Vibrisse

Résumé

thumb|La souris (Mus musculus) a des vibrisses près du nez. Les vibrisses sont des organes sensoriels propres à certains animaux, dont les mammifères. Il s'agit de longs prolongements kératinés (poils chez les mammifères et plumes chez les oiseaux) qui transmettent leurs vibrations à un organe sensoriel situé à leur base. Mammifères Chez le chat et les autres félins, ainsi que chez les rongeurs, ce sont ce qu'on appelle couramment les « moustaches ». Comme chez les autres mammifères terrestres, leurs vibrisses sont en réalité réparties en quatre groupes principaux :

de part et d'autre du museau
au-dessus des yeux
sur les joues
sous le menton. D'autres groupes peuvent être répartis sur le corps en fonction des espèces : sous les pattes pour les félins, autour de l'évent pour certains mammifères marins, etc.

Rat Chez le rat, les vibrisses, appelées communément « moustaches » servent à percevoir l'environnement, car leur vision est mauvaise

Source officielle

https://fr.wikipedia.org/wiki/Vibrisse

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Abstract Excitatory projection neurons of the neocortex are thought to play important roles in per-ceptual and cognitive functions of the brain by directly connecting diverse cortical and subcortical areas. However, many aspects of the anatomical and functional organization of these inter-areal connections are unknown. The mouse primary somatosensory whisk-er barrel cortex (S1) serves as an important model for investigating the mammalian neo-cortex, and, here, I firstly investigate the structure and secondly the function of a specific subset of S1 cortico-cortical long-range projection neurons. In the first part of my thesis, I studied long-range axonal projections of excitatory layer 2/3 neurons with cell bodies located in S1. As a population, these neurons densely projected to secondary whisker somatosensory cortex (S2) and primary/secondary whisker motor cortex (M1/2), with additional axon in the dysgranular zone surrounding the barrel field, perirhinal temporal association cortex and striatum. The execution of a goal-directed behavior requires the brain to process incoming sensory information from the environment in a context-, learning- and motivation-dependent manner in order to perform specific motor actions. Cortico-cortical communica-tion in the context of goal-directed sensorimotor transformation has begun to be studied, but little is known about how signaling between interconnected cortical areas is modified by sensorimotor learning, as well as in response to changes in reward contingencies. Hence, in the second part of my thesis, I studied cortico-cortical dynamics in primary whisker somatosensory barrel cortex (S1) of mice during a combined whisker and audito-ry task. Using transgenic mice expressing GCaMP6f combined with two-photon micros-copy and retrograde labeling techniques, I chronically monitored the activity of excitatory layer 2/3 neurons in S1 projecting to M1 or S2, while mice learned the behavioral switch task. The results demonstrated that both classes of neurons responded after whisker and auditory stimulation. However, the whisker stimulus evoked response was stronger than the auditory stimulus evoked response. Neurons projecting to S2 exhibited stronger re-sponses compared to neurons projecting to M1 neurons. Those responses remained rela-tively stable across training sessions and under different reward conditions. Furthermore, both classes of neurons responded during spontaneous licking, but neurons projecting to S2 had larger licking-related responses compared to neurons projecting to M1. This work therefore furthers our knowledge of the structure and function of specific types of cortical projection neurons, which is a necessary step towards detailed under-standing of how sensory information might be signaled from primary sensory areas to downstream brain regions for further processing.

