Habituation is an extremely simple form of learning, in which an animal, after a period of exposure to a stimulus, stops responding. The most interesting thing about habituation is that it can occur at different levels in the nervous system. Sensory systems may stop, after a while, sending signals to the brain in response to a continuously present or often-repeated stimulus (Cohen et al. 1997). Lack of continued response to strong odors is a common example of sensory habitation. Habituation to complex stimuli may occur at the level of the brain; the stimulus is still perceived, but the animal has simply "decided" to no longer pay attention (Rose and Rankin 2001).

Even odor habituation can take place centrally, in the brain. In rats Deshmukh and Bhalla (2003) hypothesized that cells in the hippocampus could time the intervals between odor inputs; frequent stimuli resulted, in their study, in a cessation of response at the level of the hippocampus..

Habituation is important in filtering the large amounts of information received from the surrounding environment. By habituating to less important signals, an animal can focus its attention on the most important features of its environment. A good example of this is species that rely on alarm calls to convey information about predators. In this case animals stop giving alarm calls when they become familiar with other species in their environment that turn out not to be predators. Habituation is an important component of "not crying wolf" when non-threatening animals come close.

Prairie dogs, Cynomys ludovicianus, give alarm calls when mammals, large birds, or snakes approach. Individual prarie dogs are particularly susceptible to becoming food for a coyote, hawk, or rattlesnake, but collectively they are quite well-defended, as their alarm calls facilitate escape in burrows.

When prairie dog towns are located near trails used by humans, giving alarm calls every time a person walks by is a waste of time and energy for the group. Habituation to humans is an important adaptation in this context.


In animal behavior studies in the field, investigators often rely on the study animals becoming habituated to the presence of the investigator. Jane Goodall's famous studies of chimpanzees, for example, depended on the chimpanzees learning to tolerate her presence. Werdenich et al (2003) and Van Krunkelsven et al. (1999) give a contemporary perspective on habituation of study animals. This complex level of habituation is far different than learning to ignore an odor, but has a similar role in helping the animal to ignore irrelevant stimuli.

Most recent work on habituation has been at the neural level, as reflected by these references:

Burrell BD, Sahley CL 2001 Learning in simple systems CURRENT OPINION IN NEUROBIOLOGY
11 (6): 757-764

Cohen TE, Kaplan SW, Kandel ER, Hawkins RD 1997 A simplified preparation for relating cellular events to behavior: Mechanisms contributing to habituation, dishabituation, and sensitization of the Aplysia gill-withdrawal reflex JOURNAL OF NEUROSCIENCE 17 (8): 2886-2899

Deshmukh SS, Bhalla US 2003 Representation of odor habituation and timing in the hippocampus JOURNAL OF NEUROSCIENCE 23 (5): 1903-1915

Rose JK, Rankin CH 2001 Analyses of habituation in Caenorhabditis elegans. LEARNING & MEMORY
8 (2): 63-69

Van Krunkelsven E, Dupain J, Van Elsacker L, Verheyen R 1999 Habituation of bonobos (Pan paniscus): First reactions to the presence of observers and the evolution of response over time FOLIA PRIMATOLOGICA 70 (6): 365-368

Werdenich D, Dupain J, Arnheim E, Julve C, Deblauwe I, van Elsacker L 2003 Reactions of chimpanzees and gorillas to human observers in a non-protected area in South-Eastern Cameroon FOLIA PRIMATOLOGIC 74 (2): 97-100



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