Characteristics of the Involvement of Hidden Nodes in the Activity of Human Brain Systems Revealed on fMRI Data

— Currently, it is generally accepted that brain functions are based on the systemic principle. At the same time, knowledge about the principles and mechanisms of the functioning of the brain system remains scarce. In the present study these principles were studied within the framework of ideas about the so-called hidden nodes of the brain systems. Previously, according to fMRI data, ìit was shown that some brain structures could be involved in work without changing their energy consumption (reflected by the blood oxygenation level-dependent signal). Their involvement was found only due to a change in the distant functional connectivity. The analysis of systemic brain activity using functional connectivity data made it possible to reveal hidden nodes that were inaccessible to detection using the standard activation approach. This study is aimed at clarifying the extent and nature of the involvement of hidden nodes in the brain maintenance of various activities using open fMRI data from the Human Connectome Project. It has been shown that the brain systems ensuring current activity are provided with a much larger number of nodes than was previously believed, and the vast majority of them are hidden. For the first time, this result clearly showed the actual scale of the brain systems providing current activity. Mental activity is actually provided by almost the entire brain working and not a minor part of it, as is usually observed in functional tomographic studies. As a result, it is shown that the idea of the existence of hidden nodes is confirmed by analyzing the activity of the human brain at the macrolevel and shows similarities with the characteristics of the microlevel activity of individual neuronal populations, confirming the previously formulated neurophysiological ideas about the systemic organization of brain activity.