When aging or neurological disease affects memory, people often say it feels as if their loved one "is no longer there." This irreplaceable role of memory in shaping one's identity and behavior makes it particularly important to clarify how the content of our memory — its precision and structure — is represented in the brain and how faithfully it is shared across people. At the center of this question is the medial temporal lobe (MTL) — a region in the brain whose interactions with neocortex we believe implement memory fidelity across timescales, content types, and individuals. Memory also offers a unique window into the brain itself: by understanding how memories are formed and retrieved, we begin to uncover the brain's underlying organizational principles — insights that may one day help us better understand complex human experiences like perception, decision-making, and mental health.
To explore these questions, our lab takes a multidisciplinary approach, studying how the human brain gives rise to memory fidelity across multiple spatial and temporal scales. In particular, we study MTL-neocortical interaction as the mechanism for memory fidelity — using tools ranging from mathematical modeling and large-scale behavioral experiments to fMRI, (i)EEG, eye-tracking, brain stimulation, and lesion case studies. Most recently, we've been fortunate to work with rare datasets that allow us to record directly from individual neurons in the awake human brain, offering a detailed view of how memory is coded in action.
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While some of our memories are vivid and precise, others are foggy and fuzzy. Why do our memories vary in the degree of quality? Our work has shown that MTL is causally necessary for memory precision even at delays of seconds, challenging the classical boundary between short- and long-term memory. Using intracranial recordings, we track how MTL and neocortical activity evolve during memory formation and retrieval, using reinstatement and memory strength as indices of fidelity. This work reveals how MTL-neocortical communication — through hippocampal-neocortical connectivity — implements representational fidelity across timescales.
Xie, W., Chapeton, J. I., Bhasin, S., Zawora, C., Wittig Jr, J. H., Inati, S. K., ... & Zaghloul, K. A. (2023). The medial temporal lobe supports the quality of visual short-term memory representation. Nature Human Behaviour, 7(4), 627-641.
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Our memories are not stored in isolation. Every object, word, or face we encounter exists within a rich web of relationships — perceptual similarities, categorical boundaries, associative connections — that together define its structural position in our mental landscape. This structure is not incidental to memory: items with richer, more central structural positions are remembered more precisely, more fluently, and more consistently across people. Understanding why requires going beyond behavior to the neural code itself. Using large-scale behavioral benchmarks, computational models of representational geometry, and direct recordings from individual neurons in the awake human anterior temporal lobe, we ask how the brain encodes structural relationships at multiple levels — from perceptual similarity to categorical organization to associative knowledge — and how this neural representation of structure determines what we remember and how faithfully we remember it.
Xie, W., Wittig Jr, J. H., Chapeton, J. I., El-Kalliny, M., Jackson, S. N., Inati, S. K., & Zaghloul, K. A. (2024). Neuronal sequences in population bursts encode information in human cortex. Nature, 635(8040), 935-942.
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Some things are remembered faithfully by almost everyone — others forgotten just as consistently. This cross-observer regularity reflects the structural position of information in representational space: items with richer associative connections are retrieved more fluently and more consistently across people. We formalize this using computational models of global matching — in which memory retrieval reflects the similarity between a cue and stored representations across both episodic and semantic components. Crucially, this same matching signal tracked by MTL activity asymmetrically shapes reconstructive recall and probe-based recognition, connecting behavioral consistency to MTL circuit dynamics.
Xie, W., Bainbridge, W. A., Inati, S., Baker, C. I., & Zaghloul, K. A. (2020). Memorability of words in arbitrary verbal associations modulates memory retrieval in the anterior temporal lobe. Nature Human Behaviour, 4(9), 937-948.