NEUROBIOLOGICAL BASIS OF HUMAN PET RELATIONSHIP
It has become common for people who have pets to refer to themselves as
"pet parents," but how closely does the relationship between people
and their non-human companions mirror the parent-child relationship? A small
study from a group of Massachusetts General Hospital (MGH) researchers makes a
contribution to answering this complex question by investigating differences in
how important brain structures are activated when women view images of their
children and of their own dogs. Their report is being published in the
open-access journal PLOS ONE.
Pets hold a special
place in many people's hearts and lives, and there is compelling evidence from
clinical and laboratory studies that interacting with pets can be beneficial to
the physical, social and emotional wellbeing of humans," says Lori Palley,
DVM, of the MGH Center for Comparative Medicine, co-lead author of the report.
"Several previous studies have found that levels of neurohormones like
oxytocin -- which is involved in pair-bonding and maternal attachment -- rise
after interaction with pets, and new brain imaging technologies are helping us
begin to understand the neurobiological basis of the relationship, which is
exciting."
In order to compare
patterns of brain activation involved with the human-pet bond with those
elicited by the maternal-child bond, the study enrolled a group of women with
at least one child aged 2 to 10 years old and one pet dog that had been in the
household for two years or longer. Participation consisted of two sessions, the
first being a home visit during which participants completed several
questionnaires, including ones regarding their relationships with both their
child and pet dog. The participants' dog and child were also photographed in
each participants' home.
The second session
took place at the Athinoula A. Martinos Center for Biomedical Imaging at MGH,
where functional magnetic resonance imaging (fMRI) -- which indicates levels of
activation in specific brain structures by detecting changes in blood flow and
oxygen levels -- was performed as participants lay in a scanner and viewed a
series of photographs. The photos included images of each participant's own
child and own dog alternating with those of an unfamiliar child and dog
belonging to another study participant. After the scanning session, each
participant completed additional assessments, including an image recognition
test to confirm she had paid close attention to photos presented during
scanning, and rated several images from each category shown during the session
on factors relating to pleasantness and excitement.
Of 16 women
originally enrolled, complete information and MR data was available for 14
participants. The imaging studies revealed both similarities and differences in
the way important brain regions reacted to images of a woman's own child and own
dog. Areas previously reported as important for functions such as emotion,
reward, affiliation, visual processing and social interaction all showed
increased activity when participants viewed either their own child or their own
dog. A region known to be important to bond formation -- the substantia
nigra/ventral tegmental area (SNi/VTA) -- was activated only in response to
images of a participant's own child. The fusiform gyrus, which is involved in
facial recognition and other visual processing functions, actually showed
greater response to own-dog images than own-child images.
"Although this
is a small study that may not apply to other individuals, the results suggest
there is a common brain network important for pair-bond formation and
maintenance that is activated when mothers viewed images of either their child
or their dog," says Luke Stoeckel, PhD, MGH Department of Psychiatry,
co-lead author of the PLOS One report. "We also observed differences in
activation of some regions that may reflect variance in the evolutionary course
and function of these relationships. For example, like the SNi/VTA, the nucleus
accumbens has been reported to have an important role in pair-bonding in both
human and animal studies. But that region showed greater deactivation when
mothers viewed their own-dog images instead of greater activation in response
to own-child images, as one might expect. We think the greater response of the
fusiform gyrus to images of participants' dogs may reflect the increased
reliance on visual than verbal cues in human-animal communications."
Co-author Randy
Gollub, MD, PhD, of MGH Psychiatry adds, "Since fMRI is an indirect
measure of neural activity and can only correlate brain activity with an
individual's experience, it will be interesting to see if future studies can
directly test whether these patterns of brain activity are explained by the
specific cognitive and emotional functions involved in human-animal
relationships. Further, the similarities and differences in brain activity
revealed by functional neuroimaging may help to generate hypotheses that
eventually provide an explanation for the complexities underlying human-animal
relationships."
The investigators
note that further research is needed to replicate these findings in a larger sample
and to see if they are seen in other populations -- such as women without
children, fathers and parents of adopted children -- and in relationships with
other animal species. Combining fMRI studies with additional behavioral and
physiological measures could obtain evidence to support a direct relationship
between the observed brain activity and the purported functions.
Stoeckel is a
clinical neuropsychologist and lecturer on psychology, and Gollub an associate
professor of Psychiatry at Harvard Medical School. Additional co-authors of the
PLOS ONE report are Eden Evins, MD, MGH Psychiatry, and Steven Niemi, DVM,
Harvard University. Support for the study includes National Institutes of
Health grants K23DA032612 and K24DA030443 and support from the Charles A. King
Trust. The study was facilitated by imaging consult support from Harvard
Catalyst.
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