Biomedical Engineering Reference
In-Depth Information
What is Abnormal Behavior?
Abnormal behavior is a broad and encompassing term that
includes any behavior which deviates from what is typical
for the species. Abnormal behaviors can arise in two ways.
In some individuals, species-typical behavior may be
expressed at abnormal levels (e.g. hyperaggressiveness).
More commonly, animals may develop unusual, non
species-typical patterns of behavior that appear to serve no
purpose. These repetitive, frequently idiosyncratic, highly
ritualized actions have been termed “stereotypies”
(
Berkson, 1967; Ridley and Baker, 1982
). Stereotypies
can be divided into whole-body motor actions and self-
directed movements (
Novak et al., 2006
). Whole-body
motor actions include pacing, somersaulting, and rocking.
Self-directed movements often involve the hands and/or
face and include eye-salutes, ear or eye covering, and digit
sucking. Most of these patterns are not dangerous to the
monkeys displaying them and may even be adaptive under
the existing environmental conditions or in the context of
the physical state of the organism (
Mason, 1991
). For
example, pacing may be a replacement for species-typical
locomotor activity that cannot be expressed fully
in monkeys housed in individual cages (
Draper and
Bernstein, 1963
).
However, nonhuman primates can also exhibit severe
forms of abnormal behavior for which the term “patho-
logic” may be appropriate. This category includes stereo-
typic behavior that is expressed at levels that interfere with
normal activities and biological functions (see the section
on Severity classification below). It also includes behavior
that may cause tissue irritation or wounds. The term “self-
injurious behavior” (SIB) is used as a general descriptor for
patterns such as hair pulling, head banging, and self-biting
which are observed in a small percentage of captive
nonhuman primates. SIB is potentially dangerous, some-
times resulting in serious wounds and increased risk of
infection. Most of this chapter will focus on stereotypic and
self-injurious behavior.
category represents data from 10 genera combined whereas
the macaque and chimpanzee categories represent a single
species. Comparisons of prevalence by these taxonomic
groups are invariably confounded with differences in early
rearing experiences, housing history, age, husbandry prac-
tices, and facility environments. In addition, the various
categories of abnormal behavior have not been standard-
ized across facilities or species. Moreover, because an
individual animal can exhibit several different forms of
pathological behavior, the actual prevalence of monkeys
showing any form of abnormal behavior cannot be obtained
by summing across categories.
A survey of 362 individually housed rhesus monkeys at
one research facility emphasizes the complexities of
understanding prevalence rates. Eighty nine percent of this
population displayed at least one abnormal behavior with
a mean of 2.3 different behaviors and a range of 1
8
behaviors (
Lutz et al., 2003
). Pacing was the most common
stereotypic behavior, occurring in 78% of the population.
A significantly higher proportion of the monkeys exclu-
sively displayed whole-body stereotypies (48%) compared
to self-directed stereotypies (4%). The two kinds of
stereotypies co-occurred in 33% of the population. About
11% of the individually housed monkeys developed SIB
and had a veterinary record for self-inflicted wounding.
Similar findings were observed in pigtailed macaques
except for the incidence of SIB where only 6% of the
monkeys had a veterinary record of wounding (
Bellanca
and Crockett, 2002
). In three species of macaques, SIB was
also significantly associated with floating limb syndrome
(
Bentson et al., 2010
).
e
Severity Classification
The mere presence of stereotypic behavior does not neces-
sarily signify pathology. Many humans show mild forms of
rhythmic stereotyped behaviors (e.g. hair twirling, face
rubbing, pen clicking, necklace chewing, knuckle cracking,
ring twisting, toe tapping, or leg swinging) that are not
detrimental to health or well-being. However, other forms of
stereotypic behavior in humans can be detrimental because
repetitions interfere with other activities (e.g. OCD-like
symptoms such as excessive hand washing) or because the
behaviors pose a significant health risk (e.g. cutting and
burning). Thus, any assessment of abnormal behavior in
nonhuman primates similarly should take into account
frequency, severity, and interference with other species-
typical behaviors. A typical classification system for
nonhuman primates might include the following three
categories: (1) mild: abnormal behavior occurs at low rates
and/or under predictable situations (e.g. pacing associated
with the anticipation of being fed); (2) substantial:
abnormal behavior is frequent (i.e. occupying a significant
part of the animal's time budget to the exclusion of other
Prevalence
Stereotypic behavior is known to vary in form and
frequency across different primate species. Some kinds of
abnormal behavior are more commonly seen in particular
taxonomic groups (e.g. regurgitation and reingestion in
apes) whereas others are typical of most primate species in
captivity (e.g. pacing). However, the actual prevalence of
abnormal behavior in large captive nonhuman primate
colonies to date has only been surveyed in prosimians
(
Tarou et al., 2005
), rhesus macaques (
Lutz et al., 2003
),
and chimpanzees (
Nash et al., 1999
).
Table 7.1
summarizes
the prevalence rates for these groups. One should use
caution in interpreting the data contained in the table. The
taxonomic groups are not equivalent. The prosimian
