I found this fascinating quote today:
Learning is dependent upon experiences. Experience activates neurons to fire and repeating the experience causes the neural networks formed to strengthen (Gross, 2008). Environmental influences, however, can have a negative impact on brain development. Early physical and psychological stress has been found to delay the development or hinder growth in the hypothalamus and brainstem (Gross, 2008). Researchers using MRI techniques have found that severely neglected and abused children have a smaller head and decreased brain mass (Gross, 2008). Another study using MRI technique found that the greater the abuse the smaller the brain volume (Gross, 2008). Studies of abused and neglected children in early childhood have detected delays in cognition, emotional factors, social skills, and physical development (Gross, 2008). Mommy Tyme, Your Thoughts on our Children, Development, and Life, Nov 2009
You should read the whole article.