When aging or neurological disease compromises one’s memory, people often say it feels as if their loved one "is no longer there." What usually fades first is not whether someone remembers, but how clearly. One may find a face familiar but only have a vague impression. These changes often begin in deep brain structures such as the medial temporal lobe (MTL), including the hippocampus and amygdala, which are among the first affected in Alzheimer's and are central to epilepsy and emotional disorders.

Our lab asks how the MTL and neocortex work together to keep memories active and clear, and whether we can reach these deep circuits without surgical intervention. Findings from brain lesions, intracranial recordings, and noninvasive stimulation have converged on a key finding: the MTL plays a key role in memory precision, separate from whether something is remembered at all. We build on this finding by combining behavioral experiments and computational models with fMRI, intracranial recordings in patients with epilepsy, lesion studies, and noninvasive stimulation targeting deep brain regions.

  • For as far as we can remember, some memories are vivid and precise, while others are foggy and fuzzy.  We have shown that the MTL is needed for remembering details precisely, even over a few seconds, a timescale long assumed to depend on other systems, and that damage to this region blurs memories rather than wiping them out. Standard memory tests ask whether something is remembered and can miss this early loss of detail. Using intracranial recordings in patients with epilepsy, we track how MTL and neocortical activity unfold as a memory forms, is maintained, and is retrieved, and ask what keeps its details active and precise in mind.

Xie, W. et al. (2023), Nature Human Behaviour; Xie, W. et al. (2025), Hippocampus; Choo et al. (2026). Brain.

  • Memories are not stored as isolated fragments. Each object, word, or face we encounter is embedded in a network of associations that places it in a larger representational space. We ask how the brain encodes that structure and how it guides what people later remember and reconstruct. Combining direct recordings from the human brain with models of representational geometry, we investigate how patterns of neural population activity, including how frequently neurons fire and the order in which they fire, carry information about individual items and their relationships.

Xie, W. et al. (2024), Nature

  • Whether a memory returns to mind at all is separate from how clearly it returns. What makes an item likely to be remembered? We find that the prior knowledge an item connects to, the cues available at the moment of recall, and the state of the brain systems jointly support retrieval. Some items are retrieved reliably by almost everyone, while others are not, and we ask how much of this reflects properties of the material itself and how much reflects the individual observer.

Xie, W. et al. (2020), Nature Human Behaviour