The present experiments continue a longitudinal study of rhesus macaque social behavior following bilateral neonatal ibotenic acid lesions of the amygdala or hippocampus, or sham operations. Juvenile animals (approximately 1.5–2.5 years) were tested in four different social contexts—alone, while interacting with one familiar peer, while interacting with one unfamiliar peer, and in their permanent social groups. During infancy, the amygdala-lesioned animals displayed more interest in conspecifics (indexed by increased affiliative signaling) and paradoxically demonstrated more submission or fear (Bauman, Lavenex, Mason, Capitanio, & Amaral, 2004a, this journal). When these animals were assessed as juveniles, differences were less striking. Amygdala-lesioned animals generated fewer aggressive and affiliative signals (e.g., vocalizations, facial displays) and spent less time in social interactions with familiar peers. When animals were observed alone or with an unfamiliar peer, amygdala-lesioned animals, compared with other subjects, spent more time being inactive and physically explored the environment less. Despite the subtle, lesion-based differences in the frequency and duration of specific social behaviors, there were lesion-based differences in the organization of behavior such that lesion groups could be identified based on the patterning of social behaviors in a discriminant function analysis. The findings indicate that, although overall frequencies of many of the observed behaviors do not differ between groups, the general patterning of social behavior may distinguish the amygdala-lesioned animals.

We present a longitudinal neuropsychological study (31 examinations over a period of 18 months) of patient DF. DF demonstrated bilateral atrophy of the hippocampal formation and globus pallidus resulting from carbon monoxide poisoning. Eighteen months after the event, the volume of the hippocampal formation was reduced by 42% on the left side and 28% on the right. The patient initially presented with a severe global amnesia. Then, he showed a gradual, yet selective recovery of episodic memory function. Verbal free recall and spatial memory performance remained reduced, whereas immediate word recall and recognition memory, as well as picture learning and memory, improved to levels at the lower range of normal performance. Interestingly, nonspatial associative learning was never much impaired and recovered completely by the end of testing. These data are taken as evidence that the human hippocampal formation does not equally support different forms of episodic memory.

Facial displays are an important form of social communication in nonhuman primates. Clues to the information conveyed by faces are the temporal and spatial characteristics of ocular viewing patterns to facial images. The present study compares viewing patterns of four rhesus monkeys ( Macaca mulatta ) to a set of 1- and 3-sec video segments of conspecific facial displays, which included open-mouth threat, lip-smack, yawn, fear-grimace, and neutral profile. Both static and dynamic video images were used. Static human faces displaying open-mouth threat, smile, and neutral gestures were also presented. Eye position was recorded with a surgically implanted eye-coil. The relative perceptual salience of the eyes, the midface, and the mouth across different expressive gestures was determined by analyzing the number of eye movements associated with each feature during static and dynamic presentations. The results indicate that motion does not significantly affect the viewing patterns to expressive facial displays, and when given a choice, monkeys spend a relatively large amount of time inspecting the face, especially the eyes, as opposed to areas surrounding the face. The expressive nature of the facial display also affected viewing patterns in that threatening and fear-related displays evoked a pattern of viewing that differed from that recorded during the presentation of submissive-related facial displays. From these results we conclude that (1) the most important determinant of the visual inspection patterns of faces is the constellation of physiognomic features and their configuration, but not facial motion, (2) the eyes are generally the most salient facial feature, and (3) the agonistic or affiliative dimension of an expressive facial display can be delineated on the basis of viewing patterns.