Observations on the M-wave and the CNV in the squirrel monkey.

A typical CNV paradigm, with food as reward, evokes in the squirrel monkey's post-arcuate and post-central cortices both M-waves in response to the cues and what appears to be a CNV in the interstimulus interval. Both wave forms appear to be generated locally in cortex and to be more closely related temporally to the cues than to the animal's behavioral response. The CNV, like the M-wave, appears to reflect the animal's level of interest in obtaining the reward. It is smaller when the animal misses the cues than when he responds correctly. It decreases as food pellets are consumed. It varies with the level of interest of the animal in a particular type of food pellet, as judged from the animal's behavior. At some recording sites in some animals it appears to reflect both interest in the reward and interest in manipulating the environment to obtain the reward. It can be maintained for at least 2 sec, but differs from the human CNV in that, with the paradigm used, it is not well resolved by the imperative cue. Averaging evoked activity with the animal's motor response as reference point reveals another negative wave form which just precedes the motor response.