Semantic memories: 10

Semantic memories

Psychologist Phyllis Koenig, PhD, explains her research on semantic memory with a simple metaphor: If you want to build a tower out of blocks and you can't, it may be that you don't have the blocks to do it-a problem with supplies. Alternatively, it may be that you don't know how to stack them-a problem with process.

It's similar for using semantic memory: the part of memory that allows us to name and categorize everything we sense. Similar to building the tower, if you can't remember what an object is, you might not have the information stored in your brain-a lack of content. Alternatively, you might not be able to put your pieces of knowledge together-a breakdown in the process.

For at least 20 years, researchers have debated which part of this equation breaks down to cause semantic memory problems, particularly in patients with Alzheimer's disease, whose frequent difficulty with semantic memory can interfere significantly with their quality of life. By most accounts, those who believe that a loss of content is the primary culprit have held most of the cards.

But new research by Koenig and her colleagues at the University of Pennsylvania's School of Medicine provides new evidence for the idea that the processes involved in semantic memory may be equally important.

In a study published in the March issue of Neuropsychology (Vol. 21, No. 2), they find that people with Alzheimer's disease retain the ability to form new semantic memories when they use a simple, automatic process to place objects into categories.

They struggle only when asked to use a more complex rule-based process to access semantic memory, which requires higher order processing.

This research not only says something about what goes wrong in Alzheimer's disease, but also sheds light on how semantic memory operates in the brain. Specifically, it shows how the two aspects of memory are intertwined, says University of California San Diego neuropsychologist David Salmon, PhD.

"While the study doesn't rule out the possibility that there's semantic degradation in Alzheimer's disease, it does allow us to rule in impaired access to semantic knowledge, " he notes.

What's more, the finding could lend insight into the biological underpinnings of various aspects of Alzheimer's disease, says psychologist Alex Martin, PhD, senior investigator in the Cognitive Neuropsychology Section of the Laboratory of Brain and Cognition at the National Institute of Mental Health.

"It would really be interesting to try to link these behavioral deficits with different patterns of neuropathology, " he says.

Categorizing 'crutters'

As a first step toward that goal, Koenig and her colleagues took on the challenge of showing that the brain uses more than one process-requiring very different brain circuits-to form and use semantic memory.

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