PSYC23H3 Lecture Notes - Lecture 6: Adrenal Cortex, Electroencephalography, Model Organism

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28 Jun 2015

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Week 6: Hidden Regulators of Attachment
This question asks what processes are responsible for the development of the behaviors, and
inferred mental states, that we refer to as the ‘‘bond’’ between infant and mother.
Research has shown that predispositions can be created prenatally, in the fetus, to respond
preferentially to specific maternal scents and sounds, and that these predispositions prepare the
way for the next phase in the development of attachment.
Regina Sullivan, Steve Brake, and I (Sullivan, Hofer, & Brake, 1986) discovered an experimental
learning paradigm in newborn rats that revealed a rapid and powerful learning capacity by which
neonates acquire the ability to discriminate, prefer, approach, and maintain proximity to their own
A specific neutral odor was presented to newborns while the pups were stroked with an artist’s
brush for 5 to 15 minutes.
-The odor was later applied to shavings under mesh in a two-compartment box.
The neonates then turned preferentially to that odor and remained on the mesh over the scented
compartment for the duration of testing.
-Control subjects were presented with the same stimuli but separated in time. They showed no
later preference for the odor.
We now know that human newborns also can distinguish their own mother’s smell, apparently on
the basis of prenatal experience, and add vocal and visual recognition postnatally—probably by
similar early-learning systems (Winberg 2005).
Next, Sullivan discovered that for the first 10 days after birth, an aversive level of stimulation (e.g.,
tail pinch, mild shock) that itself elicits vigorous escape behavior will paradoxically induce
approach and preference for an odor previously associated with it.
After those 10 days, such associative pairing results in avoidance of the odor.
The unexpected early aversive-preference learning has an obvious parallel in the strong
attachments frequently observed in abused human infants.
In this animal model, Sullivan and coworkers have mapped out the critical period for the effect,
have shown that the critical period can be extended in time by daily repetitions of the associative
experience, and have related the normal close of this period to developmental transitions in
specific brain systems that are regulated by circulating adrenocortical hormones.
In most conceptual formulations of attachment, the separation response is explained as deriving
from the strong affective nature of the bond, which when severed or ‘‘ruptured’’ by separation
results in a series of traumatic emotional reactions: the ‘‘biphasic protest–despair response,’’ in
which an initial burst of calling and active search behavior is followed by a long decline in
behavioral responsiveness.
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But there is circularity in this line of reasoning, as the evidence for the existence of the bond itself,
and for its strength, lies in the dramatic response to its being broken by separation.
But to our surprise, we found that, like primate infants, infant rats show a complex biphasic
protest–despair response to maternal separation, as well as a number of other responses that
were entirely unexpected.
We found that these changes were not the expression of an integrated psychophysiological
response (like the increase in heart rate and respiration during exercise) to the stressful event,
but were the result of a novel mechanism.
Our experiments showed that each of the individual behavioral and physiological systems of the
infant rat was responding to the loss of one or another of the components (e.g., nutrient,
thermal/metabolic, or sensorimotor) of the infant’s previous interaction with its mother and that the
complex response to separation was due to the withdrawal of all these components at once.
For example, we found that providing one of these components, warmth, to a separated pup
prevented the slow decline in the pups’ general activity level (a response similar to Bowlby’s
‘‘despair’’ phase), but this had no effect on responses in other systems.
-The pup’s cardiac rate continued to fall by 40%, regardless of whether supplemental heat or
tactile stimulation was provided. But we found that we could maintain cardiac rate in separated
pups at normal levels by continuous infusion of milk to the pup’s stomach.
Supplying enough milk to prevent weight loss had no effect, but if enough was given to produce a
normal range of weight gain, the cardiac rate at the end of a 24-hour separation was proportional
to the amount of nutrient that had been infused.
In other words, the supplied milk regulated the pups’ heart rate.
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