Imagine you’re sitting at Starbucks, absorbed in a textbook, studying for exams. The faint blip of a barista dropping an empty cup may not draw your attention, but the crash of a mug on the floor probably will. Researchers, led by Hopkins neuroscience and Psychological and Brain Sciences assistant professor Shreesh Mysore, discovered some clues as to how the brain decides where to direct attention. The group says their findings could help people with attention deficit disorder, autism and schizophrenia.
Previous studies by Mysore focused on the effects of external physical stimuli on the optic tectum. The tectum is a paired structure located in the middle of the brain that contains a “map” of the space surrounding a person.
This means that if a telephone rang or a light flashed from point X in the space surrounding you, the tectum’s corresponding pixel X would fire neurons, or brain cells, in response. The firing neurons would cause you to pay attention and perhaps even turn your gaze to the telephone or light. The brain interprets all visual and auditory information the same way; it’s like comparing apples and oranges, but the brain just compares them as bananas.
The external physical stimuli the group researched include all this visual and auditory information. They discovered a type of neuron on the tectum called the switch-like neuron.
Imagine you’re back at Starbucks, not concentrating on anything in particular, and the barista drops an empty cup. The corresponding pixel on your tectum would probably not fire many neurons at all. This is because the “strength” of the external stimulus — in this case, the empty cup — is not strong enough to draw your attention away. In fact, your tectum’s pixel would not fire enough neurons until the strength of that external stimulus matches the strength of your boredom in Starbucks.
Now, let’s say the barista drops a ceramic mug. The clatter is a stimulus stronger than your boredom, and enough neurons fire that you pay attention to the noise.
In the new study published in Neuron, scientists looked at these switch-like neurons. They are useful because they immediately tell scientists whether a brain is paying attention to something or not.
“Switch-like neurons are a direct readout to what the brain is selecting,” Mysore said.
Mysore’s lab had only investigated external stimuli before, but in the new study they explored how internal stimuli — thoughts, judgments, intentions — compete with external ones.
To test this, the group took advantage of owls’ acute hearing and vision to use them as test subjects. They plugged wafer-thin electrodes into the awake owls’ tectums. Then, they sent a tiny electric current to the front part of owls’ brains called the gaze field. This current served as the internal stimulus, causing the owls to “intentionally” focus on something. Next, the scientists showed the owls a series of dotted images and played some noise bursts.
They discovered two things from this experiment:
First, internal stimuli (i.e., an intention to do something) cause you to favor the stimulus you want to focus on. Returning to Starbucks, imagine you are intensely studying your textbook. Your intention, the internal stimulus, is to focus on your book, the external stimulus. A barista dropping an empty cup won’t draw your attention away, and perhaps even the clatter of a mug won’t distract you. This is because your intention to focus has increased the “strength” of your textbook, and only something much stronger, such as a man screaming at the barista, will draw your attention. Your intention makes you less likely to be distracted.
Second, the zone of uncertainty decreases dramatically. The zone of uncertainty exists because the brain cannot always interpret the strength of different stimuli in the world exactly.
“We are constantlyfaced with a giant set of choices,” Mysore said. There is always room for error in how the brain interprets the strength of different stimuli.
Scientists found that internal stimuli — in this study, the electrical current — decrease this zone of uncertainty to a third. This means that the brain can better interpret the strength of different stimuli.
At Starbucks, we may not usually know whether dropping a plastic spoon or a paper napkin is the stronger stimulus.
However, our intention to study the textbook automatically helps our brain better distinguish the strengths and decide if we should pay attention to the dropped spoon or napkin.
The findings were all based on a neural level — there were no behavioral effects of the owls actually turnings their heads — but Mysore and his team built a computational model to predict what others should find in the brain during decisions of attention.
Howard Egeth, a professor in the department of psychological and brain sciences who studies attention and perception, said he was interested in the study.
“I’d want to see if some of these ideas of attention could be tested in mammals,” Egeth said.
Mysore intends to do just that. He plans to test mice, since they are mammals like humans.
These can lead to breakthroughs in understanding how attention disorders, such as deficit, autism and schizophrenia, develop.
Egeth believes that disorders can be overcome if the brain trains itself through control. “The common view of ADHD is that those children are especially susceptible to distractions,” he said. “I don’t know if that’s true but if so, then we want to explore whether the distractibility can be diminished by training.”
The causes of attention disorders are not fully understood now, but Mysore hopes his research can shed some light.
“All my experiments are geared towards how a normal brain functions in the context of attention,” Mysore said, “so that we might generate hypotheses as to what goes wrong in attention disorders.”
