This project seeks to (i) extend what is presently known about the features of environmental mechanical stimuli that find representation in the primary somatosensory receiving areas in somatosensory cerebral cortex of prmates; (ii) obtain quantitative descriptions of the central neural activity evoked by mechanical stimuli that can be dscriminated in psychophysical experiments; and (iii) provide information about the nature of the mechanisms that underlie stimulus coding by cortical somatosensory neurons. The activity of individual cortical neurons shall be recorded extracellularly in the absence of general anesthesia; mechanical stimulation of the skin will be achieved by servo-controlled DC motors that move fine brushes at constant velocity over the skin; the orientation, traverse length, traverse width, direction, and stimulus location are stimulus parameters whose influence on cortical neuron response shall be investigated. Bilateral simultaneous or sequential moving tactile stimuli will be utilized to study the response properties of neurons in area S-II/r. It is anticipated that the data obtained in these studies will enable the distortions of somatic sensory performance which accompany neurological damage or drug administration to be interpreted in terms of altered stimulus coding by individual neurons.