The three children baffled doctors: They couldn’t remember what day it was or what TV program they had just watched, and they routinely got lost in familiar surroundings. Yet they somehow learned to read, write and spell as well as their classmates.
Their brain injuries, the earliest ever studied, shed new light on memory and learning, scientists say. They suggest the brain organizes memories far differently than believed - and that even people with severe amnesia can form some type of long-term memory.
The research at London’s Institute of Child Health is “striking,” said Boston University neurobiologist Howard Eichenbaum.
It shows that certain “kinds of learning … can occur normally in these patients despite their inability to recollect that it occurred,” he explained.
At issue is the hippocampus, a region long considered vital for temporarily housing new memories before shuttling them to other parts of the brain for permanent storage.
Damage that kept the hippocampus from storing immediate memories was thought to block learning. The famous example was a man who in the 1950s had about two-thirds of his hippocampus, and some surrounding brain tissue, surgically removed and could never again learn anything new, Eichenbaum said.
So if a young child’s hippocampus was injured, doctors expected severe retardation to result - but they had never actually tracked such a child.
Now, study of the British children Beth, Jon and Kate suggests the hippocampus is critical only for “episodic” memory, the recording of context-rich daily events, London neuropsychologist Faraneh VarghaKhadem reported in the journal Science, being published today. If the surrounding brain cortices are undamaged, children can have surprisingly good “semantic” memory, the accumulation of bare facts, he said.
The first three children, all unrelated, suffered brain damage from oxygen deprivation. Beth, now 14, was resuscitated at birth after about eight minutes with no heartbeat. Jon, now 19, was damaged during either premature birth or convulsions at age 4. Kate, now 22, suffered respiratory arrest at age 9.
Beth and Jon were 5 before their parents noticed amnesia; Kate’s began just after her recovery.
The three are baffling. They got average grades in mainstream schools and rattled off such facts as the capital of Italy and the definition of “encumber.” Yet they would get lost on the way to class, forget conversations they’d just had, even forget what day it was - such severe amnesia that they live under strict supervision.
The two youngest children’s knowledge was particularly astounding. How could a youngster learn the alphabet, for example, if she couldn’t remember her mother showing her the letters?
“That is the puzzle we are trying to solve,” Mishkin said.