Brain

Derailing Your Train of Thought

 Insights into how your thoughts run off the rails

 

You’re on the verge of something brilliant, a groundbreaking, game-changing idea, when suddenly a phone rings and… gone! Your train of thought derails and you’re left wondering what you were thinking about in the first place. Thanks to a new study of the brain’s electrical activity, UC San Diego researchers have a theory of just how that happens.

Neuroscientist and professor of psychology Adam Aron led the study, which suggests that the same brain system involved in interrupting body movement also interrupts cognition. The culprit appears to be one part of the brain’s overall stopping system—the subthalamic nucleus (STN).

In a study led by neuroscientist and professor of psychology Adam Aron, volunteers completed a memory task while their brain activity was analyzed via electroencephalography.
In a study led by neuroscientist and professor of psychology Adam Aron, volunteers completed a memory task while their brain activity was analyzed via electroencephalography. Photo: Nathalie Belanger

Previous research by Aron and colleagues has shown that the STN is engaged for a “broad stop”—the whole-body jolt experienced, for example, when you’re about to exit an elevator yet there’s another person waiting outside the doors.

The study analyzed signals from the scalp in 20 healthy subjects as well as signals from electrode implants in the STNs of seven people with Parkinson’s disease. (In Parkinson’s, the STN is the main target for therapeutic deep brain stimulation, or a “brain pacemaker.”)

Participants were asked to remember a string of letters while working on a memory task, and then were tested for recall. When participants were intentionally distracted by an audio clip of birdsong, however, monitors found that this unexpected sound manifested the same brain signature as physically stopping the body, engaging the STN. And the more the STN was engaged, the more it affected the subjects’ working memory, and they forgot the letters they had seen.

More study will determine a correlative or a causal link. If further research bears out the connection, researchers wonder if the phenomenon might be an adaptive feature of the brain, something that evolved long ago as a way to clear thoughts and refocus. Consider Aron’s prehistoric example: You’re walking along the African savannah gathering firewood, daydreaming about the day’s meal, when you hear a rustle in the grass. You make a sudden stop—your thoughts of dinner are gone as you shift focus to what made that noise… so you don’t become dinner yourself.

Aron’s findings may also give insights into the nature and treatment of Parkinson’s disease. The same brain system implicated in “over-stopping” or “freezing” movement in Parkinson’s patients might also be what keeps them over-focused, with a thought stream so stable it can be hard to interrupt. More speculatively, the STN may additionally play a role in conditions characterized by distractibility, like attention deficit hyperactivity disorder.