RESUMO
Different forearm postures can modulate corticospinal excitability. However, there is no consensus on whether handedness plays a role in such a mechanism. This study investigated the effects of 3 forearm postures (pronation, neutral, and supination) on the corticospinal excitability of muscles from the dominant and nondominant upper limbs. Surface electromyography was recorded from the abductor digiti minimi, flexor pollicis brevis, and flexor carpi radialis from both sides of 12 right-handed volunteers. Transcranial magnetic stimulation pulses were applied to each muscle's hotspot in both cerebral hemispheres. Motor-evoked potential peak-to-peak amplitude and latency and resting motor threshold were measured. The data were evaluated by analysis of variance. The level of significance was set at 5%. The resting motor threshold was similar for the 3 muscles and both sides. Motor-evoked potential peak-to-peak amplitude from flexor pollicis brevis was lower during supination, and the dominant upper limb latency was longer. The flexor carpi radialis presented lower motor-evoked potential peak-to-peak amplitudes for neutral and shorter latencies during supination. Abductor digiti minimi seemed not to be affected by posture or side. Different muscles from dominant and nondominant sides may undergo corticospinal modulation, even distally localized from a particular joint and under rest.
Assuntos
Eletromiografia , Potencial Evocado Motor , Antebraço , Mãos , Músculo Esquelético , Postura , Tratos Piramidais , Estimulação Magnética Transcraniana , Humanos , Músculo Esquelético/fisiologia , Masculino , Antebraço/fisiologia , Postura/fisiologia , Potencial Evocado Motor/fisiologia , Mãos/fisiologia , Feminino , Tratos Piramidais/fisiologia , Adulto , Lateralidade Funcional/fisiologia , Adulto JovemRESUMO
Reaction time is accelerated if a loud (startling) sound accompanies the cue-the "StartReact" effect. Animal studies revealed a reticulospinal substrate for the startle reflex; StartReact may similarly involve the reticulospinal tract, but this is currently uncertain. Here we trained two female macaque monkeys to perform elbow flexion/extension movements following a visual cue. The cue was sometimes accompanied by a loud sound, generating a StartReact effect in electromyogram response latency, as seen in humans. Extracellular recordings were made from antidromically identified corticospinal neurons in primary motor cortex (M1), from the reticular formation (RF), and from the spinal cord (SC; C5-C8 segments). After loud sound, task-related activity was suppressed in M1 (latency, 70-200 ms after cue), but was initially enhanced (70-80 ms) and then suppressed (140-210 ms) in RF. SC activity was unchanged. In a computational model, we simulated a motoneuron pool receiving input from different proportions of the average M1 and RF activity recorded experimentally. Motoneuron firing generated simulated electromyogram, allowing reaction time measurements. Only if ≥60% of motoneuron drive came from RF (≤40% from M1) did loud sound shorten reaction time. The extent of shortening increased as more drive came from RF. If RF provided <60% of drive, loud sound lengthened the reaction time-the opposite of experimental findings. The majority of the drive for voluntary movements is thus likely to originate from the brainstem, not the cortex; changes in the magnitude of the StartReact effect can measure a shift in the relative importance of descending systems.SIGNIFICANCE STATEMENT Our results reveal that a loud sound has opposite effects on neural spiking in corticospinal cells from primary motor cortex, and in the reticular formation. We show that this fortuitously allows changes in reaction time produced by a loud sound to be used to assess the relative importance of reticulospinal versus corticospinal control of movement, validating previous noninvasive measurements in humans. Our findings suggest that the majority of the descending drive to motoneurons producing voluntary movement in primates comes from the reticulospinal tract, not the corticospinal tract.
Assuntos
Neurônios Motores , Tratos Piramidais , Humanos , Animais , Feminino , Tratos Piramidais/fisiologia , Eletromiografia , Tempo de Reação/fisiologia , Movimento , Macaca , Reflexo de Sobressalto/fisiologiaRESUMO
RESUMEN: La neuroanatomía y la neurofisiología han permitido en gran parte entender de forma más integrada las estructuras que conforman el sistema nervioso y los mecanismos asociados con la transmisión de los potenciales de acción, relacionados con la vía corticoespinal en la ejecución de movimientos voluntarios. Se realizó una revisión histórica sobre la vía corticoespinal, desde el punto de vista neuroanatómico y neurofisiológico mediante una revisión de literatura en distintas bases de datos y libros de texto dedicados a estas vías nerviosas. La información obtenida se ordenó cronológicamente, seleccionando los datos más relevantes que desde el punto de vista neuroanatómico y neurofisiológico han permitido comprender su mecanismo funcional. Actualmente se tiene un conocimiento muy depurado de los distintos elementos que componen la vía corticoespinal, lo que permitirá su aplicación en el campo de la salud y resolver múltiples problemas de la función motora.
