TURKU, Finland — Where do our brains “go” when we fall asleep? A super network in the center of the brain could help solve one of the biggest scientific mysteries – how does human consciousness work? Scientists in Finland have discovered a central core network brimming with the same activity regardless of whether a person goes to sleep normally or loses consciousness due to anesthesia.
Researchers from the University of Turku conducted two experiments that revealed for the first time the natural mechanisms behind human consciousness and its connection to how people respond during sleep. One study examined brain activity of people being medically anesthetized, while the other looked at how the subjects responded as they slept naturally and after they woke up.
Along with using brain-imaging technology, researchers also asked participants a series of questions when they woke up. Those included topics like whether the volunteer was aware of their surroundings or remembered any of their dreams.
“One major challenge has been to design a set-up, where brain data in different states differ only in respect to consciousness. Our study overcomes many previous confounders, and for the first time, reveals the neural mechanisms underlying connected consciousness,” says principal investigator Harry Scheinin in a university release.
Unconsciousness comes in many forms
Researchers say natural sleep and experimental anesthesia are powerful research tools in the study of human consciousness. In previous studies, scientists have been baffled by the state of wakefulness versus a supposed state of unconsciousness. Whether or not a person is conscious has often been defined by their behavior. For example, some may assume a person lacking meaningful responses is unconscious. However, studies show being unresponsive does not necessarily mean a person is unaware of their surroundings and they are not necessarily unconscious.
An unresponsive person might still be aware of their surroundings, meaning they are still “connected,” while another might be unaware but still experiencing their internal world and are “disconnected.”
In the new study, scientists wanted to identify “state-specific patterns” in brain activity looking at “connected” and “disconnected” states of consciousness. They also aimed to discover the overall effects of anesthesia and sleep by comparing different doses of the drugs and different stages of sleep.
“This unique experimental design was the key idea of our study and enabled us to distinguish the changes that were specific to the state of consciousness from the overall effects of anesthesia,” explains first study and anesthesiologist Annalotta Scheinin.
Which parts of the brain make up the super network?
The researchers looked for networks in the brain linked with human consciousness. They did so by measuring the brain activity of adult men as they fell asleep and went under anesthesia via a PET scan. This is an imaging test that allows doctors to see how your brain is functioning.
Researchers woke patients mid-experiment to interview them and confirm their state of connectedness, or how aware they were of their surroundings. They discovered changes in connectedness tie in to a crucial network linking several areas deep inside the brain.
These regions include the thalamus (which shares motor and sensory signals with other parts of the brain), the cingulate cortex (emotion formation and processing), and the angular gyri (spatial cognition, memory retrieval, and attention).
Rewriting common beliefs
The study finds these regions experienced less blood flow when one of the volunteers lost connectedness and more blood flow when they regained consciousness. This is the case for both sleep and anesthesia, suggesting the changes correspond to connectedness rather than the effects of sleep or drugs.
“General anesthesia seems to resemble normal sleep more than has traditionally been thought. This interpretation is, however, well in line with our recent electrophysiological findings in another anesthesia study,” says Harry Scheinin.
“Because of the minimal delay between the awakenings and the interviews, the current results add significantly to our understanding of the nature of the anesthetic state. Against a common belief, full loss of consciousness is not needed for successful general anesthesia, as it is sufficient to just disconnect the patient’s experiences from what is going on in the operating room,” explains Annalotta Scheinin.
The findings appear in the the journal JNeurosci.
SWNS writer Laura Sharman contributed to this report.