[Paleopsych] Science Blog: Northwestern researchers pinpoint how false memories are formed
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Sun Oct 17 15:54:39 UTC 2004
Northwestern researchers pinpoint how false memories are formed
False memories are the controversial subject of hotly contested
arguments about the validity of repressed memories that can surface
years after a traumatic event and about the credibility of eyewitness
accounts in criminal trials.
Because memories are imperfect under ordinary circumstances -- forming,
storing and retrieving them, with great variations in factors
influencing those processes -- it is unlikely that a one-answer-fits-all
will settle those controversies soon.
But a group of researchers from various disciplines at Northwestern
University literally have peered into the brain to offer new evidence on
the existence of false memories and how they are formed.
Published in the journal Psychological Science, the new study used MRI
technology to pinpoint how people form a memory for something that
didn't actually happen.
''Our challenge was to bring people into the laboratory and set up a
circumstance in which they would remember something that did not
happen,'' said Kenneth A. Paller, professor of psychology and co-
investigator of the study. (Brian Gonsalves, who was a doctoral student
of Paller's and who now is a post-doctoral fellow at Stanford
University, is the first author of the paper.)
''We measured brain activity in people who looked at pictures of objects
or imagined other objects that we asked them to visualize. Later we
asked them to discriminate what they actually saw from what they
imagined,'' Paller said.
Extending upon considerable Northwestern research on what happens in the
brain when people remember versus forget, the researchers were
interested in what happens differently in the brain when false memories
''We learned that the particular parts of the brain critical for
generating visual images are highly activated when people imagine images
such as those we presented to our study participants,'' said Paller.
Many of the visual images that the subjects were asked to imagine were
later misremembered as actually having been seen.
''We think parts of the brain used to actually perceive an object and to
imagine an object overlap,'' said Paller. ''Thus, a vividly imagined
event can leave a memory trace in the brain that's very similar to that
of an experienced event. When memories are stored for perceived or
imagined objects, some of the same brain areas are involved.''
Take a real life example in which a police interrogator asks if you saw
a particular person at a crime scene. That induces putting that person
in your imagination and possibly corrupts later questioning.
''Just the fact of looking back into your memory and thinking about
whether an event happened is tantamount to imagining that event
happening,'' Paller said. ''If I ask you if something happened, you
imagine it happening. Later on -- a day or a year later -- if I ask
about that event, you have the tough judgment of deciding what happened
and what was imagined.''
It is important to know that memory is fallible, Paller said. ''We know
that we forget quite a bit, but we're not always in touch with the idea
that our memories can sometimes can be misleading.''
For this procedure of measuring brain activity, people lay down in an
MRI machine as they looked at a screen with a series of words, all
concrete nouns, and pictures, and they wore head phones to hear what was
being said. They were instructed to generate a visual image
corresponding to each object that was named. For half the words, a
photographic image of the object was presented. The subjects were told
to make no response to photos, but only to look at each one while
waiting for the next word.
They were told to make a size judgment about the objects they were to
imagine. For example, if the word was cat, they were told to imagine the
cat and decide if a cat is generally bigger or smaller than a video
The memory test was administered outside the scanner and began
approximately 20 minutes after the scanning. Subjects heard a randomly
ordered sequence of spoken words. One-third corresponded to photos they
had seen, one-third to objects they had only imagined and one-third they
had neither seen nor imagined. For each word, subjects decided whether
or not they had viewed a photo of the named object during the study
Three brain areas (precuneus, right inferior parietal cortex and
anterior cingulate) showed greater responses in the study phase to words
that would later be falsely remembered as having been presented with
photos, compared to words that were not later misremembered as having
been presented with photos. The words leading to false memories also
tended to be slightly more concrete, on average, than those that did
not. Presumably, people could generate a visual image more easily for
the more concrete words.
''At any rate, the remarkable finding is that brain activity during the
study phase could predict which objects would subsequently be falsely
remembered as having been seen as a photograph,'' Paller said.
The flip side is that memory for viewed photographs was often correct.
People gave many correct responses for objects they indeed viewed. Brain
activity produced in response to viewed pictures and measured with
functional MRI also predicted which pictures would be subsequently
remembered. Two brain regions in particular -- the left hippocampus and
the left prefrontal cortex -- were activated more strongly for pictures
that were later remembered than for pictures that were forgotten. These
two brain areas have previously been understood to play a central role
The new findings directly showed that different brain areas are critical
for accurate memories for visual objects than for false remembering --
for forming a memory for an imagined object that is later remembered as
a perceived object. The neuroanatomical evidence furthermore sheds light
on the mental mechanisms responsible for forming accurate memories
versus false memories.
''In the case of the false remembering emphasized here, the false
memories were created when vivid visual imagery was engaged and a mental
image was produced,'' Paller said. ''These mental images left a trace in
the brain that was later mistaken for the trace that would have been
produced had that object actually been seen.''
Listed as on the study, the co-investigators are Brian Gonsalves, post-
doctoral fellow, Stanford University, and Northwestern researchers Paul
J. Reber, associate professor of psychology, Darren R. Gitelman,
associate professor of neurology, Todd B. Parrish, associate professor
or radiology, M. Marsel Mesulam, Ruth and Evelyn Dunbar Professor, and
Kenneth A. Paller, professor of psychology. The Northwestern researchers
are affiliated with the department of psychology, the Institute for
Neuroscience, the Cognitive Neurology and Alzheimer's Disease Center,
the department of neurology, the department of radiology and the
Feinberg School of Medicine.
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