A major effort in modern neuroscience has been directed at understanding how the brain accomplishes sensory perception. Research on the visual system has found that different brain regions are specialized for the perception of shape, color, motion, and other aspects of the visual world. Much less is understood about the perception of emotional aspects of visual stimuli. It is not clear, for example, how animals or humans are able to differentiate an angry or threatening facial gesture from a friendly one. Monkeys, like humans, are highly visual creatures and use subtle facial gestures for communication. Electrophysiological studies have shown that neurons in the amygdaloid complex respond selectively to the presentation of static images of faces. The previous work did not determine whether or not these neurons differentiate the emotional content of the facial expressions. However, monkeys with lesions of the amygdaloid complex are indifferent to positive or negative events and are unable to appropriately interpret signals of dominance or submission by other monkeys, suggesting that the amygdaloid complex may mediate the perception of species-specific emotional stimuli. In Frederick K. Nahm's doctoral-dissertation research, videotapes of the facial expressions of socially interacting monkeys will be made. These images will then be transferred to a digital optical-laser-disk system. Epochs of monkey facial expressions will be catalogued and divided into 1-second segments. Series of these 1-second dynamic stimuli covering all forms of monkey expression will be used as stimuli for electrophysiological studies that will survey neuronal responsivity in all portions of the monkey amygdaloid complex. These studies will contribute to an understanding of the neural basis of normal emotional perception and expression in the human brain. Moreover, since the amygdaloid complex has the highest density of benzodiazepine receptors (through which the antianxiety drugs such as librium have their effects), these studies will also pave the way to an understanding of anxiety and inappropriate emotional states such as phobias.
