We describe and discuss an electronic implementation of an attractor neural network with plastic synapses. The network undergoes double dynamics, for the neurons as well as the synapses. Both dynamical processes are unsupervised. The synaptic dynamics is autonomous, in that it is driven exclusively and perpetually by neural activities. The latter follow the network activity via the developing synapses and the influence of external stimuli. Such a network self-organizes and is a device which converts the gross statistical characteristics of the stimulus input stream into a set of attractors (reverberations). To maintain for long time the acquired memory, the analog synaptic efficacies are discretized by a stochastic refresh mechanism. The discretized synaptic memory has indefinitely long lifetime in the absence of activity in the network. It is modified only by the arrival of new stimuli. The stochastic refresh mechanism produces transitions at low probability which ensures that transient stimuli do not cr...