Evolutionary Brain Circuit Identified as Key to Filtering Distractions

Researchers have identified a specialized group of neurons within an ancient region of the brain that is fundamental to the ability to focus. These cells enhance attention by filtering out irrelevant stimuli and guiding the brain toward the most critical information.

The study, conducted on mice by scientists at Johns Hopkins University, highlights a neural system shared by all vertebrates, including humans. This discovery could pave the way for more precise therapeutic interventions for attention-related disorders.

“A hallmark of ADHD is that even faint distractors draw attention away—and that’s exactly what we observe when these neurons are silenced,” explained senior author Shreesh Mysore, a neuroscientist specializing in neural circuits and behavior. “However, once the neurons are reactivated the following day, the animal regains the ability to ignore even strong distractions.”

The federally funded research was recently published in Nature Communications and featured as an editorial highlight.

Ancient Neural Origins of Selective Attention

Living organisms constantly navigate competing sensory inputs, prioritizing essential data while ignoring noise. This capacity, known as selective spatial attention, is what allows a person to maintain a conversation in a loud environment or locate a specific individual in a crowd. Deficits in this mechanism are often linked to conditions such as autism and Attention-Deficit/Hyperactivity Disorder (ADHD).

Historically, scientists believed the prefrontal cortex—highly developed in humans and primates—was the primary driver of attention. However, this theory failed to explain how animals lacking a sophisticated prefrontal cortex still exhibit strong focus.

“If we look back through evolution, birds and fish have possessed this ability for hundreds of millions of years without a highly developed prefrontal cortex,” said lead author Ninad Kothari, a postdoctoral fellow in the Department of Psychological and Brain Sciences. “We have successfully identified an evolutionarily ancient region in the brainstem that facilitates this function.”

The Brainstem’s Role as an Attentional Filter

The team discovered that attention in mice is regulated by a network of inhibitory neurons in the brainstem, a feature present across the vertebrate spectrum. This line of inquiry stemmed from Mysore’s previous research involving birds, frogs, and turtles.

To validate the role of these neurons, the researchers implemented a spatial attention task. Mice were trained to respond to visual cues centered on a screen to receive a reward, requiring them to ignore distracting cues appearing on the periphery.

The mice consistently succeeded until the researchers temporarily deactivated the targeted brainstem neurons.

“Upon inactivating these neurons, the mice became hyper-distractible,” Kothari noted.

Mechanisms of Distraction

To ensure the results were not caused by visual impairment or motor dysfunction, the scientists conducted a series of control tests, ruling out both possibilities.

The data revealed that the animals specifically lost the ability to evaluate competing stimuli and prioritize the most relevant signal.

“The only impaired function was their ability to compare competing pieces of information and focus on the most important location,” Mysore stated. “This region acts as an attentional selection engine, essentially answering the question: ‘What is the most important information I should focus on right now?'”

Implications for ADHD and Autism Research

The research team now aims to determine how these neurons influence spatial attention across different species and whether they function identically in humans.

“Current evidence suggests these neurons are present in humans as well,” Mysore said. “An exciting hypothesis is that they play a similarly crucial role in human selective spatial attention.”

Future investigations may analyze the activity of these neurons in individuals with ADHD and autism. If these cells are found to function atypically in these populations, the discovery could lead to the development of more targeted pharmacological treatments and therapies.

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