We conducted the research of the content of spontaneously arising thoughts and images during resting state fMRI session in 12 patients with tumors of the chiasmal-sellar region. We compared the results of patients with left-sided (6 people) and right-sided (6 people) tumor location. We used the ReSQ resting state questionnaire (Delamillieure et al. 2010), which estimates the fraction of the time in which a particular category of consciousness flow dominated. Statistically significant differences were revealed in the occurrence of somatic images, sensations and experiences that more often occurred with the right-sided arrangement of the tumor, and auditory images, memories and associations, which often formed with the left-sided arrangement of the volumetric formation. Following the research results we put forward the hypothesis that a voluminous extra-cerebral neoplasm with a compressing effect on the network structures of the passive mode of brain functioning leads to an exaggerated spontaneous emergence of thoughts and images of a hemisphere-specific modality.