The influence of sensory afferent input on local motor cortical excitatory circuitry in humans. (30th January 2015)

• Record Type: Journal Article
• Authors: Cash, Robin F. H.; Isayama, Reina; Gunraj, Carolyn A.; Ni, Zhen; Chen, Robert
• Is Part Of: Journal of physiology. Volume 593:Number 7(2015:Apr.)
• Page Start: 1667
• Page End: 1684
• Publication Date: 2015-01-30
• Subjects: Physiology -- Periodicals; 612.005
• DOI: 10.1113/jphysiol.2014.286245
• Languages: English
• ISSNs: 0022-3751

Abstract

<abstract abstract-type="main"> <title>Key points</title> <sec id="tjp6524-sec-0010" sec-type="section"> <p> <list id="tjp6524-list-0001" list-type="bullet"> <list-item> <p>In the human, sensorimotor integration can be investigated using combined sensory and transcranial magnetic stimulation (TMS).</p> </list-item> <list-item> <p>Short latency afferent inhibition (SAI) refers to motor cortical inhibition 20–25ms after median nerve stimulation.</p> </list-item> <list-item> <p>We investigated the influence of SAI on a local excitatory interneuronal motor cortical circuit known as short‐interval intracortical facilitation (SICF) and found that, contrary to expectations, SICF was facilitated in the presence of SAI (SICF<sub>SAI</sub>); this effect is specific to SICF since there was no effect in control conditions in which SICF was not elicited, and the facilitatory SICF<sub>SAI</sub> interaction increased with increasing strength of SICF or SAI.</p> </list-item> <list-item> <p>The influence of sensory input on excitatory motor cortical circuitry was similar across different bodily regions, different circuits within motor cortex and across functional states, suggesting that this interaction may have general applicability in sensorimotor integration and motor control.</p> </list-item> <list-item> <p>SAI and SICF were found to correlate between individuals in that those with high SAI were found to have high SICF, and this relationship was maintained when SICF was delivered in the presence of SAI, suggesting an intrinsic relationship between SAI and SICF; these findings are compatible with brain‐slice studies of sensorimotor circuitry and add to our understanding of sensorimotor integration.</p> </list-item> </list> </p> </sec> <sec id="tjp6524-sec-0020" sec-type="section"> <title>Abstract</title> <p>In human, sensorimotor integration can be investigated by combining sensory input and transcranial magnetic stimulation (TMS). Short latency afferent inhibition (SAI) refers to motor cortical inhibition 20–25 ms after median nerve stimulation. We investigated the interaction between SAI and short‐interval intracortical facilitation (SICF), an excitatory motor cortical circuit. Seven experiments were performed. Contrary to expectations, SICF was facilitated in the presence of SAI (SICF<sub>SAI</sub>). This effect is specific to SICF since there was no effect at SICF trough 1 when SICF was absent. Furthermore, the facilitatory SICF<sub>SAI</sub> interaction increased with stronger SICF or SAI. SAI and SICF correlated between individuals, and this relationship was maintained when SICF was delivered in the presence of SAI, suggesting an intrinsic relationship between SAI and SICF in sensorimotor integration. The interaction was present at rest and during muscle contraction, had a broad degree of somatotopic influence and was present in different interneuronal SICF circuits induced by posterior–anterior and anterior–posterior current directions. Our results are compatible with the finding that projections from sensory to motor cortex terminate in both superficial layers where late indirect (I‐) waves are thought to originate, as well as deeper layers with more direct effect on pyramidal output. This interaction is likely to be relevant to sensorimotor integration and motor control.</p> </sec> </abstract>