Untitled

Adolescent-Typical Behavior Patterns 19making the timing of assessment critical, as well as the lack of spatial resolutionnecessary to establish foci in specific amygdala nuclei (Zald, 2003). Thelatter point is particularly critical given the differing—and sometimes opposing—functional effects among specific subunits (nuclei) of the amygdala (Swanson& Petrovich, 1998).Thus, although intriguing, the amygdala data are highly inconsistent at present.While it has been proposed that the development of emotional control duringadolescence may be related to progressively greater PFC modulation over emotionalprocessing within the amygdala (see Killgore et al., 2001), only limitedsupport for this appealing hypothesis has been obtained to date. Judicious use ofstudies using animal models and increasing availability of higher field strengthmagnetic resonance scanners with their greater spatial resolution should ultimatelyhelp resolve frustrating inconsistencies in this literature.Summary and Other Emerging Areas of InterestThe evidence to date suggests that during adolescence the brain is sculpted to transformthe brain of the child into a more energy efficient brain of the adult. Some ofthese alterations are regressive, with a loss of a notable proportion of excitatory(glutaminergic) synapses and binding sites for both glutamate (NMDA-R) and DAin certain sites within the mesocorticolimbic system. Other alterations may involvepossible ontogenetic shifts in the balance of activity among various cortical vs.subcortical forebrain regions. To the extent that the data are available, there areconsiderable similarities across species in the nature of these alterations in adolescentbrain. Although the evidence to date suggests that this adolescent sculptingis particularly dramatic in forebrain mesocorticolimbic systems, adolescent-relatedneuronal changes are seen elsewhere as well. Generally speaking, though, considerablyless attention has been paid to adolescent brain ontogeny outside theforebrain. One exception to this generality has been the extensive literature onhypothalamic function during the pubertal portion of adolescence, with evidencefor alterations in both excitatory and inhibitory tone in the hypothalamus contributingto the reactivation of the hypothalamo-pituitary-gonadal (HPG) axis at puberty(see Grumbach, 2002; and Romeo et al., 2002; Spear, 2000, for reviews ofthis extensive literature). In contrast, evidence for adolescent-associated alterationsin cerebellum and their potential contribution to cognitive and emotional developmenthas begun to emerge more recently. The adolescent cerebellum is of particularinterest given data showing cerebellar influences on cognition and affectin both humans (Kim et al., 1994; Schmahmann & Sherman, 1997) and rodents(Bobee et al., 2000), and anatomical data detailing cerebellar projections to thePFC, along with other circuitry relating these regions (Middleton & Strick, 2000,2001). Some support for the involvement of the cerebellum in cognitivedevelopment has emerged using fMRI, with the cerebellum showing age-related