Studies of the age-variation of the effects of genotypic variants on the development of brain function will provide increasing insight into the processes of brain maturation and in particular the influences of neurophysiological factors during the transition from childhood through adolescence to adulthood. One important indicator of neurocognitive function is the P3 (or P300) response, evidenced by the production of a large positive waveform with a peak between 300 ms. and 700 ms. after the presentation of a target stimulus. The P3 response is elicited by infrequently presented target stimuli in a stream of more frequently occurring non-target stimuli in auditory or visual target detection (oddball) tasks, which call for the subject to respond to only the target stimulus. The P3 response has been proposed to index attentional and working memory resources (Polich, 2007). It has been associated with several anatomical loci including the supra-marginal gyrus, hippocampus, locus coeruleus, anterior cingulate cortex (ACC), insula, and the right-lateralized frontal and temporoparietal regions of the ventral attention network which may be part of a distributed circuit (Menon et al., 1997; Brázdil et
