LONG-LATENCY AUDITORY EVENT-RELATED POTENTIALS IN BEHAVING MONKEYS (P300 COMPONENT, VERTEX, ENDOGENOUS, COGNITIVE)

Monkeys were investigated as an animal model for human late- and long-latency auditory event-related potentials (ERPs). The studies conducted were designed to: (1) identify the components of late and long latency ERPs in the monkey, (2) examine the relationship of components to stimulus and task related variables and (3) examine the distribution of components across the skull. Two major sets of experiments were done. The first focussed on the P300 (P3b) component, while the second series of studies examined the vertex potentials (P1, N1, P2).;Three monkeys were trained to discriminate infrequent target tones (1 kHz, 400 ms duration) from frequent non-target tones (2.5 kHz, 400 ms). Subjects were required to press and hold a lever that turned on a small "ready" light. Subjects were trained to selectively release the lever within 600 ms of target tone offset for a juice reward, then immediately press and hold the lever again to continue the stimulus sequence. EEG and EOG recordings were obtained through implanted electrodes. Results showed that a long-latency (300 ms), vertex positive component of the ERP recorded from monkeys was present only when the eliciting stimulus was relevant to the task. The amplitude of this component varied inversely with stimulus probability and was dissociable from motor responses. It could also be elicited by infrequent visual stimuli.;In the second series of studies, the correspondence of the monkey ERP components P25, N70 and P130 with the human vertex potentials was examined. Data was collected from awake, non-behaving animals as the stimulus frequency, intensity and repetition rate were independently manipulated. It was found that these components in the monkey were not significantly affected by stimulus frequency although they did decrement in amplitude with decreasing intensity of stimulation. The amplitude of the ERP components was affected by stimulus repetition rate, although stimulus by stimulus changes were minimal until rates of 2/second were obtained. The amplitude of these components was also profoundly diminished under barbiturate anesthesia. Taken together, these results demonstrate that the monkey can provide a useful animal model of the human endogenous ERP components.