Too much too young is bad

new finding

A new report says that chronic over-stimulation early in life can permanently impair the development of tiny blood vessels in the brain, writes S Ananthanarayanan

Current ‘Do-it-yourself’ child psychology has it that ‘catching them young’ not only gives children a ‘competitive advantage’ over their peers but also helps their brain grow at the only time in their lives that it is possible. Commercial minds have latched onto this, and new parents wonder if they are failing the child if she is not in the most advertised nursery by the time she can walk. This parental anxiety to give their child the best in life often starts earlier, with constant attention and aural, visual and tactile stimulation right from birth.

Christina Whiteus, Catarina Freitas and Jaime Grutzendler at the Yale School of Medicine, Connecticut, USA, report in the journal Nature their finding that “Chronic over-stimulation early in life can permanently impair the development of tiny blood vessels in the brain.”

Conversely, neither reduction of sensory input nor moderately increased activity by environmental enrichment affects the same development.

The context was the observation that activity dependant development of nerve cell patterns during infancy coincides with the development of finer blood vessels in the brain. This had raised a question of whether activity of brain cells could also affect the growth of the blood vessel system.

Studying blood supply

The authors note that given the brain’s high energy consumption and susceptibility to seizure or tissue death by lack of blood supply, development of an adequate network of the narrowest blood vessels to match metabolic demands is vital.

Although the major blood vessels in the brain are formed even before birth, the final development of the blood supply system continues through early infancy, and is concurrent with development of the nerve cell connections of the brain.

As there are common regulatory mechanisms that mediate the growth of blood vessels and nerve tissue, the question of whether activity of the brain nerve cells affects the development of the blood vessel network arises and has not been investigated.                                                    To address the question, the authors investigated the effect of physical stimulation and an enriched environment, which promotes neural activity, on the development of the brain blood vessel system in experimental mice. The first trial was of the effect of reduction of sensory inputs to the brain, by trimming both the whiskers of newborn mice, on the fifteenth day after birth. Tests showed that this had no effect on the development of blood vessels in the part of the brain involved.

While trimming the whiskers had the effect of reduction of stimulation, even moderate stimulation, by providing the young mice with an ‘enriched’ environment, which is to provide them with tasks and puzzles, or even other mice to associate with, also did not affect the rate of blood vessel growth. This trial thus showed that ordinary sensory and neural activity did not have an effect on brain blood vessel development.

Further trials, however, produced unexpected results. More persistent and repeated activity as also exposure to repetitive sounds and noise over an extended period (ten hours) led to positive reduction in the development of blood vessels.

This effect became greater when the stimulation by activity and sounds was extended. And what is more, the effect was specific to the part of the brain that was engaged by the enhanced activity. When whiskers of only one side were trimmed and the remaining whiskers stimulated by an air current, for ten hours a day, for eight days, there was reduction in blood vessel development in the part of the brain associated with the stimulated whiskers.

Three hours on the treadmill every day for five days resulted in reducing blood vessel growth in the area associated with motor functions.

Over the ten-day period, from the 15th to the 25th day after birth, repetitive stimulation led to a reduction of 13 per cent in the branching and 8 per cent in the length of blood vessel development in the stimulated mice, as compared to the mice that were left alone.

This difference amounts to a 70 per cent reduction in the new branches and an 80 per cent reduction in the increase in length in blood vessels, as a result of persistent stimulation. The slowdown of blood vessel development was seen to persist and did not recover even after extended over-stimulation was stopped, which shows that the effect is long lasting.

In contrast, continuous stimulation of older mice did not have these effects, which seems to be natural, as branching and growth of blood vessels in the brain is not much after early infancy.

While the studies have been on newborn mice, its relevance to the development of human brain is obvious. That very early learning before the onset of the correct stage in development is of little avail is well known.

For instance, it is known that a child is ready to learn to read at age six. A child who is taught earlier can learn, no doubt, but may have no advantage over another child who was taught only when she was at the appropriate age. On the other hand, the study now reported says sensory and auditory stimulation of young children may be positively and permanently harmful, in a physiological sense, apart from psychological harm.

“These findings raise the concern that early childhood seizures or exposure to repetitive auditory and other sensory-motor stimuli, which are common in modern society could have lifelong repercussions,” the authors say in the paper.