Department of Neurological and Vision Sciences, University of Verona, Verona, Italy.
Neuroscience. 2010 May 19;167(3):691-9. doi: 10.1016/j.neuroscience.2010.02.010. Epub 2010 Feb 11.
Brain mechanisms for action understanding rely on matching the observed actions into the viewer's motor system. Health professionals, who treat patients affected by movement disorders as dystonia, frequently see hyperkinetic action patterns characterized by an overflow of muscle co-contractions. To avert an overload of the motor system during observation of those actions, they might need to look at dystonic motor symptoms in a cool, detached way. To investigate whether visual expertise about atypical movement kinematics influences the viewer's motor system, we applied transcranial magnetic stimulation to clinicians and to naive subjects, while they observed handwriting actions performed with two different kinematics: fluent and non-fluent. Crucially, the latter movement pattern was easily recognized by the clinicians as a typical expression of writer's cramp, whereas it was unknown to the naive subjects. Results showed that clinicians had similar corticospinal activation during observation of dystonic and healthy writings, whereas naive subjects were hyper-activated during observation of dystonic movements. Hyper-activation was selective for the muscles directly involved in the dystonic co-contractions and inversely correlated with subjective movement fluency scores, hinting at a fine-tuned association between the breakdown of observed movement fluency and corticospinal activation. These findings suggest that observation of unusual pathological actions differently modulates the viewer's motor system, depending on knowledge, visual expertise, and ability in recognizing suboptimal movement kinematics.
大脑理解动作的机制依赖于将观察到的动作与观察者的运动系统相匹配。治疗受运动障碍影响的患者（如肌张力障碍）的健康专业人员经常会看到以肌肉过度协同收缩为特征的多动动作模式。为了避免在观察这些动作时运动系统过载，他们可能需要以冷静、超然的方式看待肌张力障碍的运动症状。为了研究关于异常运动运动学的视觉专业知识是否会影响观察者的运动系统，我们对临床医生和非专业受试者应用经颅磁刺激，同时观察两种不同运动学的手写动作：流畅和不流畅。至关重要的是，临床医生很容易将后者的运动模式识别为书写痉挛的典型表现，而这对于非专业受试者来说是未知的。结果表明，临床医生在观察肌张力障碍和健康书写时具有相似的皮质脊髓激活，而非专业受试者在观察肌张力障碍运动时则过度激活。过度激活是针对直接参与肌张力障碍协同收缩的肌肉的，并与主观运动流畅性评分呈负相关，这表明观察到的运动流畅性的破坏与皮质脊髓激活之间存在精细的关联。这些发现表明，观察异常病理动作会根据知识、视觉专业知识以及识别次优运动运动学的能力，以不同的方式调节观察者的运动系统。
