Computation predicts rapidly adapting mechanotransduction currents cannot account for tactile encoding in Merkel cell-neurite complexes
Fig 2
Conceptual view of the generator function.
The diagrams demonstrate how small time constants of about 8 and 200 ms respectively for the SI and RI components are convolved together with stress in the skin to produce a composite current from which spike firing responses are ultimately derived. In (A) stress over time, under a displacement-controlled ramp-and-hold stimulation (top bar dark grey is ramp, light grey is hold), serves as the input to the generator function. Note the viscoelastic relaxation of skin stress over the stimulus hold. Then, in three cases with inputs of step stresses, (B) a single step increase in stress σ1 evokes current output I1, which is the sum of slowly inactivating current ISI and rapidly inactivating current IRI, (C) three sequentially delivered step stresses show that current decays but builds upon the prior magnitude, and (D) a single step decrease in stress from σn to σn+1 evokes an immediate decrease in current followed by a slower decay. Note that the ultra-slowly inactivating current is omitted to simplify the explanation of the concept. Also omitted for simplicity are the finite element and leaky integrate-and-fire model contributions.