The overall goal of the proposed research is to examine how reflex inputs, common drive and recurrent inhibition interact to coordinate motor nuclei. Our approach is 'bottom-up', working from basic physiology rather than proving a preferred model. The first question is how Ia EPSPs and recurrent IPSPs interact in motoneuron dendritic trees. Changes in impedance can be used to estimate the electrotonic position of active synapses. Nonlinear summation of IPSPs and EPSPs will be compared to model predictions. Another issue is how ensemble motor unit activity reflects common drive (stretch or fictive locomotion). Spectral analysis will be used to examine relations between drive and rectified neurogram, or motoneuron PSPs when a Na+ blocker is used to prevent spike firings. A last project is to build a computer model of a two-muscle joint with recurrent inhibition and beta innervation. Published data suggests that the two phenomena may not appear together in distal motor nuclei. The model will be used to explore possible interactions, beneficial and not, of the two spinal circuits.
