Thank Mom for the good memories
Anecdotal and correlational evidence abounds that parental neglect can have severe consequences for children's later cognitive development. But under normal conditions, how does maternal care contribute to brain development-and what are the mechanisms? In the August 2000 issue of Nature Neuroscience (Vol. 3, No. 8, pp. 799-803), Michael Meaney and colleagues at McGill University provide some interesting clues by studying the offspring of two different groups of female rats-those that were well above average in various aspects of maternal care (licking, grooming and arched-back nursing of their pups), and those well below average.
The major result was that the pups from the high-care mothers performed better in a test of spatial learning and memory (the effects were already apparent at an early age and were still significant in old animals). Because this test is known from other studies to depend heavily on activity in a brain region called the hippocampus, the authors then compared the hippocampus from the two groups of animals. They found that those pups from high-care mothers also had more synapses in their hippocampus, along with a higher level of inputs from other brain regions involved in learning. By comparing levels of trophic factors and neurotransmitter receptors, the authors provide evidence that the mechanism that mediates the effects of maternal care might start with a neurotransmitter receptor already known to be involved in learning and plasticity (the NMDA receptor).
One obvious possibility is that the effects could be genetic-in other words, the high-care mothers might have different genes from low-care mothers, which could explain the difference between their offspring. However, this cannot be the whole explanation; the authors performed cross-fostering experiments, and showed that pups born to low-care mothers and raised by high-care mothers were indistinguishable (both in performance on the learning and memory tests and brain development) from pups born to high-care mothers. In other words, pups that would normally have performed poorly on the tests did better as a result of receiving more maternal care. Interestingly, the converse was not always true-pups born to high-care mothers performed well even when transferred to foster mothers who gave them less care. Thus, maternal care influences brain development, but some pups are more sensitive to this influence than others. The authors suggest that the difference may be due to differences in brain chemistry that are already established by the time of birth.
Much more research is needed to understand just how maternal behavior is translated into changes in brain development, and why it affects some individuals more than others. Obviously, great care needs to be taken in generalizing these results to humans. Nevertheless, the present results point to new directions in studying a question that is of fundamental human interest.
Dr. Michael J. Meaney
Douglas Hospital Research Center
6875 Blvd. Lasalle
Montreal (Quebec) H4H 1R3
(C) Nature press release.
Message posted by: Trevor M. D'Souza