Forgetting unrelated spatial memories through suppression-induced amnesia

Active forgetting through retrieval suppression can impair memory for information encountered nearby in time ("amnesic shadow"). Whether this collateral effect extends to spatial memory is unclear. Across three experiments, we examined how suppression influences the encoding of new spatial memories. Experiment 1 used a modified hippocampal-modulation paradigm that paired the Think/No-Think task with a spatial location task. Spatial locations encoded between suppression trials were recalled less accurately than those encoded between retrieval trials or a baseline, evidencing an amnesic shadow for spatial memory. Experiment 2 introduced a 24-hour delay and showed that the deficit persisted, indicating durability beyond initial encoding. Experiment 3 manipulated control strategies: direct suppression produced the shadow, whereas thought substitution did not impair nearby spatial learning. Together, the results support systemic-suppression accounts in which prefrontal control transiently down-regulates hippocampal function, broadly weakening hippocampus-dependent processes. By extending the amnesic shadow to spatial memory and isolating it to direct suppression, this work provides a strategy-specific behavioural marker of memory control and clarifies how attempts to contain unwanted thoughts can unintentionally degrade concurrent spatial learning.