Midline structures such as the posterior cingulate cortex, medial frontal gyri, and anterior cingulate have been consistently found to “deactivate,” or respond preferentially to the baseline condition as compared to the more demanding condition of many fMRI paradigms (Binder et al., 1999; Greicius et al., 2003; Hampson et al., 2006; McKiernan et al., 2003). This increased midline activity during a passive state (e.g., fixation) or conditions requiring little cognitive processing (e.g., vigilance), relative to regions needed for cognitively demanding conditions, has been linked to a propensity for stimulus independent thought, or mind wandering (Gusnard et al., 2001; Mason et al., 2007; McGuire et al., 1996; McKiernan et al., 2006). This could in turn relate to compromised appraisal of emergent risk situations and reduced tendencies to carefully consider outcomes of behavioral selections. We observed that increased FH density was linked to more fixation-related BOLD response and less vigilance response in the cingulate. Potentially, this may indicate that adolescents with denser FH engage in less stimulus independent thought during easy task conditions (i.e., in response to a vigilance task), but more such
