Monosynaptic stochastic stimulation of cat spinal motoneurons. I. Response of motoneurons to sustained stimulation.

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Abstract
A new method of electrical stimulation was employed to evoke reflex discharges from spinal motoneurons. This method is designed to approximate natural excitation of motoneurons from primary stretch receptors, and consists of stimulating many separate branches of the nerves to a synergistic muscle group with independent impulse generators. With this method, statistically independent impulse trains converge onto motoneurons, and for a particular motoneuron, the stimulus strengths on the afferent nerve bundles may be adjusted to ensure that both temporal and spatial summation combine to produce a reflex discharge. This technique allows a precise knowledge of the temporal patterns of all converging impulse processes and is thus particularly useful for investigating input-output relationships in a reflex pathway. The use of this technique was investigated and it was compared with other stimulation methods establishing the long term characteristics of the discharge patterns which result when the stimulus is suddenly applied and maintained. All experiments were carried out on spinal (decapitate) preparations. A wide range of adapting discharge patterns were found, and the effects of stimulus intensity, stimulus frequency, and barbiturate anaesthesia on these patterns were investigated. Motoneuron discharge responses were distributed continuously between tonic and phasic characteristics and an increase in excitatory drive could demonstrate a latent tonic discharge in a motoneuron previously producing only a phasic response.

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