The Importance of Touch on Infants

Touch plays a very special role in the life of young babies. Because it is so well developed at birth, it provides these brand-new arrivals more detailed access to their fascinating new world than any other sense. Touch is obviously essential to babies' sensory-motor development, but it also has a surprisingly potent influence over their physical growth, emotional well-being, cognitive potential, and even their overall health, because of some fascinating effects on their immune function.

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Newborn rats that are handled for just a brief period each day by human experimenters show all kinds of hormonal and behavioral advantages that stay with them throughout life. Handled rats are less fearful, have more brain receptors for benzodiazepines (anxiety-reducing tranquilizers that mimic the action of a natural inhibitory neurotransmitter, GABA), less degeneration in old age of the hippocampus (a critical memory-storing area of the brain), and correspondingly better cognitive performance as they age. All of these improvements can be traced to the fact that neonatal handling permanently reduces the reactivity of rats' stress response systems. Handled animals show the normal hormonal responses to stress (see Chapter 3), but their corticosteroid levels do not rise as high as those of nonhandled animals, and they recover more quickly. Since prolonged elevation of stress hormones can be quite damaging to many organs of the body, including the brain, a better-modulated stress-response system is advantageous to both an animal's health and its mental faculties.

Perhaps the most interesting feature of this handling effect is that it works during only the first ten days or so of a rat pup's life. Pups who are handled only after this critical period do not show the same permanent advantages. Of course, human handling is not a natural stimulus for a rat, but recent research has found many of the same benefits for those rat pups who receive greater tactile stimulation from their mothers. Rat dams, like human mothers, vary in their styles of nursing and contact, and it turns out that those that lick and groom their pups more during nursing induce the same lasting benefits in their offspring. They have a better-modulated stressresponse system, including changes in brain neurochemistry that make them less fearful in novel situations.

Other animal studies have focused on the effects of maternal separation on infants' growth and immune function. Infant monkeys become very distressed when their mothers are removed; their stress hormones rise during even brief separations, while longer separations are known to suppress their immune system. This suppression reverses if mother and infant are reunited within ten days, but if they remain separated for longer than that, the effect appears to be permanent; the offspring continue to show reduced immune function as late as six years of age. Rat pups, too, derive an immune benefit from early touch, since handled animals produce higher levels of antibodies in response to an immune challenge than nonhandled rats. As in monkeys. short-term maternal separation raises rat pups' stress hormone levels and is also known to inhibit the release of growth hormone and to suppress cellular growth and differentiation. These effects, which are limited to the first three weeks of a pup's life, can be prevented by firm human stroking, suggesting that it is the mother's actual touch and contact—as opposed to, say, her warmth or nursing—that especially promote infant growth.

There is a crucial period where an infant should be touched by its mother to reduce its stress level and the stress hormones that would otherwise damage its organs.