Mirabella Giovanni, Pani Pierpaolo, Paré Martin, Ferraina Stefano
Department of Human Physiology and Pharmacology, University La Sapienza, Piazzale Aldo Moro 5, 00185, Rome, Italy.
Exp Brain Res. 2006 Sep;174(2):240-55. doi: 10.1007/s00221-006-0456-0. Epub 2006 Apr 25.
Behavioral flexibility provides a very large repertoire of actions and strategies, however, it carries a cost: a potential interference between different options. The voluntary control of behavior starts exactly with the ability of deciding between alternatives. Certainly inhibition plays a key role in this process. Here we examined the inhibitory control of reaching arm movements with the countermanding paradigm. Right-handed human subjects were asked to perform speeded reaching movements toward a visual target appearing either on the same or opposite side of the reaching arm (no-stop trials), but to withhold the commanded movement whenever an infrequent stop signal was presented (stop trials). As the delay between go and stop signals increased, subjects increasingly failed to inhibit the movement. From this inhibitory function and the reaction times of movements in no-stop trials, we estimated the otherwise unobservable duration of the stopping process, the stop signal reaction time (SSRT). We found that the SSRT for reaching movements was, on average, 206 ms and that it varied with the reaching arm and the target position even though the stop signal was a central stimulus. In fact, subjects were always faster to withhold reaching movements toward visual targets appearing on the same side of the reaching arm. This behavior strictly parallels the course of the reaction times of no-stop trials. These data show that the stop and go processes interacting in this countermanding task are independent, but most likely influenced by a common factor when under the control of the same hemisphere. In addition, we show that the point beyond which the response cannot be inhibited, the so-called point-of-no-return that divides controlled and ballistic phases of movement processing, lies after the inter-hemispheric transfer.
行为灵活性提供了非常丰富的动作和策略，但它也有代价：不同选项之间可能存在干扰。行为的自主控制恰恰始于在不同选项之间做出决定的能力。当然，抑制在这一过程中起着关键作用。在此，我们使用反指令范式研究了伸手动作的抑制控制。我们要求右利手的人类受试者对出现在伸手手臂同侧或异侧的视觉目标进行快速伸手动作（无停止试验），但在出现不频繁的停止信号时，要抑制已下达的动作（停止试验）。随着启动信号和停止信号之间的延迟增加，受试者越来越难以抑制动作。根据这种抑制功能以及无停止试验中动作的反应时间，我们估计了原本无法观察到的停止过程持续时间，即停止信号反应时间（SSRT）。我们发现，伸手动作的SSRT平均为206毫秒，并且即使停止信号是中央刺激，它也会因伸手手臂和目标位置的不同而变化。事实上，受试者总是能更快地抑制向出现在伸手手臂同侧的视觉目标的伸手动作。这种行为与无停止试验的反应时间进程严格平行。这些数据表明，在这个反指令任务中相互作用的停止和启动过程是独立的，但在同一半球的控制下，很可能受到一个共同因素的影响。此外，我们还表明，反应无法被抑制的点，即划分运动处理的受控阶段和弹道阶段的所谓不可返回点，位于半球间传递之后。
