Researchers speculated that the problem might be caused by overexposure to the enzyme cholinesterase, which the nervous system needs to function.
An examination of 26 Canadian diplomats found traces of cholinesterase-inhibiting insecticides, which were used in Cuba. Researchers also found traces of Temephos, another compound used in insecticides, in some of those tested.
"There is a lot we don't know about how much we can expose people to these chemicals and what are toxic levels, or if the damage in the brain is reversible," researcher Dr. Alon Friedman, a professor of neuroscience at Dalhousie University in Halifax, Nova Scotia, told CNN. "But it's not called a neurotoxin for nothing. The hint is in the name."