Sleep differentially and profoundly impairs recall memory in a patient with fornix damage

In March 2020, CT, a kind, bright, and friendly young woman underwent surgery for a midline tumor involving her septum pellucidum and extending down into her fornices bilaterally. Following tumor diagnosis and surgery, CT experienced significant memory deficits: CT’s family reported that she could remember things throughout the day, but when she woke up in the morning or following a nap she would expect to be in the hospital, forgetting all the information that she had learned before sleep. The current study aimed to empirically validate CT’s pattern of sleep-dependent memory loss and explore its neurological underpinnings. On two successive days, CT and age-matched controls watched an episode of a TV show and took a nap or stayed awake before completing a memory test. Although CT performed numerically worse than controls in both conditions, sleep profoundly exacerbated her memory impairment, such that she could not recall any details following a nap. This effect was replicated in a second testing session. In high-resolution MRI scans, we observed evidence of the trans-callosal surgical approach’s impact on the mid-anterior corpus callosum, showed that CT had perturbed white matter particularly in the right fornix column, and demonstrated that CT’s hippocampal volumes did not differ from controls. These findings suggest that the fornix is important for sleep-dependent consolidation of episodic memories. As the primary output pathway of the hippocampus, the fornix may ensure that specific memories are replayed during sleep, maintain the balance of sleep stages, or allow for the retrieval of memories following sleep