Forgetting is an adaptive process that plays a critical role in sustaining the efficiency of mnemonic operations and can actively inhibit unwelcome (e.g. unpleasant or irrelevant information) memories from our awareness. The intentional forgetting of unwanted memories during encoding can be accomplished, via prefrontal control regions, by directly inhibiting hippocampal encoding processes, or by engaging hippocampal retrieval processes to replace the unwanted memory with substitutes. The neural mechanisms that underlie intentional forgetting, however, is not well understood -- the goal of this research project is to characterize how competition dependent learning via neural competition of memory representations ? a neural mechanism shown to contribute to incidental forgetting ? explains intentional forgetting. We also propose using real-time neurofeedback (providing information about a person's brain activity while they are performing tasks inside an MRI scanner) to either selectively improve or impair subsequent remembering. One recent theory provides a compelling explanation for a mechanism underlying forgetting. The co- activation of multiple thoughts during encoding and retrieval of an item can lead to neural competition between these thoughts, which in turn, are detrimental to the subsequent remembering of an item. This finding is consistent with the `non-monotonic plasticity hypothesis' generated by computational models of learning. In the following proposal, Study 1 tests whether the principle of non-monotonic plasticity during memory encoding also extends to motivated forgetting. We propose to administer an item-method intentional forgetting task in which participants will be required to either remember or forget items dependent on a cue following the presentation of the item. We hypothesize that neural competition between `to be remembered' and `to be forgotten' items will contribute to the subsequent forgetting of the item representation that `loses' the competition. We will use multivariate pattern classification of fMRI data to quantify the level (i.e. low, medium or strong) of activation for the `to be forgotten and `to be remembered' items in order to decode or track the relative strength of these items across each trial. The findings of this first study also allow us to test the relationship between the amount of neural competition in ventral temporal cortex, the connectivity from control regions in the prefrontal cortex to subdivisions of the hippocampus, and subsequent forgetting behavior. Furthermore, in Study 2, we intend to use neurofeedback training to calibrate the amount of neural competition elicited during memory encoding. We will behaviorally modify encoding strategies in a closed-loop neurofeedback system in order to improve on or interfere with (i.e. induce forgetting) subsequent memory performance.
The proposed research investigates the neural mechanisms underlying forgetting by testing whether interference arising from the co-activation of memories mediates the influence of top-down cognitive control in intentional forgetting. We will assess the extent to which neural competition in ventral temporal cortex as well as other neural regions can be promoted to selectively weaken memories through direct behavioral motivation, and whether this mechanism can be utilized using closed-loop neurofeedback. Successful completion of this project will enable the development of therapeutic treatments for memory impairments associated with amnesia, mild cognitive impairment and Alzheimer's Disease.
