Doctors are facing a dilemma in trying to determine how and why COVID-19 affects the brain.

Besides its effect on the lungs, the devastating disease has shown disturbing neurological consequences. One study in China reported that over a third of COVID-19 patients had some sort of neurological symptoms, while another one in France said that among hospitalized patients with the disease, two-thirds were agitated or delirious.

AARP reports that physicians on the front lines in the U.S. have seen severe symptoms that go well beyond the typical signs of respiratory distress. Some patients have developed strokes and others have had seizures. It has become increasingly clear the disease damages more than just the lungs; it affects the brain as well.

According to ABC News, doctors are confused as to how the virus attacks the brain. Some think that it directly damages brain tissues or blood vessels. Others believe the mental agitation is caused by an aggressive inflammatory response. Dr. Lorenzo Norris, the associate dean at the George Washington University School of Medicine and Health Sciences, offers another theory. He believes the cause is a severe overreaction of the immune system, called a "cytokine storm," that causes blood clots to form in the brain.

He told ABC News that he has seen an uptick of patients with COVID-19 in his hospital experiencing delirium who also take much longer to recover. Experts say that prolonged hospitalizations can exacerbate the neurological symptoms. Isolation, limited mobility, and the absence of familiar faces make returning to a normal mental state more challenging.

"Delirium is a medical emergency that is associated with increased morbidity and mortality," he said. Caught early, delirium can be managed and the long-term complications reduced.

"We're learning something new about this virus every day, but there are concerns from folks on the front line for what will become of patients with altered mental status and COVID-19," he told ABC.