Evidence for presynaptic changes in LTP. A. Recordings of excitatory postsynaptic Ca2+ transients (EPSCaTs, upper panels) in an activated spine, and simultaneously recorded somatic EPSPs (lower panels) from a neuron in which the imaged spine was the only one contributing to the synaptic response. LTP was associated with a large increase in p(r) with no change in quantal size. Red dots represent successes and black dots failures. B. Images of the spine at rest and during a response. C. Increase in p(r) without increase in potency for three neurons that fulfilled the criteria for a single activated synapse. From .