There was no evidence of frontotemporal lobar degeneration, which affects “executive functions,” including decision-making and social interactions, and can cause personality changes and unrestrained behavior. That disease would likely have been inconsistent with someone able to engage in meticulous planning.
Mr. Paddock had complained to friends of feeling ill, in pain and fatigued, according to a preliminary report on the police investigation released last month. Mr. Paddock’s girlfriend, Marilou Danley, told investigators that he had grown more distant over the year before the shooting. The law enforcement report described Mr. Paddock as “germaphobic” and strongly reactive to smells.
A primary care physician in Las Vegas — who said he had been Mr. Paddock’s doctor since 2009 and had last seen him as a patient roughly a year before the shooting — told officials that he suspected Mr. Paddock had bipolar disorder. That psychological disorder, however, cannot be identified in a typical post-mortem examination of brain structures. And while some studies have shown that people with bipolar disorder are more likely to have a history of violent behavior than the general public, the majority of them do not, and the relationship between mental health and violence involves many other factors.
The doctor, who was not named in the report, also described Mr. Paddock as having behaved oddly, showing little emotion and expressing fear of medications. Mr. Paddock had refused prescriptions for antidepressants, but the physician had prescribed anti-anxiety medicine for him.
A toxicology report showed he did have anti-anxiety medication in his system, based on a test of his urine. It was no longer detectable in his blood, meaning it was not active. The autopsy, performed by the Clark County coroner, and its related reports were obtained by The New York Times on Friday, and were first reported on by The Las Vegas Review-Journal, which had gone to court with The Associated Press to secure their release.
The examination showed that certain sections of Mr. Paddock’s brain contained small spheres that can be seen when the tissue is treated with a stain. The structures, made up mostly of carbohydrates but also containing proteins and other components, are known as corpora amylacea. They studded parts of his hippocampus — involved in learning and memory — and the frontal lobes, among other areas. “Most people would have them at that age, but not in that profusion,” Dr. Vogel said. “It’s a striking exaggeration of an age-related finding.”
The cause and meaning of the structures remain mysterious, the subject of ongoing research. They appear as people grow older and are found at greater density in the brains of patients with Alzheimer’s disease, multiple sclerosis and epilepsy, among other disorders. Dr. Vogel searched for signs of those diseases, but he did not detect them in Mr. Paddock’s brain.
Three scientists who study corpora amylacea said in interviews that the increased presence of the structures was significant. “If you have high numbers of these, something’s not normal,” said Troy Rohn, a professor of biology at Boise State University.
Other scientists believe the structures are akin to wastebaskets that contain remnants of broken-down cells or even infectious or hazardous substances.
Dr. Hyman Schipper, a professor of neurology at McGill University in Montreal, said his laboratory’s studies have found evidence that corpora amylacea can result from the damage caused by unstable molecules known as free radicals, which can be unleashed by various stressors. “It’s telling you something and it could be very important,” Dr. Schipper said of the finding in Mr. Paddock’s brain.
Even so, Dr. Vogel, the Stanford neuropathologist, said the results of his examination should reassure the public that Mr. Paddock’s doctors had not missed diagnosing a tumor or other major brain disorder that could have been treated.
The Clark County coroner’s office had sent 129 brains to Stanford for examination before Mr. Paddock’s. Typically they arrive by FedEx, but with heavy public interest in Mr. Paddock’s case, the coroner, John Fudenberg, hand-delivered the brain — and Dr. Vogel has been asked to return it in person.
Eric Paddock, the gunman’s brother, who also received a copy of the reports, said they did not provide answers to the fundamental question of what drove his brother to his deadly actions. Still, he said, “I’m glad to have this closed out.”
Follow Sheri Fink on Twitter @SheriFink.
A version of this article appears in print on February 11, 2018, on Page A20 of the New York edition with the headline: Exam of Gunman’s Brain Keeps Motive in Las Vegas Shooting a Secret.Continue reading the main story