During a cognitively demanding Stroop Interference task, BOLD responses within the left and right DLPFC showed opposite patterns of correlated activity with self-ratings of depressed mood in a sample of young adolescent children. Higher scores on the BDI were associated with greater task related BOLD responses in the left middle and inferior frontal gyri, and the left anterior cingulate gyrus, suggesting greater compensatory responsiveness to overcome the presumed reduction in left prefrontal cortex baseline activity that is commonly demonstrated among individuals with a negative affective style and withdrawal related tendencies [3
], dysphoric mood [7
], and/or depressive disorder [13
]. In contrast, higher scores on the BDI were associated with reduced responsiveness of a similar region within the right prefrontal cortex. The hypothesis was further supported by the calculation of a laterality index to show the relative activation of the ROIs in each hemisphere. While higher BDI scores were associated with greater left lateralized activity during the highly demanding Interference condition, greater right lateralized activity was correlated with depressed mood for the less demanding baseline Color Naming condition. Thus, each hemisphere showed opposing patterns of task-related activity that was directly related to the severity of BDI score. Interestingly, we found no significant relationship between BDI scores and amygdala activity during any condition.
] has proposed that individuals showing trait-like asymmetry of anterior EEG activity also show reliable trait-like differences in affective style. Those with relatively lower left than right prefrontal EEG activity tend to exhibit a negative affective style and this asymmetry appears to serve as a diathesis toward developing a depressive disorder [4
]. The present findings are consistent with this position, suggesting that more resources within the left hemisphere were recruited to sustain performance in those adolescents with the most severe depressive mood. Similar compensatory responses occur when prefrontal blood flow is temporarily reduced due to sleep-loss [8
]. These findings are also consistent with neuroimaging research showing decreased left prefrontal resting baseline activity in patients with current [13
] or remitted depression [14
The Stroop Interference task relies heavily upon the resources of the anterior cingulate gyrus in healthy adult individuals [20
]. Because depression is disruptive to normal cognitive function [23
], additional brain resources may need to be recruited for depressed patients to achieve comparable performance, resulting in hyperactivity in left prefrontal circuits in these patients when performing highly demanding cognitive tasks [12
]. These results are similar to findings in non-medicated depressed adults who show increased activity in the left dorsolateral prefrontal cortex and rostral anterior cingulate gyrus during the Stroop task when compared to healthy controls [29
]. When viewed from a compensatory recruitment perspective, the present findings suggest that elevations in depressive mood may disrupt left anterior frontal regions, necessitating the recruitment of additional cortical resources to sustain performance. Furthermore, greater depressive mood appeared to reduce the utilization of right prefrontal regions during the Interference task but not during the baseline Color Naming task. These findings extend the theory that negative mood states and depression are associated with an alteration in the relative balance of baseline activation between the anterior regions of the left and right hemispheres [3
] to include young adolescents.
It should be pointed out that the lateralized model of resting EEG developed by Davidson and colleagues is not universally supported, as some studies find either no relationship between frontal EEG asymmetry and the severity of depression [1
] or even a reversed pattern of asymmetry during negative mood states (i.e., greater left than right) [24
]. Consequently, it could be argued that the present findings, rather than reflecting compensatory processes, may simply reflect that depressive mood state is actually characterized by greater left lateralized activity. While we acknowledge such a possibility, our finding of a correlation between greater right lateralized activity and BDI scored for the baseline Color-Naming condition argue against this possibility by suggesting that greater rightward asymmetry is observed during a less demanding task, but shows compensatory activity during a more demanding one. As with any correlational study, it is possible that the findings may have been influenced by uncontrolled factors, such as individual differences in personality, hormone levels, nutritional status, sleep status, or familiarity with similar tasks. Replication of these findings with independent samples will be necessary to disconfirm such possibilities.
Together, the findings from the present study and our previous report [17
] suggest that the neurobiological aspects of depressive mood severity, including ventromedial increases during affective face processing and left dorsolateral compensatory increases during a demanding cognitive task are consistent with findings in adults, suggesting a continuity of these processes from adolescence though adulthood. It should be pointed out, however, that the range of mood scores in the present sample were all within the non-clinical range. It is, therefore, not certain whether the observed hemisphere specific relationships would be sustained as the level of depressed mood approaches the range of clinical depression.