This area is part of the association cortex, regions of the brain responsible for incorporating and synthesizing information from multiple other brain regions. A stimulating environment can increase the proportion of glial cells and the high ratio could possibly result from Einstein's life studying stimulating scientific problems.[15] [16] The limitation that Diamond admits in her study is that she had only one Einstein to compare with 11 brains of normal intelligence individuals. S. S. Kantha of the Osaka Bioscience Institute criticized Diamond's study, as did Terence Hines of Pace University.[4] Other issues related to Diamond's study point out glial cells continue dividing as a person ages and although Einstein's brain was 76, it was compared to brains that averaged 64 in age (eleven male brains, 47–80 years of age).