Infants who cry for prolonged periods have abnormally high levels of the stress hormone cortisol, as well as lower growth hormone levels. The crying could be as a result of stressful separation from their parents, unfamiliar faces, surroundings or loud noises.

These imbalances, researchers now say, inhibit the development of nerve tissue in the brain, suppress growth, and depress the immune system.

A study conducted by scientists from Yale University and Harvard Medical School found that intense stress on a child during their early life can alter their brain’s neurotransmitter systems and can cause structural and functional changes in their brain similar to those seen in depressed adults.

One of the studies, carried out on 17 infants who persistently cried, showed that 14 of them were 10 times more likely to have attention deficit hyperactivity disorder (ADHD ) — a developmental disorder characterised by the co-existence of attention problems and hyperactivity along with poor school performance and antisocial behaviour.

The other three showed no change.

Bruce Perry, one of the researchers, said that chronic stress over-stimulates an infant’s brain stem — the part of the brain that controls adrenaline release — while the portions of the brain that thrive on physical and emotional input are neglected.

“For example, when a baby is repeatedly left to cry alone, the child will grow up with an overactive adrenaline system and so the child will display increased aggression, impulsive behaviour, and violence later in life,” said Dr Perry.

“This is because the brain stem floods the body with adrenaline and other stress hormones at inappropriate and frequent times.”

Andrew Bundi, a paediatric neurologist at Kenyatta Hospital says the stress hormone cortisol is released in response to stress and a low level of blood glucose to increase the blood sugar level in the brain. This hormone floods the brain during intense crying and other stressful events and can destroy the nerve connections in critical portions of an infant’s developing brain.

“When the portions of the brain responsible for attachment and emotional control are not stimulated during infancy, for example when a baby is repeatedly neglected, these sections will not develop,” said Dr Bundi, adding that the result is a violent, impulsive, emotionally unattached child.

He says that the sensitivity and responsiveness of a parent when a child is crying or stressed stimulates and shapes the nerve connections in key sections of the brain responsible for attachment and emotional well-being of a child. Neglect occurs when a parent is unable or unwilling to provide caring attention to a crying infant.

In another study, the researchers found that infants who were ignored did not develop healthy intellectual and social skills. The study revealed that infants who cried continuously — not due to colic — in the first 3 months of their life had an average IQ 9 points lower at 5 years of age and showed poor acquisition of fine motor skills (development of movements that require a high degree of control).

These infants showed more difficulty controlling their emotions and became even fussier when parents tried to control them at 10 months of age. “The most important influence of a child’s intellectual development is the responsiveness of the mother to the cues of her baby,” said Allan Schore, the lead researcher of the study.

According to Dr Schore, these babies have a more annoying quality to their crying, are clingier during the day and take longer to become independent as children. The study also found that prolonged crying in infants causes increased blood pressure in the brain, elevates stress hormones, obstructs blood from draining out of the brain, and decreases oxygenation to the brain.

Francis Kiare, a psychologist at Kenyatta University, said that when separated from parents, infants and children experience a vacuum that leaves them worried.

“When babies cry alone and are unattended, they experience panic and anxiety, which makes them feel abandoned and neglected. Most of them end up having a decreased REM sleep (the stage of sleep that promotes brain development),” said Mr Kiarie.

He noted that infants who endure prolonged periods of crying end up suffering from harmful neurological effects that may have permanent implications for the development of the brain.