Neuromimetic model of a neuronal filter.

Experimental work in cats has shown that a series of afferent impulses from muscle receptors activated during contractions of an ankle extensor elicit declining inhibitory potentials in homonymous and synergic motoneurones. Inhibitory potentials were ascribed to the action of Ib afferents from Golgi tendon organs that are specific contraction-sensitive mechano-receptors. The decline of inhibition was, at least partly, due to presynaptic inhibition acting as a filter of tendon organ information in the spinal cord. In the present work, a computer model of the simplest spinal pathways from Ib fibres to motoneurones was designed. In order to make the model as realistic as possible, the most pertinent of the known functional properties of the neuronal elements were incorporated. Functions simulating primary afferent depolarizations of Ib terminals, i.e. the electrophysiological correlate of presynaptic inhibition, were introduced in the network. Simulations showed that declining inhibitory potentials were computed in the output stage of the network that represented the "motoneurone-like" element. These results support the assumption that the filtering out of Ib inputs is to a great extent due to presynaptic inhibition. The model behaved as expected, suggesting that predictions of the behaviour of neural components in the biological network should be possible upon introduction in the model of other, more complex, spinal pathways from Ib fibres to motoneurones.