Calcium- and activity-dependent synaptic plasticity

Calcium ions play crucial signaling roles in many forms of activity-depende nt synaptic plasticity. Recent presynaptic [Ca2+](i) measurements and manip ulation of presynaptic exogenous buffers reveal roles for residual [Ca2+](i ) following conditioning stimulation in all phases of short-term synaptic e nhancement. Pharmacological manipulations implicate mitochondria in post-te tanic potentiation. New evidence supports an influence of Ca2+ in replacing depleted vesicles after synaptic depression. In addition, high-resolution measurements of [Ca2+](i) in dendritic spines show how Ca2+ can encode the precise relative timing of presynaptic input and postsynaptic activity and generate long-term synaptic modifications of opposite polarity.