The notion that premature babies are likely to face cognitive impairment during their life has been challenged by two recent and independent studies.

A typical characteristic of the brain of extremely premature babies is a smaller cerebral cortex. Until now it was believed that this was due to a decreased number of neurons, probably as a consequence of the hypoxia-ischemia (impaired blood flow to the brain) often experienced by premature infants. Consequently “for decades we thought of survivors of preterm birth as having a devastating permanent injury” says Stephen Back, the main author of one of the two studies.

The new studies suggest that the brain of premature babies contains a normal number of neurons but they are in an immature state. Therefore the damage is not permanent and the injured neurons can be nourished back to health by better nutrition or cognitive stimulation. 
Babies are considered moderately premature if they are born 3 or more weeks early, and extremely premature if they are born prior to 27 weeks of gestation, or about 12 or 13 weeks early (a typical pregnancy lasts 40 weeks).

Professor Back and his colleagues counted the number of neurons present in fetal brains that have suffered different intensity of induced ischemic injury and compared it with brains that had not. They conducted their experiments on fetal sheep brains, as this animal model more closely resembles the brain of human fetus.
The surprising discovery was that the number of neurons in injured cortices is the same than in the controls, despite the ischemic cortices have a smaller size.
To investigate this further, the researchers stained the neurons and look at their structure. While control neurons look like mature neurons with the typical tree-like structure, damaged brain cells have a morphology indicative of neuron immaturity.

The second study, lead by Steven Miller, analyzed the correlation between neonatal care and brain development in 95 preterm babies. The results suggest that postnatal care can have a tremendous effect on promoting brain growth, providing an incredible opportunity to reduce neurological disabilities associated to preterm birth.

http://www.newscientist.com/article/dn23091-cognitive-impairment-in-premature-babies-not-permanent.html
http://stm.sciencemag.org/content/5/168/168ra7
http://stm.sciencemag.org/content/5/168/168ra8