Self-reported locus of control is based on feelings of depression as well as on asymmetry in activation of cerebral hemispheres.

In a sample of 50 patients with primary breast cancer we obtained interviews, answers to questionnaires, blood samples, and reaction times on two stimulus discrimination tests on the day of admission to the hospital for a biopsy. Locus of control scores on Rotter's I-E Locus of Control Scale seemed to be directly associated with an indicator of depressed mood and one of relative activation of the right cerebral hemisphere. Other variables of which one might have expected a mediating role did not show significant partial relationships with the dependent variable.