Awareness of perception and sensory-motor integration: ERPs from the anterior insula

The present work follows recent evidences of studies showing that visual stimuli evoke two early prefrontal event-related potentials (ERP) concomitant to the canonical occipital activities, but originating within the anterior insula (the pN1 and the pP1 components). To clarify the exogenous/endogenous nature of these components, we performed two experiments in which stimulus physical features (Experiment 1) and motor demands of the task (Experiment 2) were considered. In a simple response task (SRT), low-visibility stimuli evoked larger pN1 over the prefrontal areas (Experiment 1) with respect to high-visibility stimuli; in contrast, the occipital P1 component (concomitant to the pN1) had reduced amplitude in the low-visibility condition as expected. Furthermore, the latency of the P1, pN1 and pP1 was slower in the low-visibility condition (from 8 to 18 ms), and the motor response was slowed down as well (on average 14 ms). Pre-stimulus analysis showed that low-visibility stimuli were preceded by greater motor readiness. On the other hand, Experiment 2 showed that, compared with the SRT, the request to passively view the same stimuli was associated with smaller pP1. ERP source analysis confirmed the anterior insula source of the prefrontal ERPs; we interpreted these activities as the correlate of two top-down perceptual processing: the sensory awareness (the pN1) and the awareness of the sensory-motor integration (the pP1), associated with the subjective experience of the visual perception and the conscious experience of the sensory-motor coupling, respectively.