Davranche Karen, Tandonnet Christophe, Burle Boris, Meynier Chloé, Vidal Franck, Hasbroucq Thierry
Laboratoire de Neurobiologie de la Cognition, CNRS et Université de Provence, Marseille, France.
Eur J Neurosci. 2007 Jun;25(12):3766-74. doi: 10.1111/j.1460-9568.2007.05588.x.
Single-pulse transcranial magnetic stimulations (TMSs) of the motor cortex (M1) were performed in order to decipher the neural mechanisms of time preparation. We varied the degree to which it was possible to prepare for the response signal in a choice reaction time (RT) task by employing either a short (500 ms) or a long (2500 ms) foreperiod in separate blocks of trials. Transcranial magnetic stimulations were delivered during these foreperiods in order to study modulations in both the size of the motor evoked potential (MEP) and the duration of the silent period (SP) in tonically activated response agonists. Motor evoked potential area and silent period duration were assumed to reflect, respectively, the excitability of the cortico-spinal pathway and the recruitment of inhibitory cortical interneurons. Shorter reaction times were observed with the shorter foreperiod, indicating that a better level of preparation was attained for the short foreperiod. Silent period duration decreased as time elapsed during the foreperiod and this decrement was more pronounced for the short foreperiod. This result suggests that time preparation is accompanied by a removal of intracortical inhibition, resulting in an activation. Motor evoked potential area decreased over the course of the short foreperiod, but not over the long foreperiod, revealing that time preparation involves the inhibition of the cortico-spinal pathway. We propose that cortico-spinal inhibition secures the development of cortical activation, preventing erroneous premature responding.
为了解析时间准备的神经机制，我们对运动皮层（M1）进行了单脉冲经颅磁刺激（TMS）。在选择反应时（RT）任务中，我们通过在不同的试验组块中采用短（500毫秒）或长（2500毫秒）的前刺激期，来改变为反应信号做准备的程度。在这些前刺激期内进行经颅磁刺激，以研究紧张性激活反应激动剂中运动诱发电位（MEP）的大小和静息期（SP）的持续时间的调制情况。运动诱发电位面积和静息期持续时间分别被认为反映了皮质脊髓通路的兴奋性和抑制性皮质中间神经元的募集情况。较短的前刺激期观察到较短的反应时间，表明短前刺激期达到了更好的准备水平。静息期持续时间在前刺激期随着时间的推移而减少，并且这种减少在短前刺激期更为明显。这一结果表明，时间准备伴随着皮质内抑制的消除，从而导致激活。运动诱发电位面积在短前刺激期过程中减小，但在长前刺激期没有减小，这表明时间准备涉及皮质脊髓通路的抑制。我们提出，皮质脊髓抑制确保了皮质激活的发展，防止错误的过早反应。
