Originally Posted by MarinaVanessa:
I'm going to stand on the opposite side of the spectrum here and say that because they are infants under 12 months that the CIO method may actually be harmful to them. I've read articles and have had trainings and taken child development courses that have said that allowing infants under the age of 12 months to cry for longer than 15 minutes at a time can be harmful. The infant stops crying because she learns that she can no longer hope for the caregiver to provide comfort, not because her distress has been alleviated.
There have been studies that show that infants that have the CIO method used on them have increased heart rate and blood pressure, reduced oxygen level, elevated cerebral blood pressure, depleted energy reserves and oxygen, brain injury, and cardiac dysfunction. Of course these are all worst case scenarios in babies that are often left to CIO and not the common case.
Babies that young are still in the early stages of early brain development and letting a child that young cry for long periods of time can cause chronic stress in that baby. That in return can lead to an over-active adrenaline system, which can then later turn into the child being more aggressive, impulsive, and violent.
I would completely agree with the CIO method if the child was older than 1 year (when the brain has mostly finished it's early stages of development) but not before then.
For now I would simply allow the infant to cry for short periods of time (a few minutes) and then go in and sooth the child with my voice and my touch but not pick the baby up. Once the baby stopped crying I would walk back out of the room. You would pretty much be teaching the baby that doesn't yet know how to self sooth that just because you are not in the room you are still nearby and available. As time goes on (depending on the baby) I would then add a few more minutes and prolong my reaction time as the baby got better and better at feeling secure about being alone.
By no means is this easy or quick, some babies learn quicker than others depending on their personalities, but it can be done. It just takes patience. I have all of my DC kids sleep in the same room now and it works. That includes a 4mo, 7mo, 1yo, two 2yo's, 3yo. 4yo and an 8yo. It took a while but it got easier over time.
Either way I hope you have luck 
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Interesting information. It makes sense if you think about it! I know I told the OP to put the baby in the crib and walk away, but I'll admit that's not the answer. I personally go get my son when he cries so I don't know why I told her to do the opposite. Now I feel bad doing it to my daughter when she was a toddler, but like you said, by the time she was 1-1 1/2 she was developmentally ready to know to go to sleep on her own. Anyways, I definitely learned something new today!