubtype = {article}

}

@article{pmid28194103,

title = {Reassessment of Non-Monosynaptic Excitation from the Motor Cortex to Motoneurons in Single Motor Units of the Human Biceps Brachii},

author = {Tsuyoshi Nakajima and Toshiki Tazoe and Masanori Sakamoto and Takashi Endoh and Satoshi Shibuya and Leonardo Abdala Elias and Rinaldo A Mezzarane and Tomoyoshi Komiyama and Yukari Ohki},

doi = {10.3389/fnhum.2017.00019},

issn = {1662-5161},

year  = {2017},

date = {2017-01-01},

urldate = {2017-01-01},

journal = {Front Hum Neurosci},

volume = {11},

pages = {19},

abstract = {Corticospinal excitation is mediated by polysynaptic pathways in several vertebrates, including dexterous monkeys. However, indirect non-monosynaptic excitation has not been clearly observed following transcranial electrical stimulation (TES) or cervicomedullary stimulation (CMS) in humans. The present study evaluated indirect motor pathways in normal human subjects by recording the activities of single motor units (MUs) in the biceps brachii (BB) muscle. The pyramidal tract was stimulated with weak TES, CMS, and transcranial magnetic stimulation (TMS) contralateral to the recording side. During tasks involving weak co-contraction of the BB and hand muscles, all stimulation methods activated MUs with short latencies. Peristimulus time histograms (PSTHs) showed that responses with similar durations were induced by TES (1.9 ± 1.4 ms) and CMS (2.0 ± 1.4 ms), and these responses often showed multiple peaks with the PSTH peak having a long duration (65.3% and 44.9%, respectively). Such long-duration excitatory responses with multiple peaks were rarely observed in the finger muscles following TES or in the BB following stimulation of the Ia fibers. The responses obtained with TES were compared in the same 14 BB MUs during the co-contraction and isolated BB contraction tasks. Eleven and three units, respectively, exhibited activation with multiple peaks during the two tasks. In order to determine the dispersion effects on the axon conduction velocities (CVs) and synaptic noise, a simulation study that was comparable to the TES experiments was performed with a biologically plausible neuromuscular model. When the model included the monosynaptic-pyramidal tract, multiple peaks were obtained in about 34.5% of the motoneurons (MNs). The experimental and simulation results indicated the existence of task-dependent disparate inputs from the pyramidal tract to the MNs of the upper limb. These results suggested that intercalated interneurons are present in the spinal cord and that these interneurons might be equivalent to those identified in animal experiments.},

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pubstate = {published},

tppubtype = {article}

}

@article{pmid29205218,

title = {A longitudinal assessment of myoelectric activity, postural sway, and low-back pain during pregnancy},

author = {Luciana Sobral Moreira and Leonardo Abdala Elias and Adriane B Gomide and Marcus Fraga Vieira and Waldemar N DO Amaral},

issn = {1509-409X},

year  = {2017},

date = {2017-01-01},

urldate = {2017-01-01},

journal = {Acta Bioeng Biomech},

volume = {19},

number = {3},

pages = {77--83},

abstract = {PURPOSE: The present study aimed at investigating the control of upright quiet standing in pregnant women throughout pregnancy, and whether low-back pain exerts influence on this motor task.



METHODS: Myoelectric signals from postural muscles and stabilometric data were collected from 15 non-pregnant and 15 pregnant women during upright quiet standing. Electromyogram envelopes and center of pressure metrics were evaluated in the control group, as well as in pregnant women in their first and third trimester of pregnancy. A correlation analysis was performed between the measured variables and a low-back pain disability index.



RESULTS: Pregnant women exhibited a decreased maximum voluntary isometric activity for all postural muscles evaluated. Additionally, the activity of lumbar muscles during the postural task was significantly higher in the pregnant women in comparison to the non-pregnant controls. The soleus muscle maintained its activity at the same level as the gestation progressed. Higher postural oscillations were observed in the anteroposterior direction while mediolateral sway was reduced in the third trimester of pregnancy. No correlation was detected between the lowback pain disability index and neuromechanical variables.



CONCLUSION: This study provides additional data regarding the functioning and adaptations of the postural control system during pregnancy. Also, we provide further evidence that postural control during quiet standing cannot be used to predict the occurrence of low-back pain. We hypothesize that the modifications in the neural drive to the muscles, as well as in postural sway may be related to changes in the biomechanics and hormonal levels experienced by the pregnant women.},

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pubstate = {published},

tppubtype = {article}

}