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The Neuroscience of Losing Your Train of Thought

The same brain system that stops physical movement may derail thought processes.

Source: wavebreakmedia/Shutterstock

We all know the experience of being in the middle of working on a project that requires focused concentration when suddenly ... you’re interrupted by the "Marimba" ringtone of an incoming call or someone in the room asking you a random question that breaks your concentration.

Just a few moments of distraction can require a couple of minutes to get your brain's electrical activity re-synchronized as you reorient yourself back to the task at hand by saying, “Now, where was I going with this thought process?”

One reason I do most of my writing in the predawn hours (before my 8-year-old daughter wakes up) is that my stream of consciousness gets easily disrupted when I’m writing. Like most people, once I’m interrupted I lose my train of thought, and it’s very difficult to get my thinking back on track.

Without distraction, I can crank out a blog post such as this one in about an hour and a half. However, once the sun is up—and I’m surrounded by the hustle and bustle of daily life—the same 1,500 words could easily take me four hours to write. Solid chunks of uninterrupted laser-like focus are the key to superfluidity of thought and prolific output for me as a writer.

The Same Brain System That Stops Physical Movement Interrupts Cognition

What is the neuroscience behind the phenomenon of losing your focus and train of thought once you're interrupted? A study released this morning by researchers at the University of California, San Diego (UCSD) offers some valuable clues.

The April 2016 study, “Surprise Disrupts Cognition Via a Fronto-Basal Ganglia Suppressive Mechanism,” was published today in Nature Communications. This research comes from the lab of Adam Aron at UCSD, who collaborated with other researchers at Oxford University in the UK. Aron is a professor of psychology in the UC San Diego Division of Social Sciences. Co-author Jan R. Wessel, is currently an assistant professor of psychology and neurology at the University of Iowa.

Wikimedia Commons/Public Domain
Source: Wikimedia Commons/Public Domain

The findings of this study suggest that the same brain system that is involved in interrupting, or stopping, movement in our bodies, also interrupts our cognition.

For this research, Aron honed in on one part of the brain's stopping system—the subthalamic nucleus (STN). The STN is a small lens-shaped cluster of densely packed neurons in the midbrain that is part of the basal ganglia system which inhibits movements.

Previous research by Aron and colleagues showed that the STN is engaged whenever slamming the brakes on a physical action is required. More specifically, the STN is responsible for the sort of whole-body jolt you experience that stops you dead in your tracks, which Aron describes as a "broad stop."

As an example, my daughter loves to scare me. One of her favorite tricks is to silently skulk her way into a hidden position close to my desk when I’m writing and scream “Boo!” Inevitably, I freeze in place and then I scream. We both crack up laughing, but my concentration is broken for at least 10 minutes.

From an evolutionary perspective, Aron gave this example of the STN inhibiting both movement and cognition in a statement:

”You're walking along one morning on the African Savannah, going to gather firewood. You're daydreaming about the meal you're going to prepare when you hear a rustle in the grass. You make a sudden stop—and all thoughts of dinner are gone as you shift your focus to figure out what might be in the grass. In this case, it's a good thing to forget what you had been thinking about.”

Aron believes that an unexpected event appears to clear out whatever you're thinking about. To test this in a lab, his study analyzed signals from the scalp with EEG in 20 healthy subjects as well as signals from electrode implants in the STN of seven people with Parkinson's disease. For a variety of reasons, the STN is the main target for therapeutic deep brain stimulation in Parkinson's disease.

All of the volunteers of this study were given a working memory task. On each trial, participants were asked to remember a string of letters and then were tested for recall. Most of the time, while they were holding the letters in mind, but before the recall test, the researchers played a simple, single-frequency tone in the background.

On a few of the trials, this sound was replaced by a birdsong segment, which wasn’t as startling as a "bang!" but was nonetheless unexpected and surprising, like a cellphone dinging or playing a ringtone. The volunteers' brain activity was recorded throughout the experiment, along with each person's accuracy in recalling the letters they'd been shown.

