title: Inducing homeostatic-like plasticity in human motor cortex through converging corticocortical inputs.
abstract: Transcranial stimulation techniques have revealed homeostatic-like metaplasticity in the hand area of the human primary motor cortex (M1(HAND)) that controls stimulation-induced changes in corticospinal excitability. Here we combined two interventional protocols that induce long-term depression (LTD)-like or long-term potentiation (LTP)-like plasticity in left M1(HAND) through different afferents. We hypothesized that the left M1(HAND) would integrate LTP- and LTD-like plasticity in a homeostatic fashion. In ten healthy volunteers, low-intensity repetitive transcranial magnetic stimulation (rTMS) of the left dorsal premotor cortex (PMD) was first applied to produce an LTP-like increase (5 Hz rTMS) or LTD-like decrease (1 Hz rTMS) in corticospinal excitability in left M1(HAND) via premotor-to-motor inputs. Following PMD rTMS, paired-associative stimulation (PAS) was applied to the right median nerve and left M1(HAND) to induce spike-time-dependent plasticity in sensory-to-motor inputs to left M1(HAND). We adjusted the interstimulus interval to the N20 latency of the median nerve somatosensory-evoked cortical potential to produce an LTP-like increase (PAS(N20+2ms)) or an LTD-like decrease (PAS(N20-5ms)) in corticospinal excitability. The amplitude of motor-evoked potentials was recorded from intrinsic hand muscles to assess stimulation-induced changes in corticospinal excitability. Premotor-to-motor preconditioning triggered a homeostatic response to subsequent sensory-to-motor PAS. After facilitatory 5 Hz rTMS, "facilitatory" PAS(N20+2ms) suppressed corticospinal excitability. Likewise, "inhibitory" PAS(N20-5ms) facilitated corticospinal excitability after "inhibitory" 1 Hz rTMS. There was a negative linear relationship between the excitability changes induced by PMD rTMS and those elicited by subsequent PAS. Excitability changes were not paralleled by changes in performance during a finger-tapping task. These results provide evidence for a homeostatic response pattern in the human M1(HAND) that integrates acute plastic changes evoked through different "input channels."
authors.affiliation: Department of Neurology, Christian-Albrechts-University, Kiel, Germany.
authors.forename: Monika
authors.initials: M
authors.lastname: Pötter-Nerger
authors.forename: Sarah
authors.initials: S
authors.lastname: Fischer
authors.forename: Claudia
authors.initials: C
authors.lastname: Mastroeni
authors.forename: Sergiu
authors.initials: S
authors.lastname: Groppa
authors.forename: Günther
authors.initials: G
authors.lastname: Deuschl
authors.forename: Jens
authors.initials: J
authors.lastname: Volkmann
authors.forename: Angelo
authors.initials: A
authors.lastname: Quartarone
authors.forename: Alexander
authors.initials: A
authors.lastname: Münchau
authors.forename: Hartwig Roman
authors.initials: HR
authors.lastname: Siebner
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D013181:Cortical Spreading Depression / Q000502:physiology; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology*; D007839:Functional Laterality / Q000502:physiology; D006225:Hand / Q000294:innervation; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D009473:Neuronal Plasticity / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology; D011712:Pyramidal Tracts / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation / Q000379:methods; D055815:Young Adult