Here, we test three often proposed hypotheses about socioeconomic status (SES), affect, and the brain, for which evidence is mixed or lacking. The first hypothesis, that negative affect is more common at lower levels of SES, has ample evidence from studies of psychiatric symptoms but is tested for the first time here across multiple measures of negative emotions in healthy young adults. The second hypothesis is actually a set of hypotheses, that SES is associated with three structural and functional properties of the amygdala. Third, and most important for the affective neuroscience of SES, is the hypothesis that SES differences in the amygdala are responsible for the affective differences. Despite the intuitive appeal of this hypothesis, it has rarely been tested and has never been confirmed. Here, we review the literature for evidence on each of these hypotheses and find in a number of cases that the evidence is weak or nonexistant. We then subject each hypothesis to a new empirical test with a large sample of healthy young adults. We confirm that negative affect is more common at lower levels of SES and we find a positive relation between SES and amygdala volume. However, evidence is weak on the relation of SES to functional properties of amygdala. Finally, the tendency toward negative affect in lower SES individuals cannot be accounted for by the structural or functional characteristics of the amygdala measured here.

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