A study indicates a mother's touch is crucial to a child's development and plays an important role in determining whether the child develops a host of illnesses later in life.

The McGill University study on rats found various stress-related illnesses, including depression, anxiety disorders, drug abuse and heart disease, could hinge on early life experience. "Some people live stressful lives and are incredibly resilient but others succumb," Michael Meaney, a McGill professor of medicine, said prior to a mental-health conference.

The study shows contact alters the chemistry in the developing brain, which causes a change in the stress response, said Meaney, who led the study.

His team identified a brain molecule from a gene that contributes to differences in stress responses.

Mother rats that repeatedly licked their young produced calmer offspring with a greater capacity to learn. The baby rats had lower levels of stress hormones.

When a rat mother licks her young, she turns on the gene involved in reducing the amount of the hormone the babies will release when stressed, said Meaney.

A similar process in which environment plays an important role also happens in human babies. People who remembered having poor relationships with their mothers also had higher measurements of stress hormones when tested with PET scans. More direct data is expected from a five-year, $4 million study involving 300 Canadian mothers and children. Meaney's team expects to follow the infants, now 12 to 18 months, for five years in an attempt to confirm the results of the animal study