Distinguishing false from true memories

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Memory accuracy does not only depend on how well one recognizes past events, but also on how well one distinguishes new information from previously exposed information. This ability is necessary to prevent people believing that they know something or someone that in fact they have never encountered. In the field of cognitive science, the mistake bringing one to confound a new stimulus with a known one is called false recognition. False recognition occurs mainly when a new stimulus resembles a known one. It is generally avoided or correctly rejected as a new stimulus, once a difference or mismatch is detected between the two stimuli. The brain mechanisms of false recognition have been widely studied and the role of recollection in this phenomenon is now relatively well documented. However, less is known about the brain mechanisms of recollection and mismatch detection involved in correct rejection. The present research program aims at studying these mechanisms within a framework involving four brain areas: the prefrontal cortex (PFC), the anterior cingulated cortex (ACC), the temporal cortex, and the visual cortex. Each of these brain areas contributes differently to correct rejection. First, when perceiving a new stimulus, mnemonic representations of resembling stimuli are reactivated in the temporal cortex. Due to memory limitations, only few features of the representation are generally reactivated. Visual areas mediating the specific features (e.g., colour) should thus also be reactivated. The PFC makes a comparison between the representation and the perceived stimulus and the ACC monitors mismatching information. The purpose of the present research program is to test this model with objects and faces. Three neuroimaging techniques recently acquired by the Douglas Institute will be used to provide a complete picture of the brain dynamics involved in false recognition and correct rejection. Functional magnetic resonance imagery (fMRI) will help identify the brain structures, event-related potentials (ERPs) will be used to define the spatio-temporal brain signature of the processes, and transcranial magnetic stimulation (TMS) will be used to test the functional role of the identified processes.