ADHD and Impulse Control

STOP/GO NEURONS PROVIDE IMPULSE CONTROL

The April issue of Psychological Review published a study based on a theoretical model proposed by neuroscientist Gordon Logan and physicist William Cowan. Vanderbilt University psychologists, Jeff Schall and Leanne Boucher co-author this study. Their data attempt to provide insight into the relationship between the brains physical movement control systems and its relationship to ‘mind.’

The theoretical model developed by Cowan and Logan posited that physical impulse control involved two independent processes: one telling stop and the other telling us to go – similar to a racing scenario.

According to co-author, Jeff Schall, the research “…helps explain the impulsivity of people with attention deficit and hyperactivity disorder.”

The researchers used physiological data collected from monkeys that were taught to look at a visual target unless a stop signal activated. With the stop signal activated, the monkeys ceased looking at the target. These stop/go tasks produced quantified data correlating to the monkeys’ abilities to stop a planned action.

The researchers found that while go processes and stop processes are independent processes, they are actually carried out on complex network of interacting neurons, which is rather paradoxical.

“For most of the race, ’stop’ and ‘go’ act independently.’Stop’ interacts with ‘go’ very briefly–it basically has one chance to knock ‘go’ out of the race. It needs to react strongly and rapidly after the stop signal is given,” Schall said. “If it is successful, the subject stops his or her planned movement. If it is unsuccessful, the subject goes ahead. In individuals with impulse control problems, ’stop’ more often loses the race.”

In relation to ADHD, Login cites, “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. We think of people who are impulsive as acting too quickly. 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.”

In a stretch, the researchers imply that their data are some of the first to bridge cognitive research and neurophysiology–making the connection between the mind and the brain.

“For years, one group of researchers was looking at what neurons are doing, and a different group of researchers was looking at what people are doing,” said Palmeri, associate professor of psychology. “Now there is a point of contact between decades of important research in neurophysiology and decades of important research in cognitive modeling. Research that has very different histories and approaches is really starting to come together.”

To be realistic, I suppose that research, insight, and information, must advance in stages. However, applying this model doesn’t seem as progressive as the authors imply. It doesn’t advance our knowledge on a practical level as we’ve known for years about the stop/go processes and impulse control of ADHD. “The ‘stop’ too slowly” comment by Login is nothing new; it’s been stated for years. Their model simply confirms what developmental psychologists and occupational therapists have been proposing for years based on field observations. The researchers’ correlations to neuronal activity aren’t especially new either.

Perhaps a better holistic model may be obtained from Marvin Minsky’s book (1988), The Society of Mind which offers a better model consisting of what Minsky calls agents. Minsky theorizes that human intelligence is the result of interactions of simple parts called agents. These agents are themselves mindless. The interactions between the simple agents constitute the “Society of Mind.” It definitely encompasses the ‘stop/go’ model espoused by the Vanderbilt scientists and predates it by almost ten years.

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