Dichotic listening tests of functional brain asymmetry predict response to fluoxetine in depressed women and men.

Patients having a depressive disorder vary widely in their therapeutic responsiveness to a selective serotonin reuptake inhibitor (SSRI), but there are no clinical predictors of treatment outcome. Studies using dichotic listening, electrophysiologic and neuroimaging measures suggest that pretreatment differences among depressed patients in functional brain asymmetry are related to responsiveness to antidepressants. Two new studies replicate differences in dichotic listening asymmetry between fluoxetine responders and nonresponders, and demonstrate the importance of gender in this context. Right-handed outpatients who met DSM-IV criteria for major depression, dysthymia, or depression not otherwise specified were tested on dichotic fused-words and complex tones tests before completing 12 weeks of fluoxetine treatment. Perceptual asymmetry (PA) scores were compared for 75 patients (38 women) who responded to treatment and 39 patients (14 women) who were nonresponders. Normative data were also obtained for 101 healthy adults (61 women). Patients who responded to fluoxetine differed from nonresponders and healthy adults in favoring left- over right-hemisphere processing of dichotic stimuli, and this difference was dependent on gender and test. Heightened left-hemisphere advantage for dichotic words in responders was present among women but not men, whereas reduced right-hemisphere advantage for dichotic tones in responders was present among men but not women. Pretreatment PA was also predictive of change in depression severity following treatment. Responder vs nonresponder differences for verbal dichotic listening in women and nonverbal dichotic listening in men are discussed in terms of differences in cognitive function, hemispheric organization, and neurotransmitter function.