Words and Faces on Left and Right: Perceptual Asymmetries as a Marker for SSRI Responsiveness
Vulnerability to depression has been associated with greater relative right hemisphere frontal activity, as measured by EEG recordings of alpha activity. However, there is much heterogeneity in the patterns of hemispheric asymmetries in people at risk for depression. These different patterns of hemispheric asymmetries may be related to whether an individual responds to Selective Serotonin Reuptake Inhibitor (SSRI) medication. Response to SSRIs is associated with a pattern of overall relative LH activity, whereas non-response to SSRIs is associated with a pattern of overall relative RH activity. Very little is known about how these asymmetries in neural activity relate to asymmetries in cognition. The current study investigated hemispheric differences in the processing of emotional faces and words, in individuals not vulnerable to depression (a Never Depressed group) and in individuals vulnerable to depression (a Previously Depressed group). In the chimeric faces task, the Previously Depressed group had a significantly larger left hemispatial bias compared to the Never Depressed group. This may reflect relatively greater posterior RH activity/arousal in the Previously Depressed group. No differences were found between SSRI Responders and Non-responders in the chimeric faces task. In the divided visual field task, hemispheric differences in the processing of emotional words were found between the SSRI Responders and SSRI Non-responders. In contrast to SSRI Responders and Never Depressed controls, SSRI Non-responders showed a relative advantage for negative over positive words when they were presented to their LVF/RH; and an advantage for negative words presented to their LVF/RH compared to their RVF/LH. Additionally, they were more sensitive to perceiving the valence of a word that was presented to their LVF/RH. This suggests that their RH semantic systems may differ from that of SSRI Responders and Never Depressed controls. Genetic, hormonal and cognitive factors are discussed in relation to these patterns of hemispheric asymmetries and responsiveness to SSRI medication.