Biology subjects

Barral, J.

Publications and source records attributed to Barral, J..

6 recordsLinked to original sources

bioRxiv2026

Direct optogenetic activation of inner hair cells improves the efficiency and fidelity of auditory encoding

Severe hearing impairment affects approximately 5% of the global population, with a prevalence projected to increase over the coming decades. Cochlear implant devices pose a neuroprosthetic treatment option to allow sound perception and speech comprehension. However, users are limited in the spectrum of auditory information they can regain because electrical stimulation of the auditory nerve generates a broad spread of current and limits the transmission of sound frequency information. Recently, optogenetic stimulation of the cochlear nerve has emerged as a promising alternative for hearing restoration. Because light can be precisely confined in space, optogenetic stimulation of the cochlea permits to activate auditory neurons within smaller tonotopic regions, thereby improving the encoding of sound frequencies compared to electrical stimulation. However, this approach is limited in terms of dynamic range and ability to follow rapidly varying inputs, thus preventing faithful transmission of auditory information. Here, we developed an alternative approach targeting directly sensory inner hair cells with optogenetics. We demonstrate that this approach decreases the amount of light energy necessary to evoke auditory responses. Direct stimulation of hair cells increases the dynamic range of intensities encoded by neurons in subcortical auditory areas and improves the temporal fidelity of optogenetic responses. Finally, a biophysical model of the auditory system suggests that preserving the synapses between inner hair cells and auditory neurons greatly improves the encoding performance of an optical cochlear implant. Together, our results suggest that targeting sensory inner hair cells is a promising approach for hearing restoration through an optical implant.

neuroscience↗

bioRxiv2025

Beta-burst dynamics in the motor cortex are reshaped through sensorimotor refinement

Beta-band activity (15-30 Hz) in motor cortex is closely linked to movement-related processing, yet its transient burst dynamics during long-term learning remain poorly understood. We used High-density electroencephalography (HD-EEG) to examine how beta bursts change over nine sessions of a bimanual coordination task, under adaptive and non-adaptive training conditions. Both training conditions led to motor skill learning, with the adaptive group improving more during training, but the non-adaptive group showing better retention. With training, contralateral primary motor cortex showed stronger beta desynchronization during movement and greater synchronization after movement. These changes reflected underlying burst dynamics: post-movement bursts became more temporally confined and consistent, with increased probability and reduced timing variability across sessions. Only the adaptive group showed a session-related increase in burst amplitude. These results demonstrate that beta burst features reorganize with practice, providing a temporally precise neural readout of training progression and revealing how different learning conditions shape cortical dynamics over time.

neuroscience↗

bioRxiv2024

Learning-Induced Effects of Practice Schedule Variability on Stimuli Discrimination Efficiency: High-Density EEG Multi-scale Analyses of Contextual Interference Effect

Contextual interference (CI) enhances motor learning by practicing skill variations in a random rather than blocked order. It has been demonstrated that performing aiming distances in a random order increased electrophysiological (EEG) markers of perceptual, attentional, and working memory processes. However, only the effect of CI on these markers before training was assessed, without evaluating whether they would decrease with learning in participants trained under the random compared to the blocked condition, indicating enhanced neural efficiency. To address this, 35 participants practiced an aiming task involving three distances over nine sessions across three weeks. They were divided into two groups: one trained with distances in a random order (HCI group) and the other in a blocked order (LCI group). Electrophysiological activity was recorded for all participants in the random condition before and after the training program using a high-density EEG multiscale approach, including topographical, source estimation, and source connectivity analyses. EEG analyses revealed post-training neural dynamic differences between groups. The HCI group showed reduced and shorter P3a-like activity compared to the LCI group, while the LCI group exhibited greater occipito-temporal-frontal gamma-band synchronization. These findings suggest that random practice enhances the efficiency of perceptual and attentional processes, particularly of stimuli discrimination, compared to blocked practice.

neuroscience↗

bioRxiv2024

Enhancing Perceptual, Attentional, and Working Memory Demands through Variable Practice Schedules: Insights from High-Density EEG Multi-Scale Analyses

Contextual interference (CI) enhances learning by practicing motor tasks in a random order rather than a blocked order. One hypothesis suggests that the benefits arise from enhanced early perceptual/attentional processes, while another posits that better learning is due to highly activated mnemonic processes. We propose to harness high-density electroencephalography in a multi-scale analysis approach, including topographic analyses, source estimations, and functional connectivity, to examine the intertwined dynamics of attentional and mnemonic processes within short time windows. We recorded scalp activity from 35 participants as they performed an aiming task at three different distances, under both random and blocked conditions using a crossover design. Our results showed that topographies associated with processes related to perception/attention (N1, P3a) and working memory (P3b) were more pronounced in the random condition. Source estimation analyses supported these findings, revealing greater involvement of the perceptual ventral pathway and the anterior cingulate and parietal cortices, along with increased functional connectivity in ventral alpha and frontoparietal theta band networks during random practice. Our results suggest that CI is driven, in the random compared to the blocked condition, by enhanced specific processes such as perceptual, attentional, and mnemonic, as well as large-scale general processes.

neuroscience↗

bioRxiv2023

Fast 2-photon stimulation using holographic patterns

Two decades after its introduction, optogenetics - a biological technique to control the activity of neurons or other cell types with light - remains a cutting edge and promising tool to study biological processes. Its increasing usage in research varies widely from causally exploring biological mechanisms and neural computations, to neurostimulation and sensory restauration. To stimulate neurons in the brain, a variety of approaches have been developed to generate precise spatiotemporal light patterns. Yet certain constrains still exists in the current optical techniques to activate a neuronal population with both cellular resolution and millisecond precision. Here, we describe an experimental setup allowing to stimulate a few tens of neurons in a plane at sub-millisecond rates using 2-photon activation. A liquid crystal on silicon spatial light modulator (LCoS-SLM) was used to generate spatial patterns in 2 dimensions. The image of the patterns was formed on the plane of a digital micromirror device (DMD) that was used as a fast temporal modulator of each region of interest. Using fluorescent microscopy and patch-clamp recording of neurons in culture expressing the light-gated ion channels, we characterized the temporal and spatial resolution of the microscope. We described the advantages of combining the LCoS-SLM with the DMD to maximize the temporal precision, modulate the illumination amplitude, and reduce background activation. Finally, we showed that this approach can be extended to patterns in 3 dimensions. We concluded that the methodology is well suited to address important questions about the role of temporal information in neuronal coding.

neuroscience↗

bioRxiv2017

Propagation of spike timing and firing rate in feedforward networks reconstituted in vitro

The manner in which information is transferred and transformed across brain regions is yet unclear. Theoretical analyses of idealized feedforward networks suggest that several conditions have to be satisfied in order for activity to propagate faithfully across layers. Verifying these concepts experimentally in networks has not been possible owing to the vast number of variables that must be controlled. Here, we culture cortical neurons in a chamber with sequentially connected compartments, optogenetically stimulate individual neurons in the first layer with high spatiotemporal resolution, and monitor the subthreshold and suprathreshold potentials in subsequent layers. In the first layer, a brief stimulus with different temporal precisions resulted in the modulation of the firing rate. This temporal to rate transformation was propagated to other layers as a sustained response, thereby preserving rate information. This novel mode of propagation occurred in the balanced excitatory-inhibitory regime and is mediated by NMDA-mediated synapses activated by recurrent activity.

neuroscience↗