The results showed that unexpected events triggered the same cognitive brain signatures as outright stopping of the body. Both recruited the STN in the same way. Interestingly, the more intensely the STN was engaged and responded to the unexpected sound, the more it affected the subjects' working memory—causing them to lose their focus and train of thought regarding the information they were trying to keep in mind.

In a statement, Wessel said, "For now, we've 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."

The Link Between the Cerebellum, Midbrain, and Cerebral Function

Photo and illustration by Christopher Bergland
The juncture of the "Super 8" in this hypothetical sketch shows how an interruption in your midbrain ("the bridge") could stop the fluidity of thoughts between various brain hemispheres. (Circa 2010)
Source: Photo and illustration by Christopher Bergland

As a neuroscientist, my father, Richard Bergland, was fascinated with the connection between both hemispheres of the cerebellum (Latin for “little brain”) and both hemispheres of the cerebrum (Latin for “brain").

My dad always referred to the midbrain as “the bridge” between these two regions. Because of this, whenever I read about activity involving motor movements, cognitive function, and the midbrain, my inclination is to immediately assume the cerebellum might somehow be involved.

When I first read the new study by Aron and colleagues this morning, it instantly reminded me of other research that linked the cerebellum to “fear-evoked freezing" and other studies linking motor systems of the cerebral cortex with both fluid intelligence in adults and social thinking in 7-month-old infants.

For example, a 2010 study by neuroscientists at the Massachusetts Institute of Technology (MIT) identified that the basal ganglia and cerebellum are both major subcortical structures that influence not only movement but also cognition.

The researchers concluded that both structures receive input from and send output to the cerebral cortex. Although, basal ganglia and cerebellar loops have been assumed to be anatomically separate and to perform distinct functional operations; this research showed that the basal ganglia and cerebellum appear to form multisynaptic loops with the cerebral cortex.

The MIT neuroscientists found that the subthalamic nucleus (STN) of the basal ganglia has a substantial disynaptic projection to the cerebellar cortex. This pathway provides a means for both normal and abnormal signals from the basal ganglia to influence cerebellar function. (Cerebellar is the sister word to cerebral, and means "relating to or located in the cerebellum.")

Taken together, the researchers concluded that their results provide evidence of two-way communication between the basal ganglia and cerebellum. Therefore, these two subcortical structures may be linked together to form an integrated functional network.

Along these lines, in a 2014 study, neuroscientists from the University of Bristol reported a new discovery of a specific brain pathway leading to a highly localized part of the cerebellum (the pyramis) which causes the body to automatically freeze in place when surprised or threatened.

If neuroscientists can pinpoint how these neural pathways between the cerebellum, midbrain, and cerebrum work more thoroughly, it could lead to the development of effective treatments for human emotional disorders and cognitive dysfunctions.

The new study by Aron et al. does not mention the cerebellum. That said, as an educated guess based on previous research, I have a hunch that these findings may offer clues that help explain how the cerebellum fine-tunes cognitive function via the midbrain, much the same way it fine-tunes muscle movements. For the record, the cerebellar link to Aron's recent findings and previous cerebellar research is pure conjecture on my part.

Conclusions: Growing Evidence Links Physical Fluidity to Cognitive Flexibility

Although the role of the STN in stopping your body and interrupting your train of thought fits anatomical models of brain circuitry ... more research is needed, to determine if there's a causal link between the inhibitory activity observed in the STN and the disruption of fluidity in working memory.

An exciting possible future angle of investigation for Aron will be to see if the STN and associated circuitry plays a role in conditions characterized by distractibility, such as Attention Deficit Hyperactivity Disorder (ADHD). "This is highly speculative," Aron said, "but it could be fruitful to explore if the STN is more readily triggered in ADHD."

"The radically new idea is that just as the brain's stopping mechanism is involved in stopping what we're doing with our bodies it might also be responsible for interrupting and flushing out our thoughts," Wessel concluded. "It might also be potentially interesting to see if this system could be engaged deliberately—and actively used to interrupt intrusive thoughts or unwanted memories." Stay tuned for future cutting-edge research!

To read more on this topic, check out my Psychology Today blog posts:

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