The inhibitory reflex, also known as the cutaneous silent period (CSP), is a spinal reflex mediated by small diameter A-δ fibers, serving to protect the body from harmful stimuli (Leis et al., 1992; Kofler, 2003). Previous investigations have suggested that the inhibitory effects of this reflex only occur within extensor muscles. The present study sought to determine the influence of the inhibitory reflex within both flexor and extensor muscles of the upper limb thereby providing further insight into the spinal organization of this reflex. Two subsets of data were collected. 22 subjects had the inhibitory reflex evoked with three different stimulation conditions (digit II, V and II+III stimulation at 10x perceptual threshold). 14 subjects returned to have transcranial magnetic stimulation (TMS) paired with digit II stimulation. Within both datasets subjects performed isometric contractions with each of the following upper limb muscles: abductor pollicis brevis (APB), flexor carpi radialis (FCR), extensor carpi radialis (ECR), biceps brachii long head (BIC), triceps brachii lateral head (TRI), anterior deltoid (AD), and posterior deltoid (PD). All stimulations were applied randomly during the isometric contractions. The first dataset included 20 stimulations in each condition within each muscle of the right arm. The second dataset included 10 stimulations of digit II only (CSP), TMS only (TMS), and a inhibitory reflex conditioned TMS (TMS+) within each muscle of the right arm. Distal muscle demonstrated the greatest influence for both the inhibitory reflex response and motor evoked potentials. A distal to proximal relationship was determined for the inhibitory response with a level of differential control occurring between the distal and proximal muscles. These results demonstrate evidence of the CSP in both flexor and extensor muscles of the upper limb, with the greatest effect taking place within the distal muscles. I hypothesize that this distal--proximal organization of cutaneous inhibitory reflexes may be influenced by the number of direct cortico-motoneuronal connections within the corticospinal tract. Thus, the cutaneous feedback plays a larger role in modulating direct descending input in distal muscles involved in grasping and manipulation, versus proximal muscles coordinating reaching.
|Advisor:||Koceja, David M., Riley, Zachary A.|
|Commitee:||Sengelaub, Dale R., Streepey, Jefferson W.|
|Department:||School of Public Health|
|School Location:||United States -- Indiana|
|Source:||DAI-B 76/01(E), Dissertation Abstracts International|
|Subjects:||Neurosciences, Behavioral psychology, Kinesiology|
|Keywords:||Cutaneous reflexes, Cutaneous silent period, Nociceptive, Upper limb|
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