We applied transcranial alternating current stimulation (tACS) to the primary motor cortex (M1) at different frequencies during an index-thumb pinch-grip observation task. To estimate changes in the corticospinal output, we used the size of motor evoked potentials (MEPs) obtained by transcranial magnetic stimulation (TMS) of M1 using an online MRI-guided simultaneous TMS-tACS approach. The results of the beta-tACS confirm a non-selective increase in corticospinal excitability in subjects at rest; an increase was observed for both of the tested hand muscles, the first dorsal interosseous (FDI) and the abductor digiti minimi (ADM). However, during action observation of the pinch-grip movement, the increase of corticospinal excitability was only observed for the prime mover FDI muscle and took place during alpha-tACS, while gamma-tACS affected both the FDI and control muscle (ADM) responses. These phenomena likely reflect the hypothesis that the mu and gamma rhythms specifically index the downstream modulation of primary sensorimotor areas by engaging mirror neuron activity. The current neuromodulation approach confirms that tACS can be used to induce neurophysiologically detectable state-dependent enhancement effects, even in complex motor-cognitive tasks. Compelling evidence indicates that, in the human motor system, the application to the scalp of low-intensity transcranial alternating current stimulation (tACS) with a frequency matching the idling beta rhythm of the resting precentral areas causes an increase in the corticospinal output, measured by the size of the motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) of the primary motor cortex (M1) 1-3. These neurophysiological effects, which point to a less selective motoneuronal recruitment driven by beta activity 1 , have an overt behavioural counterpart as tACS at beta range may slow down some kinematic aspects of voluntary movements 4-7. On the other hand, gamma-tACS tends to have prokinetic effects on visually-guided motor abilities 5,7. Taken together, these findings suggest that brain oscillations in the precentral regions are causally, rather than epiphenomenally, linked to motor control. The effects of tACS are thought to be mediated by entrainment of brain oscillations, with resonance phenomena occurring between the applied frequency of stimulation and the local endogenous rhythms 8. These local brain rhythms change during the execution of cognitive, motor and perceptual tasks. For example, during motor imagery (MI), a mental process that desynchronizes the beta rhythm of the M1 9,10 , beta-tACS can no longer modulate the corticospinal output, which it can during the resting state 1,2 , when the idling beta rhythm is locally prominent 11,12. On the other hand, theta-and alpha-tACS increase the corticospinal output (i.e. result in larger MEPs in prime mover hand muscles) during movement imagination, possibly because of the synchronization with theta-mediated working memory (WM) processes necessary to mentally process and ...

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Amyoplasia is the most severe form of arthrogryposis and is characterized by congenital multiple joint contractures, hypoplasia or aplasia of skeletal muscles, and limited or complete lack of self-service. The use of compensatory movements allows patients to be partially or completely independent in daily life. The goal. Based on their own observations and literature, describe compensatory and compensatory movements in children with amyoplasia with upper limb lesions, which patients use in performing basic self-care skills. Material and methods. From 2008 to 2019 we examined, 236 patients with amyoplasia (10 months to 16 years old) with a typical lesion of the upper extremities and limitation of self-care. Depending on the nature of the existing anatomical and functional disorders and the level of segmental muscle damage, all patients with amyoplasia were divided into 4 groups. Compensatory movements were studied in each group of patients. Results. The study showed that children's compensatory movements are numerous and depend on the degree of muscle function disorders of the upper and lower extremities, the rate of psychomotor development of the child. Elbow is a key joint to determine the functional independence in daily life. In cases of extensor contracture in the elbow patients have severe functional disorders and need personal assistance. Conclusions. Compensatory movements in children with amyoplasia are useful and help to adapt in daily life and compensate for the loss (or insufficiency) of movements in the joints. Compensatory movements in children are different. They are determined by the range of passive and active movements in the joints of the upper and low extremities.