McNulty Penelope A, Jankelowitz Stacey K, Wiendels Tanya M, Burke David
Institute of Clinical Neurosciences, The University of Sydney, Royal Prince Alfred Hospital, Sydney, Australia.
J Neurophysiol. 2008 Dec;100(6):3275-84. doi: 10.1152/jn.90435.2008. Epub 2008 Oct 15.
The interpretation of changes in the soleus H reflex is problematic in the face of reflex gain changes, a nonlinear input/output relationship for the motoneuron pool, and a nonhomogeneous response of different motoneurons to afferent inputs. By altering the stimulus intensity to maintain a constant reflex output, threshold tracking allows a relatively constant population of alpha-motoneurons to be studied. This approach was used to examine postactivation ("homosynaptic") depression of the H reflex (HD) in 23 neurologically healthy subjects. The H reflex was elicited by tibial nerve stimulation at 0.05, 0.1, 0.3, 1, and 2 Hz at rest and during voluntary plantar flexion at 2.5, 5, and 10% of maximum. A computerized threshold tracking procedure was used to set the current needed to generate a target H reflex 10% of M(max). The current needed to produce the target reflex increased with stimulus rate but not significantly beyond 1 Hz. In three subjects, the current needed to produce H reflexes of 5, 10, 15, and 20% M(max) at 0.3, 1, and 2 Hz increased with rate and with the size of the test H reflex. HD was significantly reduced during voluntary contractions. Using threshold tracking, HD was maximal at lower frequencies than previously emphasized, probably because HD is greater the larger the test H reflex. This would reinforce the greater sensitivity of small motoneurons to reflex inputs.
面对反射增益变化、运动神经元池的非线性输入/输出关系以及不同运动神经元对传入输入的非均匀反应，比目鱼肌H反射变化的解释存在问题。通过改变刺激强度以维持恒定的反射输出，阈值跟踪可以研究相对恒定的α运动神经元群体。该方法用于检查23名神经功能正常受试者的H反射（HD）的激活后（“同突触”）抑制。在休息时以及在最大收缩的2.5%、5%和10%的自主跖屈过程中，以0.05、0.1、0.3、1和2Hz的频率刺激胫神经引出H反射。使用计算机化的阈值跟踪程序来设置产生目标H反射为最大M波（M(max)）10%所需的电流。产生目标反射所需的电流随刺激频率增加，但在超过1Hz时增加不显著。在三名受试者中，在频率为0.3、1和2Hz时产生5%、10%、15%和20%M(max)的H反射所需的电流随频率以及测试H反射的大小增加。在自主收缩期间，HD显著降低。使用阈值跟踪，HD在比之前强调的更低频率时最大，可能是因为测试H反射越大，HD越大。这将加强小运动神经元对反射输入的更高敏感性。
