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Lemercier, C. E.

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

4 recordsLinked to original sources
bioRxiv2023

Audiovisual stimuli enhance narrowband gamma activity along the mouse thalamocortical visual circuit

To what extent thalamic activity can contribute to multisensory integration at cortical level is unclear. To explore this aspect, we used the mouse narrowband gamma oscillations (NBG), which arise from the lateral geniculate nucleus (LGN) and from upstream retinal inputs, as a tool to investigate potential thalamic audiovisual information transfer to the primary visual cortex (V1). We found that simultaneous bimodal audiovisual stimulation increased the power of V1 NBG. Pharmacological and optogenetic manipulations demonstrated that V1 NBG audiovisual responses occurred independently of primary auditory cortex activation. LGN recordings revealed that the majority of its neurons exhibited audiovisual properties. These properties comprised an increase of both the visual-evoked response and gamma-rhythmicity, indicating that the modulation of V1 NBG by audiovisual stimuli likely has a thalamic origin. Our results reveal a previously unreported subcortical source of audiovisual information transfer in V1 and suggest a new role for the LGN as a multisensory integration and relay center.

neuroscience↗
bioRxiv2022

Reducing Merkel cell activity in the whisker follicle disrupts cortical encoding of whisker movement amplitude and velocity

Merkel cells (MCs) and associated primary sensory afferents of the whisker follicle-sinus complex robustly code whisker self-movement, angle, and whisk phase during whisking. However, direct evidence of their roles in encoding whisker movement at cortical level is currently missing. To this end, spiking activity of primary somatosensory barrel cortex (wS1) neurons was measured in response to varying whisker deflection amplitude and velocity in transgenic mice with previously established reduced mechanoelectrical coupling at MC-associated afferents. Under reduced MC activity, wS1 neurons exhibited increased sensitivity to whisker deflection. This appeared to arise from a lack of variation in response magnitude to varying whisker deflection amplitude and velocity. This latter effect was further indicated by weaker variation in the temporal profile of the evoked spiking activity when whisker deflection amplitude and velocity varied. Nevertheless, under reduced MC activity, wS1 neurons retained the ability to discriminate stimulus features based on the timing of the first post-stimulus spike. Collectively, results from this study suggest that MCs contribute to both cortical encoding of whisker amplitude and velocity predominantly by tuning cortical response magnitude and by patterning evoked spiking activity, rather than in tuning cortical response latency.

neuroscience↗
bioRxiv2022

Comparative study between radiofrequency- and muscimol-induced inhibition of cultured networks of cortical neuron

Previous studies have shown that spontaneously active cultured networks of cortical neuron grown planar microelectrode arrays are sensitive to radiofrequency (RF) fields and exhibit an inhibitory response more pronounced as the exposure time and power increase. To better understand the mechanism behind the observed effects, we aimed at identifying similarities and differences between the inhibitory effect of RF fields (continuous wave, 1800 MHz) to the {gamma}-aminobutyric acid type A (GABAA) receptor agonist muscimol (MU). Inhibition of the network bursting activity in response to RF exposure became apparent at an SAR level of 28.6 W/kg and co-occurred with an elevation of the culture medium temperature of ~1 {degrees}C. Exposure to RF fields preferentially inhibits bursting over spiking activity and exerts fewer constraints on neural network bursting synchrony, differentiating it from a pharmacological inhibition with MU. Network rebound excitation, a phenomenon relying on the intrinsic properties of cortical neurons, was observed following the removal of tonic hyperpolarization after washout of MU but not in response to cessation of RF exposure. This implies that hyperpolarization is not the main driving force mediating the inhibitory effects of RF fields. At the level of single neurons, network inhibition induced by MU and RF fields occurred with reduced action potential (AP) half-width. As changes in AP waveform strongly influence efficacy of synaptic transmission, the narrowing effect on AP seen under RF exposure might contribute to reducing network bursting activity. By pointing only to a partial overlap between the inhibitory hallmarks of these two forms of inhibition, our data suggest that the inhibitory mechanisms of the action of RF fields differ from the ones mediated by the activation of GABAA receptors.

neuroscience↗