Neural bottleneck that thwarts multi-tasking found
— Photo:K. Pichumani
SIMPLY TOUGH: We experience severe limitations when we try to drive and talk on a cell phone simultaneously.
IN OUR everyday lives, we seem to complete so many cognitive tasks effortlessly.
However, we experience severe limitations when we try to do even two simple tasks at once. This is known as dual-task interference.
Crippling inability
Vanderbilt neuroscientist Renι Marois says, "Why is it that with our incredibly complex and sophisticated brain, with 100 billion neurons processing information at rates of up to a thousand times a second, we still have such a crippling inability to do two tasks at once?"
"For example, what is it about our brain that gives us such a hard time at being able to drive and talk on a cell phone simultaneously?"
He, and another Vanderbilt neuroscientist Paul E. Dux have found that when it comes to handling two things at once, your brain, while fast, isn't that fast.
Brain regions identified
Researchers have long thought that a central "bottleneck" exists in the brain that prevents us from doing two things at once.
Dux and Marois are the first to identify the regions of the brain responsible for this bottleneck, by examining patterns of neural activity over time. Dux, a postdoctoral research associate in the Department of Psychology, said, "We were interested in finding where in the brain this bottleneck might be taking place."
Identifying the information bottleneck required the use of functional magnetic resonance imaging, or fMRI, an imaging technology that reveals the brain areas active in a given mental task.
Limited information
While fMRI is an excellent tool for identifying a particular area in the brain involved in a given task, it generally provides limited information about how that area responds over time.
To overcome this limitation, Dux and Marois rapidly sampled brain activity using fMRI while subjects were performing two demanding tasks. Evaluation of the data produced by this rapid sampling method allowed them to characterize the temporal pattern of activity in specific brain areas.
The two tasks consisted of pressing the appropriate computer key in response to hearing one of eight possible sounds and uttering an appropriate syllable in response to seeing one of eight possible images.
Different senses and motor responses were enlisted in order to ensure that any interference between the two tasks was not specific to a particular sensory or motor modality, but instead originated at a central information-processing bottleneck, according to a Vanderbilt University press release.
Neural activity
"We determined that the lateral frontal and prefrontal cortex, and also the superior frontal cortex (brain regions) responded to tasks irrespective of the senses involved, they were engaged in selecting the appropriate response, and, most importantly, they showed `queuing' of neural activity— the neural response to the second task was postponed until the response to the first was completed," Dux said.
Inability to process
The results revealed that the central bottleneck was caused by the inability of these regions to process the two tasks at once.
Both areas have been shown in previous experiments to play a critical role in cognitive control.
"Neural activity seemed to be delayed for the second task when the two tasks were presented nearly simultaneously - within 300 milliseconds of each other," Marois said.
"If individuals have a second or more between tasks, we did not see this delay." — Our Bureau
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