Andrews Jennifer C, Stein Richard B, Roy François D
Department of Physiology, University of Alberta, Edmonton, Alberta, Canada; Neuroscience and Mental Health Institute, University of Alberta, Edmonton, Alberta, Canada.
Department of Surgery, University of Alberta, Edmonton, Alberta, Canada; and Neuroscience and Mental Health Institute, University of Alberta, Edmonton, Alberta, Canada
J Neurophysiol. 2015 Jul;114(1):485-92. doi: 10.1152/jn.01007.2014. Epub 2015 May 20.
Postactivation depression of the Hoffmann (H) reflex is associated with a transient period of suppression following activation of the reflex pathway. In soleus, the depression lasts for 100-200 ms during voluntary contraction and up to 10 s at rest. A reflex root evoked potential (REP), elicited after a single pulse of transcutaneous stimulation to the thoracolumbar spine, has been shown to exhibit similar suppression. The present study systematically characterized the effect of transcranial magnetic stimulation (TMS) on postactivation depression using double-pulse H reflexes and REPs. A TMS pulse reduced the period of depression to 10-15 ms for both reflexes. TMS could even produce postactivation facilitation of the H reflex, as the second reflex response was increased to 243 ± 51% of control values at the 75-ms interval. The time course was qualitatively similar for the REP, yet the overall increase was less. While recovery of the H reflex was slower in the relaxed muscle, the profile exhibited a distinct bimodal shape characterized by an early peak at the 25-ms interval, reaching 72 ± 23% of control values, followed by a trough at 50 ms, and then a gradual recovery at intervals > 50 ms. The rapid recovery of two successively depressed H reflexes, ∼ 25 ms apart, was also possible with double-pulse TMS. The effect of the TMS-induced corticospinal excitation on postactivation depression may be explained by a combination of pre- and postsynaptic mechanisms, although further investigation is required to distinguish between them.
霍夫曼（H）反射的激活后抑制与反射通路激活后的短暂抑制期有关。在比目鱼肌中，这种抑制在自愿收缩时持续100 - 200毫秒，在休息时可持续长达10秒。经皮刺激胸腰椎后引出的反射根诱发电位（REP）已被证明表现出类似的抑制。本研究使用双脉冲H反射和REP系统地描述了经颅磁刺激（TMS）对激活后抑制的影响。对于这两种反射，一个TMS脉冲将抑制期缩短至10 - 15毫秒。TMS甚至可以产生H反射的激活后易化，因为在75毫秒间隔时第二个反射反应增加到对照值的243±51%。REP的时间进程在定性上相似，但总体增加较少。虽然在放松的肌肉中H反射的恢复较慢，但其曲线呈现出明显的双峰形状，其特征是在25毫秒间隔处有一个早期峰值，达到对照值的72±23%，随后在50毫秒处有一个低谷，然后在间隔>50毫秒时逐渐恢复。使用双脉冲TMS也可以使两个相继被抑制的H反射快速恢复，间隔约25毫秒。TMS诱导的皮质脊髓兴奋对激活后抑制的影响可能由突触前和突触后机制共同解释，尽管需要进一步研究来区分它们。
