Schedule of Events | Symposia

Tracking the traces of forgotten memories over six months with 7 Tesla high-resolution fMRI

Poster Session C - Sunday, March 30, 2025, 5:00 – 7:00 pm EDT, Back Bay Ballroom/Republic Ballroom

Konstantinos Ioannis Zervas¹ (konstantinos.zervas2@unibe.ch), Tom Willems¹, Katharina Henke¹; ¹University of Bern, Switzerland

Forgetting naturally kicks in following episodic learning, with most forgetting occurring within the first 24 hours. We hypothesize that the traces (engrams) of forgotten information remain implemented in the episodic memory system of the human brain. Therefore, we examined the fate of 96 newly formed face-object associations over six months in 40 young, healthy participants. We tracked these memory traces using 7T whole-brain fMRI and multivariate analyses. fMRI data were collected during encoding and repeated retrieval at 30 minutes, 24 hours, one week, and six months. For each retrieval trial, participants indicated their confidence. Guess responses were considered ‘forgotten’ memories. At 30 minutes, 29% of the learned associations were forgotten, at 24 hours 35%, at one week 43%, and at six months 56%. Although guessing retrieval accuracy was at chance for each study-test interval, the underlying memory traces persisted in the episodic memory network within hippocampal and prefrontal areas. Their reactivation correlated with guessing retrieval accuracy. Memory traces of forgotten associations corresponded in locations and shape to memory traces underlying consciously accessible memories but were thinner and exhibited significant changes over time, while traces underlying accessible memories remained stable. We conclude that putatively forgotten memories remain implemented in the brain but escaped conscious access.

Topic Area: LONG-TERM MEMORY: Episodic