The Mechanics of Stopping Our Movements
Explore how our brains manage to stop movements effectively.
― 8 min read
Table of Contents
- What is Action Cancellation?
- Why Some People Struggle with This
- How Does the Brain Control Stopping Movements?
- How Do We Test Action Cancellation?
- How Do We Differentiate Between Types of Trials?
- The Role of Muscle Activity in Stopping Actions
- What’s Happening in the Brain During Stopping?
- The Study: Putting It All to the Test
- Who Participated?
- The Stop-Signal Task in Depth
- How Did the Task Work?
- Measuring Muscle Activity
- Looking at Brain Activity
- What Did the Study Find?
- Behavioral Findings
- Muscle Activity Results
- Brain Activity Insights
- Summing It Up: The Importance of Understanding Action Cancellation
- Why Should We Care?
- Original Source
- Reference Links
Movement is a big part of our daily lives. Whether we are walking, typing, or even just waving to a friend, our brains are constantly working to manage our movements. One key process that helps us control our actions is called "Response Inhibition." This is a fancy way of saying that our brains can tell our bodies when to stop doing something, especially if we didn't plan for it. Just think of it as your brain hitting the brakes while you’re driving when it sees a stop sign it didn’t expect.
What is Action Cancellation?
When we talk about action cancellation, we mean stopping a movement that we’ve already started. Imagine you’re about to take a bite of a cookie but suddenly realize you're on a diet. In that moment, your brain must do a quick “nope” and prevent your hand from reaching the cookie. This ability to stop actions is super important. If we didn’t have it, we’d constantly be running into walls or spilling drinks.
Why Some People Struggle with This
Some people have trouble with action cancellation. Conditions like Parkinson's disease, ADHD, OCD, PTSD, and schizophrenia can make it harder for individuals to stop their movements. Even as we age, many of us find it increasingly difficult to stop ourselves when needed. So, there’s a chance that one day, you might try to wave goodbye but just sort of freeze mid-wave-awkward!
How Does the Brain Control Stopping Movements?
The brain has special pathways that help with stopping movements. These pathways are like highways in your brain that send messages from one part to another. There are two main highways involved in stopping: the indirect pathway and the hyperdirect pathway. They start in the outer part of the brain and make their way down to the areas that control movement.
Indirect Pathway: This pathway is like a slow, scenic route that takes its time to think about things. It starts in a region called the pre-supplementary motor area and takes a winding path through different parts of the brain before getting to the movement control area.
Hyperdirect Pathway: This is the fast lane. It starts in a different area called the inferior frontal gyrus and zooms straight to the movement control area without many stops along the way.
Researchers are still working to figure out exactly how these pathways work together to help us stop our movements effectively.
How Do We Test Action Cancellation?
To study how well people can stop their movements, researchers often use a task called the Stop-Signal Task (SST). Here’s how it works:
- In the task, participants usually start with a go signal that tells them to do something, like press a button.
- Sometimes, right after the go signal, a stop signal appears, and participants have to cancel their movement in response to this signal.
But here’s the kicker: the stop signal doesn’t show up too often, which means it’s a surprise! This surprise factor can confuse things since participants need to pay attention not only to the stop signal but also to their original task.
How Do We Differentiate Between Types of Trials?
In research, they compare different types of trials:
- Go Trials: When participants press the button as expected.
- Stop Trials: When there’s a stopping signal, and they need to cancel their action.
- Ignore Trials: Where a signal appears, but participants should just ignore it and continue with their actions.
By looking at how participants perform in these scenarios, researchers can gather insights about action cancellation.
Muscle Activity in Stopping Actions
The Role ofTo really understand what’s going on in our bodies when we stop moving, researchers look at muscle activity. They use a technique called electromyography (EMG) to see how our muscles respond. It’s like using a superhero radar that picks up signals from our muscles.
When someone tries to stop a movement but still shows signs of muscle activity, it’s called a “partial response.” It’s like when you’re trying to hold back a sneeze-you can feel your muscles working, but you don’t end up sneezing. These partial responses can give scientists clues about how our bodies try to stop movements.
What’s Happening in the Brain During Stopping?
In addition to EMG, researchers also use brain imaging techniques like functional near-infrared spectroscopy (fNIRS) to see how different areas of the brain are activated when people are stopping their movements. This technique lets scientists peek into the brain’s activity when people make decisions to stop or continue.
The Study: Putting It All to the Test
In a recent study, participants were asked to press buttons with both hands when they saw a go signal. After that, sometimes a stop signal would appear, and they had to cancel one hand while continuing with the other. There were also ignore signals that they just had to overlook. This way, researchers could look at different muscle and Brain Activities during stopping and ignoring trials.
