Temperature Motivation 53regulation. However, when exposed to a cold environment,
rat pups clump together in a manner that reduces each pups
exposed body surface area. This huddling provides behav-
ioral thermoregulation because it lessens the heat lost to the
environment via conduction (Alberts, 1978).
Huddling behavior is modulated by environmental tem-
perature. Specifically, with decreasing environmental tem-
perature, the total surface area of the huddle diminishes.
Conversely, the total surface area of the huddle increases as
the environmental temperature rises (Alberts, 1978). Thus,
pups act as a unit by adjusting their group’s exposed surface
area in a manner that defends body temperature against envi-
ronmental changes.
Individual pups follow a typical movement pattern
through the huddle that contributes to the changes in the
whole litter’s exposed surface area. These movements are
competitive adjustments that position a pup in a thermally de-
sirable location. In colder environments pups move toward
the middle of the huddle, and in warm environments they
shift to the periphery (Alberts, 1978). Collectively, these
adjustments make the litter behave as an organized unit
sensitive to the environmental temperature.
Fever
When mammals are infected by pathogens, they display an
array of nonspecific “sickness” responses that include fever
and fatigue. Traditionally, these symptoms were thought to
result from an inability to perform normal activities because
of the compromised physiological state of the sick individual.
As an alternative, Bolles and Fanselow (1980) suggested
that illness involving fever might be a particularly strong
activator of the recuperative motivational system. Consistent
with this speculation, investigators have recently suggested
that sickness is an adaptive motivational response that aids
recuperation (Aubert, 1999; Watkins & Maier, 2000). Impor-
tantly, part of the sickness response involves fever: a sus-
tained hyperthermia. Thus, mammals actively modulate their
body temperature as an adaptive response to pathogens.
Fever and recuperation therefore may have some degree of
positive feedback between them.
Learning and Thermoregulatory Responses
Earlier we described how animals learn to anticipate things
like danger or to expect the appearance of a potential mat-
ing partner. What evidence exists that animals learn to antic-
ipate thermal conditions? Most investigations in this realm
have focused on escape behavior (e.g., Howard, 1962) or on
the effects that environmental temperatures have on learning
acquisition (e.g., Hack, 1933). In a typical escape procedure
an animal is exposed to an aversive stimulus until it performs
a response. For example, rats exposed to cold temperatures
will press a bar to gain access to a heat lamp. Over trials, rats
become very efficient at this response, and they often drive
the ambient temperature up to room temperature. But what
do the animals learn during these conditioning trials? Ani-
mals may learn that the bar pressing makes the chamber
warm, but these studies provide little evidence for the notion
that rats perform thermoregulatory responses because they
anticipatethe problem.
Very few studies demonstrate that animals will learn to
perform a response that avoids hot or cold stress. Nor do
many studies demonstrate that thermal cues can elicit learned
CRs. Interestingly, studies that demonstrate these responses
to thermal reinforcers have frequently used infant animals as
subjects. For example, newborn chicks can be autoshaped to
peck a bar for food (Wasserman, 1973). Newborn dogs will
perform an avoidance response to avoid a cold reinforcer
(Stanley, Barrett, & Bacon, 1974), and newborn rat pups ex-
hibit tachycardia as a CR when an odor is paired with cold
temperature (Martin & Alberts, 1982).
Recall that newborn animals, such as the rat pup, have lit-
tle insulation and that thermoregulation requires more elabo-
rate behavioral strategies. Perhaps we more readily observe
thermal Pavlovian conditioning in the rat pup because its
niche requires such learning. This suggestion may have im-
plications for how we view thermoregulatory behavior, and it
is further developed in the next section.A Thermoregulatory Behavior System?We have described how animals regulate body temperature
with both physiological and behavioral means. Conspicu-
ously, we have not yet provided substantial analysis of these
responses. Why then would they be included in a chapter on
the topic of motivation? Let us consider the traditional ac-
count of thermoregulatory behavior before we answer this
question.The Homeostatic ExplanationThe concept of homeostasis has been the fundamental prin-
ciple employed by traditional explanations of thermoregu-
latory behavior. This idea, first applied by Cannon (1932),
assumes that each animal has a body temperature set point,
and that thermoregulatory behavior is activated whenever
the animal is perturbed from this reference. Thus, if an ani-
mal is cold, it automatically performs a series of responses
to return to its set point. This explanation implies that the