An important aspect of Jancke and Steinmetz's model is that the slopes derived for their mathematical functions were equivalent for men and women. The authors cite this as evidence to support a relatively constant relationship between the CC and FBV for both sexes. The work of Mack and colleagues (1993) on the rat CC suggests that if brain size is measured by brain weight and the relationship between the regional CC measures and brain weight is expressed with a simple correlation of nontransformed data, there appear to be some differences in the relationships between brain size and regional CC size as a function of sex and hormonal status. For example, in rats, correlations among regional CC widths and brain weight were low to moderate, but their patterns were inconsistently so for males compared to females, ovariectomized females, and ovariectomized females with estrogen replacement (Mack et al., 1993).
When comparing results across studies, it is critical to understand that stability of CC/brain size relationships between the sexes is subject to the same intricacies and complexities as are the basic CC/brain size relationships described above. Whether application of Jancke and Steinmetz's modeling techniques using an FBV measure would lead to a result in rats paralleling that seen in humans is a matter to be tested empirically. Nevertheless, it is noteworthy that application of Jancke and Steinmetz's model to CC area and brain weight reported in 10 postmortem studies in humans did appear to follow similar patterns as their own data analysis with CC area and FBV using MRI.
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