To better understand how our gray matter accomplishes this perplexing task, a team of researchers from the University of Michigan Center for the Science of Consciousness took a closer look at what the brain does when it is fading.
What makes you aware of the noise in your stomach, of the chair in which you are sitting … has to do, logically, with the brain but, beyond that, there is still much more that we do not know.
One way to investigate this is to compare the conscious with the unconscious, such as when we are knocked out before surgery thanks to anesthesia.
Without thinking too much, we might assume that compared to a switch, being unconscious is like turning off that consciousness switch momentarily by shutting down key areas of our nervous system. Although there are experts who do not think that this is exactly the case:
“I published a theoretical paper when I was a resident in anesthesiology, suggesting that anesthesia does not work by disconnecting the brain per se , but rather by isolating processes in certain areas of the brain,” says anesthesiologist George Mashour
Like any good scientist, speculation was not enough: he wanted to put his hypothesis to the test.
Together with several teams of researchers, he conducted a variety of experiments to see exactly what was happening in the brain as it changed from conscious to unconscious.
In the first study, Mashour and her colleagues monitored blood flow in certain nerve tissues using functional MRI scans, comparing measurements in 23 patients who were sedated, undergoing surgical anesthesia, or in a vegetative state.
Specifically, they observed the momentum in areas of the brain as they coordinated incoming information. What they found indicated that some areas seem to speak more to themselves as the time of communications stretched.
“We show in the early stages of sedation that the information-processing timeline is much longer and local areas of the brain are more closely connected to each other, ” says Anthony Hudetz, leader of the work publishing the Journal. of Neuroscience.
The second study took on the challenge of measuring how that information is actually integrated into the brain.
To quantitatively describe that measure of integration, an area of research known as integrated information theory uses a value designated by the Greek letterphi. It is believed that in the brain,phiit corresponds to consciousness in some way.
The experts divided the task into more manageable and practical steps based on EEG readings: “We show that as the brain becomes more modular and has more local conversations, the extent of information integration begins to decrease,” explains the physicist and anesthesiologist, UnCheol Lee.
The results of these two studies suggest thatphi – the measure of information integration – decreases as communication time in disparate brain regions also decreases.
In their final report they reviewed their results against the more recent literature, summarizing their understanding of how our brains function during sleep, general anesthesia, and disorders of consciousness.
“We found that, during unconsciousness, disrupted connectivity in the brain and increased modularity create an environment that is inhospitable for the kind of efficient information transfer that is required for consciousness,” says Mashour.
While it still leaves many questions unanswered,the work points the way towards how the consciousness of a healthy brain arises; it could help us better distinguish when unresponsive patients are still conscious.
Referencia: Timescales of intrinsic BOLD signal dynamics and functional connectivity in pharmacologic and neuropathologic states of unconsciousness. Zirui Huang, Xiaolin Liu, George A. Mashour and Anthony G. Hudetz. Journal of Neuroscience 31 2018, 2545-17; DOI: https://doi.org/10.1523/JNEUROSCI.2545-17.2018
