By Paris Brain Institute in SciTech Daily: Until now, researchers did not know where the wave of death is initiated in the cortex or whether it propagates homogeneously across all cortical layers. “We already knew that it is possible to reverse the effects of anoxic depolarization if we manage to resuscitate the subject within a specific time window,” the researcher adds. “We still had to understand in which areas of the brain the death wave is likely to do the most damage to preserve brain function as much as possible.”
Following the path of the wave of death
To answer these questions, the researchers used, in rats, measurements of local field potentials and recordings of the electrical activity of individual neurons in different layers of the primary somatosensory cortex—an area that plays a crucial role in body representation and processing of sensory information. They then compared the electrical activity of these different layers before and during anoxic depolarization.
“We noticed that neuronal activity was relatively homogeneous at the onset of brain anoxia. Then, the wave of death appeared in the pyramidal neurons located in layer 5 of the neocortex and propagated in two directions: upwards, i.e. the surface of the brain, and downwards, i.e. the white matter,” Séverine Mahon explains. “We have observed this same dynamic under different experimental conditions and believe it could exist in humans.”
These findings also suggest that the deeper layers of the cortex are the most vulnerable to oxygen deprivation—probably because the pyramidal neurons in layer 5 have exceptionally high energy needs. However, when the researchers reoxygenated the rats’ brains, the cells replenished their ATP reserves, leading to the repolarization of neurons and the restoration of synaptic activity. More here.