Multidimensional topography of memory revealed from thousands of daily documented memories

Our memories form a rich, colorful tapestry of emotions, events, people, and places, woven across the decades of our lives. However, research has typically been limited in its ability to assess the multidimensional nature of episodic memory, given the short time scales and artificial stimulus sets often required in experiments. In an era when people are constantly recording their lives through social media, we can now examine key questions about the behavioral and neural underpinnings of diverse and extensive real-world memories. Here, we tested the neural representations of episodic memory in a naturalistic setting, specifically focusing on the age, location, subjective memory strength, and emotional content of memories. We recruited 23 users of a video diary app ("1 Second Everyday"), who had recorded a total of 9,266 daily memory videos spanning up to 7 years prior to our study. During a 3T fMRI scan, participants viewed a set of 300 of their own memory videos intermixed with 300 videos from another individual. We identified key areas specifically engaged for ones own memories versus anothers. Delving into the multidimensional nature of these memories, we find that their features are tightly interrelated, highlighting the need to consider these features in conjunction when conducting memory research. Importantly, when looking at the distinct contributions of these features, we find a topography of memory content extending across the medial parietal lobe with separate representations of a memorys age, its strength, and the familiarity of the people and places involved.