I do not know, However I do know that on on average, the brains of African-Americans are 5% smaller than the brains of Whites, according to studies of brain weight at autopsy, endocranial volume of empty skulls, head size measurements by the U.S. military and NASA, and two dozen MRI volumetric studies [#]

# ^ Ho, K. C., Roessmann, U., Straumfjord, J. V., & Monroe, G. (1980). Analysis of brain weight: I and II. Archives of Pathology and Laboratory Medicine 104, 635–645.
# ^ Johnson F. W. & Jensen (1994). Race and sex differences in head size and IQ. Intelligence 18: 309–33
# ^ Rushton JP (1991). Mongoloid-Caucasoid differences in brain size from military samples [and NASA]. Intelligence 15: 351–9.