Researchers from the university hospitals of Heidelberg and Cologne, who joined hands with collaborators from the Max Planck Institute of Neurological Research in Cologne for this study, say that depolarisation waves arise at the edges of the dead tissue and spread through the adjacent areas of the brain.
The researchers say that a repetition of such waves may cause more cells to die.
Although the same discovery has previously been observed in animal studies, the researchers claim to be the first to show that this phenomenon occurs after a stroke in humans, and is a warning sign that more nerve cells will die.
A research article in the journal 'Annals of Neurology' says that this study may help translate more than 60 years of experimental research for the diagnosis and therapy of stroke patients.
"After the stroke, circulation in the tissue surrounding the affected area of the brain is initially poor, but it can still be saved," said Dr. Christian Dohmen of the Neurology Department at Cologne University Hospital.
The researcher, who also happens to be the main author of the study, says that the spreading depolarisations additionally impair the metabolism of the weakened nerve cells.
"The more frequently such waves occur, the longer the nerve cells require to recover, until finally they die off entirely," the researcher adds.
Dr. Dohmen says that the extent of brain damage after a stroke thus depends on the number of such spreading depolarisations, and this correlations is becoming apparent in humans as well.
For their study, the researchers selected 16 patients whose brain had to be partially exposed due to a life threatening swelling of brain tissue.
Electrodes were applied to the surface of the brain around the affected tissue (electrocorticography), the incisions were closed, and brain waves were measured for five days.
All patients were in an artificial coma during this period due to their serious condition.
"Our study puts an end to the discussion as to whether these waves also occur in a human brain following a stroke," says Dr. Oliver Sakowitz, physician at the Department of Neurosurgery of the University of Heidelberg Hospital and co-author of the study.
"As they cause additional damage to the weakened tissue surrounding the stroke area, it is conceivable that we could prevent further damage by suppressing the waves," adds the neurosurgeon.
Sakowitz even says that previous animal studies have already led to the development of several therapy approaches that physicians can apply.
"The spreading depolarizations are a warning sign that other areas of the brain are at immediate risk and may be also useful as diagnostic measures," says Dr. Sakowitz.
The research team is now planning a follow-up study on a larger number of stroke patients to clarify whether cortical spreading depression has an influence on the extent of sequelae such as paralysis.