Who Participated?
The study involved 30 participants who had no significant neurological or psychiatric issues. After some careful screening, 29 participants were included. They got a bit of a reward for their time-either research credits or some cash.
The Stop-Signal Task in Depth
How Did the Task Work?
The task included various types of trials:
- Go Trials: Participants pressed both buttons quickly when presented with two green arrows.
- Stop Trials: One of the arrows would change color after a delay, signaling participants to stop using that hand but continue with the other.
- Ignore Trials: One arrow would change to a different color and participants should just ignore it but keep pressing both buttons.
The study used a staircase method to adjust the timing of the stop signals so that participants faced challenges that were just right. If they stopped successfully, the timing would speed up; if they failed, it would slow down, keeping the balance.
Measuring Muscle Activity
Using EMG, researchers could see which muscles fired up when participants attempted to stop. They looked for moments where muscle activity happened even without a visible movement, identifying those partial responses and their importance to the task.
Looking at Brain Activity
Using fNIRS, the study measured changes in oxygen levels in different parts of the brain. Increased oxygen levels usually mean that part of the brain is working hard. They focused on three key areas in the brain that are important for action stopping: the pre-supplementary motor area, and the left and right inferior frontal gyri. This is where all the action happens!
What Did the Study Find?
Behavioral Findings
The results showed that when participants attempted to stop their movements, their reaction times (how quickly they responded) were slower. For successful stop trials, they took longer compared to regular go trials. The same happened in ignore trials, indicating that even ignoring a signal takes time.
Muscle Activity Results
The study found that participants who showed partial responses during stopping trials had slower reaction times. It suggests that their brains were working harder to halt the movement. On the flip side, successful stop trials without partial responses were more efficient.
Brain Activity Insights
In analyzing brain activity, researchers found that the pre-supplementary motor area showed greater activity during successful stop trials compared to ignore trials. Meanwhile, the inferior frontal gyri didn’t show much difference between the two. This could mean that while the pre-supplementary motor area is crucial for stopping actions, the inferior frontal gyri might be more about paying attention rather than stopping.
Summing It Up: The Importance of Understanding Action Cancellation
Understanding how we stop our movements matters for many reasons. It helps us grasp how our brains work during day-to-day activities and can assist in understanding problems related to movement control in various mental health conditions.
Why Should We Care?
We care because knowing how these mechanisms work can lead to better treatments for those who struggle with stopping their actions. It can also improve methods of training for tasks that require quick reactions and responses. Plus, it can help us understand how aging affects our ability to control movements.
So, the next time you catch yourself waving goodbye only to realize you’re stuck midway, remember that your brain is wrestling with stopping and going-just like a traffic light in your head! And hey, while you’re at it, if your hand insists on reaching for that cookie, and your brain says “stop,” just know it’s not just you-it’s science!
Title: Cortical contributions to attentional orienting and response cancellation in action stopping
Abstract: Action cancellation involves the termination of planned or initiated movement. Contemporary models of action cancellation, such as the Pause-then-Cancel model, propose that this occurs via a two-stage process, initiated in the cortex by the pre-supplementary motor area (preSMA) and inferior frontal gyrus (IFG). Previous experimental work using electromyography (EMG) has identified that the cancellation of actions can involve the partial activation of the responding muscles, which does not result in an overt behavioural response. In this study, we used functional near-infrared spectroscropy (fNIRS) to investigate the neural correlates of these partial responses in a modified stopping task (a response- and stimulus-selective stop-signal task), controlling for the attentional effects that have long confounded action cancellation research by comparing responses to stop stimuli with those to ignore stimuli. We identified stopping-related activity in the preSMA but not the IFG, consistent with predictions of the Pause-then-Cancel model. Additionally, we observed increased preSMA activity in trials where no partial responses occurred, potentially due to the cumulative effect of different inhibitory processes in those trials. This study also highlights the utility of combining fNIRS and EMG in examining the cortical correlates and dynamic processes involved in action cancellation.
Authors: Sarah A Kemp, Sauro Salomoni, Pierre-Louis Bazin, Luke Pash, Rebecca J St George, Mark R Hinder
Last Update: Nov 8, 2024
Language: English
Source URL: https://www.biorxiv.org/content/10.1101/2024.11.08.622650
Source PDF: https://www.biorxiv.org/content/10.1101/2024.11.08.622650.full.pdf
Licence: https://creativecommons.org/licenses/by-nc/4.0/
Changes: This summary was created with assistance from AI and may have inaccuracies. For accurate information, please refer to the original source documents linked here.
Thank you to biorxiv for use of its open access interoperability.