Childhood emotional neglect was positively associated with amygdala reactivity only in iso homozygotes, and genotype groups differed from one another only at relatively low levels of emotional neglect, such that val carriers had elevated amygdala reactivity relative to iso homozygotes. We speculate that the nature of this gene-by-environment interaction may reflect shifts in the neuroendocrine and autonomic profiles of val allele carriers. It is possible that relatively elevated activity of the HPA axis places val carriers closer to a physiological ceiling and thus makes them relatively insensitive to further modulation of amygdala reactivity by previous emotional neglect. The finding of generally greater amygdala reactivity in val carriers relative to iso homozygotes is consistent with this speculation. Additionally, threat-related amygdala reactivity in iso homozygotes may be more sensitive to environmental conditions, for better or worse (43).
