The ability to focus attention is not exclusive to humans or even to primates. Birds, reptiles, and even fish can direct their focus toward a specific target while filtering out distractions on the periphery. This ability has existed for at least hundreds of millions of years, yet it remains unclear which precise parts of the brain enable it.
In a new study on mice, published in Nature Communications, scientists from Johns Hopkins University claim to have identified a group of evolutionarily ancient neurons that play a “surprisingly critical” role in selective spatial attention. The findings were detailed in Nature Communications.
Given our shared evolutionary history with mice, there is a chance that similar neurons exist in the human brain. Although mice, like humans, are mammals, there are many differences between their brains and ours. The fact that something works a certain way in mice does not guarantee it will function the same in humans.
However, ethics committees permit experiments on mice that would never pass review for human subjects, meaning mice often serve as one of the best tools for studying the human brain.
In this instance, the researchers believe their findings could have implications for understanding and treating attention-related issues, such as attention deficit hyperactivity disorder (ADHD).
“Animals possess a remarkable ability to select and prioritize the highest-priority stimulus in space while ignoring lower-priority distractions,” the authors explain.
This ability is known as selective spatial attention, and it is crucial in all aspects of animal life: finding food, caring for offspring, competing with rivals, and resisting the urge to scroll through an Instagram feed while trying to focus on reading exciting new scientific studies.
Selective spatial attention is compromised in several human conditions, including ADHD and schizophrenia.
“A hallmark of ADHD is that even minor distractions pull attention away—and that’s exactly what we observe when these neurons are suppressed,” says neuroscientist Shreesh Mysore from Johns Hopkins University, discussing his team’s research on mice. “But the very next day, when the neurons are reactivated, the same animal can ignore distractions, even very strong ones.”
The inhibitory neurons in question are part of the parabigeminolateral tegmental inhibitory complex, or PLTi.
These neurons use GABA, an inhibitory chemical messenger in the central nervous system (whose dysfunction, incidentally, has been linked to ADHD).
They play a role in modulating the superior colliculus, a key component of the mammalian midbrain—a region involved in integrating visual and other signals to build a spatial map of the surroundings and direct our attention.
Located in the brainstem, these neurons form a network that is largely conserved across birds, fish, and mammals.
“When we deactivate these neurons, the mice become highly distractible,” explains Ninad Kothari.
In a task designed to test their attention, mice had to focus on images on a touchscreen in front of them. They were rewarded for touching the screen with their noses while ignoring distractors appearing elsewhere on the screen.
But when the researchers introduced a virus into the mice’s brains to temporarily disable the PLTi, their concentration significantly deteriorated.
“The only thing that was impaired was their ability to process competing information, compare it, and zero in on the area containing the most important information,” says Mysore. “This part of the brain acts like a selective attention mechanism. It helps answer the question: ‘What’s the most important information I need to pay attention to right now?'”
The prevailing view has been that selective spatial attention is controlled by a more recently evolved brain region shared by humans and other primates. However, this study suggests a much older area might play a key role.
“All current evidence points to these neurons existing in humans as well,” says Mysore.
Of course, far more research will be needed to confirm whether these neurons function similarly in humans. Still, this discovery could help shed light on what shapes our strengths—and challenges—in directing attention.
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