Recognition of a mate by female mice, as measured by the pregnancy block effect caused by a novel male, is mediated in the olfactory bulbs ( Brennan and Keverne, 1997), whereas recognition of a familiar mouse in the context of social investigation appears to be mediated in the medial amygdala (MeA) and associated structures ( Young, 2002). In rodents, different neural structures have been implicated in individual recognition by odors in different contexts. The extent to which the fusiform gyrus is dedicated primarily to the recognition of faces versus objects and faces, or visual expertise in general, has been hotly debated ( Kanwisher, 2000 Tarr and Gauthier, 2000).
The most thoroughly investigated system is recognition of faces in humans and nonhuman primates, in which it has been shown that structures in the temporal lobe (e.g., the fusiform gyrus and hippocampus) are particularly important for the processing of facial stimuli and are involved in the recognition of faces (Fried et al., 1997, 2002). Although we have shown that hamsters have integrated, multicomponent representations of individuals ( Johnston and Jernigan, 1994 Johnston and Bullock, 2001), these experiments did not show different functional responses to different individuals.ĭespite the importance of individual recognition, its neural basis is not well understood. A shortcoming of these studies, however, is that the tasks that were used do not show true individual recognition (i.e., different responses to equally familiar individuals with differing significance to the subject) but rather study a simpler process, recognition of categories of individuals (e.g., familiar vs novel). Thus, some level of ability to discriminate and recognize individuals exists in a wide range of species ( Halpin, 1980 Colgan, 1983).ĭiscrimination and recognition of individuals have been investigated in several mammalian species, including recognition of lambs in the context of nursing ( Kendrick et al., 1997), mate recognition and mate preferences in rodents such as mice, voles, and hamsters ( Bunnell et al., 1977 Brennan and Keverne, 1997 Johnston, 1998 Petrulis et al., 1999 Yamazaki et al., 2000 Ferguson et al., 2002 Young, 2002), and recognition of faces in sheep and primates ( Rolls, 2000 Kendrick et al., 2001). The ability to recognize individuals is crucial for establishing stable social relationships, including membership in a group, friendship, pair bonds, social status, dominance hierarchies, territorial networks, and numerous other aspects of social behavior and organization. These results are the first to use a rodent model to characterize neural circuits involved in the recognition of equally well known individuals and the corresponding emotional responses to them. In experiment 2, temporary inactivation of the CA1 region of anterior dorsal hippocampus by microinfusion of lidocaine eliminated the avoidance of the familiar winner, but a saline control injection had no effect. Immunohistochemistry for c-Fos and Egr-1 implicate several areas of the brain in individual recognition, particularly the anterior piriform cortex, the CA1 and CA3 regions of anterior dorsal hippocampus, anterior and posterior dentate gyrus, and perirhinal cortex.
Subjects tested with the familiar winner avoided this stimulus male, but subjects tested with the familiar, neutral male were attracted to him. One day later, losers of fights were tested in a Y-maze for reactions to one of the two familiar males. In experiment 1, we use a new method for studying true individual recognition in which male hamsters first had different experiences with two stimulus males (exposures to one male across a wire-mesh barrier and fights with another male). Most laboratory studies of individual recognition in rodents have studied differential responses to familiar versus unfamiliar individuals rather than differential responses to equally well known individuals having different significance for the subject. The ability to recognize individuals is essential for many aspects of social interaction and social organization, yet we know relatively little about the neural mechanisms underlying this ability.
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