We present a VLSI device comprising an array of leaky integrate-and- fire (I&F) neurons and adaptive synapses with spike-timing dependent plasticity (STDP). The neurons transmit spikes off chip and the synapses receive spikes from external devices using a communication protocol based on the "Address- Event Representation" (AER). We studied the response properties of the neurons in the array to uniform input currents, and measured their AER outputs. We characterized the properties of the STDP synapses using AER input spike trains. Our results indicate that these circuits can be reliably used in massively parallel VLSI networks of I&F neurons to simulate real-time complex spike-based learning algorithms.