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Monday, October 24, 2016

By Geoffrey Mohan, Los Angeles Times

Memory can be altered by new experience, and isn’t nearly as accurate as courtroom testimony might have us believe, a new study suggests.

The results suggest a cheeky answer to the question posed by comedian Richard Pryor: “Who you gonna believe: me, or your lyin’ eyes?”

Turns out, Pryor was onto something. The brain behind our eyes can distort reality or verify it, based on subsequent experience. And somewhat paradoxically, the same area of the brain appears to be strongly involved in both activities, according to a study published online Tuesday in the Journal of Neuroscience.

Northwestern University cognitive neuroscientist Donna J. Bridge was testing how memory is either consolidated or altered, by giving 17 subjects a deceptively simple task. They studied the location of dozens of objects briefly flashed at varied locations on a standard computer screen, then were asked to recall the object’s original location on a new screen with a different background.

When subjects were told to use a mouse to drag the re-presented object from the center of the new screen to the place where they recalled it had been located, 16 of 17 got it wrong, by an average of about 3 inches.

When the same subjects then were given three choices — the original location, the wrong guess and a neutral spot between them — they almost unfailingly dragged the object to the incorrectly recalled location, regardless of the background screen. Their new memory was false.

But it gets trickier still. When subjects were instead told to drag the object from center screen to a pre-selected spot on the new background, then were asked to move it from a central spot to where they recalled seeing it originally, they got the original position right at an uncanny rate. (They were not told the pre-selected spot was wrong, and its misplacement distance roughly matched that of errors measured in the previous trials.)

Faced with the three position choices, these same subjects also matched the correct original position, regardless of screen background.

All the while, measures of brain activity showed that the same area of the hippocampus was highly active both for maintaining the “correct” memory and confirming a newly associated “false” memory.

“That overlapping brain activity was pretty shocking to us,” said Bridge, a postdoctoral student at the university’s Feinberg School of Medicine. “The idea is that whatever is most important to you right now, the hippocampus is responsible to either maintain a stable representation or change it.”