We are all guilty of doing it, and some of us pride ourselves for it. We text while we walk, send emails during lunch, and talk on the phone while we shop, making us self-proclaimed multitasking masters. But how exactly does the brain choose what visual and auditory stimuli to suppress when it comes to performing these various tasks?
According to a recent study published in the journal Nature, the brain’s prefrontal cortex, which is responsible for decision-making and complex behaviors like planning, saves information sent to the thalamic reticular nucleus (TRN) in order to choose how much visual or auditory information to process at a single time. The study’s results show how the brain uses the TRN “ as a switchboard to control the amount of information the brain receives, limiting and filtering out sensory information that we don't want to pay attention to,” said Dr. Michael Halassa, senior study investigator and neuroscientist, in the press release.
For the study, Halassa and his colleagues sought to explore how the brain filters out distracting or irrelevant information while multitasking by conducting a behavioral experiment on mice. The researchers monitored mice’s ability to successfully collect a milk reward by paying attention to a light or sound signal. This was designed to measure how well the mice’s prefrontal cortex could direct their focus between the two senses, sight and hearing.
To test this, the researchers distracted the mice with the opposing stimulus — when a mouse expected a flash of light to guide it to the milk reward, the researchers played a sound, and vice versa. At the same time, the researchers recorded electrical signals from the TRN and tracked the mice’s behavior. While all this happened, the researchers were also able to deactivate several regions of the mice’s brains with a laser beam.
The findings revealed that the distracted mice experienced a drop in their ability to collect the food reward — from 90 percent to 70 percent — even when the distracting stimulus was removed. Deactivating the prefrontal cortex disrupted TRN signaling and relegated mice to only random moments of success in obtaining the milk. The researchers also found that deactivating TRN neurons, while leaving the cortical regions activated, decreased the mice’s success with getting the food reward.
“This study shows how the circuits of the brain might decide which sensations to pay attention to,” said James Gnadt, program director at the NIH’s National Institute of Neurological Disorders and Stroke (NINDS), in the NIH news release.
The findings also support the fact that the prefrontal cortex is vital to functioning in our everyday lives. It gives us the ability to focus on one thing and suppress other distractions. However, that doesn’t mean that carrying out several activities at once makes us good multitaskers. Rather, our brains shift attention from one task to the other, causing us to be slower and not nearly as good at both activities — think talking on the phone while driving.
In a 2008 study published in the journal Brain Research , for example, researchers found that a person who was asked to judge whether sentences they heard were true or false experienced a 37 percent drop in their brain’s ability to focus. This study showed that oftentimes we’re not multitasking but simply paying less attention to the task at hand, which causes us to lose efficiency and quality in the way we carry them out.
So, while researchers may have found out how the brain multitasks, sometimes it’s good to just do one thing at a time.
Sources: Wimmer RD, Schmitt LI, Davidson TJ et al. Thalamic control of sensory selection in divided attention. Nature. 2015.
Just MA, Keller TA, and Cynkar J. A Decrease in Brain Activation Associated with Driving When Listening to Someone Speak. Brain Research. 2008.