Spatially extended touch sensation

Previous work ( Eastwood et al, PNAS ; Sanzeni et al, eLife; Satta et al., J. Gen Physiology, 2019) developed a new theoretical model for the coupled process by which loads applied to the skin of the worm are transduced through the tissue and TRNs are activated. The worm is modeled as a cylindrical shell under internal pressure, which is indented by a spherical ball, as in the experimental set-up. The transmission of mechanical stimuli through the tissue is obtained via simulations of nonlinear equations for elastic media. As for the gating of the neuron, the gating mechanism is supposed to be provided by tangential stimuli on MeT channels, which are read out as an increased probability of channel activation. This differs from previous models for hair cell bundles, where the gating is perpendicular. The model accounts for the observed adaptation and the symmetry of the response between onset and offset of the applied force, which was a long-standing mystery, and reproduces existing response data to various stimuli. The current state of the model is that only spatially localized stimuli have been considered so far. In reality, the worm is subject to stimuli that are spatially extended over its entire body and involve the response of multiple neurons. Furthermore, experimental possibilities of extended stimulation are becoming available with ultrasound techniques poised to stimulate the entire body of the worm. We built upon the existing model and generalized it by considering those more realistic conditions and stimulations. As the first analysis, we established the necessity to simulate the nonlinear equations for elastic media. We investigated, in particular, a stimulus directly coming from the nematode's environment, such as constricting rings which are used by carnivorous fungi that feed on the worm and other kinds of stimuli. The expected fast adaptation and symmetry of the neural response was recovered again. The importance of the position of the trapping ring-like stimulus was established and the multiple activations of different neurons linked to it.