Biology subjects

Seger, S.

Publications and source records attributed to Seger, S..

5 recordsLinked to original sources

bioRxiv2026

Time cells lead neural reinstatement of episodic memory

The episodic memory system provides humans with a unique ability to form and retrieve rich and detailed memories. This capacity requires representing temporal context at encoding and recovering it at retrieval to drive successful recall. Time cells and ramping cells in human medial temporal cortex have been proposed as substrates of temporal context, but whether they participate in context recovery during retrieval remains unknown. Using microelectrode recordings from neurosurgical patients across two classical episodic paradigms, free recall and serial reconstruction, we identify time sensitive neurons and demonstrate that these neuron populations participate in neuronal assemblies and organized sequences on gamma and theta time scales respectively. Consistent with recovery of temporal context predicted by behavioral models of episodic processing, time cell firing precedes the broader assembly population and initiates sequential activation retrieval. These properties predict contextually-mediated recall behavior. We also identify phase coding by complementary populations as convergent mechanisms whose recruitment depends on task demands. Finally, we demonstrate the emergence of context-sensitive neurons in a naturalistic viewing dataset lacking the predictable temporal scaffold of canonical assays. These findings identify cellular mechanisms by which the human medial temporal cortex represents temporal context during episodic encoding and recovers it during retrieval.

neuroscience↗

bioRxiv2024

Differences and similarities between human hippocampal low-frequency oscillations during navigation and mental simulation

Low frequency oscillations in the hippocampus emerge during by both spatial navigation and episodic memory function in humans. We have recently shown that in humans, memory-related processing is a stronger driver of low frequency oscillations than navigation. These findings and others support the idea that low-frequency oscillations are more strongly associated with a general memory function than with a specific role in spatial navigation. However, whether the low-frequency oscillations that support episodic memory and those during navigation could still share some similar functional roles remains unclear. In this study, patients undergoing intracranial electroencephalography (iEEG) monitoring performed a navigation task in which they navigated and performed internally directed route replay, similar to episodic memory. We trained a random forest classification model to use patterns in low-frequency power (2-12 Hz) to learn the position during navigation and subsequently used the same model to successfully decode position during mental simulation. We show that removal of background differences in power between navigation and mental simulation is critical to detecting the overlapping patterns. These results suggest that the low-frequency oscillations that emerge during navigation are more associated with a role in memory than specifically with a navigation related function.

neuroscience↗

bioRxiv2019

Gamma oscillations during episodic memory processing reveal reversal of information flow between the hippocampus and prefrontal cortex

A critical and emerging question in human episodic memory is how the hippocampus interacts with the prefrontal cortex during the encoding and retrieval of items and their contexts. In the present study, participants performed an episodic memory task (free recall) while intracranial electrodes were simultaneously inserted into the hippocampus and multiple prefrontal locations, allowing the quantification of relative onset times of gamma band activity in the cortex and the hippocampus in the same individual. We observed that in left anterior ventrolateral prefrontal cortex (aVLPFC) gamma band activity onset was significantly later than in the hippocampus during memory encoding, whereas its activity significantly preceded that in the hippocampus during memory retrieval. These findings provide direct evidence to support models of prefrontal-hippocampal interactions derived from studies of rodents, but suggest that in humans, it is the aVLPFC rather than medial prefrontal cortex that demonstrate these reciprocal interactions.

neuroscience↗

bioRxiv2018

MTL functional connectivity predicts stimulation-induced theta power

Abstract/SummaryFocal electrical stimulation of the brain incites a cascade of neural activity that propagates from the stimulated region to both nearby and remote areas, offering the potential to control the activity of brain networks. Understanding how exogenous electrical signals perturb such networks in humans is key to its clinical translation. To investigate this, we applied electrical stimulation to subregions of the medial temporal lobe in 26 neurosurgical patients fitted with indwelling electrodes. Networks of low-frequency (5-13 Hz) spectral coherence predicted stimulation-evoked changes in theta (5-8 Hz) power, but only when stimulation was applied in or adjacent to white matter. Furthermore, these power changes aligned with control-theoretic predictions of how exogenous stimulation flows through complex networks, such as a dispersal of induced activity when functional hubs are targeted. Our results demonstrate that functional connectivity is predictive of causal changes in the brain, but that access to structural connections is necessary to observe such effects.

neuroscience↗

bioRxiv2018

Predictive control of electrophysiological network architecture using direct, single-node neurostimulation in humans

Chronically implantable neurostimulation devices are becoming a clinically viable option for treating patients with neurological disease and psychiatric disorders. Neurostimulation offers the ability to probe and manipulate distributed networks of interacting brain areas in dysfunctional circuits. Here, we use tools from network control theory to examine the dynamic reconfiguration of functionally interacting neuronal ensembles during targeted neurostimulation of cortical and subcortical brain structures. By integrating multi-modal intracranial recordings and diffusion tensor imaging from patients with drug-resistant epilepsy, we test hypothesized structural and functional rules that predict altered patterns of synchronized local field potentials. We demonstrate the ability to predictably reconfigure functional interactions depending on stimulation strength and location. Stimulation of areas with structurally weak connections largely modulates the functional hubness of downstream areas and concurrently propels the brain towards more difficult-to-reach dynamical states. By using focal perturbations to bridge large-scale structure, function, and markers of behavior, our findings suggest that stimulation may be tuned to influence different scales of network interactions driving cognition.

neuroscience↗