Neuroscientists at the University of California, Berkeley have claimed to track a thought racing across the brain. The finding confirms how the prefrontal cortex coordinates complex interactions between different regions in the brain – to help us act in response to what we perceive (or, say things before we think).

In the study, the team recorded the electrical activity of neurons directly from the surface of the brain of 16 epilepsy patients who were undergoing open brain surgery, and they did so using a technique called electrocorticograhy (ECoG). The technique required hundreds of electrodes to be placed on the brain surface, and it could provide better time resolution than fMRI and better spatial resolution than EEG.

For a simple word repetition task, the brain received (yellow), interpreted (red) and responded (blue) within a second, during which time the prefrontal cortex (red) coordinated all areas of the brain involved. Video by Avgusta Shestyuk via UC Berkeley.

“This is the first step in looking at how people think and how people come up with different decisions; how people basically behave,” said Dr Avgusta Shestyuk, lead author of the study. “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.”

Once the researchers were done placing the electrodes on the brains of each patient, they conducted a series of eight tasks that included visual and auditory stimuli. The tasks ranged from simple action, where the participants had to repeat a word or identify the gender of a face or a voice, to a more complex version, where they had to determine a facial emotion, utter the antonym of a word or assess whether an adjective describes the patient’s personality. As the researchers continued to monitor and track the participants’ brain throughout the tasks, they observed four different types of neural activity.

They found that sensory areas of the auditory and visual cortex activate to process audible or visual cues, while areas in the sensory and prefrontal cortices activate to extract the meaning of the stimulus. The prefrontal cortex was found to remain active throughout the processes, coordinating input from different areas of the brain. And finally the prefrontal cortex stands down as the motor cortex sets in to generate a spoken response or an action, such as pushing a button.

For a more difficult task, like saying a word that is the opposite of another word, people’s brains required 2-3 seconds to detect (yellow), interpret and search for an answer (red) and respond (blue), with sustained prefrontal lobe activity (red) to coordinate all areas of the brain involved.

“This persistent activity, primarily seen in the prefrontal cortex, is a multitasking activity,” Shestyuk said. “fMRI studies often find that when a task gets progressively harder, we see more activity in the brain, and the prefrontal cortex in particular. Here, we are able to see that this is not because the neurons are working really, really hard and firing all the time, but rather, more areas of the cortex are getting recruited.”

The study, entitled “Persistent neuronal activity in human prefrontal cortex links perception and action” has been published in the journal Nature Human Behaviour.

Source: University of California, Berkeley