Selective enhancement of motor cortical plasticity by observed mirror-matched actions

Watching others learn a motor task can enhance an observer's own later performance when learning the same motor task. This is thought to be due to activation of the action observation (or mirror neuron) network. Here we show that the effectiveness of plasticity induced in human motor cortex (M1) is also significantly influenced by the nature of prior action observation. In separate sessions, 17 participants watched a video showing repeated goal-directed movements (action observation) involving either the right hand (congruent condition) or the same video mirror-reversed to simulate the left hand (incongruent condition). Participants then received pulses of transcranial magnetic stimulation over the hand area of left M1 paired with median nerve stimulation of the right hand (paired associative stimulation; PAS). The resting motor-evoked potential (MEP) in right abductor pollicis brevis (APB) increased significantly 20. minutes after PAS, but only when participants had previously watched the congruent video. In this condition, all participants showed an increase in MEP amplitude at 20. minutes post-PAS. There was no change in MEP amplitude following PAS when participants watched the incongruent video. We conclude that prior action observation is a potent modulator of subsequent PAS-induced neuroplasticity, which may have important therapeutic applications

Primary motor cortex excitability in karate athletes: A transcranial magnetic stimulation study

Purpose: The mechanisms involved in the coordination of muscle activity are not completely known: to investigate adaptive changes in human motor cortex Transcranial magnetic stimulation (TMS) was often used. The sport models are frequently used to study how the training may affect the corticospinal system excitability: Karate represents a valuable sport model for this kind of investigations for its high levels of coordination required to athletes. This study was aimed at examining possible changes in the resting motor threshold (rMT) and in the corticospinal response in karate athletes, and at determining whether athletes are characterized by a specific value of rMT. Methods: We recruited 25 right-handed young karate athletes and 25 matched non-athletes. TMS was applied to primary motor cortex (M1). Motor evoked potential (MEP) were recorded by two electrodes placed above the first dorsal interosseous (FDI) muscle. We considered MEP latencies and amplitudes at rMT, 110% of rMT, and 120% of rMT. Results: The two groups were similar for age (p > 0.05), height (p > 0.05) and body mass (p > 0.05). The TMS had a 70-mm figure-of-eight coil and a maximum output of 2.2 T, placed over the left motor cortex. During the stimulation, a mechanical arm kept the coil tangential to the scalp, with the handle at 45° respect to the midline. The SofTaxic navigator system (E.M.S. Italy, www.emsmedical.net) was used in order to correctly identifying and repeating the stimulation for every subject. Compared to non-athletes, athletes showed a lower resting motor threshold (p < 0.001). Furthermore, athletes had a lower MEP latency (p < 0.001) and a higher MEP amplitude (p < 0.001) compared to non-athletes. Moreover, a ROC curve for rMT was found significant (area: 0.907; sensitivity 84%, specificity 76%). Conclusions: As the main finding, the present study showed significant differences in cortical excitability between athletes and non-athletes. The training can improve cortical excitability inducing athletes' modifications, as demonstrated in rMT and MEP values. These finding support the hypothesis that the sport practice determines specific brain organizations in relationship with the sport challenges

Action Observation for Neurorehabilitation in Apraxia

Neurorehabilitation and brain stimulation studies of post-stroke patients suggest that action-observation effects can lead to rapid improvements in the recovery of motor functions and long-term motor cortical reorganization. Apraxia is a clinically important disorder characterized by marked impairment in representing and performing skillful movements [gestures], which limits many daily activities and impedes independent functioning. Recent clinical research has revealed errors of visuo-motor integration in patients with apraxia. This paper presents a rehabilitative perspective focusing on the possibility of action observation as a therapeutic treatment for patients with apraxia. This perspective also outlines impacts on neurorehabilitation and brain repair following the reinforcement of the perceptual-motor coupling. To date, interventions based primarily on action observation in apraxia have not been undertaken

