Translating long-term potentiation from animals to humans: a novel method for noninvasive assessment of cortical plasticity.

Long-term potentiation (LTP) is a synaptic mechanism underlying learning and memory that has been studied extensively in laboratory animals. The study of LTP recently has been extended into humans with repetitive sensory stimulation to induce cortical LTP. In this review article, we will discuss past results from our group demonstrating that repetitive sensory stimulation (visual or auditory) induces LTP within the sensory cortex (visual/auditory, respectively) and can be measured noninvasively with electroencephalography or functional magnetic resonance imaging. We will discuss a number of studies that indicate that this form of LTP shares several characteristics with the synaptic LTP described in animals: it is frequency dependent, long-lasting (> 1 hour), input-specific, depotentiates with low-frequency stimulation, and is blocked by N-methyl-D-aspartate receptor blockers in rats. In this review, we also present new data with regard to the behavioral significance of human sensory LTP. These advances will permit enquiry into the functional significance of LTP that has been hindered by the absence of a human model. The ability to elicit LTP with a natural sensory stimulus noninvasively will provide a model system allowing the detailed examination of synaptic plasticity in normal subjects and might have future clinical applications in the diagnosis and assessment of neuropsychiatric and neurocognitive disorders.