Convergence of flexor reflex and corticospinal inputs on tibialis anterior network in humans. Issue 1 (January 2016)

• Record Type: Journal Article
• Authors: Mackey, Ann S.; Uttaro, Denise; McDonough, Maureen P.; Krivis, Lisa I.; Knikou, Maria
• Is Part Of: Clinical neurophysiology. Volume 127:Issue 1(2016:Jan.)
• Page Start: 706
• Page End: 715
• Publication Date: 2016-01
• Subjects: Cutaneous afferents -- Flexor reflex -- MEP -- Sensorimotor cortex -- Sensorimotor integration -- TMS; Neurophysiology -- Periodicals; Electroencephalography -- Periodicals; Electromyography -- Periodicals; Neurology -- Periodicals; 612.8
• DOI: 10.1016/j.clinph.2015.06.011
• Languages: English
• ISSNs: 1388-2457

Abstract

Highlights: MEPs are facilitated by foot stimulation at sensory and above flexor reflex threshold. Flexor reflexes are facilitated by subthreshold and suprathreshold TMS. Facilitation of MEPs and flexor reflexes occurs when descending, somatosensory, and reflex inputs likely interact at spinal and cortical levels. Abstract: Objective: Integration between descending and ascending inputs at supraspinal and spinal levels is a key characteristic of neural control of movement. In this study, we characterized convergence of the flexor reflex and corticospinal inputs on the tibialis anterior (TA) network in healthy human subjects. Specifically, we characterized the modulation profiles of the spinal TA flexor reflex following subthreshold and suprathreshold transcranial magnetic stimulation (TMS). We also characterized the modulation profiles of the TA motor evoked potentials (MEPs) following medial arch foot stimulation at sensory and above reflex threshold. Methods: TA flexor reflexes were evoked following stimulation of the medial arch of the foot with a 30 ms pulse train at innocuous intensities. TA MEPs were evoked following TMS of the leg motor cortex area. Results: TMS at 0.7 and at 1.2 MEP resting threshold increased the TA flexor reflex when TMS was delivered 40–100 ms after foot stimulation, and decreased the TA flexor reflex when TMS was delivered 25–110 ms before foot stimulation. Foot stimulation at sensory and above flexor reflex threshold induced a similar time-dependent modulation in resting TA MEPs, that were facilitated when foot stimulation was delivered 40–100 ms before TMS. The flexor reflex and MEPs recorded from the medial hamstring muscle were modulated in a similar manner to that observed for the TA flexor reflex and MEP. Conclusion: Cutaneomuscular afferents from the distal foot can increase the output of the leg motor cortex area. Descending motor volleys that directly or indirectly depolarize flexor motoneurons increase the output of the spinal FRA interneuronal network. The parallel facilitation of flexor MEPs and flexor reflexes is likely cortical in origin. Significance: Afferent mediated facilitation of corticospinal excitability can be utilized to strengthen motor cortex output in neurological disorders.