Local regions of the cerebral cortex contain large masses of neurons that generate electrical fields of dendritic potential. In selected regions such as the olfactory bulb and cortex there are well-understood relationships between the spatial patterns of potential fields and the underlying activity patterns of the neurons. The neurons also give spatially discriminable responses to selective electrical stimulation at the surface of the cortex with electrode arrays. In order to detect the activity patterns it is necessary to record from multiple electrodes (64 or more) in geometric arrays, and to apply temporal and spatial filters to the raw electroencephalographic (EEG) and even related potential (ERP) traces. At present the spatial filtering is done off-time in a conventional computer. It is much too slow to permit interactive exploration and control of neural responses to electrical stimulation. We propose to employ an array microprocessor that can perform spatial filtering on-line as a preprocessor under the control of our present computer, and to use our system also for delivery of electrical stimuli to the same array that is used for recording. We envision this instrumentation as essential for the development of usage of the EEG and evoked activity for prosthesis control, such as an artificial limb that is controlled by EEG activity from motor cortex with continuous feedback by electrical stimulation of the somatosensory cortex. Effective use of this instrumentation will require thorough understanding of the mechanisms of neocortex. The proposed research is aimed at establishing a basis for the requisite understanding through study of the paleocortex.