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Why does memory gives us a slip

india Updated: Dec 05, 2006 15:55 IST
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Ever wonder why no matter how hard you try, you just can seem to remember something important, like giving your home phone number to a friend while wanting to give your cell one? Well boffins at the University of Wisconsin-Madison may have found the answer to that burning question.

Brad Postle, assistant professor of psychology at UW-Madison, together with Guilio Tononi of the UW-Madison School of Medicine and Public Health, and Eva Federoes, a researcher in the UW-Madison department of psychology – used a technique called “transcranial magnetic stimulation” (TMS) to determine to what extent interference, that occurs when "other remembered information disrupts, competes with or confuses the information that you want to remember", can disrupt memories.

"Interference is also often to blame in cases when we simply can't remember something," says Postle.

After that, the next step was to find out how to control interference.

From brain scans, scientists already knew that the sub-region under study, called the inferior frontal gyrus, or IFG, is active when volunteers take memory tests while confronting interference.

The boffins then set out to find whether the IFG essential to controlling interference, or was it just contributing more brain horsepower to complex memory tasks, by temporarily disrupted the IFG using TMS, which is a noninvasive technique.

"TMS is a technique that allows the induction of a current in the brain using a magnetic field that passes through the scalp and the skull safely and painlessly," said Tononi, a pioneer in refining the technique for brain research.

"TMS can be used to briefly 'scramble' neural activity in the underlying brain area for a short time, typically a second or so. This scrambling is fully reversible, and after the pulsing, the targeted brain area becomes fully functional again," he added.

In the current study, volunteers read a group of letters ("F, B, P, X"), and were asked a few seconds later whether a particular letter had appeared in the most recent group ("Did you just see a 'Z'""). In this type of test, having seen a "Z" in the string-before-last causes interference that makes the task more difficult. The subjects take longer to respond, and are more likely to incorrectly say "yes."

In previous studies of interference, the IFG consistently lit up in brain scans, showing that it does something when the memory tries to deal with interference.

The new study proved that the IFG is essential to blocking interference because accuracy plummeted when the IFG got a brief jolt of magnetic stimulation at the exact moment when the subject was confronting confusion.

The researchers now hope that locating the site of specific memory operations in the brain may help the millions of people with declining memories.

"Understanding how the brain controls interference may be a first step to helping people with memory problems," he says.

They are also positive about the use of TMS.

"TMS can be used not only to disrupt brain activity, but also to change it. If applied repeatedly, TMS can strengthen certain circuits that have become pathologically weak," said Tononi.

The study is published in the Proceedings of the National Academy of Sciences.

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