Neuroimaging techniques can help determine if the neural processes driving this retrieval of inaccurate memories are different from those that drive the retrieval of accurate memories. Several research groups are using functional magnetic resonance imaging (fMRI) to address this question. The hope is that neuroimaging can help determine the various potential sources of false memories.
Daniel Schacter, PhD, and his colleagues at Harvard University have looked at neural activity associated with the creation of false memories. Previous studies had focused on neural activity associated with the retrieval of false memories.
Relying upon earlier work that showed the right fusiform cortex is involved in encoding the exact visual details of objects and the left fusiform cortex is involved in more general processing, Schacter’s group designed an experiment to test the role of the right fusiform area in avoiding the formation of false memories for objects similar to those seen previously but not exactly the same.
In the study, led by graduate student Rachel Garoff, participants underwent brain scans using fMRI as they made judgments about the size of various objects. A surprise memory test was then given when the patients were outside the MRI scanner. During the test, patients saw objects identical to those seen earlier, objects similar to those they had seen earlier, and new objects they had not seen at all.
Although the study is still in progress, results to date indicate that the right fusiform area was more active in these individuals during the encoding of objects participants later labeled the “same” as objects they had seen before. The right fusiform area was less active when patients incorrectly labeled objects the same when they were only similar, or when they labeled objects similar when they were actually the same.
“This preliminary finding supports the idea that the right fusiform area is tied to the encoding of specific visual details,” Schacter said. “It also suggests that false memories of objects can be reduced through additional activity of the right fusiform area during encoding.”
In another study, Schacter’s group showed that visual processing regions of the brain were reactivated during true memory but not during false memory.
Scott Slotnick and Schacter constructed “prototype” shapes by adjoining four curves into various shapes, then they distorted these prototypes to form “exemplar” shapes. The twelve individuals who have taken part in the study thus far were instructed to remember each shape and whether it appeared to the left or the right on a screen. “True memory” was defined as recognizing a shape that was seen previously, and “false memory” referred to mistakenly recognizing a shape that resembled a shape seen earlier but that was not actually seen. In the next step, fMRI was used to determine which areas of the brain were associated with true and false memory.
“We found that participants gave the same response regarding whether an object was “new” or “old” during true and false memory, which leads you to expect that the associated brain activity might be indistinguishable,” Schacter said. “But fMRI revealed there is a different activation of brain regions involved in visual processing during true versus false memory. What we need to do now is understand the meaning of this difference.”
This is not as impressive as it first sounds. The researchers can not say in each instance whether the memory being recalled is true or false. They only see a difference on average over many experimental runs.
However, Schacter points out that their work currently averages brain activity over many trials, so detecting the accuracy of a single memory is not yet possible.
Still, these experiments suggest that it might be possible to train people to be more aware of the strength of their own memory recall. If there are differences in brain activity when recalling accurate and inaccurate matches between viewed images and memory it might be possible to develop a training regime to let people know when they are making fake matches between memories and viewed objects. By getting that immediate feedback people might be able to calibrate their own sense of certainty and develop a better sense of just how strong the feeling of seeing a match has to be in order for it to be likely to be accurate.
|Share |||Randall Parker, 2003 November 10 02:49 PM Brain Memory|