What happens when people wake up from anesthesia or a coma has long baffled scientists, but now new research on rats suggests the path the brain takes to regain consciousness may be even more sophisticated than thought.
“It is commonly assumed that waking from anesthesia is a simple thing: The drugs leave the brain, and the effects they produced in the brain get washed out, and the brain somehow recovers,” said Dr. Alex Proekt, an assistant professor of anesthesiology at Weill Cornell Medical College in New York. “But that ‘somehow’ part is poorly understood.”
The researchers looked at the brain’s activity patterns, hypothesizing that the activity follows a structured path, changing in a specific way as the brain moves toward consciousness. The researchers wanted to know whether the brain moves from one activity state to the next, in a stepwise fashion, or whether the brain can go from any given state to a number of other states, and therefore, that there are multiple routes to consciousness.
As technology has changed, so has our definition of “dead.”
To examine the brain’s trajectory while recovering consciousness, scientists recorded the electrical activity of certain brain regions in anesthetized rats. They slowly lowered the concentration of anesthetic vapor that the animals were breathing, until they eventually woke up.
The analysis of the rats’ brain activity suggested that the brain passes through several distinct activity states to become conscious. The researchers found that only certain transitions between activity states are possible, and some states do form hubs that connect groups of otherwise disconnected states.
“Although many paths through the network are possible, to ultimately enter the activity state compatible with consciousness, the brain must first pass through these hubs in an orderly fashion,” the researchers wrote in their study.
The researchers said the new findings could one day be used to help people in a coma. The brains of people under anesthesia as well as comatose patients show an electrical pattern known as burst suppression, which is characterized by periods of spikes in activity, alternating with periods of silence.
Both general anesthesia and coma are major perturbations to brain’s normal activity, and in some cases, the brain cannot find its way back to consciousness.
In order to help comatose patients, scientists will first have to examine whether the same phenomenon they observed in rats also exists in the human brain, and then explore how it may be possible to push the brain out of one state so it can proceed further toward recovery.