Biomedical Engineering Reference
In-Depth Information
the form of positive reinforcement training. The best
evidence that increased human contact can have beneficial
effects on general health and well-being comes from
research on chimpanzee infants. Infants receiving respon-
sive care which included an additional 4 hours of “species-
typical” interaction with human caregivers 5 days a week
showed more organized attachments and superior cognitive
performance compared to infants receiving standard care
(
van Ijzendoorn et al., 2009
). However, the relationship
between human contact and abnormal behavior in primates
is not well understood. At issue are what form the contact
should take, whether the benefit is limited to the period in
which the interaction occurs, and how the contact is to be
implemented to insure protection for both human and
animal participant. Increased human contact in the form of
feeding, playing, and grooming has been associated with
reduced stereotypic and self-directed abnormal behaviors
in chimpanzees, and similar benefits have been noted when
humans provided treats to singly housed rhesus monkeys
(
Bayne et al., 1993
). But clearly more studies are needed to
address the value of this approach.
A more recent emphasis has been placed on the effects
of positive reinforcement training (PRT). PRT is frequently
used to increase cooperation with husbandry practices and
has been shown to reduce the physiological response
to veterinary procedures in some species of primates
(
Lambeth et al., 2006
;see
Bloomsmith et al., 2007
for
review). PRT can be used either to target specific behaviors
for change (e.g. reinforcing behaviors that are incompat-
ible with abnormal behavior) or as “training enrichment”
for husbandry practices. Studies using the first approach
have demonstrated decreased appetitive stereotypy (i.e.
regurgitation and reingestion) in a chimpanzee (
Morgan
et al., 1993
) and a reduction of several abnormal behaviors
(e.g. coprophagy, self-injury, and regurgitation) in a zoo-
housed gorilla (
Pizzutto et al., 2007
). A combination of
training, enrichment, and pharmacological intervention
reduced self-injurious biting in a chimpanzee (
Bourgeois
et al., 2007
). However, in all these studies, it is unclear how
much training was needed to maintain the improvement
and whether the improvement was selectively tied to the
training period.
Husbandry training (e.g. training to enter transport cages
or to take a position at a particular part of the cage) has also
been used as a form of interactive animate enrichment in
larger groups of animals. This form of “training enrichment”
presumably stimulates cognitive function, increases activity,
and may reduce anxiety associated with certain triggers of
abnormal behavior (
Baker et al., 2009
). Training to comply
with basic husbandry procedures has been shown to reduce
abnormal behavior in baboons (
Bourgeois and Brent, 2005
)
and in zoo-housed apes (
Carrasco et al., 2009; Pomerantz
and Terkel, 2009
). In a more recent study, Baker and
colleagues (2009) reported that PRT in rhesus monkeys
(e.g. training to sit) was successful at reducing only
a particular type of abnormal behavior (mainly whole-body
stereotypies) in a subset of animals that displayed the
highest levels of those behaviors. Furthermore, the
frequency of those behaviors, although reduced, remained
high. In the most comprehensive study to date, both the
effects of PRT as training enrichment and unstructured
human interaction were assessed in 61 singly housed
macaques at two large primate facilities (
Baker et al., 2010
).
The authors failed to detect any significant change from
baseline levels with either manipulation, leading them to
conclude that PRT might be more effectively employed on
a case-by-case basis to target specific behaviors for change
depending on research or clinical needs.
Although PRT may lead to reductions in some
abnormal behaviors in captive nonhuman primates, there
are several factors that must be considered before using
PRT. First, training of animals requires a considerable time
commitment from qualified care staff. Additionally, certain
types of behavior may not be responsive to generalized
husbandry training and individual differences in behavioral
profile or dominance status may impact the effects of PRT
(
Baker et al., 2009; Pomerantz and Terkel, 2009
). An
additional factor to consider is how well the immediate
effects of training are generalized to nontraining periods.
Although there is some indication that behavioral effects
last for at least a short time beyond the training period
(
Bourgeois and Brent, 2005; Carrasco et al., 2009; Pom-
erantz and Terkel, 2009
), there is no indication that training
has long-lasting effects on abnormal behavior without
frequent periods of maintenance training (
Bloomsmith
et al., 2007
).
Nonsocial Intervention
Other (i.e. nonsocial) types of interventions have also been
used in an attempt to reduce the incidence of behavioral
pathology in individually housed nonhuman primates. Most
of the research in this area has focused either on cage size
or environmental enrichment and its impact on abnormal
behavior.
Cage Size
The impact of cage size on abnormal behavior is not fully
understood, and evidence for a role of cage size in the
development and maintenance of such behavior is clearly
mixed. The inconsistent findings for cage size may, in part,
be related to the range of cage sizes examined and the
confounding of changes in cage size with changes in loca-
tion. In general, small changes in cage size (e.g. doubling the
size of an individual cage) appear to have negligible effects
on abnormal behavior (
Line et al., 1990; Crockett et al.,
1995
). In one study, abnormal behavior actually increased
