Neuroscientists from the University of California, Berkeley, have tracked the process of a single thought as it journeys through the brain.
If it's a simple thought process (say, you're reading or repeating a word out loud), the visual and auditory cortexes light up in reaction to the stimuli (in this case, a word). Next, the prefrontal cortex boots up and interprets the meaning and then, lastly, the motor cortex is switched on in preparation for action. The whole process only takes just half a second.
If the thought is more complex (perhaps you are given a word and have to say the opposite), the brain can take several seconds to respond. The prefrontal cortex may involve other regions of the brain (for example, memory networks) before triggering the motor cortex. Often, the brain gets the motor cortex ready for action early on in the thinking process – which may explain why some of us have a tendency to speak before we think.
Overall, the research, published in Nature Human Behaviour, highlights just how important the prefrontal cortex is to the thinking process. Think of it as the conductor, coordinating the musicians (brain regions) in the orchestra (brain).
"Here we have eight different experiments, some where the patients have to talk and others where they have to push a button, where some are visual and others auditory, and all found a universal signature of activity centered in the prefrontal lobe that links perception and action,” Robert Knight, professor of psychology and neuroscience at UC Berkeley and paper co-author, explained in a statement. “It's the glue of cognition."
If the task was more difficult (ex. saying the antonym of a word), the brain needed two to three seconds to detect (yellow), interpret and find the answer (red), and respond (blue). Activity in the prefrontal lobe (red) coordinated the process. Video by Avgusta Shestyuk and Robert Knight, UC Berkeley.
To record the thought processes of 16 epilepsy patient undertaking eight different experiments, the researchers used a technique called electrocorticography (ECoG). Essentially, this involves placing several hundred electrodes on the brain's surface, where they record activity in the cortex. The good thing about ECoG is that it's more precise than alternative methods. The not-so-good thing is that it is highly invasive.
The scans also show that more complex tasks require more brain activity. Interestingly, this isn't because the individual neurons are working harder but because more areas of the cortex are activated.
So, what next? "This is the first step in looking at how people think and how people come up with different decisions; how people basically behave," said Avgusta Shestyuk, a senior researcher in UC Berkeley's Helen Wills Neuroscience Institute. "We are trying to look at that little window of time between when things happen in the environment and us behaving in response to it."