SUMMARY: Neuroanatomy and Neurophysiology have, in large part, permitted a more thorough understanding of those structures that conform the nervous system and mechanisms associated with the transmission of action potentials associated with the corticospinal tract. This assertion is made based upon a literature review of various databases and textbooks dedicated to said nerve tracts. The information obtained was ordered chronologically, and data was selected that, from the neuroanatomical and neurophysiological viewpoints, were most relevant and have permitted the comprehension of its functional mechanism. The thorough understanding of those elements that compose the corticospinal tract will permit its application in the health field and resolve multiple motor function problems.
Assuntos
Humanos , História Antiga , História do Século XVII , História do Século XVIII , História do Século XIX , História do Século XX , Tratos Piramidais/anatomia & histologia , Tratos Piramidais/fisiologia , Neuroanatomia/história , Neurofisiologia/históriaRESUMO
BACKGROUND: Movement performance depends on the synaptic interactions generated by coherent parallel sensorimotor cortical outputs to different downstream targets. The major outputs of the neocortex to subcortical structures are driven by pyramidal tract neurons (PTNs) located in layer 5B. One of the main targets of PTNs is the spinal cord through the corticospinal (CS) system, which is formed by a complex collection of distinct CS circuits. However, little is known about intracortical synaptic interactions that originate CS commands and how different populations of CS neurons are functionally organized. To further understand the functional organization of the CS system, we analyzed the activity of unambiguously identified CS neurons projecting to different zones of the same spinal cord segment using two-photon calcium imaging and retrograde neuronal tracers. RESULTS: Sensorimotor cortex slices obtained from transgenic mice expressing GCaMP6 funder the Thy1 promoter were used to analyze the spontaneous calcium transients in layer 5 pyramidal neurons. Distinct subgroups of CS neurons projecting to dorsal horn and ventral areas of the same segment show more synchronous activity between them than with other subgroups. CONCLUSIONS: The results indicate that CS neurons projecting to different spinal cord zones segregated into functional ensembles depending on their hodology, suggesting that a modular organization of CS outputs controls sensorimotor behaviors in a coordinated manner.
Assuntos
Conectoma , Tratos Piramidais/fisiologia , Medula Espinal/fisiologia , Animais , Cálcio/metabolismo , Imunofluorescência/métodos , Camundongos , Camundongos Transgênicos , Córtex Motor/metabolismo , Córtex Motor/fisiologia , Vias Neurais/metabolismo , Vias Neurais/fisiologia , Técnicas de Rastreamento Neuroanatômico/métodos , Neurônios/fisiologia , Tratos Piramidais/metabolismo , Medula Espinal/metabolismoRESUMO
Previous studies from our laboratory showed that in the anesthetized cat, the intradermal injection of capsaicin in the hindpaw facilitated the intraspinal field potentials (IFPs) evoked by stimulation of the intermediate and high-threshold myelinated fibers in the posterior articular nerve (PAN). The capsaicin-induced facilitation was significantly reduced 3-4 h after the injection, despite the persistence of hindpaw inflammation. Although this effect was attributed to an incremented descending inhibition acting on the spinal pathways, it was not clear if it was set in operation once the capsaicin-induced effects exceeded a certain threshold, or if it was continuously operating to keep the increased neuronal activation within manageable limits. To evaluate the changes in descending inhibition, we now examined the effects of successive reversible spinal blocks on the amplitude of the PAN IFPs evoked at different times after the intradermal injection of capsaicin. We found that after capsaicin the PAN IFPs recorded in laminae III-V by activation of high-threshold nociceptive Aδ myelinated fibers increased gradually during successive reversible spinal blocks, while the IFPs evoked by intermediate and low threshold proprioceptive Aß afferents were only slightly affected. It is concluded that during the development of the central sensitization produced by capsaicin, there is a gradual increase of descending inhibition that tends to limit the nociceptive-induced facilitation, mainly by acting on the neuronal populations receiving inputs from the capsaicin-activated afferents without significantly affecting the information on joint angle transmitted by the low threshold afferents.
