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Control of firing patterns of vibrissa motoneurons and vibrissa movements| old_uid | 7301 |
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| title | Control of firing patterns of vibrissa motoneurons and vibrissa movements |
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| start_date | 2009/07/08 |
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| schedule | 11h |
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| online | no |
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| summary | Whiskers of rodents need to move in order to contact and palpate objects and enable active touch. The intrinsic and extrinsic muscles that move the vibrissa are innervated by vibrissa motoneurons (vMNs). We investigate how the firing patterns of the vMNs are generated, and how they are translated to muscle contraction and whisker protraction.
vMNs are capable of producing rhythmic whisker movements in the absence of cortical input, cerebral inputs or sensory feedback. This may imply that vMN are controlled by a subcortical central pattern generator (CPG). Tonic firing can be induced in vMNs by application of serotonin that enhances gNaP, the persistent sodium conductance. Nonlinear suprathreshold resonance in firing rate is observed in response to periodic input current. To explain the various firing patterns of VMNs, we construct and analyze a single-compartment, conductance-based model of vMNs, responding to both an increase in gNaP and phasic CPG input. When the CPG input is small, increasing gNaP may switch the system abruptly from a quiescent state to a firing state that is strongly locked to the phasic input, even if the firing rate is small. Bursting behavior is obtained only for strong CPG input. These results imply that whereas the CPG input controls the firing frequency and phase and the number of spikes per cycle, serotonergic modulation may determine whether the neuron is either quiescent or fires in a stimulus-locked manner.
To characterize the transformation from vMN firing to muscle vibrissa movement, we study a biomechanical model of the vibrissa composed of whiskers, muscles and springs and dampers that mimic the elastic properties of the tissue. We find that temporal summation in intrinsic muscles in response to motoneuron spikes is supra-linear, and can be explained by a nonlinear dependency of the muscle force on the intrinsic calcium concentration. Intrinsic muscle contraction causes a deflection of the anterior connected whisker and a smaller deflection of the posterior connected whisker if the whisker points relatively backward at rest; if the whisker points forward at rest, the deflection of the posterior whisker is larger. Our observations can be used for describing motor control of whisker movement, and are confirmed by analysis of experimental data. |
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| responsibles | van Vreeswijk, Battaglia |
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