might be exposed to various behavioral stressors, such as noise and unfamiliar surroundings, and neurochemicals associated with the stress response would be measured in her offspring to determine the effects of prenatal stress on the development of stress responsiveness in young animals (Schneider et al., 1998).

The second is aimed at understanding the neural substrates or correlates of particular behaviors or aspects of temperament, including social recognition, affiliation, pair bonding and attachment, parental behavior, social dominance, aggression, predation, play, and fearfulness (Amaral, 2002; Kavaliers and Choleris, 2001; Siegel et al., 1999; Young, 2002). In those studies, animals may have lesions, be genetically modified (mouse knockouts), or be electrically or chemically stimulated, and the resulting behaviors can be observed; or neural function may be measured during or after the performance of the behaviors of interest.

The third category consists of pharmacologic studies to determine the efficacy of various compounds in reducing aggression, anxiety, or fearfulness (Mench and Shea-Moore, 1995). The purpose of those studies is usually to identify compounds that may be useful in human or veterinary clinical medicine, but pharmacologic testing can also be used for studies of underlying mechanisms of behavior: the behavior of interest is stimulated in some way, usually by staging an aggressive encounter or placing an animal in a fear-inducing situation, and compound efficacy is then evaluated with behavioral measures.

Social Disruption

Social disruption can be used as an experimental technique in neuroscience and behavioral research, but it can also be an inadvertent confounder of the research. Experimental designs that purposefully incorporate social disruption, do so through the temporary removal and reintroduction of offspring or of group or pair-mates, longer-term or repeated reorganization of social groups by removal of group members or by introduction of unfamiliar animals to groups or to one another, or even the merging of different groups of animals. Abnormal social conditions can also be created by placing animals in atypically small or large social groups, by forming groups of atypical composition (such as all-male groups or groups comprising only animals of similar age), or by crowding them. In addition to the study goals described above, this technique has recently been used to study coronary artery atherosclerosis, heart rate reactivity, and the effects of exercise in conjunction with social disruption on coronary heart disease (Kaplan et al., 1982, 1993; Manuck et al., 1983a,b; Williams et al., 1991, 2003).

The effects of social separation (such as individual housing) or social isolation on an animal’s behavioral profile have been documented in various species. The impact of social separation or isolation can depend on the species or strain of animal, the age at which an animal is removed from conspecifics, the duration of the separation, and the completeness of the separation (with respect to visual, auditory, or olfactory cues from other animals). In nonhuman primates, the lack



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