Monday, November 16, 2009

We do what's necessary to survive

Ever known someone who consistently returned to an abusive partner or spouse regardless of their resolve to end the cycle? Attempting to understand why someone would willingly subject themselves to more violence can indeed be mind-boggling. Scientists at several institutions around the country are finding out, however, that there is a biological explanation for this type of behavior, and it originates from the early years spent with our mom.

Throughout the early stages of life, it’s important that offspring remain close to their mom at all times, since she provides their basic needs for survival - nourishment, shelter, and protection. Separation or withdrawal from her during this time would put their very lives in jeopardy. To ensure this doesn’t happen, infants are born with an inherent preference for their mom, an attraction so strong that even poor treatment from her doesn’t interfere with their desire to be near her.

In their Nature Neuroscience paper published November 2, Gordon A. Barr et al. gave rats an electrical shock while exposing them to a particular odor. This conditioning caused adult rats to avoid all subsequent encounters with the scent since they associated it with getting shocked. The opposite reaction was reported in young rats, however. These pups actually exhibited a preference for the very odor they had been conditioned to avoid. It’s believed that, although they don’t have the ability to identify and avoid potentially harmful stimuli, they reach a stage at some point in development where they learn this strategy.

Further experiments revealed that the steroid corticosterone, also known as the stress hormone, reverses the preference behavior exhibited in the young rats. When corticosterone was injected into young rats prior to the electrical shock and odor exposure, they learned to avoid that odor in the future, which is the same response demonstrated by the adult rats!

At the core of this phenomenon lies dopamine, which is one of the brain’s molecules responsible for transmitting signals between cells. There is less dopamine released from neurons in young pups demonstrating preference behavior than in the young pups who avoided the odor because they were injected with corticosterone beforehand. The quantitative measurements of dopamine were taken from the amygdala, an area of the brain that processes threats and fears. The greater the release of dopamine, the stronger the synapses will be in the amygdala; this solidifies our memory of those stimuli that we’ve learned to avoid.

To further demonstrate the role of dopamine in avoidance behavior, young rats were infused with dopamine prior to conditioning. Those rat pups that would normally exhibit a preference for the odor now demonstrated an aversion for the scent. If a dopamine receptor antagonist were infused, the young rats demonstrated preference behavior. Once again, the elevated levels of dopamine are associated with the ability to learn and remember which stimuli to fear and avoid.

The preference behavior exhibited by young rats described herein has been selected for throughout many years of evolution. Obviously, nature has decided that it is more advantageous for us to prefer our mom and form an attachment to her even in instances of poor treatment or abuse. Our chances of survival are higher if we remain alongside her. After all, at birth and throughout infancy, we are virtually helpless and have no way of setting out to find better conditions and sources of nourishment.

At such a young age, we don’t have the ability to identify and learn which stimuli to fear and avoid. As we grow older and stronger and are thus better able to take care of ourselves, the dependence upon and attachment to mom lessens and we are able to learn which things to fear and avoid. Without mom right by our side to keep corticosterone levels at bay, it’s possible for us to detect stressful situations and learn how to deal with them.

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