The earthquakes that rattled Christchurch more than six years ago may have led to some suffering "quake brain" - a long-lasting effect on people's memory and basic abilities.
A new study released by the University of Otago shows 13 percent of people tested two years after the quakes had difficulty completing simple tasks, compared to those who hadn't experienced such a traumatic event.
Professor Richard Porter says the affected group included emergency responders, people injured in the quakes or relatives of victims from the February 2011 quake.
"We do not know how long this effect is likely to have lasted," he says.
"We are currently seeking funding to re-test the group of people to see if their memory has now returned to normal."
Prof Porter says there would likely be a significant effect on memory for a large percentage of the population.
He also urges people should be cautious as these problems are common and should make allowances for difficulties after such events.