High-density microelectrode arrays (MEAs) permit simultaneous recording of multiple single neurons that mediate sensory and motor processing, perception, and learning in the cerebral cortex. MEAs also have the potential to monitor functional alterations in neuronal circuits within awake, behaving subjects to better understand and quantify cortical plasticity. They can also serve in Brain Machine Interface (BMI) systems to provide real-time control of assistive devices in people with severe disability. The challenge in this project is the ability to extract the activity of many individual neurons and local field potentials (LFPs) within the constraints imposed by implantability requirements (such as chip size, power dissipation, real-time operation, and limited telemetry bandwidth), which signficantly limits the utility of MEAs in basic neuroscience and clinical applications. The objective of this project is to develop a highly modular, ultra low-power and distributed microsystem to extract some important aspects of the neural code (such as neuronal spike times, firing rates and LFPs) from large populations of neurons wirelessly and in real-time. Some example applications of this system in basic and clinical neuroscience are:1) Studies of neural coding and plasticity in freely behaving, untethered subjects interacting naturally with their surrounding.2) Real time control of neuroprosthetic devices and Brain Machine Interfaces. 3) Prediction of impending chronic seizures in epileptic patients.4) Closed loop feedback control for neuromodulation and neurostimulation (e.g.: Deep Brain Stimulation of Parkinson's disease patients).