AIM:To reveal the characteristics and patterns of mental activity in the cerebral cortex of patients with attention deficit hyperactivity disorder (ADHD) and explore the pathogenetic characteristics of ADHD.METHODS: The ADHD patients were asked to record their mental activity, general health condition and obsessions before the onset of pathological symptoms by means of psychological introspective reports.RESULTS: The direct cause of attention distraction and failure of attention focus is the patients' inability to perform cognitive tasks (including perception, memory and recollection, imagination, association and thought)in a continuously ongoing manner in relaxation. The frequent stagnancy and pause during the course of recognition precipitated the patients in a stressful state, which contributed to the onset of various hyperactivities and also resulted in the acquisition of "silent verbal thinking". This is an important psychopathological phenomenon long been neglected. All theses abnormalities caused the patients much discomfort, which was naturally relieved by means of impulsive and irritable behaviors.CONCLUSION: A series of clinical symptoms of ADHD arises from the same pathogenic factor of difficulty in mental activity and inability to carry out the activities in the cerebral cortex in a relaxed manner. The difficulty in mental activity is the key problem of ADHD and the source of various synptoms, which should be ;reated for the first place. The cause of this key problem is possibly lowered metabolism of the cerebral cortex, and the effect of "instinct" can not be neglected in the attempt to explain the pathogenesis of ADHD.