Emerging evidence suggests that psychological stress may result in behavioral and autonomic changes placing one at greater risk of disease [4
]. That a behavioral performance difference as measured by reaction time for positive images but not for neutral images in a scrambled/unscrambled judgment task lends further support to the assumption that even basic motor processes can become variable across simple choice tasks in the context of emotional tone in those living in lower SES. In such light, it is interesting that mood congruent biases in cognition and emotional responsitivity are among the most commonly reported research findings in the neuropsychiatric literature on depression – the disorder most commonly examined in association with low SES [17
Notably, while the phenomenology of depression consists of an accentuation of negative affective processing it also consists of an inability to experience pleasure or positive motivation. That the subgenual anterior cingulate (sgACC) and posterior cingulate both demonstrated reduced responsivity to positive images in those in low-SES compared to those in higher SES (Fig.
) is consistent with recent literature demonstrating volumetric deficits in the sgACC [9
] and abnormally decreased blood flow in other areas associated with reward and pleasure in depression [18
Fig. (1) low SES > high SES, positive vs. neutral. Threshold at p=.05 for visualization. Regions marked in blue (superimposed on an anatomical image) had statistically significant BOLD decreases whereas regions in red indicate significant BOLD increases. (more ...)
The relative down regulation of the caudate in those in low-SES compared to higher SES (Fig.
) is particularly interesting in light of this region's prominent role in the processing of pleasure, reward and anticipated satisfaction [19
]. Indeed, cerebral blood flow and metabolism have been shown to be abnormally decreased in the caudate in subjects diagnosed with major depression and bipolar disorder [21
]. Consistent with this, a recent fMRI study found that depressed patients demonstrated significantly less ventral striatum activation to positive linguistic stimuli [18
]. That the neural activation in the caudate, an area implicated in motivation and action [22
], differed strongly between SES groups offers additional evidence to implicate economic stress in the development of depression and possibly other mood disturbances via processes occurring in the autonomic nervous system (e.g.
) and cortical regions associated with mediating reciprocal modulation of cognitive, heteromodal sensory, limbic, and autonomic control [24
]. Interestingly, the insula which is histologically, topographically, and connectively poised to mediate reciprocal modulation of polymodal sensory, cognitive, emotional, and cerebrogenic autonomic control demonstrated both increased and decreased regulation during the activation paradigm (Fig.
). Notably, increased regulation in the anterior insula (especially left, Figure ) has been demonstrated during anticipation of a unpleasant stimuli [25
], while lowered activity (at the functional level) has been associated with long term chronic stress (e.g.
posttraumatic stress disorder; PTSD) [26
]. In such light, the conceptualization of low-SES conditions acting as a chronic stressor similar to other extended stress related disorders such as PTSD requires further exploration.
Finally, considerable evidence points to maladaptive emotional, behavioral and cognitive responses to stressful life circumstance as a hallmark of mood disorders and while those living in lower-SES are reported to be at higher risk for mood disorders [27
], questions remain concerning the causal direction. Two suspected routes are social selection
, which posits that individuals with psychopathology have a reduced ability to hold jobs and therefore a lower SES (referred to as social drift), and social causation
, which posits that people with low SES develop psychiatric disorders as a result of living with adversity. Evidence for psychiatric social selection has been demonstrated by a handful of studies in which early-onset psychiatric disorders were shown to lead to reduced educational attainment [28
], that severe early-onset disorders like schizophrenia were shown to lead to reduced income in adulthood [29
], and that attention-deficit/hyperactivity disorder lead to lower adult SES [30
]. A concern with this literature base, however, is that many studies relating SES to psychopathology have involved child/adolescent samples, making the likelihood of social selection in these cases low as subjects tend to be too young to account for a significant portion of their families’ income (with the exception of an indirect effect, in which the child’s issues reduces the parents ability to maintain their income). Rather, an overwhelming majority of results from longitudinal studies provides more evidence in support of the social causation hypothesis [2
]. Certainly, in most cases, a combined effect of both factors is likely responsible - as psychopathology can manifest in a multitude of ways and with a variety of time courses.