Author: Maria Zagorulya
Institution: University of Rochester
Throughout time, humans have been curious about what it means to be, to think and to be aware. In the 17th century, philosopher Descartes proposed theories about the nature of consciousness - the state of being aware of one’s own existence. While neuroscientists have replaced philosophers in the modern pursuit of knowledge of human consciousness, the state of human awareness remains poorly understood.
However, one scientist is working hard to shed some light on the topic; Enzo Tagliazucchi, from the Institute for Medical Psychology in Kiel, Germany, strives to understand the factors that contribute to the emergence of consciousness in the human brain. In his recent study (2016), published in Journal of the Royal Society Interface, Tagliazucchi investigated the specific changes that occur in the neural networks in the brain during the transition from the state of consciousness to that of unconsciousness and back.
The team of researchers used a drug called propofol to induce loss of consciousness in the subjects, and observed the resulting changes in their brains. Propofol is an anesthetic used for surgeries, which makes people unable to process thoughts and causes a complete loss of consciousness. The drug also prevents the brain from processing external signals, such as those that would normally induce pain, stopping any discomfort during surgeries.
While taking the drug, the participants also underwent fMRI scans, which allowed the scientists to track the changes in their brains associated with loss of consciousness. fMRI stands for functional magnetic resonance imaging, and is a technique to measure changes in the blood flow of the brain. Blood flow is a good proxy for the levels of electrical activity of neurons in the brain, and so its measurements in the states of wakefulness, sedation, loss of consciousness and subsequent recovery provided useful information for the scientists.
From the results of this experiment researchers inferred that the activity of the brain in the conscious and unconscious states differs significantly. Specifically, the study suggests that the pattern of neuronal pathways changes in the transition from consciousness to loss of consciousness and back. In the conscious brain, the connectivity between the neurons seems to provide the maximum number of unique pathways, while in the unconscious brain, this connectivity seems to be reduced.
Tagliazucchi compares neuronal connectivity to cars on the streets of a city. “If the cars move always in the same restrictive manner, if they move from point A to point B and back, at the end of the day you don’t really understand the city. But if the cars are thorough explorers and go through all possible parts of the city, you get a map that’s very close to the actual map of the city. At the critical point, the cars are exploring the streets in the optimal way.”
The new findings of the Tagliazucchi group support contemporary theories about the brain, which suggest that the brain’s response to a combination of signals from various sources constitutes consciousness. All human experiences are thought to result from a synthesis of information obtained from an array of sources such as sight, smell, taste, touch and memories. In line with this theory, the maximal neuronal connectivity of the conscious brain, suggested by the findings of the Tagliazucchi team, would allow the maximal processing of signals from the diverse sources (continuing with the analogy, the cars would maximally explore the different parts of the city). In the absence of the maximal neuronal connectivity, as in the unconscious brain, the same external signals would be processed to a lesser extent (the cars would explore only some parts of the city).
Tagliazucchi’s research contributes to our understanding of consciousness, which is a very relevant topic in medicine. The knowledge will help develop methods of treatment for critical patients in comas and vegetative states, for whom currently there is very little medical therapy available. The prospect of such medical advances is exciting. Research of consciousness could also potentially advance therapies for other brain injuries and sleep disorders, as well as improve safety of anesthetic drugs. Thus, the medical implications of research on consciousness are invaluable.
Certainly, there is still a long way until scientists are able to pinpoint the exact mechanistic processes that constitute consciousness. However, the potential implications of such knowledge are far-reaching. Today, consciousness is one of the few big unanswered questions in biology, and future research in the field will provide exciting opportunities for new developments and probably entirely change our lives.