Biology subjects

Chaieb, L.

Publications and source records attributed to Chaieb, L..

3 recordsLinked to original sources

bioRxiv2025

Attention modulates hippocampal sharp-wave ripples in humans

Hippocampal sharp-wave ripples (SWRs) are high-frequency events critical for memory consolidation, typically studied during sleep and quiet wakefulness. Emerging evidence suggests that SWRs also occur during active behavior, yet their role in awake cognition remains unclear. Here, we demonstrate that changes in sustained attention modulate both the occurrence of SWRs and their temporal alignment to ongoing hippocampal oscillations. Using intracranial EEG recordings from epilepsy patients performing a sustained attention to response task (SART), we first identified attentional states based on behavioral variability and subjective reports. Next, we observed that SWRs were more frequent during high-attention periods, despite the absence of memory demands. Importantly, SWRs during low-attention periods showed higher phase synchrony with low-frequency oscillations (theta to lower beta) indicating increased endogenous coordination of SWRs under low attentional focus. These findings show that SWRs are dynamically regulated by attentional engagement, supporting a broader role for ripples in active cognitive processing.

neuroscience↗

bioRxiv2020

Auditory beat stimulation modulates memory-related single-neuron activity in the human medial temporal lobe

Auditory beats are composed of two sine waves using nearby frequencies, which can either be applied as a superposed signal to both ears or to each ear separately. In the first case, the beat sensation results from hearing an amplitude-modulated signal (monaural beat). In the second case, it is generated by phase-sensitive neurons in the brain stem (binaural beat). We investigated the effects of monaural and binaural 5 Hz beat stimulation on neural activity and memory performance in neurosurgical patients performing an associative recognition task. Previously, we had reported that these beat stimulation conditions modulated memory performance in opposite directions. Here, we analyzed data from a patient subgroup, in which microwires were implanted in the amygdala, hippocampus, entorhinal cortex and parahippocampal cortex. We identified neurons responding with firing rate changes to binaural versus monaural 5 Hz beat stimulation. In these neurons, we correlated the differences in firing rates for binaural versus monaural beats to the memory-related differences for remembered versus forgotten items and associations. In the left hemisphere for these neurons, we detected statistically significant negative correlations between firing rate differences for binaural versus monaural beats and remembered versus forgotten items/associations. Importantly, such negative correlations were also observed between beat stimulation-related firing rate differences in the baseline window and memory-related firing rate differences in the poststimulus windows. In line with concepts of homeostatic plasticity, we interpret our findings as indicating that beat stimulation is linked to memory performance via shifting baseline firing levels.

neuroscience↗

bioRxiv2020

Saccadic modulation of neural activity in the human anterior thalamus during visual active sensing

Humans and other primates explore visual scenes by active sensing, using saccadic eye movements to relocate the fovea and sample different bits of information multiple times per second. Saccades induce a phase reset of ongoing neuronal oscillations in primary and higher-order visual cortices and medial temporal lobe. As a result, neuron ensembles are shifted to a common state at the time visual input propagates through the system (i.e., just after fixation). The extent of the brains circuitry modulated by saccades is not yet known. Here, we evaluate the possibility that saccadic phase reset impacts the anterior nuclei of the thalamus (ANT). Using rare recordings in the human thalamus of three surgical patients, we found saccade-related phase concentration, peaking at 3-4 Hz, coincident with suppression of Broadband High-frequency Activity (BHA; 80-180 Hz). Our results provide evidence for saccade-related modulation of neuronal excitability dynamics in the ANT, consistent with the idea that these nuclei are engaged during visual active sensing. These findings show that during real-world active visual exploration neural dynamics in the human ANT, a part of extended hippocampal-diencephalic system for episodic memory, exhibit modulations that might be underestimated in typical passive viewing.

neuroscience↗