London : Consciousness depends upon the way nerve cells communicate and on the degree to which they manage to differ in terms of their activity patterns, suggests a study.
To establish how the brain produces consciousness the researchers tested the neuronal activity in the brains of mice and compared how brain activity differs in conscious and anesthetised mice.
“We used a fluorescent protein that converts electrical signals into light signals. This enabled us to visualise the frequency and average amplitude of neuronal responses, and allowed us to reveal the existence of neuronal synchrony,” said Mazahir T. Hasan, researcher with Charite’s NeuroCure Cluster of Excellence, Germany.
Results suggested that consciousness is not simply dependent on the number of active neurons inside the cortex; instead, it seems to be dependent upon the way these nerve cells communicate and on the degree to which they manage to differ in terms of their activity patterns.
The awake cortex showed complex activity patterns, with individual cells firing at different times. Under anesthesia, all neurons displayed identical activity patterns and fired at the same time.
“While one might expect the brain to cease its activity under anesthesia, in reality, the situation is quite different. Neurons remain highly active but change their communication mode. During unconsciousness they become highly synchonised — in simple terms all neurons start doing the same thing,” said Thomas Lissek, Neurobiologist from Heidelberg, Germany.
Another surprising finding was that neurons were more sensitive to environmental stimuli under anesthesia than when the brain was awake.
“This is especially surprising, as anesthesia is used to block both pain and environmental stimuli during surgery. Some of the brain regions that are normally dedicated to tactile perception even responded to sound information,” Lissek added.
These new insights into neuronal activity patterns provide information regarding the identity of the cellular parameters involved in producing consciousness and the loss of consciousness.