EPFL2018

Chargement

Sparse, reliable, and long-term stable representation of periodic whisker deflections in the mouse barrel cortex

Johannes Maria Mayrhofer

The rodent whisker system is a preferred model for studying plasticity in the somatosensory cortex (barrel cortex). Contrarily, only a small amount of research has been conducted to characterize the stability of neuronal population activity in the barrel cortex. We used the mouse whisker system to address the neuronal basis of stable perception in the somatosensory cortex. Cortical representation of periodic whisker deflections was studied in populations of neurons in supragranular layers over extended time periods (up to 3 months) with long-term two-photon Ca2+ imaging in anesthetized mice. We found that inmost of the neurons (87%), Ca2+ responses increased sublinearly with increasing number of contralateral whisker deflections. The imaged population of neurons was activated in a stereotypic way over days and for different deflection rates (pulse frequencies). Thus, pulse frequencies are coded by response strength rather than by distinct neuronal sub-populations. A small population of highly responsive neurons (similar to 3%) was sufficient to decode the whisker stimulus. This conserved functional map, led by a small set of highly responsive neurons, might form the foundation of stable sensory percepts. (C) 2015 Elsevier Inc. All rights reserved.

Academic Press Inc Elsevier Science2015

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Motor Control in the Mouse Whisker System

Varun Sreenivasan

The motor systems of the mammalian brain are a remarkable product of many millions of years of evolution. It is the motor systems that make us and other mammals mobile, that guide our actions in response to sensory information and conversely modulate the very nature of the sensory input that our brain receives. The mystacial vibrissae or whiskers present on the face of mice are important sensors that provide high resolution tactile information to the brain. Whereas the pathways that are involved in signaling and processing sensory information from the whiskers have been the subject of intense investigation for many years, we know relatively little about how whisker movements are controlled by the brain. In the first part of the thesis, I present evidence for two parallel pathways originating from the neocortex that control antagonistic movements of the whiskers. I first describe whisker movements elicited upon Channelrhodopsin-2 (ChR2) stimulation of whisker somatosensory cortex (wS1) and whisker motor cortex (wM1). At short latencies, optogenetic stimulation of wS1 drove whisker retraction while optogenetic stimulation of wM1 drove rhythmic whisker protraction. Next, using recent developments in Rabies virus retrograde tracing, I mapped the location of the motor neurons in the facial nucleus, finding two distinct neuron pools for the extrinsic (retractor) muscle Nasolabialis and the intrinsic (protractor) follicular muscle. These distinct motor neuron populations received premotor input from different sources in the brainstem. While the premotor neurons of the extrinsic muscle were located more densely in the spinal trigeminal nucleus (Sp5), the premotor neurons of the intrinsic muscle were located more densely in the reticular formation (Rt). Anterograde tracing from wS1 and wM1 cortex revealed a complementary distribution of axons in the brainstem. Whereas wS1 strongly innervated Sp5, wM1 innervated the Rt. These data therefore begin to unravel the circuitry from the neocortex to the whisker motor neurons. In the second part of the thesis, I investigated the subthreshold and spiking correlates of whisker movements using whole-cell current clamp recordings of individual excitatory neurons in wM1. Brief 1 ms optogenetic stimulation of wS1 elicited rhythmic whisking after long latencies which was abolished upon pharmacological inactivation of wM1. Whole-cell recordings in wM1 during wS1 stimulation showed that the long-range synaptic input from wS1 to wM1 is encoded as a bi-phasic membrane potential response with an early depolarizing post-synaptic potential (Dep. PSP), followed by a hyperpolarizing post-synaptic potential (Hyp. PSP) in individual wM1 neurons. Approximately 150 ms after the wS1 stimulus, the Vm showed a rebound depolarization, which, on most trials, was followed by late rhythmic whisking. Whole-cell recordings during self-generated whisker movements showed that upon whisking, wM1 undergoes a profound cortical state change, where the mean Vm is more depolarized, slow fluctuations of the Vm are reduced and spike rates in layer 5 increase. Aligning the membrane potential trajectories to the onset of whisker movement epochs revealed that changes in Vm occurred almost 100 ms before movement onset. Finally, an examination of the Vm dynamics during rhythmic whisking showed that the Vm of individual wM1 neurons is modulated by the phase of the whisk cycle. This modulation is stronger in layer 2/3 compared to layer 5.

EPFL2015

Chargement

Motor Control in the Mouse Whisker System

Varun Sreenivasan

EPFL2015

EPFL2018