Derailed train of thought? Blame brain's stopping system

Did you forget what you were about to say when the phone rang? Your brain's stopping system may be to blame!
The same brain system that is involved in interrupting, or stopping, movement in our bodies also interrupts cognition which derails your train of thought, a new study has found.
The findings may give insights into Parkinson's disease, researchers from University of California in the US and Oxford University in the UK said.
The disease can cause muscle tremors as well as slowed-down movement and facial expression. Parkinson's patients may also present as the "opposite of distractible," often with a thought stream so stable that it can seem hard to interrupt.

The same brain system that is implicated in "over-stopping" motor activity in these patients might also be keeping them over-focused, researchers said.
The study focused particularly on one part of the brain's stopping system - the subthalamic nucleus (STN). This is a small lens-shaped cluster of densely packed neurons in the midbrain and is part of the basal ganglia system.

Earlier research had shown that the STN is engaged when action stopping is required. Specifically, it may be important for a "broad stop."
A broad stop is the sort of whole-body jolt we experience when, for example, we are just about to exit an elevator and suddenly see that there is another person standing right there on the other side of the door.

The study analysed signals from the scalp in 20 healthy subjects as well as signals from electrode implants in the STN of seven people with Parkinson's disease. The STN is the main target for therapeutic deep brain stimulation in Parkinson's disease.
All the volunteers were given a working memory task. On each trial, they were asked to hold in mind a string of letters, and then tested for recall.
Most of the time, while they were maintaining the letters in mind, and before the recall test, they were played a simple, single-frequency tone.
On a minority of trials, this sound was replaced by a birdsong segment - which is not startling like a "bang!" but is unexpected and surprising, like a cell phone chirping suddenly.

The volunteers' brain activity was recorded, as well as their accuracy in recalling the letters they had been shown.
The results show that unexpected events manifest the same brain signature as outright stopping of the body, researchers said.
"For now we have shown that unexpected, or surprising, events recruit the same brain system we use to actively stop our actions, which, in turn, appears to influence the degree to which such surprising events affect our ongoing trains of thought," said Jan Wessel from University of California.
The findings were published in the journal Nature Communications.