The primary aim of this study is to increase understanding of two cortical event-related potentials (ERPs), the M-wave and the CNV, by examining the firing of single cortical neurons in relation to these ERPs. The M-wave is a short-duration, surface-negative waveform evoked by tone cues signalling the availability of a food reward if the subject, a squirrel monkey, bar-presses. The CNV, a longer-latency surface-negative waveform, originally recorded in human subjects and now observed in monkeys, develops in and is sustained for the interval (typically 1 sec) between a pair of cues, the second of which requires a response. Both waveforms are absent in untrained animals, and both are larger when the animal's interest in the reward is greater. Largely on empiric grounds, the CNV is being used by audiologists, neurologists and psychiatrists as a diagnostic tool. Evidence indicates that both ERPs are generated locally in cortex by neuronal mechanisms, but neither has been investigated at the single neuron level. The primary goals of the proposed work are to increase understanding of the ERPs by determining: 1) whether changes in neuronal activity occur in temporal relation to one or both ERPs; 2) whether such changes are, like the ERPs, infuenced by the level of interest of the animal in the reward, and 3) whether neurons whose activity changes during the CNV also show changes in firing in relation to the motor act (bar-press) for which the monkey is preparing during the CNV.