title: Metaplasticity in human primary somatosensory cortex: effects on physiology and tactile perception.
abstract: Theta-burst stimulation (TBS) over human primary motor cortex evokes plasticity and metaplasticity, the latter contributing to the homeostatic balance of excitation and inhibition. Our knowledge of TBS-induced effects on primary somatosensory cortex (SI) is limited, and it is unknown whether TBS induces metaplasticity within human SI. Sixteen right-handed participants (6 females, mean age 23 yr) received two TBS protocols [continuous TBS (cTBS) and intermittent TBS (iTBS)] delivered in six different combinations over SI in separate sessions. TBS protocols were delivered at 30 Hz and were as follows: a single cTBS protocol, a single iTBS protocol, cTBS followed by cTBS, iTBS followed by iTBS, cTBS followed by iTBS, and iTBS followed by cTBS. Measures included the amplitudes of the first and second somatosensory evoked potentials (SEPs) via median nerve stimulation, their paired-pulse ratio (PPR), and temporal order judgment (TOJ). Dependent measures were obtained before TBS and at 5, 25, 50, and 90 min following stimulation. Results indicate similar effects following cTBS and iTBS; increased amplitudes of the second SEP and PPR without amplitude changes to SEP 1, and impairments in TOJ. Metaplasticity was observed such that TOJ impairments following a single cTBS protocol were abolished following consecutive cTBS protocols. Additionally, consecutive iTBS protocols altered the time course of effects when compared with a single iTBS protocol. In conclusion, 30-Hz cTBS and iTBS protocols delivered in isolation induce effects consistent with a TBS-induced reduction in intracortical inhibition within SI. Furthermore, cTBS- and iTBS-induced metaplasticity appear to follow homeostatic and nonhomeostatic rules, respectively.
authors.affiliation: Department of Kinesiology, McMaster University, Hamilton, Ontario, Canada; and.
authors.forename: Christina B
authors.initials: CB
authors.lastname: Jones
authors.affiliation: Department of Kinesiology, McMaster University, Hamilton, Ontario, Canada; and.
authors.forename: Tea
authors.initials: T
authors.lastname: Lulic
authors.affiliation: Department of Kinesiology, McMaster University, Hamilton, Ontario, Canada; and.
authors.forename: Aaron Z
authors.initials: AZ
authors.lastname: Bailey
authors.affiliation: Department of Kinesiology, McMaster University, Hamilton, Ontario, Canada; and.
authors.forename: Tanner N
authors.initials: TN
authors.lastname: Mackenzie
authors.affiliation: Department of Kinesiology, McMaster University, Hamilton, Ontario, Canada; and.
authors.forename: Yi Qun
authors.initials: YQ
authors.lastname: Mi
authors.affiliation: Biomedical Engineering, University of North Carolina, Chapel Hill, North Carolina.
authors.forename: Mark
authors.initials: M
authors.lastname: Tommerdahl
authors.affiliation: Department of Kinesiology, McMaster University, Hamilton, Ontario, Canada; and nelsonaj@mcmaster.ca.
authors.forename: Aimee J
authors.initials: AJ
authors.lastname: Nelson
mesh_terms: D000293:Adolescent; D000328:Adult; D005073:Evoked Potentials, Somatosensory; D005260:Female; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000502:physiology; D009473:Neuronal Plasticity; D013003:Somatosensory Cortex / Q000502:physiology*; D013826:Theta Rhythm; D055698:Touch Perception
keywords: neural plasticity; paired pulse; primary somatosensory cortex; somatosensory evoked potential; temporal order judgment