For decades, experts believed that human attention was controlled almost entirely by the prefrontal cortex, the highly evolved outer layer of the brain.
However, a groundbreaking study by researchers at Johns Hopkins University reveals that our ability to filter out distractions actually relies on a tiny, evolutionarily ancient cluster of neurons in the brainstem.
The federally funded study, published in Nature Communications, points to a foundational focus system shared by all vertebrates, including humans, birds, and fish.
Evolution’s hidden filter
Humans and animals constantly filter out background noise to survive, whether it is a person trying to follow a conversation in a loud restaurant or a predator tracking prey.
Because birds and fish can focus remarkably well without a highly developed cortex, the Johns Hopkins team decided to look deeper into the brain’s evolutionary history.
“If we really go back in evolution, for hundreds of millions of years, birds have had this ability, fish have had this ability,” said lead author Ninad Kothari, a postdoctoral fellow in the university’s Department of Psychological and Brain Sciences. “We were able to identify an evolutionarily old region in the brainstem which affords this ability.”
Turning off the “selection engine”
To test the circuit, researchers trained mice to focus on visual cues directly in front of them while ignoring distracting lights appearing off to the side.
The mice performed perfectly until the researchers temporarily switched off the specific inhibitory neurons in the brainstem.
Without those cells active, the mice became instantly and severely distractible. Thorough testing ruled out any issues with the animals’ vision or movement; they simply lost the ability to prioritise information.
“This part of the brain is like an attentional selection engine,” explained senior author Shreesh Mysore, a neuroscientist who studies neural circuits tied to behaviour. “It helps solve the question: ‘What is the most important information I should pay attention to right now?’”
Clues for ADHD and autism
Crucially, the scientists found that the distraction effect was completely reversible. The very next day, when the neurons were switched back on, the mice regained their normal focus and could easily ignore even the strongest distractions.
This dramatic shift closely mirrors the sensory struggles faced by humans with attention disorders.
“A hallmark of ADHD is that even faint distractors draw attention away, and that’s exactly what we see here when these neurons are silenced,” Mysore noted.
All evidence suggests these exact same neurons exist in humans. While circuit-specific therapies are still in the early stages, the team hopes future studies will examine how these cells function in people with ADHD and autism spectrum disorders.
By targeting this ancient “focus switch,” scientists may eventually be able to develop far more precise medications and behavioural therapies.
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