David and I have an ongoing communication problem since Elizabeth was born. He'll tell me something and often I will have no recollection of him having mentioned it at all. At times, I have worried that maybe I was getting Alzheimers or something because this isn't like me. A paragraph toward the end of this article, Parents' brains tuned to babies' tears, on Nature's news site, sheds some light on my problem:

Men and women also respond differently to infant sounds, according to the study. When females hear baby noises, activity drops in a brain region called the prefrontal cortex, which filters out irrelevant sounds. Males are unaffected.

Crying may open up the noise filter in the prefrontal cortex, so that a woman interprets the toddler's sounds as important. Electrical impulses are then relayed to other brain areas, triggering strong emotions, as well as caring behaviour such as feeding or cuddling.

The main point of the article has to do with brain imaging and comparing parents and non-parents in how they respond to infant sounds:

The brains of mums and dads are tuned in to the sound of toddlers' cries, reveals a brain-imaging study. Non-parents, on the other hand, remain largely oblivious.

Researchers at the University of Basel, Switzerland, played parents and childless adults recordings of babies' cries and laughter. They measured their brain activity using functional magnetic resonance imaging (fMRI).

Parents' brains fired up more in response to sobs than giggles, the researchers found. The cries activated one brain region in particular, called the amygdala, which is involved in processing emotions.

This is so obvious to me that my first reaction was to wonder why they needed brainimaging to figure this out. One of the researchers comments "Childless grown-ups, by contrast, reacted more to infant laughter than whimpers. This shows that the parental brain activity is learned." I think he's really pushing the envelope on the definition of learned here. I suggest he try this study with first-time mom's with newborns who haven't had the chance to "learn" yet. I suspect he'd find that this effect is much stronger in them than in experienced moms. I think much of this kinds of "learning" is hormonally mediated.