Figure 1.

(a) Layout of neuron cell bodies, dendritic network and axonal fibres (grey) transmitting action potentials (red arrows). One dendrite of interest is designated by arrowheads (see below). (b) The mosaic of astrocytic domains is superimposed to the background neuronal network. (c) Different contiguous segments of the same dendrite (arrowheads in A) intersect distinct astrocytic domains. Synapses are controlled independently within each of these domains (synaptic islands). (d) One astrocyte covers portions of different dendrites, belonging to four distinct neurons, surveying the activity of a total 20 000–160 000 synapses.