Ans. C: Deficiency of cyanocobalamin Korsakoff's psychosis/amnesic-confabulatory syndrome is a neurological disorder caused by the lack of thiamine (vitamin B1) in the brain. There are six major symptoms of Korsakoff's syndrome: Anterograde amnesia and Retrograde amnesia, severe memory loss Confabulation, that is, invented memories which are then taken as true due to gaps in memory sometimes associated with blackouts Meager content in conversation Lack of insight Apathy - the patients lose interest in things quickly and generally appear indifferent to change. These symptoms are caused by a deficiency of thiamine, which is thought to cause damage to the medial thalamus and possibly to the mammillary bodies of the hypothalamus as well as generalized cerebral atrophy. When Wernicke's encephalopathy accompanies Korsakoff's syndrome, the combination is called the Wernicke-Korsakoff syndrome. Korsakoff's is a continuum of Wernicke's encephalopathy, though a recognised episode of Wernicke's is not always obvious. Korsakoff's involves damage to neurons; gliosis which is a result of damage to suppoing cells of the central nervous system; and hemorrhage or bleeding in mammillary bodies.