Figure 16.2 The developmental course of four pubertal processes for boys. From J. M. Tanner (1962), Growth at Adolescence, p. 30. Oxford: Blackwell Scientific. Copyright 1962 by Blackwell Scientific, reprinted with permission.

breast. For example, breast development is partly controlled by the number and type of breast tissue receptors and other intracellular conditions (Layman, 1995). End-organ sensitivity in the CNS, that is, how reactive neural tissues are to hormones and neurotransmitters, may also play a role, although more research is needed in this area (Sanborn & Hayward, 2003).

Steroid hormones may affect sexual differentiation of the brain via influencing cell proliferation, cell migration, ontogenetic cell death, synaptogenesis, and neuroregulation (Casper, 1998; MacLusky & Naftolin, 1981; Phoenix, Goy, Gerall, & Young, 1959). As most sexual dimorphisms in brain morphology are established prenatally, changes human brain anatomy have not been well studied during the pubertal development period (Giedd, Castellanos, Rajapakse, Vaituzis, & Rapoport, 1997). In one cross-sectional study that examined brain dimorphisms in children between 4 and 18 years of age, amygdala and hippocampal volume increased for both sexes but with the amygdala increasing significantly more in males than females and hippocampal volume increasing more in females (Giedd et al., 1997). Research with rats that involves highly specific probes for estrogen action in the CNS has uncovered new classes of estrogen receptors in the rat brains (Laflamme, Nappi, Drolet, Labrie, & Rivest, 1998; Mitchner, Garlick, & Ben-Jonathon, 1998; Osterlund, Kuiper, Custafsson, & Hurd, 1998). The nature of these estrogen receptors in humans, and how they may relate to pubertal variation between individuals, is not known.

The majority of studies that assess secondary sexual characteristic development include self- or parent-report ratings of Tanner's 5 stages of development (Marshall & Tanner, 1969). Although the most accurate Tanner ratings are those assessed by health professionals via visual inspection and sometimes palpation of the breast, self- or parent-report ratings are much more feasible to obtain. Studies report correlations between parent and examiner ratings of Tanner stages ranging from 0.75 to 0.87 (Brooks-Gunn, Warren, Rosso, & Gargiulo, 1987; Dorn, Susman, Nottelmann, Inoff-Germain, & Chrousos, 1990). Studies have also examined the validation of self-reported maturation based on Tanner drawings. Pearson correlation coefficients, when excluding testicular size, have been reported as .6 or above for the self- and physician-reports (Morris & Udry, 1980). Dorn and colleagues (1990) reported correlations between self- and physician-reports ranging between 0.77 and 0.91, which were slightly more accurate than the parent ratings in the same study. The Pubertal Development Scale (PDS) is another

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