Neurone firing behaviour is a result of complex interaction between synaptic inputs and cellular intrinsic properties. Intriguing firing behaviour, delayed spiking, was shown in some neurones, in particular, in cat neocortical neurones and rat pyramidal hippocampal neurones. In contrast, the similar spiking mode was not reported for animal spinal motoneurones. In the present study, an attempt was made to look for possible evidence of delayed spiking in human motoneurones firing within the low-frequency, sub-primary range, characteristic for voluntary muscle contractions and postural tasks. Forty-seven firing motor units (MUs) were analyzed in ten experiments on three muscles (the flexor carpi ulnaris, the tibialis anterior, and the abductor pollicis brevis) in four healthy humans. Single MUs were activated by gentle voluntary muscle contractions. MU peri-stimulus time histograms, durations of inter-spike intervals, and motoneurone excitability changes within a target interspike interval were analyzed. It was found that during testing the firing motoneurone excitability by small, transient excitatory Ia afferent volley, depending firstly on volley timing within a target interspike interval and excitatory volley strength, the same motoneurone displayed either the direct short-latency response (the H-reflex) or the delayed response (with prolonged and variable latency). Thus, the findings, for the first time, provide evidence for a possibility of two modes of spiking in firing motoneurones. Methods of the estimation of delayed responses and their possible functional significance are discussed. It is emphasized that, for understanding of this issue, the integration of data from studies on experimental animals and humans is desirable.

神经元放电行为是突触输入和细胞内在特性之间复杂相互作用的结果。在某些神经元中，特别是在猫新皮层神经元和大鼠锥体海马神经元中，显示出令人着迷的射击行为，延迟的尖峰放电。相反，没有报道动物脊髓运动神经元具有相似的加标模式。在本研究中，试图寻找可能的证据来证明人运动神经元在低频，次主要范围内发射的延迟性突波，这是自愿性肌肉收缩和姿势任务的特征。在十个实验中，在四名健康人的三块肌肉（腕屈腕，胫骨前胫骨和短韧带外展肌）上对47个射击运动单位（MU）进行了分析。单个MU由轻度的自愿性肌肉收缩激活。MU周围刺激时间直方图，钉间间隔的持续时间和目标钉间间隔内的运动神经元兴奋性变化进行了分析。结果发现，在测试小型瞬态兴奋性Ia传入抽射的激发运动神经元兴奋性时，首先取决于目标尖峰间间隔和激发性凌空强度的齐射时间，同一运动神经元显示出直接的短时延响应（H反射） ）或延迟的响应（延迟时间长且可变）。因此，这些发现首次为在发射运动神经元中出现两种尖峰模式提供了证据。讨论了延迟响应的估计方法及其可能的功能意义。需要强调的是，为了理解这个问题，