Embodied simulation and ambiguous stimuli: The role of the mirror neuron system

According to the "embodied simulation theory," exposure to certain visual stimuli would automatically trigger action simulation in the mind of the observer, thereby originating a "feeling of movement" modulated by the mirror neuron system (MNS). Grounded on this conceptualization, some of us recently suggested that when exposed to the Rorschach inkblots, in order to see a human movement (e.g., "a person running") in those ambiguous stimuli, the observer would need to experience a "feeling of movement" via embodied simulation. The current study used repetitive transcranial magnetic stimulation (rTMS) to further test this hypothesis. Specifically, we investigated whether temporarily interfering with the activity of the left inferior frontal gyrus (LIFG; a putative MNS area) using rTMS would decrease the propensity to see human movement (M) in the Rorschach inkblots. Thirty-six participants were exposed to the Rorschach stimuli twice, i.e., during a baseline (without rTMS) and soon after inhibitory rTMS. As for the rTMS condition, half of the sample was stimulated over the LIFG (experimental group) and the other half over the Vertex (control group). In line with our hypothesis, the application of rTMS over LIFG, but not over Vertex, yielded a statistically significant reduction in the attribution of M to the ambiguous stimuli, with large effect size. These findings may be interpreted as being consistent with the hypothesis that there is a link between the MNS and the "feeling of movement" people may experience, when observing ambiguous stimuli such as the Rorschach cards

Occlusion of LTP-Like Plasticity in Human Primary Motor Cortex by Action Observation

Passive observation of motor actions induces cortical activity in the primary motor cortex (M1) of the onlooker, which could potentially contribute to motor learning. While recent studies report modulation of motor performance following action observation, the neurophysiological mechanism supporting these behavioral changes remains to be specifically defined. Here, we assessed whether the observation of a repetitive thumb movement – similarly to active motor practice – would inhibit subsequent long-term potentiation-like (LTP) plasticity induced by paired-associative stimulation (PAS). Before undergoing PAS, participants were asked to either 1) perform abductions of the right thumb as fast as possible; 2) passively observe someone else perform thumb abductions; or 3) passively observe a moving dot mimicking thumb movements. Motor evoked potentials (MEP) were used to assess cortical excitability before and after motor practice (or observation) and at two time points following PAS. Results show that, similarly to participants in the motor practice group, individuals observing repeated motor actions showed marked inhibition of PAS-induced LTP, while the “moving dot” group displayed the expected increase in MEP amplitude, despite differences in baseline excitability. Interestingly, LTP occlusion in the action-observation group was present even if no increase in cortical excitability or movement speed was observed following observation. These results suggest that mere observation of repeated hand actions is sufficient to induce LTP, despite the absence of motor learning

Top-down and bottom-up stimulation techniques combined with action observation treatment in stroke rehabilitation: a perspective

Stroke is a central nervous system disease that causes structural lesions and functional impairments of the brain, resulting in varying types, and degrees of dysfunction. The bimodal balance-recovery model (interhemispheric competition model and vicariation model) has been proposed as the mechanism of functional recovery after a stroke. We analyzed how combinations of motor observation treatment approaches, transcranial electrical (TES) or magnetic (TMS) stimulation and peripheral electrical (PES) or magnetic (PMS) stimulation techniques can be taken as accessorial physical therapy methods on symptom reduction of stroke patients. We suggest that top-down and bottom-up stimulation techniques combined with action observation treatment synergistically might develop into valuable physical therapy strategies in neurorehabilitation after stroke. We explored how TES or TMS intervention over the contralesional hemisphere or the lesioned hemisphere combined with PES or PMS of the paretic limbs during motor observation followed by action execution have super-additive effects to potentiate the effect of conventional treatment in stroke patients. The proposed paradigm could be an innovative and adjunctive approach to potentiate the effect of conventional rehabilitation treatment, especially for those patients with severe motor deficits

Interazione tra cTBS cerebellare e movimenti volontari semplici e complessi dell'arto superiore : nuove acquisizioni sui processi di plasticità omeostati e di formazione della memoria motoria

