When a person suffers a cerebrovascular accident (a stroke or a subarachnoid hemorrhage), electrochemical waves are generated that slowly travel through the tissue from the damaged area, killing neurons as they pass. In a period of a few hours, several of these waves will produce irreversible damage to an increasing volume of the cerebral cortex, which is why it is considered a critical window of time for the medical team to try to save the tissue and reduce the neurological damage, or in a large number of cases, death. In the hospitals, the extent of damaged brain tissue is monitored using “strips” of electrodes placed on the brain surface. The area where electrical activity (EEG) is lost gradually extends due to what is called spreading depression, and the extension of this silent area (flat EEG) helps the clinician determine when and with what strategy will try to protect brain tissue.

In this study carried out in parallel with patients and in animal models, and published in the journal Nature Communications, Dr. Herreras’ group from the Cajal-CSIC Institute, in collaboration with groups from the Aix-Marseille University and the University of Medicine at Berlin has discovered that cortical tissue that still shows EEG activity may, in fact, already be suffering irreversible death of the most superficial neuronal layers of the cortex. The activity that is recorded would be passively propagated from lower layers of the cortex. Knowing this, the clinician must readjust the treatment and response times to avoid arriving too late.

These findings have been obtained using a complex biomathematical technique for analyzing brain electrical potentials that was previously optimized in experimental animals in Madrid, and allows us to separate and “see” activity of different neuronal layers. The findings challenge the concept of extent of EEG depression as a strict indicator of tissue that has died. The authors advise rethinking the criteria and perhaps the practice in the monitoring and treatment of stroke.

Nasretdinov A, Vinokurova D, Lemale CL, Burkhanova-Zakirova G, Chernova K, Makarova J*, Herreras O*, Dreier JP, Khazipov R. Diversity of cortical activity changes beyond depression during Spreading Depolarizations. Nat Commun. 2023 Nov 25;14(1):7729. doi: 10.1038/s41467-023-43509-3.

Find more information at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10676372/