Scientists re-established some activities within the brains of pigs slaughtered hours ago, raising hopes for medical advances and questions about the definition of death.
The brains could neither think nor feel, the researchers emphasized. By medical standards, "this is not a living brain," said Nenad Sestan of the Yale School of Medicine, one of the researchers who reported the findings on Wednesday in Nature .
The work, however, revealed a surprise level of resistance between cells in a brain that has lost its supply of blood and oxygen, he said.
"Cell death in the brain occurs over a longer time window than we thought before," Sestan said.
Researchers could lead to new therapies for stroke and other diseases and provide a new way to study the brain and how drugs work in it. They said they currently have no plans to try their technique on human brains.
The study was funded primarily by the National Institutes of Health.
The 32 brains came from pigs killed in a local slaughterhouse for food. Scientists put the brain in an apparatus in their laboratory. Four hours after the animals died, the scientists began to pump a specially designed blood substitute through the organs.
The brains did not show large-scale electrical activity that would alert them to consciousness. The restoration of consciousness was not the goal of the study, but aimed to investigate whether certain functions could be restored long after death.
After six hours of pumping, the scientists found that individual brain cells in one area of the brain had retained the key details of their structure, while cells from untreated brains were severely degraded.
When scientists removed these neurons from the treated brain and stimulated them electrically, the cells responded in a way that indicated viability.
And by studying the artificial blood before it got into the treated brain, and after its emergence, the researchers found evidence that brain cells absorb blood sugar and oxygen and produce carbon dioxide, a signal that they work.
They Also Found
Sestan said the researchers did not know if they could restore normal brain function if they chose this target. If such awareness had surfaced in the reported experiments, scientists would have used anesthesia and low temperatures to suppress it and end the experiment, said co-author of the study, Stephen Latham of Yale.
There is no good ethical consensus about such research when the brain is conscious, he said.
Researchers now see if they can sustain their observed brain function for more than six hours, Latham said The technology should be used as a research tool.
Christof Koch, president of Allen Institute for Brain Science in Seattle, who did not participate in the study, said he was surprised by the results, especially as they were achieved in a large animal.
"This type of technology could help improve our knowledge to bring people back to the land of the living," after a drug overdose or other catastrophic event had deprived the brain of oxygen for an hour or two.
Unlike pig experiments, any such treatment would not involve removing the brain from the body.
The pig work also enters an ethical minefield, he said. First, it touches on the widespread definition of death as the irreversible loss of brain function, because irreversibility "depends on the state of the art, and as this study shows, this is progressing steadily," he said.
And someday someone might try this with a human brain, he said. If future experiments restored the large-scale electrical activity, would that indicate consciousness? Would the brain experience "confusion, deception, pain or agony?" he asked.
That would be unacceptable even in an animal brain, he said.
In a Comment Nature bioethicists Stuart Youngner and Insoo Hyun from the Case Western Reserve School of Medicine in Cleveland said that if such work was possible it would lead to better brain resuscitation methods in humans It could make it more difficult to decide when to remove organs for a transplant.