The aim of the present study was to investigate in healthy subjects whether continuous theta-burst stimulation (cTBS) applied over the lateral cerebellum alters motor learning (acquisition and retention phases) during ipsilateral simple and complex movements. Eighteen healthy subjects participated in the study. We delivered cTBS over the lateral cerebellum immediately before a motor learning task involving repeated simple (i.e. index finger-abductions) and complex (i.e. reaching) movements. As motor learning measures we evaluated kinematic variables for simple and complex movements during the task. To see whether cerebellar cTBS-induced changes in motor learning take place through changes in primary motor cortex (M1) activity we used single-pulse transcranial magnetic stimulation (TMS) and evaluated changes in motor evoked potential (MEP) amplitude throughout the experiment. Cerebellar cTBS left the practice-related increase in peak acceleration unchanged but decreased peak acceleration for index finger and reaching movements during motor retention. The smoothness and straightness for trajectories related to reaching movements remained unchanged. When subjects repeated simple and complex movements performed alone, M1 excitability, as measured by the TMS-induced MEP facilitation, increased and MEP amplitudes increased more during simple movements than during complex movements. Cerebellar cTBS given before simple and complex movement tasks decreased the MEP facilitation induced by simple movements, whereas it increased the MEP facilitation induced by complex movements. During simple and complex movement tasks testing motor learning, no matter how complicated the motor task, cerebellar cTBS interferes with motor memory formation. cTBS induces changes in cerebellar activity thus altering motor-learning-related synaptic activity in M1

Interazione tra cTBS cerebellare e movimenti volontari semplici e complessi dell'arto superiore : nuove acquisizioni sui processi di plasticità omeostati e di formazione della memoria motoria

The aim of the present study was to investigate in healthy subjects whether continuous theta-burst stimulation (cTBS) applied over the lateral cerebellum alters motor learning (acquisition and retention phases) during ipsilateral simple and complex movements. Eighteen healthy subjects participated in the study. We delivered cTBS over the lateral cerebellum immediately before a motor learning task involving repeated simple (i.e. index finger-abductions) and complex (i.e. reaching) movements. As motor learning measures we evaluated kinematic variables for simple and complex movements during the task. To see whether cerebellar cTBS-induced changes in motor learning take place through changes in primary motor cortex (M1) activity we used single-pulse transcranial magnetic stimulation (TMS) and evaluated changes in motor evoked potential (MEP) amplitude throughout the experiment. Cerebellar cTBS left the practice-related increase in peak acceleration unchanged but decreased peak acceleration for index finger and reaching movements during motor retention. The smoothness and straightness for trajectories related to reaching movements remained unchanged. When subjects repeated simple and complex movements performed alone, M1 excitability, as measured by the TMS-induced MEP facilitation, increased and MEP amplitudes increased more during simple movements than during complex movements. Cerebellar cTBS given before simple and complex movement tasks decreased the MEP facilitation induced by simple movements, whereas it increased the MEP facilitation induced by complex movements. During simple and complex movement tasks testing motor learning, no matter how complicated the motor task, cerebellar cTBS interferes with motor memory formation. cTBS induces changes in cerebellar activity thus altering motor-learning-related synaptic activity in M1

Disrupting the ventral premotor cortex interferes with the contribution of action observation to use-dependent plasticity

Action observation (AO), observing another individual perform an action, has been implicated in several higher cognitive processes including forming basic motor memories. Previous work has shown that physical practice (PP) results in cortical motor representational changes, referred to as use-dependent plasticity (UDP), and that AO combined with PP potentiates UDP in both healthy adults and stroke patients. In humans, AO results in activation of the ventral premotor cortex (PMv), however, whether PMv activation has a functional contribution to UDP is not known. Here, we studied the effects disruption of PMv has on UDP when subjects performed PP combined with AO (PP+AO). Subjects participated in 2 randomized-crossover sessions measuring the amount of UDP resulting from PP+AO while receiving disruptive (1Hz) transcranial magnetic stimulation (TMS) over the fMRI activated PMv or over orbito-frontal cortex (FC, Sham). We found that unlike the sham session, disruptive TMS over PMv reduced the beneficial contribution of AO to UDP. To ensure that disruption of PMv was specifically interfering with the contribution of AO and not PP, subjects completed two more control sessions where they performed only PP while receiving disruptive TMS over PMv or FC. We found that the magnitude of UDP for both control sessions was similar to PP+AO with TMS over PMv. These findings suggest that the fMRI activation found in PMv during action observation studies is functionally relevant to task performance, at least for the beneficial effects that AO exerts over motor training