This is a "revised" R21 application submitted in response to the "Neurotechnology Research, Development, and Enhancement" program announcement to develop and test a 3D multi-channel wireless optical neural recording system. The "first goal" of the proposed research is to develop a wireless optical neural recording system to overcome the limitations of current systems which are expensive, complex, and difficult to use. Current cabling to connect the neural implant to the amplifiers and computers limit the range of experiments that can be done. A wire-less system would greatly simplify and extend recording technology for behavioral neuroscience and find uses in epilepsy and other disease studies. The proposed system has a 3D topology. It consists of an array of optical pixel elements that are connected to a silicon platform containing an array of through holes that contain folded microfabricated silicon electrodes. The pixels amplify the neuron signals and optically transmit the signals to a remote camera. The system cannot be fabricated using traditional methods due to the required 3D topology. Traditional methods, including surface micromachining and robotic assembly lines limit the biomedical device community to 2D device topologies. The "second goal" of the proposed research is to overcome this limitation. The development of novel tools are proposed to realize the neural recording system. The tools are based on self-assembly and folding; in particular, a (i) sequential self-assembly process to fabricate, assemble, and electrically connect the pixel elements with the recording electrodes, and a (ii) folding process to rotate the recording electrodes in an out-of-plane position. The tools benefit the biomedical device community in general as they enable the rapid prototyping of 3D-miniaturized systems. The "third goal" is to test the realized system. The first system will contain an array of 96 pixels connected to 16 electrodes with 6 recording sites. The system will be used to measure local field potentials in awake-behaving rats to gain insight into the role of striatal local field potentials in behavior. [unreadable] [unreadable] [unreadable]