Dynamic pupil responses and neuronal correlates during free view exploration in one rhesus macaque

The physiological correlates of the salience of specific stimuli have primarily been investigated by exposing subjects (or trained primates) to maintain fixation on static stimuli. Pupil dilation emerges as a crucial variable in this context; indeed, transient pupil dilations can be influenced by the salience of visual stimuli. In natural conditions, however, eyes are free to explore the visual scene, and ocular movement is directed by stimuli that appear within the scene. Despite its significance, this aspect of visual exploration remains poorly understood, with limited knowledge about pupil variations during free visual exploration and the underlying neural activity. To explore these aspects, single unit recording of neurons in three areas (premotor dorsal rostral, premotor dorsal caudal, dorsolateral prefrontal cortex) and ocular behavior measurements were conducted in one rhesus macaque during free exploration of videos. Different categories of stimuli were identified within the video, including natural scenes, conspecifics, and threatening non-conspecific animals. Statistical tests were performed to identify if the pupil dilatation and the neuronal activity differ between the different categories of stimuli. Pupillometry revealed greater dilation when the monkey was exposed to conspecifics compared to natural landscapes, and to dangerous non-conspecifics, as jaguars, compared to harmless ones, as deer. Of interest, neuronal activity in the studied cortical areas was higher under conditions where pupil dilation was greater. The results suggest that both pupil dilation and neuronal activity in the examined areas of the frontal cortex reflect the degree of scene salience.