The monosynaptic reflex: a tool to investigate motor control in humans. Interest and limits

The principle of the monosynaptic reflex used as a tool to explore the exci tability of the motoneurones (MNs) is explained and the general methodology of the H reflex is described. The different drawbacks inherent in the tech nique are then considered: mechanisms other than the monosynaptic la excita tion of MNs contributing to the H reflex size (limitation of the H reflex s ize by disynaptic IPSPs, presynaptic inhibition of la terminals, post-activ ation depression); non-linearity and changes in the 'recruitment gain' in t he MN pool; and poor time resolution of the method. Despite these drawbacks , it is emphasized that the H reflex is the only available technique enabli ng one to investigate changes in transmission in spinal pathways during mot or tasks. (C) 2000 Editions scientifiques et medicales Elsevier SAS.