Attachment behaviour is both
biologically important and technically difficult
to study. The behaviour is complex and there are
changes in several cognitive and affective
variables to consider.Nevertheless, recent
studies with chicks, rats, sheep, voles and
now humans have
begun to reveal some important candidates for
the neurobiology of social attachment.
The neuropeptides oxytocin and vasopressin
have yielded a model that links molecular,
cellular and systems approaches. Dopamine
pathways in the forebrain, especially the
nucleus accumbens and ventral pallidum, seem to
be important for certain aspects of partner
preference formation. It seems likely that for
attachment to occur, these neuropeptides must
link social stimuli to dopamine pathways
associated with reinforcement.
It is also possible that neural mechanisms
that we associate with drug abuse and addiction
might have evolved for social recognition,
reward and euphoria,critical elements in the
process of attachment. In the very near
future,we can hope that discoveries of the
molecular and cellular mechanisms of addiction
might be applied to the neurobiology of
attachment, providing a new understanding of one
of our most complex and intriguing emotions.
Of
human bonding
Are animal studies of attachment relevant to
human love? In the human brain, oxytocin
receptors are concentrated in several
dopamine-rich regions, especially the substantia
nigra and globus pallidus, as well as the
preoptic area.Whereas this pattern is consistent
with a monogamous brain, the receptors are not
found in the ventral striatum or ventral
pallidum, areas in which either oxytocin or
vasopressin V1a receptors are abundant in
monogamous voles and monkeys. There is no
evidence, at this time, that these pathways are
involved in human attachment. A recent
functional magnetic resonance imaging (fMRI)
study of adults looking at pictures of their
partners, as opposed to close non-romantic
friends, found bilateral activation in the
anterior cingulate (Brodmann's area 24), medial
insula (Brodmann's area 14) as well as caudate
and putamen. The pattern of cortical activation
was distinct from previous studies of face
recognition, visual attention, sexual arousal or
other emotional states, but resembled
preliminary results from an fMRI study of new
mothers listening to infant cries. Both studies
of human attachment show marked overlap between
the pattern of activation when looking or
hearing a loved one and a previous report of
activation during cocaine-induced euphoria. It
seems likely that pathways that mediate the
hedonic properties of psychostimulants evolved
as neural systems for social attachment.
Graves, F. C., K. Wallen, et
al. "Opioids and attachment in rhesus macaque
(Macaca mulatta) abusive mothers." Behav
Neurosci (2002). 116(3): 489-93.
This study investigated the
role of the endogenous opioid system in maternal
and affiliative behavior of group-living rhesus
macaque (Macaca mulatta) mothers with a history
of abusive parenting. Eighteen mothers received
an injection of the opioid antagonist naltrexone
or saline for 5 days per week for the first 4
weeks of the infant's life. After treatment,
mother-infant pairs were focally observed.
Naltrexone did not significantly affect infant
abuse or other measures of maternal behavior.
Naltrexone increased the amount of grooming
received by mothers from other group members and
reduced the mothers' rate of displacement
activities such as scratching, yawning,
and self-grooming. These results concur with
previous primate studies in suggesting that
opioids mediate the rewarding effects of
receiving grooming and affect anxiety-related
behaviors.
