Cancelling actions in the blink of an eye
by Liisa Raud
Know the feeling when you are just about to say something and another person starts speaking instead, so you will swallow your tongue? Or when you are running on the street to catch a bus and suddenly, somebody cuts your way and you need to stop running to avoid an accident? It turns out that it takes about 150 ms to stop our actions, which is about twice the speed of the blink of an eye.
In the laboratory, stopping is investigated by asking volunteers to push a button as soon as they see a picture on the computer screen, and to stop their initiated button press when another picture appears. By measuring the electrical activity in the muscles, it was found that the muscle activity initiated after the first picture started to decline at about 150 ms after the second picture.
At the same time, the electrical activity in the brain was measured using electrodes attached to the head. It was found that the activity in the motor areas of the brain before stopping played a role in successful stopping as well. Further, this motor activity was different, if participants knew that they may need to stop in the future. For example, when running to catch a bus in a busy area with lots of other people and traffic, the motor areas in the brain are biased so that you are more likely to stop, if someone should cut your way. Thus, the readiness to stop makes a difference whether you avoid an accident or not.
Previously, it was thought that people with poor impulse control and related disorders, such as gambling or addiction, have impaired stopping networks in the brain. However, this was based on the idea that stopping is slow and effortful control process. Our new findings indicate that stopping may be fast and automatic. Thus, it remains to be seen whether people with impulse control disorders really have impaired stopping processes in the brain, or whether the problems arise from the networks that bias the motor regions in the brain before stopping.
In the laboratory, stopping is investigated by asking volunteers to push a button as soon as they see a picture on the computer screen, and to stop their initiated button press when another picture appears. By measuring the electrical activity in the muscles, it was found that the muscle activity initiated after the first picture started to decline at about 150 ms after the second picture.
At the same time, the electrical activity in the brain was measured using electrodes attached to the head. It was found that the activity in the motor areas of the brain before stopping played a role in successful stopping as well. Further, this motor activity was different, if participants knew that they may need to stop in the future. For example, when running to catch a bus in a busy area with lots of other people and traffic, the motor areas in the brain are biased so that you are more likely to stop, if someone should cut your way. Thus, the readiness to stop makes a difference whether you avoid an accident or not.
Previously, it was thought that people with poor impulse control and related disorders, such as gambling or addiction, have impaired stopping networks in the brain. However, this was based on the idea that stopping is slow and effortful control process. Our new findings indicate that stopping may be fast and automatic. Thus, it remains to be seen whether people with impulse control disorders really have impaired stopping processes in the brain, or whether the problems arise from the networks that bias the motor regions in the brain before stopping.