Cutaneous anesthesia of the forearm enhances sensorimotor function of the hand.
Author(s): Petoe MA(1), Jaque FA, Byblow WD, Stinear CM.
Affiliation(s): Author information:
(1)Clinical Neuroscience Laboratory, Department of Medicine, The University of
Auckland, Auckland, New Zealand.
Publication date & source: 2013, J Neurophysiol. , 109(4):1091-6
Temporary deafferentation of the upper limb, with ischemic or anesthetic nerve
block, has rapid effects on sensorimotor cortex. Cutaneous anesthesia of the
forearm has recently been found to improve sensory and motor function of the
paretic hand in chronic stroke patients. However, the neurophysiological
mechanisms are unknown. The aim of this study was to investigate the behavioral
and neurophysiological effects of cutaneous forearm anesthesia. Twenty-five
healthy right-handed adults participated in this double-blind, randomized study.
Participants completed two sessions, with either a topical anesthesia cream
(EMLA) or placebo applied to their left forearm in each session. Thresholds for
cutaneous sensation and spatial acuity of the left hand were measured before and
after the intervention. Transcranial magnetic stimulation was used to measure
corticomotor excitability and short-interval intracortical inhibition in the left
first dorsal interosseous and abductor digiti minimi muscles before and after the
intervention. Manual dexterity was assessed with the grooved pegboard task after
the intervention in each session. Left-hand dexterity improved to a greater
extent after treatment with EMLA than placebo, and this was related to improved
spatial acuity at the fingertips. Corticomotor excitability remained stable, and
short-interval intracortical inhibition increased after EMLA treatment. We have
confirmed and extended previous reports that cutaneous forearm anesthesia results
in improved spatial acuity and manual dexterity of the ipsilateral hand. The
neurophysiological mechanisms involve an increase in intracortical inhibition,
which may improve the precision of voluntary movement. These results lend support
to the therapeutic application of EMLA in movement rehabilitation.
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