sheathed in myelin, thereby improving the efficiency of neural signaling. DTI-based connectivity studies of prefrontal white matter tracts suggest an association between connection strength and self-regulation (Liston et al., 2006; Casey et al., 2007; Asato et al., 2010). Combining DTI and fMRI, Casey and colleagues have linked connection strength between prefrontal cortex and subcortical brain regions with the capacity to effectively engage in self-control in both typically and atypically developing individuals (Casey et al., 2007). A similar increase in number and strength of prefrontal connections to cortical and subcortical regions from age 13 to young adulthood has been shown to be associated with improvements in self-control by Hwang and colleagues (2010).
The second method, resting state fMRI, assesses the strength of functional connections within a network by quantifying correlated spontaneous activity between brain regions at rest. Resting state fMRI studies show that brain maturity involves connections between distal brain regions increasing while connections between proximal or local brain regions simultaneously decrease (Fair et al., 2007; Dosenbach et al., 2010). Together, these findings support the claim that cognitive maturation occurs not in unitary structures but in the connectivity and interactions between developing structures (Fair et al., 2007; Thomason et al., 2010; Uddin, Menon, and Supekar, 2010). Thus, the relative immaturity of adolescent abilities will rely on specific immaturity of the circuitry.
Overall the findings suggest that in emotionally charged situations with limited time to react, as may be the case for most juvenile offenses, basic emotional circuits may drive adolescent actions. In more neutral contexts, more top-down cortical circuits may have a greater impact on decisions (Steinberg, 2009; Casey and Jones, 2010; Somerville, Fani, and McClure-Tone, 2011).
Pubertal Influences on Brain and Behavior
Puberty involves physical changes to the body initiated by gonad hormones to which the adolescent must adjust. These hormones also impact brain and behavior by binding to testosterone and estrogen receptors in the brain. These hormonal and brain changes coincide with increased sexual activity and interest (Sisk and Zehr, 2005) and with changes in arousal and the salience of motivational stimuli (Friemel, Spanagel, and Schneider, 2010). Brain changes specifically associated with puberty are consistent with broader brain and behavior patterns that occur during adolescence—that is, poor self-control, heightened sensitivity to peer influence, and heightened responsivity to immediate rewards.
Importantly, individual differences in the timing of puberty affect long-term outcomes. Early puberty has been associated with poor outcomes