Biology subjects

Remi, J.

Publications and source records attributed to Remi, J..

5 recordsLinked to original sources

bioRxiv2026

Non-invasive tracking of ripple-like activity during human sleep using MEG

Hippocampal ripples are considered a key mechanism of sleep-dependent memory consolidation. In humans, however, their direct investigation has relied on invasive recordings from patients with epilepsy, because EEG provides limited access to fast activity from deep medial temporal structures. Here, we tested whether source-resolved magnetoencephalography can reveal physiologically meaningful ripple-like activity during NREM sleep in healthy humans. These events showed hallmarks expected of sleep ripples: they were most prominent in medial temporal regions and embedded within slow oscillation (SO)-spindle dynamics, occurring preferentially during SO up-states and spindle centers. To test mnemonic relevance, we combined sleep MEG with targeted memory reactivation, in which learning cues were replayed during sleep. TMR improved memory performance, and later remembered cues preferentially recruited medial temporal ripple-like events alongside cortical spindles. Ripple-like events also coincided with enhanced item-specific reactivation during successful TMR. Together, these findings establish MEG as a non-invasive window onto hippocampo-cortical memory dynamics during sleep.

neuroscience↗

bioRxiv2025

Low-frequency brain oscillations reflect the dynamics of the oculomotor system: a new perspective on subsequent memory effects

Neural activity and eye movements are two well-established predictors of memory performance in humans. Successful memory formation is typically associated with reduced alpha/beta power (i.e., the alpha/beta subsequent memory effect) and an increased number of eye movements. However, the functional relevance of these two memory correlates has primarily been investigated in isolation, leaving their coupling and combined contribution to memory formation largely unknown. Here, we address this gap through four experiments involving simultaneous eye-tracking and scalp or intracranial electroencephalography recordings while participants viewed scenes either freely or under varying levels of visual constraint. Across experiments and cohorts, we identified the degree of visual exploration, rather than subsequent memory performance, as the consistent and robust modulator of alpha/beta power reductions. Going beyond correlations, manipulating eye movements dissociated alpha/beta power reductions from memory. Combined with the finding that saccade parameters predicted the dynamics of alpha/beta activity, our results directly link alpha/beta activity to the oculomotor system. Moreover, we show that the accumulation of saccades over time accounted for the reduced alpha/beta power, resembling the pattern typically observed after stimulus onset. Our work demonstrates that neglecting eye movements results in an incomplete understanding of the alpha/beta subsequent memory effect. Together, the evidence points at alpha/beta activity directly reflecting eye movements, and only indirectly, memory formation. The current study thus bridges two lines of previous research and advocates for new perspectives on the specific interpretation of the alpha/beta subsequent memory effect and on the function of alpha/beta activity in general.

neuroscience↗

bioRxiv2025

Thalamic oscillations distinguish natural states of consciousness in humans

Natural states of consciousness are thought to be regulated by deep brain structures such as the thalamus. However, very little is known about the underlying electrophysiology in humans. Here, using a rare opportunity to directly record from the human thalamus, we identify a hitherto-unreported brain-state-specific oscillation of approximately 19-45 Hz. This oscillation is present only during Rapid Eye Movement (REM) sleep and wakefulness, while being absent during Non-REM sleep. The 19-45 oscillation further distinguishes REM sleep microstates, co-occurring with bursts of eye movements, and is specific to the Central Thalamus, a structure implicated in causing global brain state transitions. The discovery of a distinct oscillatory signature in the Central Thalamus that distinguishes conscious states opens up avenues to further investigate thalamic contributions to states of consciousness in humans and potentially to refine interventions to treat disorders of consciousness.

neuroscience↗

bioRxiv2023

Memory reactivation of real-world spatial orientation revealed by human electrophysiology.

Memory consolidation relies on the reactivation of previous experiences during sleep. The precise interplay of sleep-related oscillations (slow oscillations, spindles and ripples) is thought to coordinate the information flow between relevant brain areas, with ripples mediating memory reactivation. However, in humans empirical evidence for a role of ripples in memory reactivation is lacking. Here, we investigated the relevance of sleep oscillations and specifically ripples for memory reactivation during human sleep using targeted memory reactivation (TMR). Intracranial electrophysiology in epilepsy patients and scalp EEG in healthy participants revealed that elevated levels of SO-spindle activity promoted the read-out of TMR induced memory reactivation. Importantly, spindle-locked ripples recorded intracranially from the medial temporal lobe were found to be instrumental for memory reactivation to unfold during non-rapid eye movement (NREM) sleep. Our findings establish ripples as key-oscillation in human systems consolidation and emphasize the importance of the coordinated interplay of the cardinal sleep oscillations.

neuroscience↗

bioRxiv2023

Electrophysiological signatures of veridical head direction in humans

Information about heading direction is critical for navigation as it provides the means to orient ourselves in space. However, given that veridical head direction signals require physical rotation of the head and most human neuroimaging experiments depend upon fixing the head in position, little is known about how the human brain is tuned to such heading signals. To address this, we asked fifty-two healthy participants undergoing simultaneous EEG and motion tracking recordings (split into two experiments) and ten patients undergoing simultaneous intracranial EEG and motion tracking recordings to complete a series of orientation tasks in which they made physical head rotations to target positions. We then used a series of forward encoding models and linear mixed-effects models to isolate electrophysiological activity that was specifically tuned to heading direction. We identified a robust posterior central signature that predicts changes in veridical head orientation after regressing out confounds including sensory input and muscular activity. Both source localisation and intracranial analysis implicated the medial temporal lobe as the origin of this effect. Subsequent analyses disentangled head direction signatures from signals relating to head rotation and those reflecting location-specific effects. Lastly, when directly comparing head direction and eye gaze-related tuning, we found that the brain maintains both codes while actively navigating, with stronger tuning to head direction in the medial temporal lobe. Together, these results reveal a taxonomy of population-level head direction signals within the human brain that is reminiscent of those reported in the single units of rodents.

neuroscience↗