Episodic memories reflect a bound representation of multimodal features that can be recollected with varying levels of precision. Recent fMRI investigations have demonstrated that the precision and content of information retrieved from memory engage a network of posterior medial-temporal and parietal regions co-activated with the hippocampus. Yet, comparatively, little is known about how memory content and precision affect common neural signatures of memory captured by electroencephalography (EEG), where recollection has been associated with changes in ERP and oscillatory measures of neural activity. Here, we used a multifeature paradigm previously reported in [Cooper, R. A., & Ritchey, M. Cortico-hippocampal network connections support the multidimensional quality of episodic memory. eLife, 8 , e45591, 2019] with continuous measures of memory, in conjunction with scalp EEG, to characterize the content and quality of information that drives ERP and oscillatory markers of episodic memory. A common signature of memory retrieval in the left posterior regions, called the late positive component, was sensitive to overall memory quality and also to precision of recollection for spatial features. The analysis of oscillatory markers during recollection revealed that alpha/beta desynchronization was modulated by overall memory quality and also by individual features in memory. Importantly, we found evidence of a relationship between these two neural markers of memory retrieval, suggesting that they may represent complementary aspects of the recollection experience. These findings demonstrate how time-sensitive and dynamic processes identified with EEG correspond to overall episodic recollection and also to the retrieval of precise features in memory.

In March 2020, C.T., 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, C.T. experienced significant memory deficits: C.T.'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 C.T.'s pattern of memory loss and explore its neurological underpinnings. On two successive days, C.T. and age-matched controls watched an episode of a TV show and took a nap or stayed awake before completing a memory test. Although C.T. 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. High-resolution MRI scans showed evidence of the trans-callosal surgical approach's impact on the mid-anterior corpus callosum, indicated that C.T. had perturbed white matter particularly in the right fornix column, and demonstrated that C.T.'s hippocampal volumes did not differ from controls. These findings suggest that the fornix is important for processing episodic memories during sleep. As a key 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.