In the sci-fi movie Eternal Sunshine of the Spotless Mind, a company named Lacuna wipes away painful memories. While once considered pure fiction, recent advances in neuroscience have brought memory manipulation closer to reality. Tracing back to the concept of the "engram"—the physical trace of memory proposed over a century ago—scientists have successfully implanted false memories and reactivated specific neural circuits in laboratory animals.

In his book How to Change a Memory, neuroscientist Steve Ramirez explores these groundbreaking developments. During his doctoral studies at MIT, Ramirez pioneered the use of optogenetics to reactivate fear memories in mice. His subsequent research demonstrated that artificial light signals could trigger false memories or reactivate positive experiences to alleviate depression-like behaviors in animal models.

The book outlines the current state of memory-editing technology while examining its philosophical and ethical implications. Ramirez emphasizes that human memory is not a static recording. Each time a memory is recalled, it undergoes reconsolidation, subtly altering its content. Because memories are interconnected with emotions and experiences, surgically erasing a single isolated memory remains complex. However, Ramirez argues that this inherent malleability provides therapeutic potential for treating conditions such as post-traumatic stress disorder (PTSD) and clinical depression.

Beyond scientific findings, the author shares personal reflections, including the loss of his research colleague Xu Liu and its impact on his life's work. The narrative balances scientific history with ethical questions about technology, warning against the misuse of memory control and stressing that human attitudes toward memory remain far more critical than the technology itself.