Wireless systems could improve neural prostheses

In the past, doctors usually treated disorders of the nervous system by substitution instead of correction, including wheelchairs for walking, braille for text, and sign language for speech. However, as our understanding of the nervous system increases, so does our ability to treat its disorders with neural prostheses that directly stimulate the nervous system. Cochlear implants are one example of neural prostheses. Control of such prosthetics with brain-derived electrical signals is now possible due to the development of microelectrode arrays such as the Utah Intracortical Electrode Array (UIEA), the University of Florida flexible substrate microelectrode array, and others.1–3 A large number of microelectrodes are typically needed, especially when interfacing with the central nervous system to restore a sensory function such as vision or hearing, because the quality of perception increases with the number of stimulated sites and the stimulation rate.4–6 On the other hand, using a large bundle of ultra-thin wires that pass through the skin to record neural activity from implanted microelectrode arrays introduces significant technological hurdles for the development of practical prosthetic devices. Communication with implanted microelectrodes is better accomplished wirelessly. The Interstim-3 and the UIEA-based telemetry circuit are the state of the art in microelectrode arrays with wireless transmitters mounted on them.7, 8 Both systems face major challenges, however, including crosstalk and digital interference. An additional limitation is that data transmission in these systems is based on fixed data rates and synchronous protocols, in which actions occur at specific times. An asynchronous scheme, in which actions occur in response to a signal, would provide more flexibility and adaptability to different environments. Figure 1. Standard address event representation (AER) protocol. The address of the spiking neuron is encoded as a unique binary address, which is broadcasted on a digital bus. The decoder on the receiver decodes the address and directs the signal to the appropriate location. The diagram is modified from another paper.9