The patients know who they are, and can remember the details of their distant past. But they can't recall most things that have happened in the years since their brains were damaged. The doctor they met a week ago is a stranger, lunch is forgotten as soon as it has been eaten.
Yet, in Asaf Gilboa's lab, they quickly learn and retain information about exotic fruits or animals they had never heard of before, like an Australian anteater called the numbat.
It's the way they acquired this new knowledge that seemed to make it stick, said Dr. Gilboa, who is helping patients with amnesia tap into a dormant memory process in the brain. The learning was incidental – the new information was picked in the process of doing something else – and is similar to the way many researchers believe young children add 10 or more new words to their vocabulary every day.
This mechanism is called fast-mapping, and Dr. Gilboa and his colleagues at Baycrest's Rotman Research Institute in Toronto are using brain imaging to learn more about how it works. Their goal is to develop a new rehabilitative therapy for patients with neurological disorders that affect memory, including Alzheimer's disease. They hope shedding light on how the brain learns will help their patients move beyond animals and fruit to remembering faces and names.
"The brain has a number of memory systems. Different kinds of memory are supported by different networks of brain regions. There is overlap, but every system has an epicentre, which is critical," said Dr. Gilboa, who moved to Toronto from Israel last year.
In healthy adults, the hippocampus is the epicentre for episodic memory – remembering what happens in our lives. But in young children, the hippocampus and surrounding circuitry are still developing, Dr. Gilboa said. Fast-mapping, a study he published earlier this year suggests, doesn't involve the hippocampus, and instead engages parts of a large area of the brain known as the neocortex.
It is essentially learning by exclusion, and it's thought to be the mechanism by which children acquire many new words in a short period of time. For example: If a preschooler is faced with a truck, a ball, a doll and a stuffed animal with a blue face, and someone says, ``let's play with the Dax,'' the child picks up the stuffed animal. Since the child knows the words for the other three toys, it's deduced that the unfamiliar toy must be the Dax. Two weeks later, most children have retained that information.
Dr. Gilboa suspects that as the brain matures, the hippocampus offers the most effective way to learn and remember, and fast-mapping becomes largely dormant.
His studies focus on patients with a rare cases of amnesia, who have sustained damage to the hippocampus (which is also one of the first areas hit in Alzheimer's disease). He uses the fast-mapping technique to enlist the neocortex in the making new memories. So far, he has worked with about a dozen patients between the ages of 40 and 60 in both Israel and Toronto.
He presents patients with an image of two animals, for example, a zebra and a numbat, and asks them, "Is the numbat's tail pointed up?" The patients deduce that the unfamiliar animal with its tail in the air must be the numbat and they retain that information a week later, even though they don't remember learning it, or meeting Dr. Gilboa and his colleagues.
Healthy volunteers don't learn as well with fast-mapping – for them, it is easier to memorize what the exotic animals and fruits looked like.
Dr. Gilboa's post-doctoral fellow, Eve Attali, is investigating fast-mapping in Alzheimer's patients. "It is very nice to learn all these exotic animals and fruits and vegetables, but that is not a day-to-day thing. We want to know how we can take this mechanism and use it to help patients," Dr. Gilboa said.