Assuntos
Capsaicina/farmacologia , Neurônios Aferentes/efeitos dos fármacos , Nociceptores/efeitos dos fármacos , Células do Corno Posterior/efeitos dos fármacos , Tratos Piramidais/efeitos dos fármacos , Fármacos do Sistema Sensorial/farmacologia , Animais , Gatos , Feminino , Masculino , Neurônios Aferentes/fisiologia , Nociceptores/fisiologia , Células do Corno Posterior/fisiologia , Tratos Piramidais/fisiologiaRESUMO
PURPOSE: The aim of this study was to investigate whether hypnotic suggestions can alter knee extensor neuromuscular function at rest and during exercise. METHODS: Thirteen healthy volunteers (8 men and 5 women, 27 ± 3 years old) took part in this counterbalanced, crossover study including two experimental (hypnosis and control) sessions. Knee extensor neuromuscular function was tested before and after hypnosis suggestion by using a combination of voluntary contraction, transcutaneous femoral nerve electrical stimulation and transcranial magnetic stimulation (TMS). A fatiguing exercise (sustained submaximal contraction at 20% maximal voluntary contraction (MVC) force) was also performed to evaluate the potential influence of hypnosis on the extent and origin of neuromuscular adjustments. RESULTS: Hypnosis did not (p>0.05) alter MVC force or knee extensor neural properties. Corticospinal excitability, assessed with the amplitude of knee extensor motor evoked potentials, was also unchanged (p>0.05), as was the level of intracortical inhibition assessed with paired pulse TMS (short-interval intracortical inhibition, SICI). Time to task failure (~300 s) was not different (p>0.05) between the two sessions; accordingly, hypnosis did not influence neuromuscular adjustments measured during exercise and at task failure (p>0.05). CONCLUSION: Hypnotic suggestions did not alter neuromuscular properties of the knee extensor muscles under resting condition or during/after exercise, suggesting that hypnosis-induced improvement in exercise performance and enhanced corticospinal excitability might be limited to highly susceptible participants.
Assuntos
Exercício Físico/fisiologia , Fadiga Muscular/fisiologia , Músculo Esquelético/fisiologia , Sugestão , Adulto , Estudos Cross-Over , Potencial Evocado Motor , Fadiga/fisiopatologia , Fadiga/terapia , Feminino , Nervo Femoral/fisiologia , Humanos , Joelho , Articulação do Joelho , Masculino , Córtex Motor/fisiologia , Contração Muscular/fisiologia , Tratos Piramidais/fisiologia , Descanso , Estimulação Magnética Transcraniana , Estimulação Elétrica Nervosa TranscutâneaRESUMO
In brain cortex-ablated cats (BCAC), hind limb motoneurons activity patterns were studied during fictive locomotion (FL) or fictive scratching (FS) induced by pinna stimulation. In order to study motoneurons excitability: heteronymous monosynaptic reflex (HeMR), intracellular recording, and individual Ia afferent fiber antidromic activity (AA) were analyzed. The intraspinal cord microinjections of serotonin or glutamic acid effects were made to study their influence in FL or FS During FS, HeMR amplitude in extensor and bifunctional motoneurons increased prior to or during the respective electroneurogram (ENG). In soleus (SOL) motoneurons were reduced during the scratch cycle (SC). AA in medial gastrocnemius (MG) Ia afferent individual fibers of L6-L7 dorsal roots did not occur during FS Flexor digitorum longus (FDL) and MG motoneurons fired with doublets during the FS bursting activity, motoneuron membrane potential from some posterior biceps (PB) motoneurons exhibits a depolarization in relation to the PB (ENG). It changed to a locomotor drive potential in relation to one of the double ENG, PB bursts. In FDL and semitendinosus (ST) motoneurons, the membrane potential was depolarized during FS, but it did not change during FL Glutamic acid injected in the L3-L4 spinal cord segment favored the transition from FS to FL During FL, glutamic acid produces a duration increase of extensors ENGs. Serotonin increases the ENG amplitude in extensor motoneurons, as well as the duration of scratching episodes. It did not change the SC duration. Segregation and motoneurons excitability could be regulated by the rhythmic generator and the pattern generator of the central pattern generator.
