A 62-year-old man. Over the past 3 years for no apparent reason began to grow helplessness, memory loss. In a mental state it is established: correctly names the last name, first name, patronymic, date of birth; age can not say. Disoriented in terrain, in time. Memory is reduced to current and remote events. Intelligence is reduced. Violated higher cortical functions with the phenomena of aphasia, apraxia, agnosia. There is no criticism. Determine the leading pathogenetic mechanism of formation of the described condition: