Schematic representation of functional synaptic islands. A, Diagram showing three astrocytes. The holes are filled with neurons, one of which is shown to have its processes extending out to other astrocytes pointing to the potential of different neuronal compartments being modulated by different astrocytes. B, Diagram illustrating the concept of functional synaptic islands: a group of dendrites from several neurons are enwrapped by a single astrocyte. Synapses localized within the territory of this astrocyte have the potential to be modulated in a coordinated manner by gliotransmitter(s) released from this glial cell.