PMID- 30589956 OWN - NLM STAT- MEDLINE DCOM- 20200527 LR - 20200527 IS - 1460-9568 (Electronic) IS - 0953-816X (Linking) VI - 49 IP - 10 DP - 2019 May TI - Electrical stimulation of human corticospinal axons at the level of the lumbar spinal segments. PG - 1254-1267 LID - 10.1111/ejn.14321 [doi] AB - Electrical stimulation over the mastoids or thoracic spinous processes has been used to assess subcortical contribution to corticospinal excitability, but responses are difficult to evoke in the resting lower limbs or are limited to only a few muscle groups. This might be mitigated by delivering the stimuli lower on the spinal column, where the descending tracts contain a greater relative density of motoneurons projecting to lower limb muscles. We investigated activation of the corticospinal axons innervating tibialis anterior (TA) and rectus femoris (RF) by applying a single electrical stimulus over the first lumbar spinous process (LS). LS was paired with transcranial magnetic stimulation (TMS) at interstimulus intervals (ISIs) of -16 (TMS before LS) to 14 ms (LS before TMS). The relationship between muscle contraction strength (10%-100% maximal) and the amplitude of single-pulse TMS and LS responses was also investigated. Compared to the responses to TMS alone, responses to paired stimulation were significantly occluded in both muscles for ISIs >/=-8 ms (p