Humans can produce a variety of accurate motor behaviors even in the face of constantly changing demands and environments. Such behavior relies on the ability to acquire a new motor skill (for example playing the musical instruments) and the ability to modify an existing motor behavior to face sustained changes. These abilities are subserved by plasticity of the nervous system.
The acquisition and retention of skilled sequential movements is a fundamental part of human behavior. It is critical to almost every voluntary action we perform. Even so, we know little about where and when plastic changes occur in the cortical motor areas to acquire and retain skilled sequential movements. It now is well-established that there are multiple cortical motor areas in the frontal lobe. Each of these cortical motor areas has disynaptic access to motoneurons. Thus, there is the potential for each of these motor areas to make a contribution to skilled motor performance. Among the motor areas, primary motor cortex (M1) and dorsal premotor cortex (PMd) are poised to contribute to the acquisition and retention of motor skills. Extensive practice on sequential movements leads to reorganization of M1, as indicated by learning-related changes of fMRI activation and enlarged gray-matter volume in humans, and modulation of neuron discharge and decreased metabolic activity (2DG signal) in monkeys. In PMd of monkeys, neural activity was modulated after training on internally-generated sequential movements. Inactivation of PMd disrupts the performance of internally-generated sequential movements but not the visually guided reaching. Therefore, we proposed that PMd contributes to internally-generated sequential movements through building and maintaining the motor-motor associations between the movement elements in a sequence. Neural activity underlying learning have been postulated to operate on different time scales between areas and thus may involve distinct mechanisms. We are studying the temporal evolution of the learning and maintenance of skilled sequential movements in cortical motor areas.
The motor adaptation is the ability to modify an existing motor behavior to face sustained changes in their environment. This mechanism can be tested using a shift of the visual field while subjects are asked to point at a visual target. The shift displaces the viewed position of the target. If the aiming movement is fast enough or if no visual feedback is available, this results in a reaching end point error as individuals are not able to point at the object in its real position . The reaching error is gradually compensated for once it is noticed, and successive trials are performed. This motor adaption enables us to produce accurate movements. When visual shifts are removed, an error in the opposite direction of the deviation is observed. This after-effect error can also be compensated for if feedback is available. We are studying the neural basis of the motor adaptation in animal models.
Ohbayashi M. Inhibition of protein synthesis in M1 of monkeys disrupts performance of sequential movements guided by memory. Elife. 2020 Feb 10;9 PubMed Central PMCID: PMC7010406.
Ohbayashi M, Picard N, Strick PL. Inactivation of the Dorsal Premotor Area Disrupts Internally Generated, But Not Visually Guided, Sequential Movements. J Neurosci. 2016 Feb 10;36(6):1971-6. PubMed Central PMCID: PMC4748079.
Ohbayashi M, Ohki K, Miyashita Y. Conversion of working memory to motor sequence in the monkey premotor cortex. Science. 2003 Jul 11;301(5630):233-6. PubMed PMID: 12855814.
Tomita H, Ohbayashi M, Nakahara K, Hasegawa I, Miyashita Y. Top-down signal from prefrontal cortex in executive control of memory retrieval. Nature. 1999 Oct 14;401(6754):699-703. PubMed PMID: 10537108.
Machiko Ohbayashi, Ph.D.
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Machiko Ohbayashi, Ph.D.
Department of Neurobiology & Systems Neuroscience Center
University of Pittsburgh School of Medicine
4070 Biomedical Science Tower-3
3501 Fifth Ave, Pittsburgh, PA15261