Increasingly, new research is undermining what has been the traditional picture of how the brain functions, namely that different parts of the brain are responsible for specific or unique actions. For example, that the brain’s speech area is activated when we speak.
In its stead is a developing understanding that wide-ranging networks of neural connections are at work during any given task. Now an international team of researchers suggests that the entire cortex, not just the area responsible for a certain function, is activated when a given task is initiated, with waves of activity rolling from one side of the brain to the other.
The brain can be studied on various scales, said researcher David Alexander, Ph.D., of Belgium’s University of Leuven: “You have the neurons, the circuits between the neurons, the Brodmann areas — brain areas that correspond to a certain function — and the entire cortex.
“Traditionally, scientists looked at local activity when studying brain activity, for example, activity in the Brodmann areas. To do this, you take EEG’s (electroencephalograms) to measure the brain’s electrical activity while a subject performs a task and then you try to trace that activity back to one or more brain areas.”
In the new study, researchers took a different approach as they examined the activity in the cerebral cortex as a whole.
“The brain is a non-stop, always-active system,” Alexander said. “When we perceive something, the information does not end up in a specific part of our brain. Rather, it is added to the brain’s existing activity. If we measure the electrochemical activity of the whole cortex, we find wave-like patterns.”
Alexander believes this shows that brain activity is not local but rather that activity constantly moves from one part of the brain to another. That is, the local activity in the Brodmann areas only appears when you average over many such waves.
Researchers believe that each activity wave in the cerebral cortex is unique.
“When someone repeats the same action, such as drumming their fingers, the motor center in the brain is stimulated. But with each individual action, you still get a different wave across the cortex as a whole,” Alexander said.
Although the reason for this is unknown, perhaps the person was more engaged in the action the first time than he was the second time, or perhaps he had something else on his mind or had a different intention for the action, say the researchers.
Additionally, the direction of the waves is also meaningful. It is already clear, for example, that activity waves related to orienting move differently in children – more prominently from back to front – than in adults.
Investigators hope that future research will help unravel what these different wave trajectories mean.
The full text of the study is available on the website of Neuroimage.
Source: University of Leuven