As humans, we are practically in constant interaction with our internal thoughts, and our minds often tend to wander when left alone for even a few seconds. Yet the brain mechanisms that govern our thought flow are still poorly understood by scientists. A team from the University of California at Berkeley (UC Berkeley) in the United States looked into the subject: their results, published in the journal Proceedings of the National Academy of Sciences (PNAS), indicate that there are electrophysiological signatures specifically linked to different states of internal thought, allowing for example to identify if our mind is concentrated or on the contrary if it wanders.
Different streams of internal thought
The American team first taught its 39 participants to distinguish 4 distinct states of thought: related to a task (“task-related”), Wandering (“freely moving”), Deliberately constrained (“deliberately constrained”) And automatically constrained (“automatically constrained”). Our thoughts are strained when our attention is focused on something for an extended period of time. We speak of deliberately constrained thoughts when a person actively directs his or her thoughts to information related to a goal (for example, a scientist planning their next experiment). In contrast, automatically constrained thoughts relate to important emotional or personal information that is difficult to get rid of (for example, “when you are worried about your niece who is going to have surgery, ”As the study indicates).
When these two types of constraints are weak, thoughts roam freely, aimlessly: this is what happens when you think of a movie that reminds you of that meeting you attended that morning, which Makes you think you have to do some shopping for dinner, besides what the hell are you going to be able to cook… Approximately that way.
Electroencephalography to visualize these thought flows
Once these distinctions were clear to the participants, they had to perform a relatively simple task requiring their attention: arrows appeared on a screen and they had to indicate by pressing keyboard keys whether they pointed to the left or to the left. right. After each sequence, they were asked to rate on a scale of 1 to 7 how closely their thoughts during the sequence matched each category studied previously: task-related, roaming freely, deliberately constrained, or automatically constrained.
While performing this task, the researchers recorded their brain activity using electroencephalography (EEG): electrodes placed on the participants’ skulls picked up electrical signals which were then compared to their post-sequence responses. This is what made it possible to identify certain brain waves corresponding specifically to different “states” of thought in the participants: these electrical signal patterns can then reveal whether a person is focused on the task at hand, or on the contrary lost in the task. his wandering thoughts.
Neurophysiological evidence to distinguish thought patterns
Scientists observed a sharp increase in alpha waves in the participants’ prefrontal cortex as their thoughts wandered aimlessly during the experiment. These brain waves, typically characteristic of a calm or creative state of consciousness, oscillate at frequencies between 8.5 and 12 hertz and constitute a kind of electrophysiological signature of disordered, free, unconstrained thought. At the same time, P300 brain waves (also called P3) were seen in the parietal lobe, albeit more faintly: another marker for situations where people were not paying attention to the task at hand.
In contrast, when participants were focused on their task, thus indicating deliberately constrained thoughts, these P3 waves were observed in the frontal lobe, instead of alpha waves. These different electrophysiological signatures are the first neurophysiological evidence allowing to distinguish different internal thought patterns.