this explains a lot.
Viruses that cause a range of ills from the common cold to polio may be able to infect the brain and cause steady damage, a team at the Mayo Clinic in Minnesota reports.[...]The viruses are called picornaviruses and infect more than 1 billion people worldwide each year. They include the virus that causes polio, as well as colds and diarrhoea. People contract an average of two or three such infections a year. [...] "Our findings suggest that picornavirus infections throughout the lifetime of an individual may chip away at the cognitive reserve, increasing the likelihood of detectable cognitive impairment as the individual ages," the researchers write. "We hypothesise that mild memory and cognitive impairments of unknown aetiology may, in fact, be due to accumulative loss of hippocampus function caused by repeated infection with common and widespread neurovirulent picornaviruses." Other viruses kill brain cells, including the herpes virus and HIV.click the link to read more EXTERNAL LINK
