title: Motor Cortex Reorganization and Impaired Function in the Transition to Sustained Muscle Pain.
abstract: Primary motor cortical (M1) adaptation has not been investigated in the transition to sustained muscle pain. Daily injection of nerve growth factor (NGF) induces hyperalgesia reminiscent of musculoskeletal pain and provides a novel model to study M1 in response to progressively developing muscle soreness. Twelve healthy individuals were injected with NGF into right extensor carpi radialis brevis (ECRB) on Days 0 and 2 and with hypertonic saline on Day 4. Quantitative sensory and motor testing and assessment of M1 organization and function using transcranial magnetic stimulation were performed prior to injection on Days 0, 2, and 4 and again on Day 14. Pain and disability increased at Day 2 and increased further at Day 4. Reorganization of M1 was evident at Day 4 and was characterized by increased map excitability. These changes were accompanied by reduced intracortical inhibition and increased intracortical facilitation. Interhemispheric inhibition was reduced from the "affected" to the "unaffected" hemisphere on Day 4, and this was associated with increased pressure sensitivity in left ECRB. These data provide the first evidence of M1 adaptation in the transition to sustained muscle pain and have relevance for the development of therapies that seek to target M1 in musculoskeletal pain.
authors.affiliation: School of Science and Health, University of Western Sydney, Penrith, NSW 2751, Australia.
authors.forename: S M
authors.initials: SM
authors.lastname: Schabrun
authors.affiliation: Laboratory for Musculoskeletal Pain and Motor Control, Center for Sensory-Motor Interaction (SMI), Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Aalborg, Denmark.
authors.forename: S W
authors.initials: SW
authors.lastname: Christensen
authors.affiliation: Laboratory for Musculoskeletal Pain and Motor Control, Center for Sensory-Motor Interaction (SMI), Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Aalborg, Denmark.
authors.forename: N
authors.initials: N
authors.lastname: Mrachacz-Kersting
authors.affiliation: Laboratory for Musculoskeletal Pain and Motor Control, Center for Sensory-Motor Interaction (SMI), Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Aalborg, Denmark.
authors.forename: T
authors.initials: T
authors.lastname: Graven-Nielsen
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D019054:Evoked Potentials, Motor; D005260:Female; D006801:Humans; D006930:Hyperalgesia / Q000139:chemically induced; D008297:Male; D009044:Motor Cortex / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000503:physiopathology; D063806:Myalgia / Q000139:chemically induced / Q000503:physiopathology*; D020932:Nerve Growth Factor; D009433:Neural Inhibition; D010147:Pain Measurement; D017288:Pain Threshold / Q000502:physiology*; D011712:Pyramidal Tracts / Q000503:physiopathology; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult
chemical_list: D020932:Nerve Growth Factor
keywords: elbow pain; interhemispheric inhibition; nerve growth factor; primary motor cortex; transcranial magnetic stimulation