Additional research supports the hypothesis that children and adolescents subjected to child abuse and neglect have less grey matter than children who have not been ill-treated.
Medical professionals investigating the long-term effects of spanking have consistently found a link between corporal punishment and increased aggression in children.
Physical punishment undermines trust between parent and child and breeds hostility toward authority figures.
Being hit may subsequently hinder social relations in the classroom where there is a power differential between teacher and child.
This inquiry synthesized 20 years of published research on the topic and aims to "shift the ethical debate over corporal punishment into the medical sphere," says Joan Durant, a professor at University of Manitoba and one of the authors of the study.
According to the report, spanking may reduce the brain's grey matter, the connective tissue between brain cells.
Gershoff also noted that "we as a society think of spanking and physical abuse as distinct behaviors.
Spanking erodes developmental growth in children and decreases a child's IQ, a recent Canadian study shows.
In the United States, spanking has declined since the civil rights movements of the 1960s.
Most parents who use physical punishment today express regret for it and scant belief that it improves a child's behavior.