A. C. Logan and R. Katzman have argued the beneficial role of probiotics in the conditions of human fatigue and depressive disorders. Probiotic is in essence described as a substance that is secreted by one microorganism which stimulates the growth of another. The Diagnostic and Statistical Manual of Mental Disorders goal ever since has been to map knowledge about the brain and psychopathologies, and to guide clinical professionals on the diagnosis of mental health disorders. Psychopathology is the scientific study of mental disorders, and includes the scientific exploration in order to understand the underlying genetic, biological, psychological, and social causes, their development and their manifestations, and a study of the treatments. However, a more complete definition that was commonly accepted was first used by R. Parker, organisms and substances which contribute to intestinal microbiota balance. The evidence of the brain-gut bidirectional pathway is unequivocal, but the precise nature of the communication is still unknown.