Introduction. Rapid advances in critical care medicine have led to an increased survival rate of patients with severe brain damage and, consequently, to an increased prevalence of chronic disorders of consciousness (CDC). The lack of or fluctuations in signs of consciousness, which accompany the restoration of alertness after recovery from coma, indicate whether the type of CDC is a vegetative state or minimally conscious state. Correct diagnosis determines not only the rehabilitation outcome but also the economic outlook for a particular patient. However, the subjective nature of signs of consciousness, which are identified during clinical examination using neurological scales, is a common cause of diagnostic errors. The study of spontaneous activity using resting-state functional magnetic resonance imaging (fMRI) has helped to identify resting state networks. The default mode network (DMN) is one of the most studied brain networks. Its signal can change or be absent in patients with various types of CDC. Purpose. To study the signal of residual spontaneous brain activity in patients with CDC at rest. Materials and methods. Twenty-two patients with permanent CDC underwent resting state fMRI as an additional tool in the differential diagnosis between vegetative state and minimally conscious state at the Research Centre of Neurology. Results. It was found that the nature of the signal coming from anatomical regions that are part of the DMN changes when signs of consciousness emerge. Conclusion. These changes confirm that resting state fMRI is an important additional tool for differential diagnosis of CDC types. Accumulating knowledge about the brain's functional state helps us to expand our overall understanding of the nature of consciousness.