Impulsivity in the ADHD Brain
New Research Offers Insight Into Cause Of Impulsivity in ADHD
We have often felt sorry for those impulsive children who blurt out the first thing that comes to their mind when asked a question, especially if they are about to get into trouble. As most parents know, that first thing that comes out as the answer is usually a lie. And then the child has to spend the rest of the hour covering up the lie, that both he and his parents know is a lie. This is a classic scene of a child with ADHD getting into trouble because of his impulsivity.
As a remedy, we encourage parents to warn the child that they are about to be asked a very serious question, and that their honesty is absolutely required. And that the child is not to answer the question for 30 seconds after being asked, so that they can clearly think about what they want to answer and get it right the first time. This works.
But it is not what this article is about...
Impulsivity in ADHD
Impulsivity in ADHD is seen in two ways: (1) either doing or saying something without thinking first; or (2) not saying “no” to yourself, inhibiting yourself, when you ought to do so.
It seems that a person with impulsivity as a part of their ADHD has a normal ability to say “Go” at the neurological level, but their ability to say “No” or “Stop” comes just a fraction of a second slower. As a result, things are often done, or said, without much self-control practiced.
Vanderbilt Research on ADHD
There is some very interesting new research out of Vanderbilt University’s Center for Integrative and Cognitive Neuroscience that helps to explain impulsivity in ADHD. From their press release, here are the basics of the study:
"We think of people who are impulsive as acting too quickly," said Gordon Logan, one of the researchers. "Kids with ADHD are actually slower on the 'go' task than the control kids. It's not that they go too quickly; they stop too slowly."
"The research provides new insights into how the brain controls movements, which helps explain the impulsivity of people with attention deficit and hyperactivity disorder," according to study co-author Jeffrey Schall, E. Bronson Professor of Neuroscience. "It also shows how mathematical models can be used to discover how the brain produces thought and action."
Vanderbilt psychologists Leanne Boucher, Thomas Palmeri, Gordon Logan and Schall published the findings in the April issue of Psychological Review.
The new paper uses physiological data collected in Schall's laboratory to show how a theoretical model Logan developed more than 20 years ago is implemented by the brain.
"I developed the race model to explain behavior on a task called the stop signal task with a friend of mine, William Cowan, who is a theoretical physicist, in the 1980s," Logan, Centennial Professor of Psychology, said. Stop signal tasks measure an individual's ability to stop a planned action, like pressing a key on a keyboard or looking at a target, in response to a signal. "Our race model proposed that two independent processes were underway, one telling us to 'go' and one telling us to 'stop' in response to the stop signal.
"Applying the model to children's behavior revealed that stop signal task times are significantly longer in children with attention deficit and hyperactivity disorders than in other children," he said.
In this model, "go" and "stop" processes independently race one another - whichever one crosses the finish line first determines whether a movement is made or not. Though the model accurately explains behavior, it left neuroscientists scratching their heads. Their work found that 'go' and 'stop' processes are produced through a complex network of interacting neurons. If so, then how could 'go' and 'stop' be acting independently as required by the race model?
"The model proposes that there are two processes happening in our brain, one making us 'go' and another making us 'stop'," Boucher, a postdoctoral fellow, said. "However, as neurophysiologists, we know these processes are intricately linked, not independent.”
The findings are some of the first to bridge cognitive research and neurophysiology - making the connection between the mind and the brain.
For more information about this study visit the Vanderbilt website.
Press Release by Melanie Moran