Scientists at the University of Wisconsin School of Medicine and Public Health, led by brain researcher Fabio Ferrarelli, reported their findings in this week's edition of the Proceedings of the National Academy of Science.
The group gave the anesthetic midazolam, commonly used at lower doses in "conscious sedation" procedures such as colonoscopies, to volunteers.
Then they used transcranial magnetic stimulation (TMS), a noninvasive technique to stimulate the brain cortical neurons from the scalp, in combination with electroencephalography (EEG), which recorded the TMS-evoked brain responses. What they found is a pattern that looks much as it does when the brain is in deep, non-rapid eye movement (non-REM) sleep, another condition when consciousness fades.
Co-author and consciousness expert Giulio Tononi says that when the brain is unconscious it appears to lose the connectivity that underlies the coordinated, yet differentiated responses to electrical stimuli observed when the brain is awake or in REM sleep. The group's earlier studies demonstrated the differences between the sleeping and awake brain.
"Based on a theory about how consciousness is generated, we expect to see a response that is both integrated and differentiated when the brain is conscious,'' says Tononi, professor of psychiatry. "When there is a loss of consciousness, either due to sleep or anesthesia, the response is radically different. We see a stereotyped burst of activity that remains localized and fades quickly."
The team believes that the response patterns observed in the awake brain, characterized by long-lasting activations moving over time to different cortical areas, reflect the connectivity of the cortical areas activated by TMS. This could be because when we are awake, the cortex is involved in many activities which require a constant communication between different cortical areas. But in the unconscious brain, this connectivity is temporarily lost, and therefore the TMS-evoked brain responses remain localized.
Ferrarelli says the results lend weight to the idea that a breakdown of cortical connectivity is a key aspect of loss of consciousness, and are consistent with the "integrated information theory of consciousness."
Co-author Dr. Robert Pearce, chair and professor of anesthesiology at UW SMPH, said it is interesting that the cortical responses under anesthesia were so similar to changes seen during natural sleep.
"The idea that some anesthetics "hijack" the natural sleep-promoting centers was proposed recently by others,'' says Pearce. "While our present findings do not directly confirm this hypothesis, they are consistent with a set of shared mechanisms. That is, that the loss of functional connectivity between brain regions is a characteristic that sleep and anesthesia share, and that we think might be causal in the loss of consciousness in both cases."
Tononi says that a similar test of cortical connectivity could be used to provide a non-invasive way to test an unresponsive patient for consciousness during anesthesia or in medical conditions such as coma.
"One practical application would be a test to help assess how conscious a patient is,'' Tononi says. Current tests rely partly on clinical observations, and may be altered by drugs or medical conditions that render an otherwise conscious patient unable to respond.
"We want to know whether a person is really there, and to us, it is important that the method is grounded on a theoretical model of what is required for consciousness,'' Tononi says.
Other authors include Simone Sarasso and Brady Riedner of the UW psychiatry department, Giuditta Angelini of the UW anesthesiology department, and Marcello Massimini and Adenauer Casali of the University of Milan. The research was funded by the National Institutes of Health, and other federal agencies.
Susan Lampert Smith | EurekAlert!
Rutgers-led innovation could spur faster, cheaper, nano-based manufacturing
14.02.2018 | Rutgers University
New study from the University of Halle: How climate change alters plant growth
12.01.2018 | Martin-Luther-Universität Halle-Wittenberg
Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale
Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...
For photographers and scientists, lenses are lifesavers. They reflect and refract light, making possible the imaging systems that drive discovery through the microscope and preserve history through cameras.
But today's glass-based lenses are bulky and resist miniaturization. Next-generation technologies, such as ultrathin cameras or tiny microscopes, require...
Scientists from the University of Zurich have succeeded for the first time in tracking individual stem cells and their neuronal progeny over months within the intact adult brain. This study sheds light on how new neurons are produced throughout life.
The generation of new nerve cells was once thought to taper off at the end of embryonic development. However, recent research has shown that the adult brain...
Theoretical physicists propose to use negative interference to control heat flow in quantum devices. Study published in Physical Review Letters
Quantum computer parts are sensitive and need to be cooled to very low temperatures. Their tiny size makes them particularly susceptible to a temperature...
Let’s say the armrest is broken in your vintage car. As things stand, you would need a lot of luck and persistence to find the right spare part. But in the world of Industrie 4.0 and production with batch sizes of one, you can simply scan the armrest and print it out. This is made possible by the first ever 3D scanner capable of working autonomously and in real time. The autonomous scanning system will be on display at the Hannover Messe Preview on February 6 and at the Hannover Messe proper from April 23 to 27, 2018 (Hall 6, Booth A30).
Part of the charm of vintage cars is that they stopped making them long ago, so it is special when you do see one out on the roads. If something breaks or...
15.02.2018 | Event News
13.02.2018 | Event News
12.02.2018 | Event News
16.02.2018 | Information Technology
16.02.2018 | Health and Medicine
16.02.2018 | Physics and Astronomy