Title/Introduction
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1. Defense and the Conditional Reflex
Page 1
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2. Flight, Locomotion and Image Memory
Page 2
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3. Olfactory Familiarity and Imprinting
Page 3
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Neophobia and Object Memory
Page 4
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Learning of "Wildness"
Page 5
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Habituation to Handling
Page 6
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Learning of Visually-Released Boxing
Page 7
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Conclusion
Page 8
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Bibliography
Page 10
I have suggested elsewhere that one of the major motivating inputs to the offense motivational mechanism comes from an olfactory comparator mechanism which is activated by unfamiliar conspecific odors [2]. This hypothesis can explain why muroid rodents do not attack members of their own group, but attack unfamiliar conspecifics. It can also explain the often documented finding that isolated individuals are more likely to attack, i. e. , the odors of their opponents are no longer familiar. Isolation is not effective if the test animal is regularly given the odors of his future opponent [33, 29] or if he is isolated from his opponent by a wire mesh rather than a glass partition [64].
It has been suggested that olfactory familiarity may be developed by a process of "imprinting" at a critical period of development [43]. Experience with particular odors which is restricted to ages 3-10 or 11-18 days in infant rats can influence their social behavior more profoundly than does experience with the same odors at an older age [39]. Infants of various muroid rodent species prefer members of other species if they are cross-fostered to those other species; this has been shown for Baiomys and Mus [49], Acomys and Mus [40] and Onychomys and Peromyscus [46]. Data from our laboratory suggest that such imprinting may be important for aggressive behavior; we have found more competitive fighting among pairs of non-littermates than among littermates, even though the pairings were made at the age of weaning, four months before the test [68].
Olfactory familiarity degrades over time. This may be due to a fading of the memory of the odors of the other animal, or it may be due to actual changes in the odor of the other animal, or to a combination of both. According to most experimental data, animals remain familiar with each other for at least several weeks following separation. Rowe and Redfern [52] have determined that if a mouse is removed from a colony and then replaced within a week, it is not attacked, but if it is removed for two or more weeks, then it is treated like a stranger and attacked. Norris and Adams [44] have noted that replacement of a Mongolian gerbil into a colony from which it has been removed for 15 days does not provoke attack, but after 30 days absence, it is attacked as if it were now a stranger. Most investigators find that several weeks of isolation are necessary for the development of vigorous offense against an opponent whether the animals are mice [26, 35, 21], rats (Adams, unpublished data), Mongolian gerbils [51, 58], or golden hamsters [12, 66]. Although one hundred percent of the animals may attack after three or four weeks of isolation, an even longer period of isolation up to 15 weeks may produce an even greater frequency of attacks per test session [47, 65].
Olfactory familiarity also has important effects upon defense. It facilitates the conspecific defense modulator and inhibits the defense motivational mechanism (Figure 1). Socially isolated rats show more upright posture and boxing in response to footshock [19, 61], and wild mice are more likely to show escape behavior when paired with strange conspecifics for the first time, while escape behavior then decreases as the opponents become more familiar over repeated tests [16].
The processes of olfactory imprinting, olfactory memory, and olfactory recognition are still mysteries, and they deserve much more experimentation. At the earliest levels of vertebrate evolution, they may have been developed to a great level of sophistication. For example, it is thought that the salmon imprints on the odors of its home stream, and uses its olfactory memory to return thousands of miles in order to spawn [17].
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