The M-wave and CNV in the squirrel monkey: generality of cue modality and of reward.

Typical M-waves and CNVs were produced in squirrel monkey frontal and rostral parietal cortex by light cues, as well as by tone cues. With light cues, M-waves were about 50% as large as with tone cues, whereas CNVs were of about the same magnitude with either type of cue. Typical M-waves and CNVs were also produced when avoidance of tail-shock was substituted for food as a reinforcer. The magnitude of both ERPs appeared to follow an inverted-U function with increasing shock intensity. The use of tail-shock as a reinforcer generated more complexities both in ERP changes and in behavior than did food. In some animals, at high shock intensities, ERP increased, rather than decreased, as each session progressed. In some animals, a combination of food and avoidance of tail-shock produced a decrease, rathan than an increase, in ERPs and did not improve behavioral performance. Furthermore, animals would not perform effectively on a CNV paradigm with punishment for aborting the trial. It was also demonstrated that increased stress (immobilization of head or tail) resulted in a reduced magnitude of both the M-wave and the CNV. This may account for some of the complexities encountered with avoidance of tail-shock as a reinforcer.