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Memories persist even when forgotten, study suggests

Sept. 9, 2009
Courtesy UC Irvine
and World Science staff

A wom­an looks fa­mil­iar, but you can’t re­mem­ber her name or where you met her. New re­search sug­gests the mem­o­ry ex­ists – you simp­ly can’t re­trieve it.

Us­ing brain im­ag­ing, neu­ro­sci­en­tists at the Uni­vers­ity of Cal­i­for­nia, Ir­vine found that a per­son’s brain ac­tiv­ity while re­mem­bering an event is very si­m­i­lar to when it was first ex­pe­ri­enced, even if spe­cif­ics can’t be re­called.

The elon­gat­ed struc­ture at the cen­ter of the green-tinted zone of this im­age rep­re­sents the hip­po­cam­pus, a brain re­gion cru­cial to mem­o­ry for­ma­tion. (Im­age cour­te­sy NIH)


“If the de­tails are still there, hope­ful­ly we can find a way to ac­cess them,” said Jeff John­son, a post­doc­tor­al re­searcher at the uni­ver­sity and lead au­thor of the stu­dy, ap­pear­ing Sept. 10 in the sci­ent­ific jour­nal Neu­ron.

“By un­der­stand­ing how this works in young, healthy adults, we can po­ten­tial ly gain in­sight in­to situ­a­t­ions where our mem­o­ries fail more no­tice­ably, such as when we get old­er,” he said. “It al­so might shed light on the fate of viv­id mem­o­ries of trau­mat­ic events that we may want to for­get.”

John­son and col­leagues used func­tion­al mag­net­ic res­o­nance im­ag­ing, a brain scan­ning tech­nique, to study the brain ac­tiv­ity of stu­dents.

The stu­dents were shown words and asked to per­form var­i­ous tasks: im­ag­ine how an art­ist would draw the ob­ject named by the word, think about how the ob­ject is used, or pro­nounce the word back­ward in their minds. The scan­ner cap­tured im­ages of their brain ac­tiv­ity dur­ing these ex­er­cises.

About 20 min­utes lat­er, the stu­dents viewed the words a sec­ond time and were asked to re­mem­ber any de­tails linked to them. Again, brain ac­tiv­ity was recorded.

Uti­liz­ing a math­e­mat­i­cal meth­od called pat­tern anal­y­sis, the sci­en­tists as­so­ci­at­ed the dif­fer­ent tasks with dis­tinct pat­terns of brain ac­tiv­ity. When a stu­dent had a strong rec­ol­lec­tion of a word from a par­tic­u­lar task, the pat­tern was very si­m­i­lar to the one gen­er­at­ed dur­ing the task. When rec­ol­lec­tion was weak or non­ex­ist­ent, the pat­tern was not as prom­i­nent but still rec­og­niz­a­ble as be­long­ing to that par­tic­u­lar task, the re­search­ers said.

“The pat­tern an­a­lyz­er could ac­cu­rate­ly iden­ti­fy tasks based on the pat­terns gen­er­at­ed, re­gard­less of wheth­er the sub­ject re­mem­bered spe­cif­ic de­tails,” John­son said. “This tells us the brain knew some­thing about what had oc­curred, even though the sub­ject was not aware of the in­form­at­ion.”


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A woman looks familiar, but you can’t remember her name or where you met her. New research suggests the memory exists – you simp ly can’t retrieve it. Using brain imaging, neuro scientists at the Un ivers ity of California, Irvine found that a person’s brain activ ity while remembering an event is very similar to when it was first experienced, even if specifics can’t be recalled. “If the details are still there, hopeful ly we can find a way to access them,” said Jeff Johnson, postdoctoral researcher at the un ivers ity and lead author of the study, appearing Sept. 10 in the journal Neuron. “By un derstanding how this works in young, healthy adults, we can potential ly gain insight into situ ations where our memories fail more noticeably, such as when we get older,” he said. “It also might shed light on the fate of vivid memories of traumatic events that we may want to forget.” Johnson and colleagues used functional magnetic resonance imaging, a brain scanning techique, to study the brain activ ity of students. The students were shown words and asked to perform various tasks: imagine how an artist would draw the object named by the word, think about how the object is used, or pronounce the word backward in their minds. The scanner captured images of their brain activ ity during these exercises. About 20 minutes later, the students viewed the words a second time and were asked to remember any details linked to them. Again, brain activ ity was recorded. Utilizing a mathematical method called pattern analysis, the scientists associated the different tasks with distinct patterns of brain activ ity. When a student had a strong recollection of a word from a particular task, the pattern was very similar to the one generated during the task. When recollection was weak or nonexistent, the pattern was not as prominent but still recognizable as belonging to that particular task, the researchers said. “The pattern analyzer could accurate ly identify tasks based on the patterns generated, regardless of whether the subject remembered specific details,” Johnson said. “This tells us the brain knew something about what had occurred, even though the subject was not aware of the inform ation.”