Fact Memory Spared Despite Hippocampal Damage

July 17, 1997

Research by scientists at the Institute of Child Health in London, published in the July 18th issue of Science, provides new insight into how memory works.

Even if the hippocampus - the part of the brain long thought of as being critical for memory - is damaged, the underlying regions can still carry out some important memory functions, reports the research team, which includes senior author Mortimer Mishkin, Ph.D., National Institute of Mental Health, NIH, Bethesda, MD.

The findings may hold new hope for children with memory problems and have implications for healthcare professionals and teachers involved in the assessment and education of children with special needs.

The researchers studied three young people who had suffered oxygen deprivation and consequent brain injury early in life. Brain scans using magnetic resonance imaging techniques revealed damage to the hippocampus, an especially vulnerable structure in the middle of the brain. Although they suffered from amnesia and were unable to recall events from their everyday life with any reliability, the children all attended mainstream schools and were able to gain average grades in most of their classwork, particularly in speech and language, reading and writing, and factual knowledge.

For example, they might know the name of the capital of Italy, but remember nothing about their vacation there last year. Similarly, they cannot reliably remember messages or appointments or find their way around even familiar surroundings. These types of deficits did not become obvious until the age of five or six, but now severely restrict their independence.

One influential school of thought holds that if the memory system is damaged, both 'episodic' memory (memory for events) and 'semantic' memory (memory for facts) would be impaired equally. The new study suggests that even though these two different types of memory normally work together and interdependently, if only the hippocampus is damaged, a child can develop fact memory surprisingly well through the functioning of the underlying cortices.

"These new case studies offer a particularly impressive example (of preserved fact memory) that can be attributed to selective focal hippocampal damage early in life," observes Boston University neurobiologist and NIMH grantee Howard Eichenbaum, Ph.D., in an accompanying "perspective" in the same issue of Science.

Previously, there had been no report of this kind of amnesia after very early brain damage, and it was thought that early injury to the hippocampus might well stunt intellectual development -- with the result being not just amnesia, but mental retardation.

"As a result of this study, we need to rethink how children with special needs are assessed and diagnosed," said Dr. Faraneh Vargha-Khadem, neuropsychologist at the Institute of Child Health, who led the research. "If children with this type of amnesia can be diagnosed early, then appropriate remediation can be given early on, perhaps even before school entry. If we can do this, we may be able to give these children the opportunity to live a more independent life."

Since their discovery of the syndrome, Dr Vargha-Khadem and colleagues have so far identified some 15 children suffering from such amnesia due to oxygen deprivation, which can occur during difficult or premature birth or heart surgery. The research team plans to screen groups of young children who may be at risk in hopes of providing early intervention.

The National Institute of Mental Health is a component of the NIH, an agency of the U.S. Public Health Service, part of the U.S. Department of Health and Human Services.

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NIH/National Institute of Mental Health

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