Distractions are everywhere, yet our brains are able to focus while filtering distracting stimuli. However, the neural mechanisms that enable us to respond to target stimuli while ignoring distractor stimuli are poorly understood. Now researchers at the University of California (UC), Riverside, have discovered the answer. Experimenting on mice, the researchers were able to pinpoint the area in the brain where distracting stimuli are blocked. The blocking disables the brain from processing these stimuli, which allows concentration on a particular task to proceed.
Their study, “Functional Localization of an Attenuating Filter within Cortex for a Selective Detection Task in Mice,” is published in the Journal of Neuroscience and led by Edward Zagha, MD, PhD, assistant professor of psychology at UC Riverside.
“An essential feature of goal-directed behavior is the ability to selectively respond to the diverse stimuli in one’s environment. However, the neural mechanisms that enable us to respond to target stimuli while ignoring distractor stimuli are poorly understood. To study this sensory selection process, we trained male and female mice in a selective detection task in which mice learn to respond to rapid stimuli in the target whisker field and ignore identical stimuli in the opposite, distractor whisker field,” the researchers wrote.
“We observed responses to target stimuli in multiple sensory and motor cortical regions,” stated Zagha. “In contrast, responses to distractor stimuli were abruptly suppressed beyond the sensory cortex.”
“Our discovery may have important implications for the understanding and treatment of neuropsychiatric diseases such as attention deficit hyperactivity disorder and schizophrenia,” Zagha noted. “By studying the mechanisms underlying the blocking of distracting stimuli we may be able to unravel the neural circuitry underlying attention and impulse control.”
“In expert mice, we used widefield Ca2+ imaging to analyze target-related and distractor-related neural responses throughout dorsal cortex. For target stimuli, we observed strong signal activation in primary somatosensory cortex (S1) and frontal cortices, including both the whisker region of primary motor cortex (wMC) and anterior lateral motor cortex (ALM). For distractor stimuli, we observed strong signal activation in S1, with minimal propagation to frontal cortex,” noted the researchers.
Zagha noted that scientists only have a growing understanding of how groups of neurons organize to mediate behaviors.
“But now we know exactly where to look in the brain, and we will be pursuing these questions in the future,” he said. “We know that when someone is highly distractible, their cortex is not sufficiently deploying the intentional signals needed to prevent the distractor stimuli from propagating into working memory or triggering a behavioral response. These processes—’gatekeepers’ of sensory signals—allow through only those signals that are task relevant. We believe this process is orchestrated by the prefrontal cortex; this is only one of the many possibilities we will be testing,” Zagha explained.
The researchers presented identical tactile stimuli to opposite sides of the mice’s whiskers in random order. They focused on their whiskers because they work like human fingertips in terms of sensitivity and exploration; their deflection activates brainstem pathways. Then they trained the mice to respond, via licking, to tactile stimuli on only one side and ignore the identical stimuli on the opposite side.
The team used transgenic mice that express fluorescent calcium sensors in cortical neurons, which allowed them to view brain activity with a camera that helped localize the process.
“When distracting stimuli are intentionally being ignored by the mice, we can now see where that distracting stimulus response is blocked,” Zagha said. “In the future, we would want to know how it is blocked.”
Zagha believes that the better they understand the circuits, the better they can design targeted treatments to improve impulsivity in disorders such as attention deficit hyperactivity disorder and schizophrenia.
The researchers plan to study which specific neural mechanisms prevent the propagation out of this first cortical region.
“The spatial precision of our finding gives us confidence that we know where to look in future studies to reveal how distractor stimuli are blocked, thereby allowing us to retain focus on the task at hand,” Zagha said.
The research team will also focus on understanding what the roles are of specific types of neurons and neural pathways involved, how these circuits get disrupted in neuropsychiatric disease, and how the neural system can be modulated to improve distractibility in human disease.