On the methods employed to record and measure the human soleus H-reflex.
The aim of this study was to investigate if the magnitude of the soleus H-reflex is different depending on the method employed to measure its size (peak-to-peak amplitude vs. area). In this study, 13 healthy human subjects participated, while the soleus H-reflex was induced via conventional methods. In the first experiment, the soleus H-reflex was recorded via two monopolar electrodes and was evoked at least at eight different stimulation intensities in respect to the recovery curve of the H-reflex and at three different inter-stimulus intervals (ISIs) (8, 5, and 2 s). The ISI refers to the time delay between the single pulses delivered to the posterior tibial nerve within a single trial. In the second experiment, the effects of common peroneal nerve (CPN) stimulation at short (2-4 ms) and at long (60-120 ms) conditioning test (C-T) intervals on the soleus H-reflex elicited every 5 s were established. Control and conditioned reflexes were recorded via a single differential bipolar electrode. In both experiments, H-reflexes were quantified by measuring their size as peak-to-peak amplitude and as area under the full-wave rectified waveform. The reflex responses recorded through two monopolar electrodes across stimulation intensities and ISIs measured as peak-to-peak amplitude had larger values than measured as area. In contrast, the magnitude of the reflexes, conditioned by CPN stimulation at either short or long C-T intervals and recorded via a single differential electrode, were not significantly different when measured as peak-to-peak amplitude or as area. Our findings indicate that monopolar recordings yield different reflex sizes depending on the method employed to measure the reflex size, and that the H-reflex measured as area might detect better the homosynaptic reflex depression. The lack of observing such differences with bipolar recordings might be related to changes of the reflex shape at a given stimulus intensity due to inhibitory inputs. The implications of our findings are discussed in respect to human reflex studies.
Knikou
Maria
M
Department of Rehabilitation Medicine, Staten Island University Hospital, Staten Island, NY 10314, USA. knikou@mail.csi.cuny.edu
Taglianetti
Cory
C
D000200:Action Potentials / Q000502:physiology; D000328:Adult; D004558:Electric Stimulation / Q000379:methods*; D004566:Electrodes; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D018482:Muscle, Skeletal / Q000294:innervation* / Q000502:physiology; D009433:Neural Inhibition / Q000502:physiology; D010543:Peroneal Nerve / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D013116:Spinal Cord / Q000502:physiology; D013979:Tibial Nerve / Q000502:physiology*