Scientists may have found the brain’s attention switch and it instantly produced ADHD-like symptoms when turned off
The standard explanation for how attention works in the human brain has been, for decades, a story about the prefrontal cortex. This region, located at the front of the brain and highly developed in humans and primates, is where executive control lives. When you force yourself to stay focused on a difficult task in a noisy room, ignoring the conversations happening around you and the movement at the edge of your vision, the prefrontal cortex is generally credited with making that possible.
The problem with this explanation has always been fish.
Fish have brains. Fish can focus. Fish can track a specific target while ignoring other moving objects in their visual field, demonstrating something that looks functionally identical to selective spatial attention. And fish do not have a meaningfully developed prefrontal cortex. Neither do birds, frogs, or turtles. But all of them show the same capacity to filter distractions and lock onto what matters most, a capacity that the prefrontal cortex explanation cannot account for.
A new study from Johns Hopkins University, published in Nature Communications has found the structure that explains it. Deep in the brainstem, in a circuit so old it predates the mammalian cortex by hundreds of millions of years, researchers identified a small cluster of inhibitory neurons that functions as the brain’s primary attention filter. When they silenced those neurons in mice, the animals became immediately and profoundly distractible in a way that precisely matched the defining behavioral signature of ADHD. When they reactivated the neurons the following day, normal focus returned completely.
What the brain is actually doing when you pay attention
Selective spatial attention is the cognitive process that decides, at any given moment, which piece of incoming information deserves to be processed and which can be ignored. It is what allows you to track one person’s voice in a crowd, or notice the one unusual object in a familiar room, or keep your eyes on the road while filtering out the billboard on the side of it.
For this system to work, the brain cannot simply amplify the signal it wants to attend to. It has to actively suppress the signals it does not. The brain is constantly receiving input from every direction, and without a mechanism for ranking those inputs and suppressing the lower-ranked ones, everything becomes noise.
The neurons the Johns Hopkins team identified are inhibitory neurons in the brainstem, located in a structure called the superior colliculus. They form a circuit that the researchers describe as an attentional selection engine, a competitive system that constantly evaluates incoming sensory signals against each other and enforces a decision: this location matters, those locations do not.
“This part of the brain is like an attentional selection engine,” said senior author Shreesh Mysore. “It helps solve the question: what is the most important information I should pay attention to right now?”
The experiment: switching focus on and off
The researchers trained mice on an attention task designed to mirror the tests used in human ADHD studies. The mice viewed visual cues on a screen and were rewarded for correctly responding to information displayed directly in front of them while ignoring distracting stimuli appearing to the side. Once the animals had learned the task reliably, the researchers used a technique to temporarily silence the brainstem neurons.
The effect was immediate. Animals that had been performing normally on the task became unable to filter out even weak peripheral distractions. They were pulled toward irrelevant stimuli at the edges of their visual field and lost the ability to hold focus on the primary target. Their behavior matched what is clinically observed in people with ADHD: not a failure of vision, not a failure of motivation, but a specific failure of the competitive evaluation process that ranks incoming signals and suppresses the ones that do not matter.
To confirm that the problem was attentional rather than sensory or motor, the team ran a series of control tests. The mice showed no impairment in vision. They showed no difficulty with movement. The only thing that changed was their ability to compare competing stimuli and select the one that deserved focus.
“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.
The next day, the researchers reactivated the neurons. Focus returned. The same animals that had been hyper-distractible hours earlier were again able to ignore strong distractions and hold attention on the task.
Why this overturns the leading theory
The prefrontal cortex account of attention has always struggled with an evolutionary inconsistency. If selective spatial attention is a product of the prefrontal cortex, it should be limited to, or at least much stronger in, animals with a well-developed one. But the evidence does not support that. Birds demonstrate remarkably precise attentional selection. So do frogs. So do fish. These animals have brainstems. They do not have prefrontal cortices that would qualify as the supposed seat of attention.
Lead author Ninad Kothari, a postdoctoral fellow at Johns Hopkins, put the question directly: “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?”
The brainstem circuit the team identified answers that question. It is present across all vertebrate species, from fish to mice to, almost certainly, humans. It predates the prefrontal cortex by an evolutionary margin measured in hundreds of millions of years. And it appears to implement the core function of attentional filtering directly, without requiring the cortex to manage it.
This does not mean the prefrontal cortex plays no role in attention. It almost certainly does, particularly in the kinds of complex, goal-directed, abstract attention that humans engage in. But it appears the fundamental mechanism of filtering competing spatial signals and selecting the most relevant one is not a prefrontal invention. It is a brainstem function that evolution preserved across virtually every vertebrate lineage because it was too useful to lose.
What this means for ADHD
The clinical implications depend on a question the researchers have not yet answered: do these neurons work the same way in humans, and do they function differently in people with ADHD?
The evidence so far is indirect but suggestive. The same brainstem structure exists in humans. The behavioral profile produced by silencing the neurons in mice, sudden onset of hyper-distractibility that disappears when the neurons are reactivated, matches the core attentional deficit in ADHD with a precision that has not previously been achievable in a single targeted experiment.
“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 said. “But the very next day, when the neurons are turned back on, the same animal can ignore distractors again, even very strong ones.”
Current ADHD medications work primarily on the dopamine and norepinephrine systems of the prefrontal cortex. They are effective for many people and largely ineffective for others. If the brainstem circuit identified in this research turns out to be the actual site of dysfunction in at least some ADHD cases, then the drugs most commonly prescribed for the condition may be targeting the wrong part of the brain entirely. Not because the prefrontal cortex is irrelevant, but because the primary engine of attentional selection may sit somewhere else.
The researchers plan to examine how these neurons behave across vertebrate species and whether they play a comparable role in human attention. If that investigation confirms what the current findings suggest, it would represent one of the more significant reorientations in the neuroscience of attention in decades, and potentially the opening of a new target for treatments that have so far remained elusive.
Source
Ninad B. Kothari, Arunima Banerjee, Qingcheng Zhang, Wen-Kai You, Shreesh P. Mysore. “Evolutionarily old brainstem neurons are required for the control of selective spatial attention.” Nature Communications, June 24, 2026.
DOI: 10.1038/s41467-026-72340-9