Assuntos
Potencial Evocado Motor , Locomoção , Neurônios Motores/fisiologia , Músculo Esquelético/fisiologia , Tratos Piramidais/fisiologia , Animais , Gatos , Descorticação Cerebral , Pavilhão Auricular/inervação , Pavilhão Auricular/fisiologia , Feminino , Ácido Glutâmico/farmacologia , Extremidade Inferior/inervação , Extremidade Inferior/fisiologia , Masculino , Córtex Motor/fisiologia , Neurônios Motores/efeitos dos fármacos , Músculo Esquelético/inervação , Tratos Piramidais/efeitos dos fármacos , Reflexo Monosináptico , Serotonina/farmacologiaRESUMO
The descending corticospinal (CS) projection has been considered a key element for motor control, which results from direct and indirect modulation of spinal cord pre-motor interneurons in the intermediate gray matter of the spinal cord, which, in turn, influences motoneurons in the ventral horn. The CS tract (CST) is also involved in a selective and complex modulation of sensory information in the dorsal horn. However, little is known about the spinal network engaged by the CST and the organization of CS projections that may encode different cortical outputs to the spinal cord. This study addresses the issue of whether the CS system exerts parallel control on different spinal networks, which together participate in sensorimotor integration. Here, we show that in the adult rat, two different and partially intermingled CS neurons in the sensorimotor cortex activate, with different time latencies, distinct spinal cord neurons located in the dorsal horn and intermediate zone of the same segment. The fact that different populations of CS neurons project in a segregated manner suggests that CST is composed of subsystems controlling different spinal cord circuits that modulate motor outputs and sensory inputs in a coordinated manner.
Assuntos
Córtex Cerebral/fisiologia , Potenciais Evocados/fisiologia , Tratos Piramidais/anatomia & histologia , Tratos Piramidais/fisiologia , Medula Espinal/fisiologia , Potenciais de Ação/fisiologia , Animais , Mapeamento Encefálico , Córtex Cerebral/citologia , Estimulação Elétrica , Masculino , Neurônios/fisiologia , Ratos , Ratos Wistar , Tempo de Reação , Medula Espinal/citologiaRESUMO
Viewing a person perform an action activates the observer's motor system. Whether this phenomenon reflects the action's kinematics or its final goal remains a matter of debate. One alternative to this apparent controversy is that the relative influence of goal and kinematics depends on the information available to the observer. Here, we addressed this possibility. For this purpose, we measured corticospinal excitability (CSE) while subjects viewed 3 different grasping actions with 2 goals: a large and a small object. Actions were directed to the large object, the small object, or corrected online in which case the goal switched during the movement. We first determined the kinematics and dynamics of the 3 actions during execution. This information was used in 2 other experiments to measure CSE while observers viewed videos of the same actions. CSE was recorded prior to movement onset and at 3 time points during the observed action. To discern between goal and kinematics, information about the goal was manipulated across experiments. We found that the goal influenced CSE only when its identity was known before movement onset. In contrast, a kinematic modulation of CSE was observed whether or not information regarding the goal was provided.
Assuntos
Objetivos , Percepção de Movimento/fisiologia , Atividade Motora/fisiologia , Adulto , Braço/fisiologia , Fenômenos Biomecânicos , Eletromiografia , Feminino , Humanos , Masculino , Músculo Esquelético/fisiologia , Estimulação Luminosa , Tratos Piramidais/fisiologia , Estimulação Magnética Transcraniana , Gravação em Vídeo , Adulto JovemRESUMO
UNLABELLED: Chronic myofascial pain syndrome has been related to defective descending inhibitory systems. Twenty-four females aged 19 to 65 years with chronic myofascial pain syndrome were randomized to receive 10 sessions of repetitive transcranial magnetic stimulation (rTMS) (n = 12) at 10 Hz or a sham intervention (n = 12). We tested if pain (quantitative sensory testing), descending inhibitory systems (conditioned pain modulation [quantitative sensory testing + conditioned pain modulation]), cortical excitability (TMS parameters), and the brain-derived neurotrophic factor (BDNF) would be modified. There was a significant interaction (time vs group) regarding the main outcomes of the pain scores as indexed by the visual analog scale on pain (analysis of variance, P < .01). Post hoc analysis showed that compared with placebo-sham, the treatment reduced daily pain scores by -30.21% (95% confidence interval = -39.23 to -21.20) and analgesic use by -44.56 (-57.46 to -31.67). Compared to sham, rTMS enhanced the corticospinal inhibitory system (41.74% reduction in quantitative sensory testing + conditioned pain modulation, P < .05), reduced the intracortical facilitation in 23.94% (P = .03), increased the motor evoked potential in 52.02% (P = .02), and presented 12.38 ng/mL higher serum BDNF (95% confidence interval = 2.32-22.38). No adverse events were observed. rTMS analgesic effects in chronic myofascial pain syndrome were mediated by top-down regulation mechanisms, enhancing the corticospinal inhibitory system possibly via BDNF secretion modulation. PERSPECTIVE: High-frequency rTMS analgesic effects were mediated by top-down regulation mechanisms enhancing the corticospinal inhibitory, and this effect involved an increase in BDNF secretion.