title: Hebbian and anti-Hebbian spike-timing-dependent plasticity of human cortico-cortical connections.
abstract: Learning of new skills may occur through Hebbian associative changes in the synaptic strength of cortical connections [spike-timing-dependent plasticity (STDP)], but how the precise temporal relationship of the presynaptic and postsynaptic inputs determines the STDP effects in humans is poorly understood. We used a novel paired associative stimulation protocol to repeatedly activate the short-latency connection between the posterior parietal cortex and the primary motor cortex (M1) of the left-dominant hemisphere. In different experiments, we systematically varied the temporal relationships between the stimuli and the preferential activation of different M1 neuronal populations by applying transcranial magnetic stimulation over M1 with different coil orientations and in different states of cortical excitability (rest vs muscular contraction). We found evidence for the existence of both Hebbian and anti-Hebbian STDP in human long-range connections. The induction of bidirectional long-term potentiation or depression in M1 depended not only on the relative timing between the stimuli but, crucially, on the stimulation of specific neuronal populations and the activity state of the cortex. Our findings demonstrate that these mechanisms are not fixed but susceptible to rapid adaptations. This sudden transition from anti-Hebbian to Hebbian plasticity likely involves local dynamics of interaction with different populations of postsynaptic neurons.
authors.affiliation: Non-Invasive Brain Stimulation Unit, Santa Lucia Foundation, Institute for Inpatient Treatment and Scientific Studies, I-00179 Rome, Italy. g.koch@hsantalucia.it
authors.forename: Giacomo
authors.initials: G
authors.lastname: Koch
authors.forename: Viviana
authors.initials: V
authors.lastname: Ponzo
authors.forename: Francesco
authors.initials: F
authors.lastname: Di Lorenzo
authors.forename: Carlo
authors.initials: C
authors.lastname: Caltagirone
authors.forename: Domenica
authors.initials: D
authors.lastname: Veniero
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000328:Adult; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology; D009473:Neuronal Plasticity / Q000502:physiology*; D010296:Parietal Lobe / Q000502:physiology*; D013997:Time Factors; D050781:Transcranial Magnetic Stimulation / Q000379:methods; D055815:Young Adult