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Intentional forgetting

Forgetting is often viewed as memory failure and it has been hypothesized to result from various processes including interrupted consolidation, passive decay, interference and retrieval failure. In contrast, intentional forgetting may be thought of as an adaptive memory function that helps to reduce interference in the processing and retrieval of relevant information. Selecting information to forget or disregard is often aided by explicit cues. In the item-method directed forgetting paradigm each stimulus (word) is followed by an instruction to remember (R) or to forget (F) and participants are asked to follow these cues (study phase). In the recognition test that follows, all words are re-presented, mixed with the same number of new words and subjects have to categorize each word as new or old, irrespective of previous instruction. In the ERP study on directed forgetting we identified changes in brain activity related to the successful and unsuccessful retrieval of words that were intended to be either forgotten or remembered. F and R instructions proved to work efficiently: recognition rate was significantly higher for to-be-remembered (TBR) than to-be-forgotten (TBF) words. We observed a typical old/new effect for TBR words that were correctly recognized (TBR_R). However, the old/new effect was absent for TBF words that were – despite the F instruction – successfully retrieved (TBF_R). Interestingly, actually forgotten TBF words (TBF_F) yielded ERPs that were more negative-going in comparison to ERPs for correctly rejected new items (the reversed old/new effect). Thus, our findings may be viewed as a kind of continuum with the old/new effect for TBR_R items on one side, the reversed old/new effect for TBF_F items on the other side and no effect for TBF_R items in between.

Furthermore, we were interested why some subjects – despite the F instruction - are able to correctly recollect a high number of TBF stimuli. We examined whether this ability is reflected in the structure of brain regions involved in memory and the control of retrieval processes. In subjects with high recognition rates for TBF stimuli, voxel-based morphometry revealed increased gray matter volume in the left ventrolateral prefrontal cortex and the right hippocampus. Gray matter volume in these regions correlated positively with the TBF recognition rate. On the other hand, no significant differences were detected in subjects who forgot many TBF stimuli. Our findings indicate that the right hippocampus and the left ventrolateral prefrontal cortex are of particular relevance in releasing TBF items from inhibition caused by the F instruction.

Nowicka A., Marchewka A., Jednoróg K., Tacikowski P., Brechmann A. Forgetting of emotionally negative stimuli is hard: fMRI study of directed forgetting. Cerebral Cortex, 21: 539-549, 2011 

Nowicka, A., Jednoróg, K., Wypych, M., & Marchewka, A. Reversed old/new effect for intentionally forgotten words: the ERP study of directed forgetting. International Journal of Psychophysiology, 71(2): 97-102, 2009

Nowicka, A., Jednoróg, K., Marchewka, A., & Brechmann, A. Successfully overcoming the inhibitory impact of the forget instruction: a voxel-based morphometric study of directed forgetting. Psychophysiology, 46: 1108-1012, 2009

 

Nencki Institute of Experimental Biology (c) 2015