RESUMO
One of the most striking properties of the adult central nervous system is its ability to undergo changes in function and/or structure. In mammals, learning is a major inducer of adaptive plasticity. Sensorimotor adaptation is a type of procedural--motor--learning that allows maintaining accurate movements in the presence of environmental or internal perturbations by adjusting motor output. In this work, we will review experimental evidence gathered from rodents and human and nonhuman primates pointing to possible sites of adaptation-related plasticity at different levels of organization of the nervous system.
Assuntos
Adaptação Fisiológica , Encéfalo/fisiologia , Aprendizagem , Movimento , Plasticidade Neuronal , Animais , Humanos , Córtex Motor/fisiologia , Destreza MotoraRESUMO
Savings is a fundamental property of learning. In motor adaptation, it refers to the improvement in learning observed when adaptation to a perturbation A (A1) is followed by re-adaptation to the same perturbation (A2). A common procedure to equate the initial level of error across sessions consists of restoring native sensorimotor coordinates by inserting null--unperturbed--trials (N) just before re-adaptation (washout). Here, we hypothesized that the washout is not innocuous but interferes with the expression of the new memory at recall. To assess this possibility, we measured savings following the A1NA2 protocol, where A was a 40° visual rotation. In Experiment 1, we increased the time window between N and A2 from 1 min to 24 h. This manipulation increased the amount of savings during middle to late phases of adaptation, suggesting that N interfered with the retrieval of A. In Experiment 2, we used repetitive TMS to evaluate if this interference was partly mediated by the sensorimotor cortex (SM). We conclude that the washout does not just restore the unperturbed sensorimotor coordinates, but inhibits the expression of the recently acquired visuomotor map through a mechanism involving SM. Our results resemble the phenomenon of extinction in classical conditioning.
Assuntos
Extinção Psicológica/fisiologia , Aprendizagem/fisiologia , Rememoração Mental/fisiologia , Movimento/fisiologia , Desempenho Psicomotor/fisiologia , Córtex Sensório-Motor/fisiologia , Adaptação Fisiológica , Adulto , Análise de Variância , Eletroencefalografia , Potencial Evocado Motor/fisiologia , Feminino , Humanos , Masculino , Estimulação Luminosa , Tempo de Reação/fisiologia , Rotação , Fatores de Tempo , Estimulação Magnética Transcraniana , Adulto JovemRESUMO
The neural mechanisms mediating the activation of the motor system during action observation, also known as motor resonance, are of major interest to the field of motor control. It has been proposed that motor resonance develops in infants through Hebbian plasticity of pathways connecting sensory and motor regions that fire simultaneously during imitation or self movement observation. A fundamental problem when testing this theory in adults is that most experimental paradigms involve actions that have been overpracticed throughout life. Here, we directly tested the sensorimotor theory of motor resonance by creating new visuomotor representations using abstract stimuli (motor symbols) and identifying the neural networks recruited through fMRI. We predicted that the network recruited during action observation and execution would overlap with that recruited during observation of new motor symbols. Our results indicate that a network consisting of premotor and posterior parietal cortex, the supplementary motor area, the inferior frontal gyrus and cerebellum was activated both by new motor symbols and by direct observation of the corresponding action. This tight spatial overlap underscores the importance of sensorimotor learning for motor resonance and further indicates that the physical characteristics of the perceived stimulus are irrelevant to the evoked response in the observer.
Assuntos
Imageamento por Ressonância Magnética/métodos , Desempenho Psicomotor , Adulto , Humanos , AprendizagemRESUMO
The neural bases of motor adaptation have been extensively explored in human and nonhuman primates. A network including the cerebellum, primary motor cortex, and posterior parietal cortex appears to be crucial for this type of learning. Yet, to date, it is unclear whether these regions contribute directly or indirectly to the formation of motor memories. Here we trained subjects on a complex visuomotor rotation associated with long-term memory (in the order of months) to identify potential sites of structural plasticity induced by adaptation. One week of training led to (1) an increment in local gray matter concentration over the hand area of the contralateral primary motor cortex and (2) an increase in fractional anisotropy in an area underneath this region that correlated with the speed of learning. Moreover, the change in gray matter concentration measured immediately after training predicted improvements in the speed of learning during readaptation 1 year later. Our study suggests that motor adaptation induces structural plasticity in primary motor circuits. In addition, it provides the first piece of evidence indicating that early structural changes induced by motor learning may impact on behavior up to 1 year after training.