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(National Geographic.com, 4, Oct 2012) - Primates, rodents may show signs of sadness, study suggests.
Learning more about depression in animals could one day
benefit humans, say scientists who believe that mammals share the same basic
wiring in their brain for emotions as humans do. (Although not every scientist
agrees with that premise.)
In the October 5 issue of Science, Assistant Professor of
Neuroscience Olivier Berton and his colleagues at the University of
Pennsylvania reviewed recent studies of rodents, primates, and fish who lacked
interest in their environment and their fellow animals.
We spoke with Berton about what we do—and don't—know about
animal depression.
Do animals get depressed?
Depression is diagnosed in humans based on a list of
symptoms that are all very subjective. Common core symptoms include feelings of
guilt, thoughts of death, and loss of pleasure. Because animals can't
communicate even if they have these kinds of experiences, strictly the answer
is: We can't say.
What signs may indicate if an animal is depressed?
There are certain aspects of the disease that may be
measured in animals. One of the core symptoms of depression is anhedonia, the
decrease and loss of interest in pleasurable activities. We measure interest in
food that animals like a lot or in motivation for sexual activity. We also
measure how they are interacting socially with other animals in the group, and
changes in sleep patterns and daytime activities. Another behavior that has
been used frequently to measure animal depression is whether they readily give
up when exposed to a stressful situation.
What animals seem to exhibit signs of depression?
Definitely the most convincing observations derive from
nonhuman primates. Based on behavioral observation, trained observers can say a
monkey looks depressed. Because their emotional behaviors are similar to that
of humans, just by looking at their facial expressions or the way their gaze is
directed, we can get an indication of whether an animal may be experiencing
sadness.
Can you really study animals in this environment?
One problem is that many lab studies in primates and rodents
are conducted in captive animals that are raised in relatively impoverished
conditions compared to their natural habitat. This can cause depression-like
changes. Currently there is not a lot of data available that compares animal
emotional behaviors in the wild versus in laboratory setting.
How would animals deal with depression in nature?
I don't know. There are very few systematic studies of this
kind. It is possible that behavioral disorders in animals in the wild may
impair their chances of survival. Maybe there is a point where they cannot deal
and are more easily preyed upon.
Could domestic animals be depressed?
Veterinarians frequently give antidepressants to dogs to
treat their behavioral disorders. For example, if an owner leaves the house and
the dogs experience stress related to being separated, they may develop
abnormal behaviors such as scratching themselves until they bleed or eating the
door. These are thought to represent canine versions of psychiatric disorders.
Although human treatments seem to work in dogs, large-scale studies are
lacking.
