The discovery, made in mice by researchers at Johns Hopkins University, points to a brain system that is shared by all vertebrates, including humans. The findings could eventually help researchers develop more precise treatments for attention-related 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," said senior author Shreesh Mysore, a neuroscientist who studies neural circuits tied to behavior. "But the very next day, when the neurons are turned back on, the same animal can ignore distractors again, even very strong ones."

The federally funded study was recently published in Nature Communications and selected as an editorial highlight.

Ancient Brain Region Linked to Attention

Humans and other animals constantly sort through competing information, focusing on what matters most while ignoring less important signals. This ability, known as selective spatial attention, allows people to follow a conversation in a noisy room or spot a friend in a crowded space. Difficulties with this process are associated with conditions such as autism and Attention-Deficit/Hyperactivity Disorder (ADHD).

For many years, scientists believed that attention was controlled primarily by the prefrontal cortex, a brain region that is especially developed in humans and other primates. However, that explanation leaves an important question unanswered. Many animals can also focus their attention despite lacking a highly developed prefrontal cortex.

"If we really go back in evolution, for hundreds of millions of years, birds have had this ability, fish have had this ability. And they do not typically have a highly developed prefrontal cortex, so how does the brain solve this problem?" 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."

Brainstem Neurons Act as a Focus Filter

The researchers found that attention in mice is also regulated by a network of inhibitory neurons located in the brainstem. These neurons are present across vertebrate species, including birds and fish. The decision to investigate these cells in mice grew out of earlier work by Mysore and other researchers studying birds, frogs, and turtles.

To test the neurons' role, the team designed an attention task similar to those used in human studies. Mice viewed visual cues on a screen and were rewarded when they correctly responded to information displayed directly in front of them while ignoring distracting cues appearing off to the side.

The mice performed the task successfully until researchers temporarily switched off the brainstem neurons.

"When we inactivate these neurons, the mice become hyper distractable," Kothari said.

Distraction Increases When Neurons Are Disabled

The scientists conducted additional tests to determine whether the mice were failing because of vision problems or movement difficulties. Those possibilities were ruled out.

Instead, the experiments showed that the animals specifically lost the ability to evaluate competing information and focus on the most relevant signal.

"The only thing impaired was their ability to take the competing pieces of information, compare them, and pay attention to the location with the most important information," Mysore said. "This part of the brain is like an attentional selection engine. It helps solve the question: 'What is most important information I should pay attention to right now?'"

Potential Implications for ADHD and Autism

The researchers now want to better understand exactly how these neurons influence spatial attention across vertebrate species and whether they serve a similar function in humans.

"All the evidence to date suggests that these neurons exist in humans too," said Mysore. "But are they responsible for selective spatial attention in humans? An exciting hypothesis is that they play a crucial role."

Future studies may examine the activity of these neurons in people with ADHD and autism. If researchers find that the cells function differently in those conditions, the discovery could help guide the development of more targeted medications and therapies.

The study's authors also include Arunima Banerjee, Qingcheng (Jessica) Zhang, and Wen-Kai You of Johns Hopkins University.