| Facial displays are an important cue for semi-terrestrial non-human primates who rely heavily upon vision for social communication. To elucidate the salient features of facial expressions to which monkeys attend, we studied the viewing patterns of monkeys to a range of dynamic and static facial displays. In parallel, neurophysiological experiments were performed in the monkey amygdaloid complex, a neuroanatomical structure which plays an important role in the acquisition of associations between sensory percepts and their behavioral significance. To investigate the degree to which activity in the non-human primate amygdala reflects the perceptual or affective qualities of behaviorally significant images, neuronal activity was recorded from the amygdaloid complex of the awake-behaving monkey during the presentation of ethologically salient visual stimuli such as monkey faces, human faces, foods and other non-food objects. To improve our ability to identify the neuroanatomical location of isolated neurons during an experimental session, a new technique was developed for imaging the intra-cranial position of microelectrodes using MRI and radiography.;Recording the eye-positions of monkeys viewing a range of facial displays revealed that monkeys inspect major features of the face such as the eyes and mouth, and that the relative amount of time spent viewing these features depended upon the nature of the expression. These results were used in the analysis of our neuronal data which showed that a small population of single cells in the amygdala selectively respond to particular expressions of facial displays, and certain food items. Another population of neurons responded to categories of stimuli such as all monkey faces, or all food objects. Based on the neuronal data we conclude that the amygdala is involved in the higher-order visual processes related to ethologically salient visual images. |
