After patients undergo surgery for severe brain injuries, the early recovery period is especially critical. During their first few weeks in the ICU, they’re at risk for secondary injuries. These can cause long-term disability or death.
Researchers may have finally uncovered the mechanism behind these secondary injuries. Spreading depolarizations (SD) are massive waves of brain activity that elude normal EEG recordings, explains UVA Health neurosurgeon Andrew Carlson, MD.
Carlson hopes to build on this knowledge by finding treatments to reduce severe adverse effects in patients after large strokes. But that’s just the tip of the iceberg for what SDs can help neuroscientists understand and ultimately treat.
“We think that these events may play a major role in many conditions,” Carlson says. “These kinds of observations could have direct effects on how we treat not only patients with severe brain injuries and strokes, but also conditions such as brain tumors, migraine, dementias, concussions, and maybe even recovery and rehabilitation after brain injuries.”
First Recordings of Spreading Depolarizations
SDs are “one of a few kinds of behaviors that the brain can do that we haven't even known was going on until relatively recently,” Carlson says.
Since at least the 1940s, preclinical models suggested SD happened in human brains. But researchers only began recording these events relatively recently, in part because regular scalp EEGs can’t detect them.
“Looking for seizures is like understanding the trees in a forest,” Carlson explains. “And spreading depolarization is the whole forest and the hills surrounding it. When you're hyper focused on events like seizures, you miss these other big, long events. You don’t even set up your monitors to capture them.”
Recording SDs required putting monitors on the surface of the brain at the time of surgery. And using a new analysis approach to the signals an SD produces.
“Sure enough, they occurred with some frequency in some of these severe brain injuries like strokes and traumatic brain injury,” Carlson says.
Preventing Large Strokes From Spreading
Both these earlier studies and preclinical models suggest physical touch and other stimulation in the early ICU recovery period may trigger SDs. Carlson recently received R01 funding from the National Institutes of Health to study this further in patients after large strokes.
“We’re monitoring patients in the touch and stimulation centers of the brain and correlating that with blood flow and stroke expansion,” he explains.
Based on the findings, researchers could then test ways to reduce SDs. This could prevent large strokes from spreading and reduce permanent disability and death in this patient population.
These interventions could include:
- Stimulating and touching patients less frequently
- Identifying new optimal blood pressure and temperature ranges
- Using neuroprotective agents like ketamine
A Gateway to Better Understand Other Neurological Conditions
In the future, researchers hope to find ways to record SDs through non-invasive measures on the scalp. That opens the door to learning how SDs could play a role in other neurological conditions, like migraine and dementia.
“We’re fairly confident that spreading depolarizations, particularly after severe brain injury, cause additional stress,” Carlson says. “And there are other possibly even beneficial effects we clearly need to understand better.”