Biology subjects

Elger, C. E.

Publications and source records attributed to Elger, C. E..

3 recordsLinked to original sources

bioRxiv2026

Episodic memory consolidation by reactivation of human concept neurons during sleep reflects contents, not sequence of events

How do our brains manage to store our everyday experiences into memory? Neurons in the human temporal lobe that respond to the concept of an individual person or object have been shown to provide the semantic building blocks for episodic memory. Recording from 1433 neurons in neurosurgical patients who learned a story involving specific concepts, we found reactivation of neurons representing these concepts during slow-wave sleep after learning. Concept neurons were conjointly reactivated, particularly during sharp-wave ripples, with time lags suitable for synaptic modification. However, the temporal sequence of reactivation did not reflect the sequence of concepts in the learned story. Unlike rodent place cells, which can acquire preferred firing locations during exploration of new environments according to their pre-existing preferred sequence of activation, human concept neurons are tuned to specific semantic contents before learning starts. Consequently, pre-existing firing sequences correlate with consecutive place fields in rodents, but not with sequences of events in human experience. Thus, in contrast to reactivation of rodent place cells, reactivation of human concept cells does not reflect sequences of events in human experience.

neuroscience↗

bioRxiv2022

Phase of firing does not reflect temporal order in sequence memory of humans and recurrent neural networks

A prominent theory proposes that the temporal order of a sequence of items held in memory is reflected in ordered firing of neurons at different phases of theta oscillations 1. We probe this theory by directly measuring single neuron activity (1420 neurons) and local field potentials (LFP, 921 channels) in the medial temporal lobe of 16 epilepsy patients performing a working memory task for temporal order. We observe theta oscillations and preferential firing of single neurons at theta phase during memory maintenance. We find that - depending on memory performance - phase of firing is related to item position within a sequence. However, in contrast to the theory, phase order did not match item order. To investigate underlying mechanisms, we subsequently trained recurrent neural networks (RNNs) to perform an analogous task. Similar to recorded neural activity, we show that RNNs generate theta oscillations during memory maintenance. Importantly, model neurons exhibit theta phase-dependent firing related to item position, where phase of firing again did not match item order. Instead, we observed a mechanistic link between phase order, stimulus timing and oscillation frequency - a relationship we subsequently confirmed in our neural recordings. Taken together, in both biological and artificial neural networks we provide validating evidence for the role of phase-of-firing in memory processing while at the same time challenging a long-held theory about the functional role of spiking and oscillations in sequence memory.

neuroscience↗

bioRxiv2017

Forgot what you like? Evidence for hippocampal dependence of value-based decisions

Consistent decisions are intuitively desirable and theoretically important for utility maximization. Neuroeconomics has established the neurobiological substrate of value representation, but brain regions that provide input to the value-processing network is less explored. The constructed-preference tradition within behavioral decision research gives a critical role to cognitive processes that rely on associations, suggesting a role for the hippocampus in making decisions and to do so consistently. We compared the performance of 31 patients with mediotemporal lobe (MTL) epilepsy and hippocampal lesions, 30 patients with extratemporal lobe epilepsy, and 30 healthy controls on two tasks: binary choices between candy bars based on their preferences and a number-comparison control task where the larger number is chosen. MTL patients make more inconsistent choices than the other two groups for the value-based choice but not the number-comparison task. These inconsistencies increase with the volume of compromised hippocampal tissue. These results suggest a critical involvement of the MTL in preference construction and value-based choices.\n\nSignificanceOur days are full of choices that reflect our preferences. Economics lays out models of how to optimally make these decisions. Neuroeconomics has identified a cortical value-processing network whose activity correlates with constructs related to valuation and choice in economic models. However open questions remain: How are these value signals formed, and what regions might be necessary for retrieving and computing these value signals? Inspired by cognitive models calling on associative processes in value-based decisions, this paper uses unique neuropsychological data to establish the critical role of the medial temporal lobe in making consistent choices and further informs our understanding of the value-processing network.

animal behavior and cognition↗