The SISO monosynaptic reflex threshold and gain: relationship to motoneuron pool parameters

Single-input single-output (SISO) synapse models describe the input firing-rate - output firing-rate relationship of a motoneuron (MN) pool. While the MN pool is very complex, containing many MNs with a range of properties, the SISO model contains very few parameters: a presynaptic threshold, a linear postsynaptic gain, and some form of output firing-rate saturation. In this study, the parameters of the SISO synapse model are related to the patterns of MN recruitment and rate coding in the MN pool. Using this general analysis, SISO models are then generated for two specific MN pools, one healthy, one unhealthy. It is concluded that the SISO model represents healthy synaptic. behaviour well, even across large ranges of input firing-rates. Estimation of SISO models for unhealthy behaviour, however, should be treated with caution.