Poor early experiences, such as limited stimulation, can reduce brain size and lower IQ.
While good early experiences help the brain develop well, poor experiences can literally cause a genetically normal child to have a lower I.Q. Scientific evidence shows that maltreated children who receive little stimulation – children who are exposed to fewer colors, less touch, little interaction with adults, fewer sights and sounds, and less language – actually have smaller brains.
De Bellis, M.D., Keshaven, M.S., Clark,D.B., Caseey, B.J., Giedd, J.B., Boring,A.M., Frustaci, K., & Ryan, N.D. (1999).Developmental traumatology. Part 2: Brain development. BiologicalPsychiatry, 45, 1271-1284