Biomedical Engineering Reference
In-Depth Information
self-biting or self-slapping). In this model, the stereotypic
behavior should be linked to other clinical signs related to
the condition or illness and should be reduced or eliminated
with targeted medical treatment.
The psychopathology model posits that stereotypic
behavior is a manifestation of “psychological dysfunctions”
including anxiety ( Lutz and Meyer, 2008 ) and impulse
control disorders, both of which may be linked to an inter-
action between the quality of the environment and genetic
risk factors in vulnerable animals. In humans, treatments for
these disorders range from behavioral/cognitive training to
pharmacotherapy. There is no universal treatment for these
conditions, and treatment efficacy varies considerably
( Nock, 2010; Symons et al., 2004 ). The assumption of this
model is that other symptoms for these psychological
disorders should also be present and that pharmacotherapy
should be at least somewhat effective in reducing the
abnormal behavior.
eliminated, then pharmacotherapy might be used in an
attempt to reduce stereotypic behavior.
ETIOLOGY OF PSYCHOLOGICAL
DISORDERS
Many factors are known to play a role in the development
of abnormal behavior in nonhuman primates. The early
social environment has received particular attention due to
the pioneering research by Harry Harlow and his colleagues
during the period from 1959 to 1970 ( Harlow and Harlow,
1962, 1965 ). Harlow and his colleagues examined several
rearing environments in which infants received different
kinds of social experience. In some of these environments,
monkeys developed psychological disorders manifested by
inadequate social development, cognitive deficits, and the
appearance of stereotypic and other abnormal behaviors. In
the rearing environment research described below, the
focus will be primarily on behavioral abnormalities, social
development, and physiology. Additional information
about adult social outcomes, effects on brain function, and
cognitive deficits is summarized in Novak et al. (2006) .Itis
important to review this research to insure that husbandry
practices employed in laboratory animal facilities today do
not inadvertently mimic Harlow's conditions for experi-
mentally induced psychopathology.
Coping Models
Two opposing models suggest that the presence of stereo-
typic and abnormal behavior is a coping strategy. Mason
and Latham (2004) argue that stereotypic behavior may be
a form of “do it yourself enrichment” serving to increase
sensorimotor stimulation and allowing animals to express
species-typical behavior in impoverished environments.
This model posits that stereotypic and abnormal behavior
should be reduced by adding the appropriate stimulation in
the form of environmental enrichment.
In contrast, the arousal reduction model assumes that
stereotypies reduce rather than increase arousal, although in
this case arousal initially is excessively high due to a state of
anxiety or distress. For example, apparently purposeless
pacing may actually serve to relieve anxiety ( Mason, 1991;
Wechsler, 1991 ). Even self-biting behavior, the most
common manifestation of SIB in monkeys, has been asso-
ciated with reductions in heart rate ( Novak, 2003 ). Similarly,
arousal reduction and anxiety relief have been described in
humans who cut and burn themselves ( Brain et al., 1998;
Nixon et al., 2002 ). The actual relationship between
stereotypic rituals and anxiety in humans is born out by
parallel findings that the anxiolytic effect is usually depen-
dent on completion of the ritual ( Szechtman and Woody,
2004 ) and that interruptions of this ritual may serve to
increase anxiety ( Goodman et al., 1989 ). Based on this
model, if stereotypies are adaptive coping responses to
anxiety-provoking situations in nonhuman primates, then
devising strategies to eliminate them without removing the
stressor might actually decrease animal well-being ( Mason,
1991 ). The optimal strategy, therefore, is to identify poten-
tial stressors and eliminate them from the environment.
However, if this strategy is impossible to achieve either
because the stressors cannot be identified or they cannot be
Experimental Rearing Environments and
their Effect on Behavior
A primary objective of Harlow's research with infant rhesus
monkeys was to identify factors that were crucial to the
development of species-appropriate social behavior. In
these studies, monkeys were typically separated from their
mothers at birth and then reared under varying levels of
social restriction for the first 6
12 months of life. The
impact of social restriction was assessed by comparing
restricted infants with normally developing infants
(mother-peer reared) and following both groups through
adolescence and into adulthood.
e
Total and Partial Isolation Rearing
The most severe form of social restriction was total isola-
tion, an experimental condition in which newborn rhesus
monkeys were separated from their mothers at birth and
reared in chambers in which they could not see, hear, or
physically contact members of their own species. Although
partial isolation differed from total isolation in that the use
of mesh instead of solid cages allowed the infants to see and
hear (but not contact) other monkeys, it yielded somewhat
similar negative outcomes. Consequently, both types of
early social restriction are considered together. Although
early social isolation is rarely used as an experimental
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