By the time you’re finished reading this sentence, your brain will have rapidly assessed your surroundings 14 times to see if you should focus on something else. At least, that’s what new research suggests.
This is a departure from the way we typically think our brains hold attention—neuroscientists have suggested that neurons fire in a consistent stream when you’re focusing on one thing (like reading this Gizmodo blog, for instance). The new research suggests it instead has a kind of rhythm, where neurons become less active four times per second. During those little blips, the researchers suggest your brain visually checks your surroundings for something more important to pay attention to—like maybe something exceptionally threatening (a clumsy coworker about to douse you in hot coffee) or interesting (a dog in the office).
“Your brain’s checking in on the rest of environment to see if it should focus on something else,” Ian Fiebelkorn, a study author and cognitive neuroscientist at Princeton University, told Gizmodo. “Not that it unfocuses, but to see if something else beats out your current focus.”
It would make sense that the brain works that way, from an evolutionary standpoint. To survive in this world, you’ve got to be constantly aware of potential dangers.
“It’s like if you’re going after this shiny red apple in a tree, you want to know if something bigger or with sharper teeth is also going for that apple,” Fiebelkorn said. “Yeah, you’re focused on the apple. But not so focused you don’t see danger coming.”
The researchers measured this hidden brain rhythm in both humans and macaques, as noted in a pair of studies published Wednesday in Neuron. Both studies had a near-identical setup and included both humans and macaques who had electrodes implanted in their brains (the humans had received them as a part of epilepsy treatment). Either a monkey or human sat in front of a computer screen and was instructed to focus at one point in the middle of the screen. A camera monitored eye movements, so trials were thrown out if subjects shifted their gazes, which implied they’d also shifted their focus.
Then, very faint, nearly undetectable horizontal or vertical rectangles were briefly flashed on the screen. If a monkey detected the shape, it pulled a lever. (The macaques had previously been trained on this setup and rewarded with juice for successful lever pulls.) If a human detected the shape, he or she released the computer mouse button they’d been holding down. Throughout the trials, researchers used the electrodes to measure brain activity.
After analysing the data on how the brain’s neurons behaved while a person or macaque was focusing on one thing, the researchers saw near-identical dips in neuron activity at a frequency of four times per second in both monkeys and humans. That extreme similarity across species could mean this brain rhythm exists in other primates, too. At the very least, it’s good validation that monkey studies on attention and brain activity can be translated to humans.
“The monkey is the typical animal model for understanding attention,” Fiebelkorn said. “But I can’t think of another example where it’s been checked in humans with the same exact study. Neural activities we discover in monkeys should be true in humans, and this is a rare case where we verified that.”
But the fact that only people with epilepsy were included in the study is a definite limitation. The researchers did point out, though, that because results were so similar between humans and monkeys, it’s likely that the results would also be similar between humans with and without epilepsy.
Continuing to understand these brain rhythms could be useful for studying attention deficit disorders. The team speculated that people who get hyper-focused or very easily distracted at the hand of attention-deficit/hyperactivity disorder (ADHD) might be getting “stuck” in one of the two states of neuron activity described in their papers.
“In either case of ADHD, brain rhythms may be disturbed in some way and kids get locked into one state or the other, and not the regular attention processing we see laid out by our study,” said Sabine Kastner, a study author and cognitive neuroscientist also at Princeton. “It’s just our hypothesis, but it could be tested in kids or any population with an attention deficit.”