Phantom Images on Brain 763

The brain can compensate for some memory loss

Brain research over the past 30 years has shown that if a part of the brain controlling movement or sensation or language is lost because of a stroke or injury, other parts of the brain can take over the lost function — often as well as the region that was lost.

New research at the University of California, Berkeley, shows that this holds true for memory and attention as well, though — at least for memory — the intact brain helps out only when needed and conducts business as usual when it’s not.

These results support the hypothesis that memory is not stored in one place, but rather, is distributed in many regions of the brain, which means that damage to one storage area is easier to compensate for.

“It’s not just specific regions, but a whole network, that’s supporting memory,” said Bradley Voytek, a UC Berkeley postdoctoral fellow in the Helen Wills Neuroscience Institute and first author of two recent journal articles describing EEG (electroencephalogram) studies of people with strokes. Voytek recently completed his Ph.D. in neuroscience at UC Berkeley.

“The view has always been, if you lose point A, point B will be on all the time to take over,” said co-author Dr. Robert Knight, UC Berkeley professor of psychology and head of the Wills Institute. “Brad has shown that’s not true. It actually only comes on if it’s needed.

“Most of the time, it acts like a normal piece of brain tissue. It only kicks into hyperdrive when the bad part of the brain is particularly challenged, and it does it in less than a second. This is a remarkably fluid neural plasticity, but it isn’t the standard ‘B took over for A,’ it’s really ‘B will take over if and when needed.'”

One of the papers, published Nov. 3 in the online edition of Neuron and scheduled for the Nov. 4 print issue of the journal, describes a study of stroke patients who have lost partial function in their prefrontal cortex, the area at the top front of each hemisphere of the brain that governs memory and attention.

Voytek put electrodes on the scalps of six stroke patients as well as six controls with normal prefrontal cortex function, and showed each patient a series of pictures to test his or her ability to remember images for a brief time, so-called visual working memory. Visual working memory is what allows us to compare two objects, keeping one in memory while we look at another, as when we choose the ripest of two bananas.

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